WO2019011224A1

WO2019011224A1 - Method for transfer of graphene

Info

Publication number: WO2019011224A1
Application number: PCT/CN2018/095073
Authority: WO
Inventors: Ping Gao; Tianshou Zhao; Runlai LI; Jin Li; Qiao GU; Qinghua Zhang
Original assignee: Hong Kong University of Science and Technology
Current assignee: Hong Kong University of Science and Technology
Priority date: 2017-07-10
Filing date: 2018-07-10
Publication date: 2019-01-17
Anticipated expiration: 2020-01-10
Also published as: CN110831768A

Abstract

Provided herein is a method for the direct transfer of a graphene layer to a substrate and transfer of a graphene layer to an arbitrary target substrate and products thereof.

Description

Method for Transfer of Graphene

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority of United States provisional application 62/530,292, filed on July 10, 2017, and United States provisional application 62/708,614, filed on December 18, 2017, the contents of which being hereby incorporated by reference in their entirety for all purposes.

FIELD OF THE INVENTION

The present disclosure generally relates to an improved method for transferring a graphene layer to a substrate, such as a polymer substrate or an arbitrary target substrate. More particularly, provided herein is a process for manufacturing one or more graphene layers on a polymer substrate that employs Van der Waals interactions between the graphene layer and polymer substrate to enable the direct transfer of the graphene layer to the polymer substrate without the need of an intermediary transfer substrate, such as poly (methyl methacrylate) (PMMA) . Also provided is an improved method for transferring one or more layers of graphene to an arbitrary target substrate utilizing a petroleum oil intermediary transfer layer.

BACKGROUND OF THE INVENTION

Since the development of mechanical exfoliation methods for preparing single layer graphene in 2004, an intense amount of research has focused on developing improved methods for preparing high quality large-area graphene. Amongst these methods, chemical vapor deposition (CVD) has emerged as the most promising and frequently used method for the preparation of high quality graphene.

Graphene prepared by CVD is typically produced on a metal substrate, such as platinum, cobalt, nickel, or copper. In many cases, the graphene must then be transferred or removed from the metal substrate for further treatment and/or use. A number of methods have been developed to accomplish this task, including the use of temporary intermediary transfer substrates, such as PMMA, or thermal tape.

Conventional intermediary transfer substrates, such as PMMA and thermal tape, are disadvantaged by chemical contamination of the graphene layer by residue left behind after the intermediary transfer substrate has been removed. This contamination can interfere with properties of the transferred graphene layer and the preparation of clean graphene free of PMMA residue has been extremely challenging.

Other approaches have been developed to avoid or minimize the negative effects of PMMA-mediated transfer: to replace PMMA with other organic coating (polydimethylsiloxane (PDMS) , polycarbonates (PC) , etc) or supporting layers and tapes, to place substrates underneath graphene/copper during etching, or to peel off graphene with adhesive layers. Unfortunately, these methods are too complicated and/or introduce additional chemical contaminants that are difficult to remove. In view of at least the foregoing reasons, a clean and facile method for transferring graphene to a polymer substrate or an arbitrary substrate is still needed.

Graphene transfer methods are typically limited to the transfer of graphene to substrates having substantially planar surfaces. If the substrate that the graphene is transferred to is not substantially planar (e.g., has a rough, irregular, or non-planar surface) , the resulting transferred graphene layer may suffer from surface imperfections and/or may not satisfactorily cover the surface of the substrate. Such imperfections and/or unsatisfactory coverage of the substrate can negatively impact the performance and/or properties of the transferred graphene.

Accordingly, there exists a need for improved methods for the transfer of graphene to arbitrary target substrates having surfaces having non-planar and/or rough surfaces.

SUMMARY OF THE INVENTION

At least some of the aforementioned shortcomings are overcome by the present disclosure, which provides a simplified method for direct transfer of a graphene layer to a polymer substrate, which does not require the use of an intermediary transfer substrate and consequently eliminates or at least reduces contamination of the graphene during the transfer process. Also provided herein is an improved method for transferring one or more layers of graphene to an arbitrary substrate, having a non-planar and/or rough surface, utilizing a petroleum jelly intermediary transfer layer.

In a first aspect provided herein is a method for transferring a graphene layer to a polymer substrate comprising: providing the graphene layer on a substrate; contacting the graphene layer with the polymer substrate thereby forming a sandwich structure; applying a solvent to the sandwich structure; removing the solvent from the sandwich structure; and removing the substrate.

In a first embodiment of the first aspect provided herein is the method of the first aspect, wherein the step of removing the solvent from the sandwich structure induces the formation of Van der Waals interactions between the graphene and the polymer substrate having sufficient force to adhere the graphene to the polymer substrate.

In a second embodiment of the first aspect provided herein is the method of the first aspect, wherein the graphene and the polymer substrate are separated by average distance of about 0.6 to about 1 nm.

In a third embodiment of the first aspect provided herein is the method of the first aspect, wherein the substrate comprises platinum, cobalt, nickel, or copper.

In a fourth embodiment of the first aspect provided herein is the method of the first aspect, wherein the step of applying the solvent to the sandwich structure comprises applying the solvent to the surface of the polymer substrate.

In a fifth embodiment of the first aspect provided herein is the method of the first aspect, wherein the polymer substrate comprises pores having an average diameter greater than about 1 nm.

In a sixth embodiment of the first aspect provided herein is the method of the first aspect, wherein the polymer substrate has an average thickness of less than 400 nm.

In a seventh embodiment of the first aspect provided herein is the method of the first aspect, wherein the polymer substrate comprises ultra-high molecular weight polyethylene (UHMWPE) .

In an eighth embodiment of the first aspect provided herein is the method of the seventh embodiment of the first aspect, wherein the UHMWPE has an average molecular weight of about 1 to about 7 million amu.

In a ninth embodiment of the first aspect provided herein is the method of the eighth embodiment of the first aspect, wherein the UHMWPE is monaxially or biaxially oriented UHMWPE.

In a tenth embodiment of the first aspect provided herein is the method of the first aspect, wherein the solvent is selected from the group consisting of ketones, alcohols, esters, ethers, alkyl halides, alkanes, aryls, and combinations thereof.

In an eleventh embodiment of the first aspect provided herein is the method of the first aspect, wherein the polymer substrate is UHMWPE and the method comprises: providing the graphene layer on a copper substrate; contacting the graphene layer with the UHMWPE substrate thereby forming a sandwich structure, wherein the UHMPE substrate is monaxially or biaxially oriented UHMWPE with an average molecular weight of about 1 to about 7 million amu and having an average thickness of less than 400 nm; applying a solvent to the surface of the UHMWPE substrate; removing the solvent from the sandwich structure thereby inducing the formation of Van der Waals interactions between the graphene layer and the UHMWPE substrate having sufficient force to adhere the graphene layer to the UHMWPE substrate; and removing the copper substrate.

In a second aspect provided herein is a composite comprising a first graphene layer on a first surface of a first UHMWPE substrate, wherein the distance between the first graphene layer and the first UHMWPE substrate is about 0.6 to about 1 nm and the first graphene layer and the first UHMWPE substrate are bound together with Van der Waals interactions of sufficient force to physically adhere the first graphene layer to the first UHMWPE substrate.

In a first embodiment of the second aspect provided herein is the composite of the second aspect, wherein the first UHMWPE substrate has an average molecular weight of about 1 to about 7 million amu.

In a second embodiment of the second aspect provided herein is the composite of the second aspect, wherein the first UHMWPE substrate has an average thickness of less than 400 nm.

In a third embodiment of the second aspect provided herein is the composite of the second aspect, wherein the first graphene layer is a graphene monolayer.

In a fourth embodiment of the second aspect provided herein is the composite of the second aspect further comprising a second graphene layer disposed on the opposing face of the first UHMWPE substrate from the first graphene layer.

In a fifth embodiment of the second aspect provided herein is the composite of the second aspect further comprising a second UHMWPE substrate disposed on the opposing face of the first graphene layer from the first UHMWPE substrate.

In a sixth embodiment of the second aspect provided herein is the composite of the second aspect, wherein the first UHMWPE substrate has an average molecular weight of about 1.5 to about 4 million amu, has an average thickness of less than 400 nm, and comprises pores having an average diameter greater than about 1 nm.

In a third aspect provided herein is a method for transferring a graphene layer to an arbitrary target substrate comprising: providing graphene layer on a substrate; contacting the graphene layer with a petroleum oil substrate thereby forming a sandwich structure; removing the substrate thereby forming a graphene layer on the petroleum oil substrate; contacting the graphene layer on the petroleum oil substrate with the arbitrary target substrate; and removing the petroleum oil substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects and features of the present disclosure will become apparent from the following description of the invention, when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a schematic outlining the method for transferring a graphene layer to a polymer substrate according to certain embodiments of the present disclosure.

FIG. 2A is a photograph of an UHMWPE/graphene composite during etching of the copper substrate according to certain embodiments of the present disclosure.

FIG. 2B is a photograph of an UHMWPE/graphene composite after etching of the copper substrate according to certain embodiments of the present disclosure.

FIG. 2C depicts the raman spectra of CVD-grown graphene on copper foil according to certain embodiments of the present disclosure.

FIG. 2D depicts the raman spectra of an graphene/UHMWPE composite according to certain embodiments of the present disclosure. The shaded areas at indicate the peaks of UHMWPE and graphene.

FIG. 2E is a photograph of a pure UHMWPE nano-porous membrane according to certain embodiments of the present disclosure with a Hong Kong University of Science and Technology business card visible in the background.

FIG. 2F is a photograph of an UHMWPE/graphene composite according to certain embodiments of the present disclosure with a Hong Kong University of Science and Technology business card visible in the background.

FIG. 3A depicts a scanning electron microscopy (SEM) image of the surface morphology of the UHMWPE/graphene composite according to certain embodiments of the present disclosure coated with gold coating.

FIG. 3B depicts an atomic force microscopy (AFM) image of the surface morphological of the UHMWPE/graphene composite according to certain embodiments of the present disclosure.

FIG. 3C depicts SEM micrographs of a graphene on UHMWPE substrate according to certain embodiments of the present disclosure with gold coating.

FIG. 3D depicts SEM micrograph of a graphene on UHMWPE substrate according to certain embodiments of the present disclosure without gold coating.

FIG. 3E depicts AFM height and peak force error images of graphene on UHMWPE substrate according to certain embodiments of the present disclosure of cross-sectional height profiles of region marked with lines in FIG. 3C and 3D.

FIG. 3F depicts AFM height and peak force error images of graphene on UHMWPE substrate according to certain embodiments of the present disclosure of cross-sectional height profiles of region marked with lines in FIG. 3C and 3D.

FIG. 3G depicts AFM height and peak force error images of graphene on UHMWPE substrate according to certain embodiments of the present disclosure of cross-sectional height profiles of region marked with lines in FIG. 3C and 3D.

FIG. 4A is a schematic illustrating the nanocomposite of graphene on UHMWPE substrate according to certain embodiments of the present disclosure. (B) Graphene laminated UHMWPE composite on both surfaces according to certain embodiments of the present disclosure.

FIG. 4B is a schematic illustrating the nanocomposite structure and tensile stress-strain curves of graphene sandwiched on both faces of UHMWPE substrate according to certain embodiments of the present disclosure.

FIG. 4C depicts stress-strain curves measured at room temperature and a strain rate of 25 mm/min for 1) UHMWPE; 2) graphene on UHMWPE substrate according to certain embodiments of the present disclosure; and 3) graphene sandwiched on both faces of UHMWPE substrate according to certain embodiments of the present disclosure.

FIG. 5 (A) and (B) depict SEM photographs of graphene/UHMWPE composite membrane prepared using the methods described herein, with (A) and without gold coating (B) and (C) and (D) depict AFM height and peak force error images of graphene/UHMWPE composite membrane prepared by the methods described herein.

FIG. 6 is a schematic illustrating a (A) graphene-encapsulated UHMWPE membrane according to certain embodiments of the present disclosure; (B) UHMWPE-encapsulated graphene according to certain embodiments of the present disclosure; and (C) multi-layer sandwich structure comprising 4 layers of graphene and 3 layers of UHMWPE in alternating fashion according to certain embodiments of the present disclosure and prepared according to the methods described herein.

FIG. 7 depicts (A) a single graphene layer on copper foil with a thin layer of petrolatum on the graphene layer; (B) a single graphene layer on copper foil with a thin layer of petrolatum on the graphene layer with the copper face down in an aqueous solution of ammonium persulfate; (C) a thin layer of petrolatum on a single graphene layer after the copper foil has been etched off; and (D) a thin layer of petrolatum on a single graphene layer on a UHMWPE T-class membrane.

It should be understood that the drawings described herein are for illustration purposes only. The drawings are not necessarily to scale, with emphasis generally being placed upon illustrating the principles of the present teachings. The drawings are not intended to limit the scope of the present teachings in any way.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

Throughout the application, where compositions are described as having, including, or comprising specific components, or where processes are described as having, including, or comprising specific process steps, it is contemplated that compositions of the present teachings can also consist essentially of, or consist of, the recited components, and that the processes of the present teachings can also consist essentially of, or consist of, the recited process steps.

In the application, where an element or component is said to be included in and/or selected from a list of recited elements or components, it should be understood that the element or component can be any one of the recited elements or components, or the element or component can be selected from a group consisting of two or more of the recited elements or components. Further, it should be understood that elements and/or features of a composition, an apparatus, or a method described herein can be combined in a variety of ways without departing from the spirit and scope of the present teachings, whether explicit or implicit herein

The use of the terms "include, " "includes" , "including, " "have, " "has, " or "having" should be generally understood as open-ended and non-limiting unless specifically stated otherwise.

The use of the singular herein includes the plural (and vice versa) unless specifically stated otherwise. In addition, where the use of the term "about" is before a quantitative value, the present teachings also include the specific quantitative value itself, unless specifically stated otherwise. As used herein, the term "about" refers to a ±10%variation from the nominal value unless otherwise indicated or inferred.

It should be understood that the order of steps or order for performing certain actions is immaterial so long as the present teachings remain operable. Moreover, two or more steps or actions may be conducted simultaneously.

Provided herein is a method for direct transfer of graphene to a polymer substrate and products thereof. Without wishing to be bound by theory, it is believed that the transfer method described herein utilizes Van der Waals (VdW) attractions between, e.g., the planar surface of the graphene layer and the planar surface of the polymer substrate. For planar surfaces, the VdW interaction energy per unit area is given by F=-A/6πd ³, where F is the force per unit area, A is the Hamaker constant, e.g., for hydrocarbons ≈0.5×10 ^-19J, d is the distance between two planar surfaces. By assuming a contact distance of 1 nm, the attractive pressure between the two surfaces is calculated to be 2.65 MPa.

As the attractive pressure is inversely proportional to d ^-3, it is essential that the two surfaces are brought together intimately. Here, the VdW interaction between graphene and the polymer substrate is established by conforming the polymer substrate to the graphene surface. The problem of bringing the graphene layer and the polymer substrate in to intimate contact necessary to establish VdW interactions was surprisingly solved by infiltration of a solvent (e.g., ethanol) between the graphene layer and the polymer substrate followed by evaporation of solvent molecules. The evaporation of the solvent molecules can occur at the periphery of the contact zone between the graphene layer and the polymer substrate where the solvent is exposed to the external environment and/or optionally through pores present throughout the polymer substrate, which allow the solvent to diffuse through the polymer and out of the contact zone between the graphene layer and the polymer substrate. Advantageously, once the VdW interactions are established between the polymer substrate and the graphene layer, the polymer substrate remains adhered to graphene throughout the transfer process, including etching and any post-treatment steps.

FIG. 1 depicts an overview of certain embodiments of the method for transferring a graphene layer to a polymer substrate. The method requires the provision of the graphene layer 11 on a substrate 10 depicted in Step 2 of FIG. 1. The graphene layer on substrate composite structure can be formed by any method known in the art for producing high quality graphene on a substrate 10 depicted in Step 1 of FIG. 1. The substrate can comprise any material. However, it is typically composed of a growth substrate, i.e., a substrate on which graphene is formed, for example by CVD or thermal graphitization of SiC. Such substrates include, but are not limited to gold, copper, iron, manganese, nickel, cobalt, palladium, titanium, platinum, silver, tungsten, germanium, silicon carbide, boron nitride, and combinations thereof.

The graphene layer can consist of a single layer of graphene or multiple layers of graphene. For example, the graphene layer can consist of 2, 3, 4, 5, 6, 7, 8, 9, 10 or more layers of graphene.

The graphene on substrate composite depicted in Step 2 of FIG. 1 is then brought into contact with the polymer substrate 12 by contacting the surface of the polymer substrate with the surface of the graphene layer 11 thereby forming a sandwich structure depicted in Step 3 of FIG. 1.

The polymer substrate can comprise a polyolefin polymer. The polyolefin polymer can be polyethylene, polypropylene, poly (1-butene) , poly (2-butene) , polyisobutylene, polymethylpentene, poly (1-hexene) , poly (1-octene) , poly (1, 2-butadiene) , poly (1, 4-butadiene) , polystyrene, poly (2-methylstyrene) , poly (4-methylstyrene) , poly (α-methylstyrene) , polyvinylchloride, or polyvinylflouride. Alternatively, the polyolefin polymer can be an alternating, periodic, statistical, or block copolymer or terpolymer prepared from monomors selected from the group consisting of ethylene, propylene, 1-butene, 2-butene, isobutene, 2-methyl-1-pentene, 1-hexene, 1-octene, 1, 2-butadiene, 1, 4-butadiene styrene, 2-methylstyrene, 4-methylstyrene, α-methylstyrene, vinylchloride, and vinylflouride.

In instances wherein the polymer substrate comprises a polyolefin polymer containing a side chain (i.e, prepared from an alpha-olefin) , such as polypropylene or polystyrene, the polymer can be isotactic, syndiotactic, atactic, or a combination thereof. In certain embodiments in which the polyolefin polymer is prepared from an alpha-olefin, the polymer is isotactic.

The average molecular weight of the polymer substrate can be between about 100,000 and about 7,000,000 amu. In certain embodiments, the average molecular weight of the polymer substrate is between about 500,000 and about 7,500,000 amu; about 1,00,000 and about 7,500,000 amu; about 1,00,000 and about 7,000,000 amu; about 1,00,000 and about 6,500,000 amu; about 1,00,000 and about 6,000,000 amu; about 1,00,000 and about 5,500,000 amu; about 1,00,000 and about 5,000,000 amu; about 1,00,000 and about 4,500,000 amu; about 1,50,000 and about 4,500,000 amu; about 2,00,000 and about 4,500,000 amu; about 2,00,000 and about 4,000,000 amu; or about 2,00,000 and about 3,500,000 amu.

In certain embodiments, the polymer substrate comprises ultra-high molecular weight polyethylene (UHMWPE) . In such instances, the UHMWPE has an average molecular weight of about 1,00,000 and about 7,500,000 amu; about 1,00,000 and about 7,000,000 amu; about 1,00,000 and about 6,500,000 amu; about 1,00,000 and about 6,000,000 amu; about 1,00,000 and about 5,500,000 amu; about 1,00,000 and about 5,000,000 amu; about 1,00,000 and about 4,500,000 amu; about 1,50,000 and about 4,500,000 amu; about 2,00,000 and about 4,500,000 amu; about 2,00,000 and about 4,000,000 amu; or about 2,00,000 and about 3,500,000 amu.

In certain embodiments, the polymer substrate can be prepared as a film. The length and width of the polymer substrate film can be selected based on the desired size of the manufactured graphene on polymer substrate.

The thickness of the polymer substrate film can be selected to ensure that the VdW attraction between the surface of the graphene sheet and the surface of the polymer substrate sheet is strong enough to maintain the adhesion of each together. A person of ordinary skill in the art can select the appropriate thickness of the polymer substrate sheet based, on a number of factors, such as the density of the polymer sheet membrane and the portion of the surface of the graphene sheet that is available to participate in VdWs interactions and the strength of those interactions per area. Thus, in certain embodiments, the polymer substrate sheet can have a thickness of less than about 50 μm; about 40 μm; about 30 μm; about 20 μm; or about 10 μm.

The polymer substrate can be prepared using any method known to those of skill in the art, such as by injection molding or by extrusion. In instances in which the polymer substrate comprises UHMWPE film, an UHMWPE film can be prepared according to any method known in the art, such as the methods described in WO2018091966, which are herein incorporated by reference, or according to the protocols described herein.

The methods disclosed herein advantageously can:

(A) increase the inter-chain distances of UHMWPE polymer network, reduce the interaction (friction) between neighboring polymer chains, increase the mobility of polymer chains, and reduce the chain entanglement density significantly. Where the “entanglement density” determines the melt viscosity of polymers, the higher it is, the more difficult it will be for processing the polymer. Increase the degree of orientation of polymer chains, and ensure the orientation to be biaxial. Orientation of polymer chains determines the mechanical strength, the higher orientation degree, the better mechanical properties.

(B) Simultaneously, the orientation direction should be biaixal, which means the mechanical properties are equivalent in two perpendicular directions for UHMWPE films. Further increase the mechanical properties by transfer the UHMWPE crystals from relatively weaker crystals to relatively stronger crystals. There are two major kinds of crystals occurring of polyethylene during crystallization: folded chain crystals (FCC, the weaker crystals) and extended chain crystals (ECC, the stronger crystals) . The method needed to execute the transfer is annealing.

(C) Furthermore, annealing can heal the crystallization defects, thickening the crystals and eliminate internal stress during orientation step.

Generally, the overall procedure is a modified gel spinning method. However, unlike the traditional well-established gel fiber spinning process, the modified method differs in three major aspects:

(A) The conventional gel fiber spinning method uses extruder to produce fiber, the modified method uses extruder also employs extruder, but the resultant product is in film form.

(B) The conventional gel fiber spinning method combines extrusion and stretching in a step, which is so-called fiber spinning during extrusion. But the modified method to be disclose hereby divides extrusion and stretching into two separate steps. The only purpose of extrusion step is to prepare homogeneous un-oriented UHMWPE gel films. The orientation is then accomplished afterwards in hot stretching step.

(C) In most cases, conventional gel fiber spinning protocol can only perform the stretching in non-isothermal environment. Resultant products from isothermal stretching outperforms the non-isothermal counterpart in mechanical properties. The modified method thus uses isothermal hot stretching method to orient polymer chains.

To reduce the high melt viscosity of UHMWPE for processing, a thermodynamically miscible solvent can be used to swell into the UHMWPE polymer chain network. Swelling enlarges the interchain distances and as a result the entanglement density can be reduced. Here a solvent with similar chemical composition and structure to UHMWPE is used, e.g., Protopet 1S from Sonneborn, cas#8009-03-8, or “petrolatum” can be used as the solvent for UHMWPE.

To stabilize the material at high temperature, antioxidants can be used to prevent and terminate free radical cascade reaction. Phenolic and phosphatic antioxidants, or “Irganox 1010” and “Irgafos 168” can be used as antioxidants.

Petrolatum is mixed with UHMWPE (e.g., 90-95: 5-10 w/w ratio of UHMWPE to petrolatum) resin and antioxidants to make into a suspension, being heated at 120 ℃ with stirring.

Then the suspension is automatically fed into a twin-screw extruder to prepare a gel filament. Regardless of the specific mode and configuration of extruder, a temperature gradient temperature profile should be set: from feeding zone to exit zone, from 120 ℃ to 220 ℃. At the very exit zone, the temperature is preferably no higher than 180 ℃, or phase separation or flow instabilities may occur.

The extruded gel filament will be collected after cooled down and reeled onto a roller. Then the gel filament can then be fed into the feeding zone to be extruded again. This time the filament die at the exit zone is changed to a film die, which produces the extruded product as a film. The temperature profile is an important parameter to determine the homogeneity and quality of the extruded films. For the second time extrusion, the temperature profile is the same with the first time extrusion, except for the exit zone temperature. It is preferably be no higher than 170 ℃, but no lower than 140 ℃.

As explained above, another major difference of this method from conventional one lies on the product at extrusion step: in-oriented homogeneous gel films. Thus at this step, it should be guaranteed that no oriented may be made during extrusion. ) To avoid orientation on the extruded gel films right after extrusion, a roller group set up is used that the collection linear speed is identical with the extrusion speed.

After collection, the gel film is stretched in an environment chamber at a constant temperature. The stretching speed can be around 200%/min, and stretching temperature is about 120 ℃.

The last step can be accomplished in a biaxial stretching apparatus, but if that is unavailable, a uniaxial stretching apparatus can still accomplish the task by performing the stretching in two perpendicular directions in sequence. The typical drawing ratio is 600%times 600%.

Right after stretching, a post-stretching annealing at 125 ℃ is performed for no less than 5 minutes and no more than 15 minutes. After annealing the film is slowly cooled before unloading the film.

The petrolatum is then extracted using a solvent extraction method, e.g., n-hexane extraction at 50 ℃. During extraction, the constraints to prevent the film to shrink should be applied all time to ensure the “porous” structure of the final polymer substrate.

In an alternative protocol Protopet 1S from Sonneborn, cas#8009-03-8, or “petrolatum” is used as the solvent for UHMWPE. Phenolic and phosphatic antioxidants, or “Irganox 1010” and “Irgafos 168” are used as antioxidants.

In certain embodiments, petrolatum is mixed with UHMWPE (e.g., 90-95: 5-10 w/w ratio of UHMWPE to petrolatum) , resin and antioxidants to make into a suspension, being heated at 120 ℃ with stirring. Then the suspension is automatically fed into a twin-screw extruder to prepare gel filament. Regardless of the specific mode and configuration of extruder, a temperature gradient temperature profile should be set: from feeding zone to exit zone, from 120 ℃ to 200 ℃. At the very exit zone, the temperature should preferably be no higher than 170 ℃, or phase separation or flow instabilities may occur.

The extruded gel filament can be collected after it is cooled down and reeled onto a roller. Then the gel filament can be fed into the feeding zone to be extruded again. This time the filament die at the exit zone can be changed to a film die, thus the extruded product will be film. The temperature profile is an important operation parameter to determine the homogeneity and quality of the extruded films. For the second extrusion, the temperature profile is the same as the first extrusion, except for the exit zone temperature. It should preferably be no higher than 160 ℃ but no lower than 140 ℃.

To avoid orientation on the extruded gel films right after extrusion, a roller group set up is used that the collection linear speed is identical with the extrusion speed.

After collection, the gel film is stretched in an environment chamber at constant temperature. The stretching speed can be around 500%/min, and stretching temperature can be about 120 ℃. The draw ratio can be 2000%times 2000%.

The last step can be accomplished using a biaxial stretching apparatus, but if that is unavailable, a uniaxial stretching apparatus can still accomplish the task by performing the stretching in two perpendicular directions in sequence.

Right after stretching, a post-stretching annealing at 135 ℃ is performed for no less than 5 minutes and no more than 15 minutes. Then the film is slowly cooled down before it is unloaded.

The petrolatum can then be extracted using a solvent extraction method, e.g., n-hexane extraction at 50 ℃. During Extraction, the constraints to prevent the film to shrink should be applied at all times, which ensures the resultant “porous” structure.

After extraction, isopropanol-dissolved Nafion sprayed onto the membrane. Then pure isopropanol is sprayed on the other side, thus through the capillary pump effect, the Nafion will be dragged into the pore structures. The membrane is then dried, then repeat the operation several times on both sides to fully impregnate Nafion into the porous structures.

The membrane is then annealed in vacuum at 130 ℃ for 12 hours and then washed sequentially with hydrogen peroxide, sulfuric acid and deionized water.

In certain embodiments, the UHMWPE polymer is monaxially or biaxially oriented. The monaxially or biaxially oriented UHMWPE polymer can comprises polymer strands having an average cross-sectional width of about 10 nm and about 80 nm;about 10 nm and about 70 nm; about 10 nm and about 60 nm; or about 15 nm and about 80 nm. The polymer cross-sectional width of the monaxially or biaxially oriented UHMWPE polymer strands have a cross-sectional width between about 17 nm and about 58 nm. The spaces between the monaxially or biaxially oriented UHMWPE polymer strands define pores within the UHMWPE polymer substrate.

In order to facilitate removal of the solvent, the polymer substrate can comprise a porous structure that allows the solvent to diffuse directly through the polymer, e.g., through a pore network. The pores can be of any dimension, but are generally greater than about 0.1 μm in diameter on average.

In certain embodiments, the pores have an average diameter of between about 0.1 μm and about 20 μm; about 0.1 μm and about 10 nm; about 0.1 μm and about 5 μm; about 1 μm and about 10 μm; or about 1 μm and about 5 μm.

The volumetric porosity of the polymer substrate can be characterized by a liquid absorption technique. In this method weight uptake of mineral oil at room temperature can be performed and the porosity can be estimated according to the following equation.

wherein W, W ₀ are the weights of the separator membrane before and after immersion in liquid mineral oil, p _L is the density of mineral oil, and V ₀ is the geometric volume of the separator membrane, respectively.

The volumetric porosity of the polymer substrate can thus be greater than about 10%; about 20%; about 30%; about 40%; about 50%; about 60%; or about 70%; and less than about 80%. In certain embodiments, the volumetric porosity of the polymer substrate is between about 10%and about 70%; about 20%and about 70%; about 30%and about 70%; about 40%and about 70%; about 40%and about 60%.

A solvent is then applied to the sandwich structure. The solvent can be any solvent capable of being substantially or completely removed under conditions (e.g., temperature and pressure) that do not damage or limit damage to the polymer substrate. Suitable solvents, include but are not limited to ketones, alcohols, esters, ethers, alkyl halides, alkanes, aryls, and combinations thereof.

Ketones suitable for carrying out the present method include branched and/or unbranched C ₃-C ₁₂ alkyl ketones. Exemplary ketones include acetone, methyl ethyl ketone (MEK) , methyl isobutyl ketone (MIBK) , ethyl isopropyl ketone, methyl amyl ketone (MAK) , 4-hydroxy-4-methyl-2-pentanone, 2-heptanone, hexanone, isophorone, and the like and combinations thereof. Cyclic acetones, such as cyclopentanone can also be used.

Alcohols suitable for carrying out the present method include straight chain, secondary, or tertiary C ₁-C ₁₀ alcohols. Exemplary alcohols include methanol, ethanol, propanol, isopropanol, butanol, isobutyl alcohol, tertbutyl alcohol, pentanol, isopentyl alcohol, neopentyl alcohol, hexanol, heptanol, octanol, nonanol, and decanol as well as all possible positional isomers of the above alcohols, and the like and combinations thereof. Cyclic alcohols, such as cyclopropanol, cyclobutanol, cyclopentanol, cyclohexanol, cycloheptanol, cyclooctanol, cyclononanol and cyclodecanol , and the like and combinations thereof can also be used.

Esters suitable for carrying out the present method include branched and/or unbranched C ₃-C ₁₀ alkyl esters. Exemplary alcohols include methyl acetate, methyl lactate, methyl propionate, propyl acetate, ethyl acetate, butyl acetate, benzyl acetate, sec-butyl acetate, tert-butyl acetate, ethyl butyrate, ethyl lactate, ethyl acetoacetate, hexyl acetate, isoamyl acetate, isobutyl acetate, isopropyl acetate, and the like and combinations thereof. Cyclic carbonates, such as propylene carbonate and ethylene carbonate, and the like and combinations thereof can also be used.

Ethers suitable for carrying out the present method include branched and/or unbranched C ₂-C ₁₀ alkyl ethers. Exemplary ethers include cyclopentyl methyl ether, di-tert-butyl ether, dibutyl ether, diethyl ether, diisopropyl ether, dimethoxyethane, ethyl tert-butyl ether, methoxyethane, methyl tert-butyl ether, and the like and combinations thereof. Cyclic ethers, such as 1, 4-dioxane, tetrahydrofuran,

tetrahydropyran

2, 2, 5, 5, -tetramethyltetrahydrofuran, and 2-methyltetrahydrofuran , and the like and combinations thereof can also be used.

Alkyl halides suitable for carrying out the present method include branched and unbranched C ₁-C ₆ alkyl halides. Exemplary alkyl halides include dichloromethane, chloroform, carbon tetrachloride, and dichloroethane.

Alkanes suitable for carrying out the present method include branched and/or unbranched C ₄-C ₂₀ alkanes. Exemplary alkanes include butane, pentane, methylbutanes (such as 2-methylbutane) , hexane, dimethylbutanes (such as 2, 2-dimethylbutane and 2, 3-dimethylbutane) , methylpentanes (such as 2-methylpentane and 3-methylpentane) , heptane, trimethylbutanes (such as 2, 2, 3-trimethylbutane) , dimethylpentanes (such as 2, 2-dimethylpentane, 2, 4-dimethylpentane, and 3, 3-dimethylpentane) , methylhexanes (such as 2-methylhexane and 3-methylhexane) , octane, trimethylpentanes (such as 2, 2, 4-trimethylpentane) , dimethylhexanes (such as 2, 4-dimethylhexane) , methylheptanes (such as 2-methylheptane) , nonane, dimethylheptanes (such as 2, 3-dimethylheptane) , decane, petroleum ether, and the like and combinations thereof. Cycloalkanes such as, cyclopentane, cyclohexane, methylcyclopentane, cycloheptane, ethylcyclopentane, methylcyclohexane, cyclooctane, dimethylcyclohexanes (such as 1, 2-dimethylcyclohexane and 1, 3-dimethylcyclohexane) , ethylcyclohexane, cyclononane, cyclodecane, and the like and combinations thereof can also be used.

Aryls suitable for carrying out the present method include C ₆-C ₈ aryls. Exemplary aryls include benzene, toluene, benzonitrile, xylenes, chlorobenzene, dichlorobenze, difluorobenzene, nitrobenzene, pyridine, naphthalene, methyl naphthalene, and the like and combinations thereof.

Other suitable solvents include, but are not limited to, acetonitrile, dimethylformamide, nitromethane, ethylene glycol, diglyme, 1, 2-dimethoxy ethane, water, and the like and combinations thereof.

The solvent can be applied to the sandwich structure at any location of the sandwich structure. In certain embodiments, the solvent is applied to sandwich structure by at least one methods selected from the group consisting of contact with the surface of the polymer substrate and contact with the sides of the sandwich structure. In alternative embodiments, the solvent is applied to the graphene layer surface before the polymer substrate is brought in to contact with the graphene layer surface. Combinations of the aforementioned methods for applying the solvent to the sandwich structure can be employed.

After the solvent is applied to the sandwich structure, sufficient time should be provided to ensure that, e.g., the solvent has diffused through the polymer substrate to the interface between the polymer substrate surface and the graphene layer surface; and/or migrated from the point of application on the sandwich structure to the interface between the polymer substrate surface and the graphene layer surface. The amount of time required can depend on the porosity of the polymer substrate, the density of the polymer substrate, the thickness of the polymer substrate, the viscosity of the solvent, the volume of solvent added, the contact point on the sandwich structure, the surface tension of the solvent, the hydrophobicity of the solvent, etc. The selection of the appropriate wait time is within the skill of a person of skill in the art.

After sufficient time has passed after solvent application to the sandwich structure, the solvent is then removed. This can be accomplished using any method known in the art, such as by heat, under reduced pressure, and combinations thereof. The solvent can also be removed by evaporation at room temperature and standard pressure.

The selection of the appropriate conditions for removing the solvent can depend on the boiling point of the solvent used.

In certain embodiments, the solvent is removed by heating the sandwich structure with solvent to about 40 ℃, about 50 ℃, about 60 ℃, about 70 ℃, about 80 ℃, about 90 ℃, about 100 ℃, about 110 ℃, about 120 ℃, or about 130 ℃. In certain embodiments, the solvent is removed by heating the sandwich structure to about 60 ℃ to about 200 ℃; about 60 ℃ to about 200 ℃; about 60 ℃ to about 180 ℃; about 60 ℃ to about 160 ℃; or about 60 ℃ to about 140 ℃.

Without wishing to be bound by theory, it is believed that upon removal of the solvent that the formation of VdW interactions is facilitated by hydrophobic-hydrophobic interactions between the surface of the polymer substrate and the surface of the graphene layer. The porosity of the polymer substrate can facilitate the removal of the solvent. The provided method thus provides a gentle yet effective method of adhering a graphene layer to a polymer substrate without the use of excessive force or an intermediary transfer layer.

After the solvent has been removed, VdW interactions adhere the surface of the polymer substrate and the surface of the graphene layer. Advantageously, the VdW interactions are strong enough to ensure that the polymer substrate and the graphene layer remain firmly affixed during removal of the substrate and any necessary post-treatment steps after substrate removal.

The substrate is then optionally removed to yield the graphene on the polymer substrate depicted in Step 4 of FIG. 1. The substrate can be removed using any method known in the art. Exemplary methods include mechanical cleavage and chemical etching. Chemical etchants include, but are not limited to, iron (III) chloride, ammonium persulfate, iron (III) nitrate, hydrochloric acid, hydrobromic acid, nitric acid, sulfuric acid, sodium hydroxide, hydrogen peroxide, chromium oxide, phosphoric acid, or combinations thereof.

Figure 2E and 2F demonstrate photographs of UHMWPE substrate before and after the transfer of graphene, the change in transparency due to graphene loading can be clearly seen. As shown in Figure 3A, the portion of the UHMWPE substrate is highly porous and rough in surface with numerous nano-pores. Transmittance of optical waves through the UHMWPE substrate will be significantly reduced due to Mie scattering since the dimensions of particle or pore structure are comparable to the wavelength of visible light, especially at the interfaces. By overlaying of a graphene layer, the rough porous surface of UHMWPE substrate is covered by a smooth atomic thin graphene layer, and the effective VdW range is far less than optical light wavelength (0.157 nm) , a large proportion of Mie scattering due to the UHMWPE surface vanishes.

To check the layer number and defects, Raman spectroscopy was characterized of graphene/copper film after CVD growing, and of graphene/UHMWPE composite membrane after transfer. 2D and G bands were at 2690 cm ^-1 and 1596 cm ^-1 respectively, with intensity ratio (I _2D/I _G) of 2.21, as shown in Figure 2C. After transfer no obvious D bend (1350 cm ^-1) was observed in Figure 2D, indicating the no sp63 defects were generated during the transfer in graphene.

To better investigate the transfer effect of graphene on UHMWPE substrate, SEM and AFM were performed to observe the composite membrane surfaces (graphene on top of UHMWPE) . Figure 3A shows graphene/UHMWPE composite membrane prepared using the direct transfer method described herein. It can be seen that the graphene layer was fully extended on the UHMWPE substrate without ripples or folds. Whereas, transfer methods utilizing conventional PMMA-mediated intermediaries to UHMWPE yield micrometer level ripples and folds. If the ripples are millimeter sized, graphene will be tore-away during the removal of PMMA. Figure 3C and 3D are AFM height and peak force error images of graphene/UHMWPE composite membrane surface, respectively. Graphene closely pressed itself against UHMWPE, thus it fitted the surface roughness of UHMWPE so well that the probe can still detect part of the contour of crisscrossed polymer chain superstructure. By more carefully investigating the height profile at cross-sections, the difference of with and without graphene covering become apparent. Figure 3F is the cross-sectional height profile taken from Figure 3C marked with a line. The upper parts (tops) of polymer chain structure can always be detected no matter with or without graphene covering. However the lower parts (bottoms) cannot be reached by probes because of the existence of graphene. Thus it can be concluded that: (1) graphene is closely stuck against UHMWPE surface by VdW force and fits the surface contour well, (2) graphene and UHMWPE are not closely contacted at each point, micro-chambers enclosed by graphene and relatively rough UHMWPE surface exist, (3) which is quite promising to be used to study intrinsic properties of graphene, such as its mechanical properties.

One of the most considerable applications of graphene/UHMWPE composite structures prepared using the methods described herein is that it presents a new approach to directly observe crystallization and phase behaviors of UHMWPE. These topics have been intensively studied for several decades, however the real time direct structural observation on sub-micron level has seldom been performed, especially for UHMWPE-solvent systems. In situ AFM once was used to investigate the formation of shish-kebab structures of UHMWPE, but due to the trade-off of scanning speed and resolution of AFM, the results were either not real-time or with not enough resolution. The methods and products thereof described herein may solve this problem by utilizing graphene as both the conductive coating layer and the encapsulating material in case the solvent involved. As shown in Figure 5A, after coated with gold, graphene loaded on UHMWPE substrate was not transparent at all to SEM, since the electrons immediately dissipated upon reaching highly conductive gold coating layer, and also the gold coating was far thicker than graphene. But if no gold was coated, SEM could ‘see’ through graphene and observe the UHMWPE directly (which is not possible for UHMWPE alone since it has quite low electrical conductivity) , as shown in Figure 5B. This SEM micro-photograph is somewhat similar to those captured by AFM, as shown in Figure 5C-D, they all showed the surface morphology and micro-structure of UHMWPE membrane through graphene, but with different mechanisms. AFM probe can “touch” UHMWPE through graphene, because graphene is atomic-thin, highly flexible and closely stuck against UHMWPE by VdW forces, thus the upper part of UHMWPE structure is easily captured by AFM. While SEM can “see” UHMWPE through graphene by simply conducting electron through is more impressive, since it implies the possibility of direct in situ electron microscopic observations (e.g., TEM) of crystallization process and phase behaviors of UHMWPE and even other polymers in the presence of its solvent and thermal treatment. The only obstacle seems to be the need to coat both sides of UHMWPE with graphene, which is also a huge challenge for conventional graphene transfer methods.

Fortunately, this obstacle is not a problem for the methods described herein, which have solved this problem. Due to the hydrophobic-hydrophobic interactions and strong VdW force between graphene and UHMWPE, they will not easily split up any more once stuck together, even though they are immersed into water or aqueous solutions again. Thus, the methods described herein can be performed more than once, e.g., graphene/UHMWPE/graphene (graphene-encapsulated UHMWPE) and UHMWPE/graphene/UHMWPE (UHMWPE-encapsulated graphene) composite membranes were prepared by simply repeating this method to transfer an extra layer of graphene or UHMWPE onto prepared graphene/UHMWPE membrane. In fact, the multi-layer sandwich structure 2D composite membrane can be prepared at ease with desired number of layers, as illustrated in Figures 4B and 6. Thus, the methods provided herein can optionally be used iteratively to produce more complex composite structures, e.g., having more than one layer of graphene and/or polymer substrate. For example, composite structures having two polymer substrates and having a graphene layer in between; two graphene layers and having a polymer substrate in between; or even more complex composite structures having 3, 4, 5, 6, 7, 8, 9, 10, or more graphene and/or polymer substrates alternatingly layered between each other.

Preparation of polymeric composite materials consisting of embedded graphene has been reported, while 2D layered composite membrane of one single layer large-area graphene and polymer is rarely studied. By performing the methods described herein, large-area layered graphene/UHMWPE composite membranes were prepared, with desired number of layers and layers arrangement. To better investigate the adhesion between graphene/UHMWPE and effect of existence of graphene on mechanical properties of UHMWPE, a series of stretching with assigned strains was performed. Three groups of samples were demonstrated after stretching with strain of 20%, 50%and 80%, respectively.

As draw ratio increases, UHMWPE originally biaxial chains became more oriented along stretching direction. Thus graphene above was tearing up by aligning UHMWPE, this would not occur except the strong adhesion existed between the two layers. With higher draw ratios, split graphene was pulled away from each other and even became isolated, and piled up normal to stretching direction on account of the Poisson effect. Exposed UHMWPE which lost the covering of graphene charged severely, and the structure details could be hardly distinguished. While with graphene fragments above (even rippled ones) , chain orientation and shish-kebab structures could still be identified.

Table 1. Tensile properties of graphene/UHMWPE composite membranes depicted in FIG. 4B

Cracks on stretched graphene on UHMWPE might stem from original defects, and did not overlap with possible domain boundaries of graphene. Strengthening effect of graphene in graphene/UHMWPE layered composite membranes has been observed. With the covering of atomic-thin graphene on one side or both sides, UHMWPE would increase in maximum stress (16.8%and 10.3%) , ductility (8.2%and 14.4%) and fracture energy (46.2%and 61.9%) , as demonstrated in Table 1.

Also provided herein is a method for transferring a graphene layer to an arbitrary target substrate comprising: providing graphene disposed on a metal substrate; contacting the graphene with a petroleum oil substrate thereby forming a sandwich structure; removing the metal substrate thereby forming a graphene layer on the petroleum oil substrate; contacting the graphene layer on the petroleum oil substrate with the arbitrary target substrate; and removing the petroleum oil substrate.

The arbitrary target substrate can be of any size and shape. Moreover, the method for transferring a graphene layer to an arbitrary target substrate according to the instant disclosure may be used both on rigid substrates and on fragile, thin and flexible substrates or substrates with smooth or rough surfaces.

The method for transferring a graphene layer to an arbitrary target substrate calls for the provision of a graphene layer on a substrate. The graphene layer on substrate composite structure can be formed by any method known in the art for producing high quality graphene on a substrate and the substrate can comprise any material. However, it is typically composed of a growth substrate, i.e., a substrate on which graphene is formed, for example by CVD or thermal graphitization of SiC. Such substrates include, but are not limited to gold, copper, iron, manganese, nickel, cobalt, palladium, titanium, platinum, silver, tungsten, germanium, silicon carbide, boron nitride, and combinations thereof.

A sandwich structure comprising the graphene layer on a substrate and a petroleum oil substrate can be formed by application of a thin layer of the petroleum oil to the exposed surface of the graphene layer on the substrate. The amount and thickness of the petroleum oil layer can be selected based on mechanical properties of the petroleum oil and the selection of which is well within the skill of a person of ordinary skill in the art. In certain embodiments, the petroleum oil layer is about 500 nm to about 1,500 nm; about 800 nm to about 1,200 nm; or about 900 nm to about 1,100 nm. In certain embodiments, the petroleum oil layer is about 1,000 nm thick.

In certain embodiments, the petroleum oil substrate is selected from the group consisting of mineral oil, Vaseline (white petrolatum, CAS number 8009-03-8) , paraffin wax, microcrystalline petroleum wax, slack wax, ozokerite, lignite wax, and peat wax.

The substrate can be removed from the sandwich structure thereby forming graphene on a petroleum oil substrate. The substrate can be removed using any method known in the art. Exemplary methods include mechanical cleavage and chemical etching. Chemical etchants include, but are not limited to, iron (III) chloride, ammonium persulfate, iron (III) nitrate, hydrochloric acid, hydrobromic acid, nitric acid, sulfuric acid, sodium hydroxide, hydrogen peroxide, chromium oxide, phosphoric acid, or combinations thereof.

The graphene layer on the petroleum oil substrate is then brought in to contact with the arbitrary target substrate by contacting the surface of the graphene layer with the surface of the arbitrary target substrate thereby forming a second sandwich structure. The arbitrary target substrate can be any shape and/or size. The arbitrary target substrate can comprise any material. Suitable arbitrary target substrate materials include, but are not limited to, conductive material, a dielectric material, and a semiconductor material.

The petroleum oil substrate is then removed from the second sandwich structure thereby forming the graphene layer on the arbitrary substrate. The petroleum oil substrate can be removed using any method known to those of skill in the art including solvent extraction and/or evaporation (e.g., under reduced pressure and/or heat) . In instances where solvent extraction is used to remove the petroleum oil substrate, any solvent can be used. Preferably, the solvent is one in which the petroleum oil substrate is at least partially soluble under the conditions that the solvent extraction takes place. The solvent extraction can take place at room temperature or elevated temperature. When the solvent extraction takes place at elevated temperature, the extraction solvent and/or the second sandwich structure can be heated to e.g., about 40 ℃, about 50 ℃, about 60 ℃, about 70 ℃, about 80 ℃, about 90 ℃, about 100 ℃, about 110 ℃, or about 120 ℃. In certain embodiments, the extraction solvent and/or the second sandwich structure can be heated to between about 40 ℃ to about 100 ℃; about 60 ℃ to about 100 ℃; or about 60 ℃ to about 90 ℃.

In certain embodiments, the method for transferring a graphene layer to an arbitrary target substrate can be used in connection with certain steps of the method for transferring a graphene layer to a substrate described herein. In such embodiments, the method for transferring a graphene layer to a polymer substrate comprising: providing the graphene layer on a substrate; contacting the graphene layer with a petroleum oil substrate thereby forming a first sandwich structure; removing the substrate thereby forming a graphene layer on the petroleum oil substrate; contacting the graphene layer on the petroleum oil substrate with the polymer substrate thereby forming a second sandwich structure; applying a solvent to the second sandwich structure; removing the solvent from the second sandwich structure; and removing the petroleum oil substrate. Such method benefits can benefit from the VdW interactions between the surface of the graphene layer and the surface of the polymer substrate to ensure strong attachment of the graphene layer to the polymer substrate.

Accordingly, the arbitrary target substrate can comprise a polymer substrate. The polymer substrate can comprise a polyolefin polymer selected from the group consisting of polyethylene, polypropylene, poly (1-butene) , poly (2-butene) , polyisobutylene, polymethylpentene, poly (1-hexene) , poly (1-octene) , poly (1, 2-butadiene) , poly (1, 4-butadiene) , polystyrene, poly (2-methylstyrene) , poly (4-methylstyrene) , poly (α-methylstyrene) , polyvinylchloride, and polyvinylflouride. Alternatively, the polyolefin polymer can be an alternating, periodic, statistical, or block copolymer or terpolymer prepared from monomors selected from the group consisting of ethylene, propylene, 1-butene, 2-butene, isobutene, 2-methyl-1-pentene, 1-hexene, 1-octene, 1, 2-butadiene, 1, 4-butadiene styrene, 2-methylstyrene, 4-methylstyrene, α-methylstyrene, vinylchloride, and vinylflouride.

In instances wherein the arbitrary target substrate comprises a polymer substrate containing a polyolefin having a side chain (i.e, prepared from an alpha-olefin) , such as polypropylene or polystyrene, the polymer substrate can be isotactic, syndiotactic, atactic, or a combination thereof. In certain embodiments in which the polyolefin polymer is prepared from an alpha-olefin, the polymer is isotactic.

The average molecular weight of the polyolefin polymer can be between about 100,000 and about 7,000,000 amu. In certain embodiments, the average molecular weight of the polyolefin polymer is between about 500,000 and about 7,500,000 amu; about 1,00,000 and about 7,500,000 amu; about 1,00,000 and about 7,000,000 amu; about 1,00,000 and about 6,500,000 amu; about 1,00,000 and about 6,000,000 amu; about 1,00,000 and about 5,500,000 amu; about 1,00,000 and about 5,000,000 amu; about 1,00,000 and about 4,500,000 amu; about 1,50,000 and about 4,500,000 amu; about 2,00,000 and about 4,500,000 amu; about 2,00,000 and about 4,000,000 amu; or about 2,00,000 and about 3,500,000 amu.

In certain embodiments, the polyolefin polymer comprises ultra-high molecular weight polyethylene (UHMWPE) . In such instances, the UHMWPE has an average molecular weight of about 1,00,000 and about 7,500,000 amu; about 1,00,000 and about 7,000,000 amu; about 1,00,000 and about 6,500,000 amu; about 1,00,000 and about 6,000,000 amu; about 1,00,000 and about 5,500,000 amu; about 1,00,000 and about 5,000,000 amu; about 1,00,000 and about 4,500,000 amu; about 1,50,000 and about 4,500,000 amu; about 2,00,000 and about 4,500,000 amu; about 2,00,000 and about 4,000,000 amu; or about 2,00,000 and about 3,500,000 amu.

In certain embodiments, the arbitrary target substrate can be prepared as a film. The length and width of the film can be selected based on the desired size of the manufactured graphene on arbitrary target substrate.

The thickness of the film can be selected to ensure that the VdW attraction between the surface of the graphene layer and the surface of the film is strong enough to maintain the adhesion of each together. A person of ordinary skill in the art can select the appropriate thickness of the film based, on a number of factors, such as the density of the film and the portion of the surface of the graphene layer that is available to participate in VdWs interactions and the strength of those interactions per area. Thus, in certain embodiments, the film can have a thickness of less than about 50 μm; about 40 μm; about 30 μm; about 20 μm; or about 10 μm.

In certain embodiments, once the graphene has been brought in contact with the arbitrary substrate (e.g., polymer substrate, such as UHMWPE) thereby forming a second sandwich structure, a solvent can then be applied to the sandwich structure. The solvent can be any solvent capable of being substantially or completely removed under conditions (e.g., temperature and pressure) that do not damage or limit damage to the polymer substrate. Suitable solvents, include but are not limited to ketones, alcohols, esters, ethers, alkyl halides, alkanes, aryls, and combinations thereof as described above.

The solvent can be applied to the second sandwich structure at any location of the sandwich structure. In certain embodiments, the solvent is applied to the second sandwich structure by at least one methods selected from the group consisting of contact with the surface of the polymer substrate and contact with the sides of the sandwich structure. In alternative embodiments, the solvent is applied to the graphene layer surface before the polymer substrate is brought in to contact with the graphene layer surface. Combinations of the aforementioned methods for applying the solvent to the sandwich structure can be employed.

After the solvent is applied to the second sandwich structure, sufficient time should be provided to ensure that, e.g., the solvent has diffused through the polymer substrate to the interface between the polymer substrate surface and the graphene layer surface; and/or migrated from the point of application on the sandwich structure to the interface between the polymer substrate surface and the graphene layer surface. The amount of time required can depend on the porosity of the polymer substrate, the density of the polymer substrate, the thickness of the polymer substrate, the viscosity of the solvent, the volume of solvent added, the contact point on the sandwich structure, the surface tension of the solvent, the hydrophobicity of the solvent, etc. The selection of the appropriate wait time is within the skill of a person of skill in the art.

After sufficient time has passed after solvent application to the second sandwich structure, the solvent is then removed. This can be accomplished using any method known in the art, such as by heat, under reduced pressure, and combinations thereof. The solvent can also be removed by evaporation at room temperature and standard pressure.

In certain embodiments, the solvent is removed by heating the second sandwich structure with solvent to about 40 ℃, about 50 ℃, about 60 ℃, about 70 ℃, about 80 ℃, about 90 ℃, about 100 ℃, about 110 ℃, about 120 ℃, or about 130 ℃. In certain embodiments, the solvent is removed by heating the second sandwich structure to about 60 ℃ to about 200 ℃; about 60 ℃ to about 200 ℃; about 60 ℃ to about 180 ℃; about 60 ℃ to about 160 ℃; or about 60 ℃ to about 140 ℃.

The petroleum oil substrate is then removed from the second sandwich structure thereby forming the graphene layer on the arbitrary substrate. The petroleum oil substrate can be removed using any method known to those of skill in the art including solvent extraction and/or evaporation (e.g., under reduced pressure and/or heat) as described above.

In alternative embodiments, the petroleum oil substrate and the solvent can be removed in one step.

EXAMPLES

Example 1–Preparation of Biaxially Oriented UHMWPE

UHMWPE (GUR 4022) was purchased from Celanese, and the average molecular weight was about 3.5 x 10 ⁶ g/mol. Petrolatum (Protopet I S) was purchased from

average Mw -600 g/mol. 1.1 wt%antioxidant mixture of Irganox

and Irgafos

(1: 1 by weight) was used to stabilize the polymer during processing. Then the gel film was freely extruded by HAAKE twin screw extruder with a tape take-up unit. Then the free extruded gel films were hot stretched twice at 120 ℃ in two perpendicular directions in sequence on the INSTRON 5567 universal testing system fixed with an environmental chamber. Gel films were drawn sequentially to a total draw ratio of 6 x 6. Dimensional shrinkages were prevented in transverse direction during hot stretching by confining the films laterally during drawing. Films were annealed at 125 ℃for 15 min after stretching to relieve internal stresses and induce self-reinforced composite formation. Petrolatum, the solvent for UHMWPE, was optionally extracted by N-hexane. Dimensional constraint was applied through all the procedures to introduce membrane porosity after oil removal.

Example 2–Transfer of Graphene to Biaxially Oriented UHMWPE Polymer Substrate

As depicted in Figure 1, firstly thin UHMWPE membrane was covered onto the top of CVD-grown graphene/copper film. At this step the distance between UHMWPE and graphene was far more than the effective range of VdW force, thus they two needed to be brought closer to each other. 96%ethanol was dripped on to swell UHMWPE membrane and then filled up the gap in-between UHMWPE and graphene (nano-porous UHMWPE membranes allow ethanol to permeate with high flux, 195.4 L/

at 0.75 bar) . Hydrophobic-hydrophobic interactions between UHMWPE and graphene along with the drying of ethanol, surface tension of ethanol continuously pulled the two layers closer until VdW force became significant causing the graphene layer to strongly adhere to the UDMWPE membrane. Then the bottom copper layer was removed away by etching in a solution of FeCl ₃ solution, followed washing with HCl and then deionized water. Next the UHMWPE/graphene composite membrane was collected by wafers or glass slides. Since UHMWPE is highly hydrophobic and low in density, it would not be wet by water or aqueous solution and always floated on the solution surface throughout the transfer process. The whole transfer did not involve any organic coating and removing, compressing or thermal treatment.

Example 3–Transfer of Graphene using Petrolatum to an UHMWPE Substrate

The graphene surface of a single layer of CVD grown graphene on copper foil was covered with a thin layer (approximately 1,000 nm) of melted petrolatum, which was then allowed to cool to room temperature. At which point, the petrolatume, graphene copper foil sandwich composite was transferred onto the surface of an 0.1 M aqueous solution of ammonium persulfate with the copper foil face down in the solution. After about one and a half hour, most of copper layer was etched away by the action of the ammonium persulfate solution leaving the single layer of graphene covered with the thin layer of petrolatum composite film.

The petrolatum/graphene composite film was scooped up with a 100 nm thick UHMWPE T-class membrane, excess ammonium persulfate was removed and the surface of the composite film was washed with deionized water and then allowed to air dry. Ethanol was then sprayed on the backside of UHMWPE T-class membrane to establish a firm VdW force between graphene and UHMWPE T-class membrane and was again allowed to air dry. Once dry the UHMWPE/graphene/petrolatum sandwich composite was submerged into a n-hexane solution to remove petrolatum.

Claims

A method for transferring a graphene layer to a polymer substrate comprising:

a. providing the graphene layer on a substrate;

b. contacting the graphene layer with the polymer substrate thereby forming a sandwich structure;

c. applying a solvent to the sandwich structure;

d. removing the solvent from the sandwich structure; and

e. removing the substrate.
The method of claim 1, wherein the step of removing the solvent from the sandwich structure induces the formation of Van der Waals interactions between the graphene and the polymer substrate having sufficient force to adhere the graphene to the polymer substrate.
The method of claim 1, wherein the graphene and the polymer substrate are separated by average distance of about 0.6 to about 1 nm.
The method of claim 1, wherein the substrate comprises platinum, cobalt, nickel, or copper.
The method of claim 1, wherein the step of applying the solvent to the sandwich structure comprises applying the solvent to the surface of the polymer substrate.
The method of claim 1, wherein the polymer substrate comprises pores having an average diameter greater than about 1 nm.
The method of claim 1, wherein the polymer substrate has an average thickness of less than 400 nm.
The method of claim 1, wherein the polymer substrate comprises ultra-high molecular weight polyethylene (UHMWPE) .
The method of claim 7, wherein the UHMWPE has an average molecular weight of about 1 to about 7 million amu.
The method of claim 8, wherein the UHMWPE is monaxially or biaxially oriented UHMWPE.
The method of claim 1, wherein the solvent is selected from the group consisting of ketones, alcohols, esters, ethers, alkyl halides, alkanes, aryls, and combinations thereof.
The method of claim 1, wherein the polymer substrate is UHMWPE and the method comprises:

a. providing the graphene layer on a copper substrate;

b. contacting the graphene layer with the UHMWPE substrate thereby forming a sandwich structure, wherein the UHMPE substrate is monaxially or biaxially oriented UHMWPE with an average molecular weight of about 1 to about 7 million amu and having an average thickness of less than 400 nm;

c. applying a solvent to the surface of the UHMWPE substrate;

d. removing the solvent from the sandwich structure thereby inducing the formation of Van der Waals interactions between the graphene layer and the UHMWPE substrate having sufficient force to adhere the graphene layer to the UHMWPE substrate; and

e. removing the copper substrate.
A composite comprising a first graphene layer on a first surface of a first UHMWPE substrate, wherein the distance between the first graphene layer and the first UHMWPE substrate is about 0.6 to about 1 nm and the first graphene layer and the first UHMWPE substrate are bound together with Van der Waals interactions of sufficient force to physically adhere the first graphene layer to the first UHMWPE substrate.
The composite of claim 13, wherein the first UHMWPE substrate has an average molecular weight of about 1 to about 7 million amu.
The composite of claim 13, wherein the first UHMWPE substrate has an average thickness of less than 400 nm.
The composite of claim 13, wherein the first graphene layer is a graphene monolayer.
The composite of claim 13 further comprising a second graphene layer disposed on the opposing face of the first UHMWPE substrate from the first graphene layer.
The composite of claim 13 further comprising a second UHMWPE substrate disposed on the opposing face of the first graphene layer from the first UHMWPE substrate.
The composite of claim 13, wherein the first UHMWPE substrate has an average molecular weight of about 1.5 to about 4 million amu, has an average thickness of less than 400 nm, and comprises pores having an average diameter greater than about 1 nm.
A method for transferring a graphene layer to an arbitrary target substrate comprising:

a. providing graphene layer on a substrate;

b. contacting the graphene layer with a petroleum oil substrate thereby forming a sandwich structure;

c. removing the substrate thereby forming a graphene layer on the petroleum oil substrate;

d. contacting the graphene layer on the petroleum oil substrate with the arbitrary target substrate; and

e. removing the petroleum oil substrate.