WO2008144111A1

WO2008144111A1 - Energy absorbing materials

Info

Publication number: WO2008144111A1
Application number: PCT/US2008/058712
Authority: WO
Inventors: Xi Chen; Yu Qiao
Original assignee: Columbia University in the City of New York
Current assignee: Columbia University in the City of New York
Priority date: 2007-03-29
Filing date: 2008-03-28
Publication date: 2008-11-27
Anticipated expiration: 2009-09-29

Abstract

An energy absorbing material (EAM) includes a nanoporous composite arrangement formed of a nanocomposite material (e.g., a nanoporous solid) and a liquid that is together sealed in one or more housings, for example, a honeycomb structure. The EAM is useful in a wide array of energy absorbing applications, such as bulletproof armors, engine mounts, shoe cushioning, and the like.

Description

ENERGY ABSORBING MATERIALS

SPECIFICATION

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 60/908,783, filed March 29, 2007, which is incorporated by reference herein.

BACKGROUND

Developing advanced energy absorbing materials (EAM) is of both scientific interest and technological importance. As EAMs are subjected to external loadings, the associated kinetic and strain energies can be converted, often irreversibly, to other forms of energy (e.g., heat, electricity, surface/interface tension). Based on the desired characteristics, a wide range of energy absorbing devices (e.g., protection and/or damping devices) can be designed (e.g., car bumpers, soldier armors, and blast resistant layers). Such devices can be designed to be used a relatively few number of times, such as bulletproof armor, or used in repeated loading and unloading cycles, such as the insole of a running shoe.

Due to its high energy absorption efficiency, cellular structures can be attractive EAMs. Cellular structures include, among others, space-filling foams and their two-dimensional counterparts, honeycombs, which are lightweight and can be made with relative ease from many materials. In these materials, performance can be affected by geometric arrangement of the solids in space in various arrangements, for example, to form interconnected or isolated cells. When compressive loadings are applied, the cell walls can buckle, which is one energy absorption mechanism. Cellular structures are applied in a variety of applications, for example, for shock mitigation, packaging, as well as damping. While existing energy absorbing materials have found applicability in some applications, it is desirable to increase and/or customize the energy absorbing characteristics of energy absorbing materials. SUMMARY

Energy absorbing cushioning media are described. Some embodiments include an energy absorbing material including a housing and a nanocomposite material contained within the housing, the nanocomposite material including a nanoporous solid material and a liquid phase, the liquid phase entering one or more nanopores of the nanoporous solid material at an infiltration pressure and the energy absorbing material thereby absorbing energy. The housing can include a honeycomb structure. The liquid phase can include a non- wetting liquid. The liquid phase can include water or water-based solution. The energy absorbing material can be reusable. The liquid phase can include sodium chloride. The nanocomposite material can include a gas phase, including carbon dioxide or air.

Some embodiments include an energy absorbing device including an energy absorbing material, the energy absorbing material including a housing and a nanocomposite material contained within the housing, the nanocomposite material including a nanoporous solid material and a liquid phase, the liquid phase entering one or more nanopores of the nanoporous solid material at an infiltration pressure and the energy absorbing device thereby absorbing energy. The energy absorbing device can be an engine mount, a protective frame, an armor, a shoe pad, a sports helmet, a vehicle bumper, a protective coating, or a soundproof coating.

Some embodiments include a cushioning medium for an article of footwear including a housing adapted for integration into the article of footwear and a nanocomposite material within the housing, the nanocomposite material including a liquid phase, and a nanoporous solid material, the liquid phase entering one or more nanopores of the nanoporous solid material at an infiltration pressure and the cushioning medium thereby absorbing energy. The liquid phase can include water or water-based solution. The nanoporous solid material can include a nanoporous material. The cushioning medium can be in removable contact with the article of footwear. The cushioning medium can include an insole. The housing can include a cellular structure. BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the presently described subject matter and its advantages, reference is now made to the following description, taken in conjunction with the accompanying drawings, in which: Fig. 1 depicts an example schematic diagram of an demonstration setup of the described subject matter.

Fig. 2 depicts example stress-strain curves of the described subject matter.

Fig. 3 depicts an example finite element simulation of empty and nanocomposite enhanced cells of the described subject matter.

Fig. 4 depicts example testing results of shoes and liquid super-sponge.

Fig. 5 depicts an example cross section of a running shoe.

Fig. 6 depicts an example cross section of the heel of a running shoe.

Figs. 7a and 7b depict graphical data in accordance with some embodiments of the described subject matter.

Fig. 8 depicts graphical data in accordance with other embodiments of the described subject matter.

Fig. 9 depicts graphical data in accordance with further embodiments of the described subject matter. Fig. 10 depicts graphical data in accordance with yet other embodiments of the described subject matter.

DETAILED DESCRIPTION

An example energy absorbing material (EAM) that satisfies at least the described needs includes a nanoporous composite arrangement formed of a nanocomposite material (e.g., a nanoporous solid) and a liquid that is together sealed in one or more housings, for example, a honeycomb structure whose cells are filled with a nanocomposite material.

Nanoporous materials include solids containing large volume fractions of nano-sized pores. These materials can have substantially high areas of pore surfaces. Traditionally, nanoporous materials have been used for absorption, catalysis and filtering purposes, but the high interface energy between nanoporous materials and liquid phases have not been explored for energy absorption applications. A flexible material, for example, a liquid phase such as water, or a water-based solution, is used as the nanofiller in the nanocomposite material to take advantage of the extensive surface/interface area. Once a critical pressure is reached, the nanofiller begins to be forced into the nanopores, thereby converting the loading energy into interfacial energy. Thus, the solid-liquid interactions (i.e., the capillary effect) can be greatly amplified by the large specific area. Accompanied by the pressure-induced infiltration, a large amount of external work is transformed into the solid-liquid interfacial energy, which can be regarded as being absorbed.

Many techniques exist for constructing nanoporous materials with varying characteristics such as surface area, and pore size. For example, in one commonly used templating technique, the network surrounding the template is produced first through phase separation or nanocasting. The template is then removed by etching or heating, leaving the empty space inside as nanopores. In another technique, a thermostable polymer is combined with a thermolabile (thermally decomposable) polymer. The mixture is cross-linked and thermalized, resulting in a nanoporous material. In still another technique, a polymer is formed from a solution in the presence of microdroplets of a second solution. The microdroplets are then evaporated, leaving nanopores in the polymer. Nanoporous materials can include microporous materials with a pore radius (r) between about 0.5 and about 2 nm, mesoporous materials with r between about 2 and about 50 nm, and macroporous materials with r > about 50 nm.

In one embodiment, a nanocomposite material is constructed by dispersing surface charged nanoporous particles in a nonwetting liquid. Nonwetting liquids include, for example, those liquids which, under ambient conditions (for example, without external pressure) the liquid is not likely to automatically flow into the pores of the nanoporous solid. Of course, it is contemplated that other techniques for forming nanocomposites can be employed.

When liquid molecules are confined in a macropore, their behaviors are determined by both the solid-liquid interface diffusion and the normal flow in the interior. In a mesopore, the liquid behavior is more dependent on the interface zone. In the smallest micropore, since there are only a few atoms across the pore cross- section, the solid-liquid interaction often exhibits unique characteristics. The microporous materials, such as activated carbons, carbon nanotubes, and zeolites have been widely applied as electrodes, filters, sorption agents, etc. Many mesoporous materials, such as transition metal oxides, silicon nitride, and alumina, can be synthesized through synergistic co-assembly or precision imprinting. Their pore sizes, pore shapes, pore volume fractions, pore distributions (ordered or disordered), and surface properties can be adjusted quite precisely in broad ranges. Macroporous materials, such as monel, copper, polymers, etc., can be synthesized through sintering of nanoparticles or reversed phase techniques. These materials can be in powder form with the grain size at the sub-μm or μm level, in membrane form with thickness around 10-1000 μm, or in bulk about 10-100 mm large.

Energy absorption is one important criteria in designing materials for protective structures such as car bumpers, soldier armors, etc. Cellular solids (e.g., metal foams, honeycombs) are well known energy absorbing materials. Composite materials, such as chopped carbon fiber-polymer composites, fiber-cement composites, and knitted textile composites, have also been used as energy absorbing materials. Combinations of composites and cellular structures have also been proposed, such as grid-domed textile composites and particle-reinforced syntactic foams. Active materials, such as piezoelectrics and shape memory alloys, are capable of dissipating mechanical energy (impacts or vibrations), which enables active energy absorption. Table 1 compares the absorption capacities of a few important materials.

Table 1: Comparison of High-Strain-Rate Energy Absorption Effectiveness

The described subject matter is useful in advanced cushioning materials in a variety of national security and consumer applications, such as engine mounts and protective frames for land vehicles, aircrafts, satellites and spacecrafts, lightweight liquid armors, healthcare products, such as shoe pads or insoles to alleviate stress on joints, sports helmets, vehicle bumpers, protective coatings for consumer electronics devices, such as cellphones or laptops, soundproof coatings, and the like.

In some embodiments, the nanocomposites are contained within a housing, for example, within a cellular structure such as a honeycomb. A honeycomb structure can be used, not only to contain the nanocomposite, but also to provide additional energy absorption. As can be seen, the addition of a nanocomposite to the empty spaces of a honeycomb structure can enhance the energy absorbing capacity of the honeycomb material. In some embodiments, the housing can be rigid such that it absorbs relatively less energy. For example, an engine mount for an automobile can include a substantially rigid cylinder and a piston which, when compressed, absorbs energy from the force of the compression. In other embodiments, the housing can be deformable such that its deformation also contributes to energy absorption. For example, a cell well of a cell containing a nanocomposite can provide additional energy absorption as it is compressed, contributing to a great energy absorption capacity of the device. A deformable housing can also allow the EAM to conform to different tailored and flexible shapes for different applications (e.g., the sole of a running shoe in one application and a bullet proof armor in another). As the empty space in the ductile cell is filled by an aqueous suspension of hydrophobic nanoporous silica gel or other hydrophobic nanoporous materials, the work done by the compressive load along the axial direction can be dissipated, not only through the ordinary cell-wall buckling, but also via the extended yielding and the pressure-induced infiltration of the nanocomposite filler. As a result, the energy absorption efficiency, on either mass or volumetric basis, is considerably improved.

Traditionally, when honeycomb materials are compressed from the lateral direction, the cell walls can deform quite smoothly. However, if the compressive load is applied along the out-of-plane direction, during the buckling process, the working load can be non-uniform. Under this condition, especially in a thin- walled structure, the wavelengths of wrinkles in cell walls are much smaller than the structural size. Initially, as the cell wall is nearly perfect, buckling initiation demands a large stress. As the cell wall becomes locally sigmoidal, the critical stress for the expansion of the wrinkled zone becomes much lower. That is, while the cell- wall buckling is activated at a high stress level, the major portion of the energy absorbing process, which dominates the overall energy absorption efficiency, takes place at a relatively low stress level, significantly lowering the overall protection/damping capacity.

One technique to solve this problem is to reinforce the honeycomb with a nanocomposite filler, which shows much improved performance in comparison with empty cells and water-filled cells. The liquid-based nanocomposite fits well with the cell wall, avoiding possible problems of filler-network mismatch. The thermal, electrical, and magnetic properties of the structure can also be adjusted in broad ranges, depending on specific requirements; that is, the combination of nanoporous solid and non-wetting liquid, together with the housing, can have a variable thermal, electrical, and magnetic properties, such that the device can achieve its energy absorption goal without compromising other thermal, electrical and magnetic functionalities.

Fig. 1 depicts an example schematic diagram of a setup for demonstrating the described principles, including a housing, such as a stainless steel cylinder 100, a hydrophobic nanoporous particle (such as a hydrophobic nanoporous silica gel 102 (or a mixture of silica nanoparticles with water)), loading plates 104 and 105, and a liquid phase 106, such as water. The height, outer diameter, and wall thickness of the cylinder 100 are h=25.4 mm, 2R=6.86 mm, and t=0.13 mm, respectively. Both ends of the cell are fixed on stainless steel loading plates 104 and 105 using a J-B Weld epoxy glue. The cell is filled with an aqueous suspension of 0.4 g of Fluka 100 C8 reversed-phase nanoporous silica gel. The sample preparation is performed underwater so that no air is entrapped. The nanoporous silica gel 102 is hydrophobic. The average nanopore size is 7.8 nm. The specific nanopore volume is 0.55 cm3/g.

It can be seen that the deformability of the empty cell is high. After the initial linear compression stage, as the buckling initiates and continues, a broad plateau is formed, with the width being more than 70% of the initial cell height. As discussed above, due to the change in cell-wall configuration, the buckling initiation stress is much higher than the buckling development stress. The buckling plateau is quite jerky, consisting of a number of "bumps." Each bump reflects the stress accumulation, formation, and folding process of a wrinkle.

As the cell is filled with distilled water, since the compressibility of water is negligible, the cell-wall buckling is suppressed, and initially the energy dissipation is dominated by the extended cell wall yielding along the radial direction. As a result, the structure becomes quite rigid, and shortly after the peak load is reached, the inner pressure becomes sufficiently high such that abrupt cracking takes place along the longitudinal direction. After the liquid leaks, the behavior resembles that of an empty cell, except that, since the crack weakens the cell wall, the buckling of the fractured cell occurs at a relatively low stress level. Depending on the crack length, the decrease in buckling stress is in the range of 5-25%. Therefore, the energy absorption capacity is reduced, as shown in Table 2, where the absorbed energy U is calculated as the average area under the load-displacement curves in the nominal strain range of 0-0.75, and m and V are the mass and the volume, respectively. The solid curve 218 in Fig. 2 indicates the behavior of a cell filled with the nanocomposite. After the initial linear compression section 202, as the critical nominal stress of about 35 MPa is reached, the cell wall deforms plastically along the radial direction, since the buckling is suppressed by the liquid phase. As the cell is compressed, the pressure increases continuously. Eventually, at point 204, the pressure-induced infiltration in the largest nanopores is activated and the liquid phase becomes highly compressible. As a result, buckling takes place. As a major wrinkle is formed, the stress quickly drops to point 206. In the nanocomposite cell, because the cell wall is supported by the liquid phase, the buckling can occur only outward, leading to a sudden increase in volume, V, and thus the cell becomes only partly filled. Under this condition, the behavior is similar to that of an empty cell, until the cell is compressed to point 208 and V is "consumed" by wrinkle folding. Table 2: Comparison of empty, water-filled, and NMF liquid enhanced cells

Mass m (g) Volume V Absorbed Wm (J/g) u/v

(cm³) energy (J) (J/cm³)

Empty Cell 0.57 0.94 6.54 11.5 6.96

Water-filled 1.48 0.94 5.80 3.92 6.17

Cell

Nanocomposite

Enhanced Cell 1.20 0.94 16.7 13.9 17.8

As the liquid phase starts to carry load again, the nominal stress increases from points 208 to 210. When P rises to 32 MPa, the pressure-induced infiltration is reactivated, forming the second plateau 210-212. As the plastic strain in the cell wall is increasingly large, abrupt cracking occurs at point 212, somewhat similar to the failure observed in the water-filled cell. The total volume change associated with the second loading is about 170 mm³, smaller than the total nanopore volume; that is, the energy absorption capacity of the nanoporous silica gel is not fully utilized. As the cell empties, the nominal stress drops to 7 MPa, after which the behavior is similar to that of an empty cell (214-216). According to Table 1, compared with the energy absorption efficiency of an empty cell, U/m of the nanocomposite-filled cell is more than 20% larger and UN is more than two times higher. 220 represents the behavior of an empty cell and 222 represents the behavior of a water-filled cell.

Fig. 3 depicts an example finite element simulation of the empty and the nanocomposite enhanced cells. Curve 300 represents a simulation for a nanocomposite enhanced cell and 302 represents a simulation for an empty cell. A numerical protocol closely simulates the behavior under various situations. To simulate the behavior of the nanocomposite filled cell, a phenomenological approach was taken: the tube was first filled with a liquid with the bulk modulus of 2.1 GPa, the same as that of water; upon loading, the pressure of the liquid quickly increased to 18 MPa, at which point infiltration and the cell-wall buckling started. It can be seen that the simulation has well captured the buckling initiation condition of the pressurized cell used in the tests. The data and the numerical simulation examples have shown that the energy absorption efficiency of a honeycomb is improved by using nanocomposite filler. The energy absorption is achieved at least via cell-wall buckling, extended yielding, as well as pressure-induced infiltration. The buckling in this example is largely non-uniform.

The cellular structures (e.g., honeycomb) are formed in accordance with any appropriate technique known to someone of ordinary skill in the art. For example, a honeycomb structure can be formed by cutting strips from a sheet material, forming the strips, joining the strips intermittently to form a core by welding, gluing, or chemical bonding, and affixing face sheets atop the core. The nanocomposite material can be made to fill the spaces between the intermittently joined strips prior to affixing the face sheets to the core. Alternatively, the core can be formed by extrusion techniques, the spaces filled with the nanocomposite material, and the face sheets affixed to the core to seal the cells. Still another honeycomb formation technique is described in United States Patent No. 6,057,025, issued to O. Kalman. In this technique, the nanocomposite material can be inserted into the domed portions prior to affixing the face sheets to the core.

Any appropriate technique that completely or partially fills the cells with the nanocomposite material can be employed to introduce the nanocomposite into the cells. For example, a core that is capable of holding material in the cells can be dipped into the nanocomposite material, allowing the nanocomposite material to fill the cells before sealing the cells.

It should be noted that combining a nanocomposite with a honeycomb structure is not an intuitive practice since, for example, the addition of the nanocomposite can increase the weight of the EAM. However, since a nanocomposite can have a greater energy absorption density (i.e., energy absorption per mass) compared with air, the employment of a nanocomposite in honeycomb can provide a significant gain of energy absorption capacity, thereby offsetting the increased weight. Additionally, combining a nanocomposite with a honeycomb structure can also allow the honeycomb material to be reduced, thereby providing the same energy absorption capacity as a honeycomb structure with more honeycomb material or a honeycomb structure with greater weight. It should also be understood that these characteristics can also be achieved with housings other than honeycomb structures.

In some embodiments, the nanocomposites can be directly filled into existing cellular materials or honeycombs. If the EAM is to be used for high-pressure applications, the cell wall can be enhanced (e.g., thickened or combined with other additives or support materials) so as to sustain higher pressures. If the EAM is to be used for low-pressure applications, the cell wall can be reduced (e.g., thinned). The alignment and shape of cells can also be adjusted for optimized energy absorption performance. For example, when designing a shoe insole, the cells can be aligned in a way such that when a person is walking, the pressure flow/distribution is consistent with the optimized ergonomics. Such an arrangement may include shapes and arrangements that result in higher energy absorption, a faster response time, or the like where it is determined that such properties are desirable. When designing a body armor the cell alignment and shapes can be designed so as to provide maximum and more effective protection of the body. Different nanocomposites can be filled into different cells to tailor the energy absorption profile. For example, some cells can be filled with an EAM with a lower infiltration pressure, and some cells can be filled with an EAM with a higher infiltration pressure. Such arrangements can make the EAM capable of absorbing both lower and higher pressures under different circumstances. In some embodiments, since the energy absorption can start as soon as liquid starts to flow into cells, the response time of the EAM can be very quick, on the order of microseconds. This can render certain EAMS suitable for impact or blast protection. In some embodiments, a smaller pore size can yield a faster response time and a larger surface area, possibly leading to higher energy absorption capabilities. In some embodiments, during application, the housing can be non- deformable (e.g., so as to enhance maximum pressure increase within the cell), or the housing can be deformable (e.g., to allow certain flexibility). Deformation can be recoverable (e.g., the shoe insole example below), or non-recoverable (e.g., deformation of a thin wall of the honeycomb cell during buckling). In different applications, different reusability can be achieved.

In some embodiments, the liquid-solid interaction can also be tailored. By using smaller pore sizes (when the nanopores size is smaller than 2 nm) the gas solubility can be reduced in nanopores. Thus, the undissolved gas cluster can help to repel the infiltrated liquid segment out during unloading, contributing to reusability (e.g. for cyclic protection). If a larger pore size is used, a certain barrier can be formed for defiltration during unloading - if the barrier is high, the liquid can be prevented from exiting the pore during unloading. As a result, the EAM can be used for single use applications (e.g., body armor or a car bumper). The barrier can be lowered by adding admixtures into the liquid to make the nanocomposite less hydrophobic, and thus making it easier for the liquid to defiltrate from the pores during unloading. In this way, a reusable device can be constructed for damping protection, for example, applied to health products described below. Other damping/cyclic protections include sound proof coatings, engine mounts, protective covers for electronics or sensitive instruments, etc.

In connection with examples related to Fig. 7a, nanoporous silica- water components are sealed in a steel housing. The average pore size is IOnm and the liquid is confined in the nanopore after the load is removed, and the energy absorption capability (hysteresis area within a cycle) is small in subsequent cycles. Cycles 700-704 are depicted in Fig. 7a. The portion of cycle 700 before point 706 shows a linear compression of the empty nanoporous solid and liquid. The portion from point 706 to 708 shows infiltration as the liquid starts to flow into the nanopores. The portion from point 708-710 shows that the pores are filled and shows a linear compression of the filled nanoporous solid and the liquid. The portion from points 710 to 712 shows unloading.

In examples in connection with Fig. 7b, a 2 nm pore size of silica is employed and the defiltration occurs which can contribute to reusability. A similar principle can apply to other nanoporous solid-liquid combinations, where the pore size variation can lead to controlled defiltration properties for different properties of energy absorption. Lines 750-754 depict three cycles of these examples.

In some embodiments, a nanoporous silica can become less hydrophobic, for example, by increasing alcohol content in water. Fig. 8 shows that with increased ethanol the energy absorption capability is decreased. However, the device can be used for absorbing lower pressures because the infiltration pressure is reduced. Lower pressure absorption can be useful for typical consumer applications, such as for shoe insoles. In some embodiments, more viscous liquids can be used. Fig. 9 shows different water-glycerin mixtures, and with the increase of glycerin content, energy absorption can be enhanced. This is due to the additional friction between viscous liquid molecules. Moreover, by increasing the loading rate, the energy absorption can be enhanced due to friction between liquid molecules and nanoporous solid, as shown in Fig. 10 for water-silica components.

In some embodiments, the EAMs of the described subject matter are applied to healthcare products, for example, shoe insoles, sports helmets, mattresses, replacement knee joints, therapeutic cushions, stretchers, ambulance beds, and the like.

A comparison of the energy absorption of two shoes, a running shoe and a walking shoe, with a nanocomposite sealed in a steel container with a sliding piston, demonstrates some principles of the described subject matter. An exemplary running shoe includes an initial heel thickness of 36.88 mm and weighs 568.74 grams (of which about 50 gram of insole material is dedicated for impact absorption). An exemplary walking shoe includes an initial heel thickness of 27.31 mm and weighs 601 grams (of which about 50 gram of insole material is dedicated for impact absorption). The example nanocomposite material is 5 g of water with 2 g of silane group treated nanoporous silica gel, sealed in a rubber container with a length of 190 mm and a diameter of 19.05 mm. Of course, the types and amounts of the nanoporous solid, liquid phase, and housing can vary and are presented for illustrative purposes only.

To demonstrate the compression capacity and deformation of the shoes enhanced with the EAM, MTS compression demonstrations were performed. The steel rod was centered at the sole of the heel or the piston of the steel container. As an external load was applied, the specimen underwent a compression rate of 1 mm per minute until reaching the set point. The set point was similar to the weight of an average person. Then, the steel rod was moved back at the same speed, completing a loading-unloading cycle. Fig. 4 depicts example results of shoes compared with EAMs. It can be seen that, by using only 7 g of the EAM, the energy absorption performance of the latter (measured by the area enclosed by the cycle) is better than that of the shoes. Table 3 shows that the energy absorption efficiency, which is calculated as the total absorbed energy divided by the weight of the insole is nearly 10 times higher than that of the conventional shoe insoles.

Table 3: Comparison of energy absorption performance

Absorbed energy (J) Energy absorption efficiency (mJ/g)

Running Shoe 0.43 -8.6

Walking Shoe 0.28 -5.6

Liquid Super- Sponge 0.61 87

In one embodiment, a cushioning medium includes a nanocomposite material, including water (liquid phase) mixed with a silane group treated nanoporous silica gel (nanoporous material), Fluka Cl 8 end-capped reversed-phase silica gel, sealed in a rubber container. Figs. 5 and 6 show an example inner surface of a running shoe, demonstrating one technique of inserting the cushioning medium (for example, a cushioning layer) inside. Fig. 5 depicts an example cross section of a running shoe. Fig. 6 depicts an example cross section of the heel of a running shoe. The shoes of Figs. 5 and 6, respectively, each include layers 500 and 600 above soles 502 and 602, respectively. The cushioning layer can be incorporated into the layers 500 or 600, or can be inserted above or below these layers as desired.

In some embodiments, the cushioning medium can include one or more cells and can form a cellular structure. Each cell can be formed of a cell wall enclosing a nanocomposite material. In one embodiment, the cellular structure includes a honeycomb structure. In some embodiments, all cells include a nanocomposite material. In other embodiments, one or more cells are filled with air or other materials as appropriate, while other cells are filled with a nanocomposite material. In still other embodiments, individual cells can differ in the amount, type, or particular formulation of nanocomposite material used to fill the cells. For example, a nanocomposite material with a greater energy absorption capacity can be used for the heel of the cushion (where the impact is greater), and a less absorbent material can be used for the forefoot portion. Various nanoporous solid and liquid combinations, as well as the particular housing, can be chosen by someone of ordinary skill in the art, depending on factors including performance, environment, temperature, ergonomics, and comfort considerations. In one embodiment, the cushioning medium can be removably attached to the shoe, such as an insole which can be changed by the end user. In other embodiments, the EAM liquid shoe layer can be formed as part of the structure of the shoe itself. In still other embodiments, the EAM shoe layer can form a full layer of the shoe or can form a partial layer, such as a portion covering the heel or the forefoot part of the shoe. In some embodiments, the cushioning medium can be integrated into various articles of footwear, for example, boots, slippers, flip-flops, running shoes, walking shoes, dress shoes, and the like.

Depending on the condition of application (e.g., cold or hot weather, for use by men or women, for running or walking, or where the required infiltration pressure is high or low), the chemical admixture (such as salt) content can be varied such that infiltration can be activated at high or low pressures. The described subject matter is applicable to other cushioning applications and its performance can be adjusted in a wide range. For example, the EAM can be incorporated into a sports helmet, elbow and knee pads, seat cushion, or any appropriate article for energy absorption purposes.

In some embodiments, the pore size of the nanoporous particles used in EAMs can include any appropriate size at which outflow occurs for repeatable usage. For example, outflow can occur due to the gas present within the nanopores with an average pore size of less than about 3 nm. However, it should be understood that materials with average pore sizes larger than 3 nm can be used, such as, for example, if the particular application requires the "outflow" performance to be customized. Gas molecules in relatively large nanopores can be dissolved in the liquid during pressure-induced infiltration, leading to the phenomenon of "nonoutflow". By contrast, gas molecules can form clusters in relatively small nanopores, which triggers liquid defiltration at a reduced, defiltration pressure. Outflow can also occur by adding chemical admixtures such as salt into water-silica mixtures. Increasing the salt content can change the interface energy and make outflow possible after unloading (for example for larger pores). It should be understood that appropriate materials other than salt can be used to enhance outflow.

In one embodiment, a hydrophobic nanoporous Fluka C₈ end-capped reversed-phase silica gel with an average pore size of r=7.8 nm and a standard deviation of 2.4 nm can be used to create a nanocomposite material enhanced for gas- induced outflow. To form the nanocomposite material, initially, 0.5 g of the nanoporous silica gel is immersed in 7 g of 15 wt % aqueous solution of sodium chloride. Sodium chloride is added to enhance the gas-induced outflow properties of the nanocomposite material. In one embodiment, the gas used is CO₂, but it should be understood that any appropriate gas can be used. Therefore, an EAM containing the gas-enhanced nanocomposite material is reusable, where the energy absorbing capacity of the EAM survives multiple loading/unloading cycles.

The housing can be made of a variety of materials, for example, metals, polymers, rubbers and the like. In some embodiments, the housings are formed of a material which is ductile and capable of withstanding the pressures for the particular application.

Again, it should be noted that the EAM can be applied in a wide range of functions, as mentioned above. For example, EAMs have application in body armor, where shear thickening liquids have already been used. Shear thickening liquids typically work under shear forces and under high strain rates. However, the EAM functions directly under compression, which is better suited for blast/impact protection. Moreover, EAMs can function under both quasi-static loads and a wide range of strain rates. Furthermore, EAMs can be combined with shear thickening liquids to further enhance the energy absorption capability of these liquid armors. The liquid phase can include, without limitation, water and water- based solutions (e.g., sodium chloride), alcohols (including methanol, ethanol, hexanols, etc.), liquid metals, polyols (glycerin, mineral oil, etc.), and their mixtures. The nanoporous material can include, without limitation, silica, metal, zeolite, carbon, etc. In some embodiments, a gas phase can be used to control the nanofluidic behavior. The gas includes, without limitation, air, oxygen, nitrogen, carbon dioxide. The nanocomposites can be sealed in a housing, without limitation, including metal (steel, copper, aluminum, titanium, etc.), polymer, plastic, etc. The shape of the housing includes, without limitation, one or multiple cells, and the cells can be closed or interconnected, or a mixture of both. In some embodiments, the properties of the EAM can be tuned to provide the desired energy absorption profile as needed by the particular application. In one embodiment, different liquids can be mixed together so that the surface energy, and therefore the energy absorption characteristics of the EAM varies. For example, the use of water as the liquid phase and the use of water with additives such as salt can provide absorption characteristics different from one another. The addition of salt can assist in liquid defiltration, making an EAM more reusable as compared with an EAM without salt. In other embodiments, the specific type of housing can be selected to provide any additional energy absorption capacity as required. For example, the deformability characteristics of the housing can contribute to the energy absorption capacity, reusability, recovery time, etc. These parameters can be tailored depending on the specific needs of the EAM to be used. In other embodiments, the size of the housing, combination of housings, and specific arrangement of housings in the EAM can be customized. For example, a bullet proof armor can include a first layer of housed nanocomposite in which the housing has particular characteristics to absorb the energy needed for smaller loads (e.g., a blow from an assailant's fist) and another layer in which the housed nanocomposite material includes a housing suitable for larger loads (e.g., to absorb energy from a bullet). In another example, the specific arrangement of housed nanocomposite can be tailored for the specific applications. The forefoot portion of an energy absorbing insole of a running shoe can include a housed composite with greater absorption characteristics in portions of the insole where the foot requires additional cushioning.

In other embodiments, nanoporous materials with different pore sizes and pore characteristics can be chosen, alone or in combination, to achieve the desired absorption characteristics. The housing can be a single celled or multiple celled, and different cells can host different nanoporous material and liquid combinations. The tuning of the properties of each element would enable different characteristics and performances of energy absorption of the EAM, suitable for various applications.

The foregoing merely illustrates the principles of the disclosed subject matter. Various modifications and alterations to the described embodiments will be apparent to those skilled in the art in view of the teachings herein. It will thus be appreciated that those skilled in the art will be able to devise numerous techniques which, although not explicitly described herein, embody the principles of the disclosed subject matter and are thus within the spirit and scope thereof.

Claims

1. An energy absorbing material, comprising: a housing; and a nanocomposite material contained within the housing, the nanocomposite material including a nanoporous solid material and a liquid phase, the liquid phase entering one or more nanopores of the nanoporous solid material at an infiltration pressure and the energy absorbing material thereby absorbing energy.

2. The energy absorbing material of claim 1, wherein the housing includes a honeycomb structure.

3. The energy absorbing material of claim 1, wherein the liquid phase includes a non-wetting liquid.

4. The energy absorbing material of claim 1, wherein the liquid phase includes water or water-based solution.

5. The energy absorbing material of claim 1, wherein the energy absorbing material is reusable.

6. The energy absorbing material of claim 1, further comprising: an energy absorbing device, the energy absorbing material integrated into the energy absorbing device to provide energy absorption.

7. The energy absorbing material of claim 6, wherein the energy absorbing device is selected from the group consisting of an engine mount, a protective frame, an armor, a shoe pad. a sports helmet, a vehicle bumper, a protective coating, and a soundproof coating.

8. The energy absorbing material of claim 6, wherein the energy absorbing device is a cushioning medium for an article of footwear and the housing is adapted for integration into the article of footwear.

9. The energy absorbing material of claim 8, wherein the cushioning medium is an insole.

10. The energy absorbing material of claim 1, wherein one or more properties of the energy absorbing materials is tuned to provide a desired energy absorption characteristic.

11. A method for absorbing energy, comprising: (a) applying a load to an energy absorbing material, the energy absorbing material including a nanocomposite material, the nanocomposite material including a nanoporous solid material and a liquid phase;

(b) infiltrating one or more nanopores of the nanoporous solid material by the liquid phase at an infiltration pressure; and (c) absorbing the load.

12. The method of claim 11, further comprising:

(d) releasing the load;

(e) defiltrating the one or more nanopores by the liquid phase at a defiltration pressure; and (f) repeating (a) to (e).

13. The method of claim 11, wherein the liquid phase includes a non- wetting liquid.

14. A method for absorbing energy, comprising:

(a) Tuning one or more properties of an energy absorbing material; (b) applying a load to the energy absorbing material, the energy absorbing material including a nanocomposite material, the nanocomposite material including a nanoporous solid material and a liquid phase;

(c) infiltrating one or more nanopores of the nanoporous solid material by the liquid phase at an infiltration pressure; and (d) absorbing the load.

15. The method of claim 14, wherein the property is selected from the group consisting of the level of deformability of one or more housings used to contain the energy absorbing material, the material used to construct the housing, the specific liquid phase used, the specific combination of one or more liquid phases used, the specific nanoporous solid used, the specific combination of one or more nanoporous solids used, the arrangement of the one or more housings, the addition of additives to the liquid phase, or a combinations of two or more of the properties herein.