ULTRA-LOW THERMAL CONDUCTIVITY DIVING SUIT MATERIAL FOR ENHANCED PERSISTENCE IN COLD WATER DIVES
Disclosed are ultra-low thermal conductivity fabrics, methods for preparing them and methods of using them, in particular as diving suit materials for enhanced persistence in cold-water dives.
This application claims the benefit of priority to U.S. Provisional Patent Application Ser. No. 62/424,828, filed Nov. 21, 2016.
GOVERNMENT SUPPORTThis invention was made with government support under Grant No. N00014-16-1-2144, awarded by the Office of Naval Research. The government has certain rights in the invention.
BACKGROUNDUnderwater diving, as a human activity, is the practice of descending below the water's surface to interact with the environment. Immersion in water and exposure to high ambient pressure have physiological effects that limit the depths and duration possible in ambient pressure diving. This is because humans are not physiologically and anatomically well adapted to the environmental conditions of diving. In particular, in cold-water environments (e.g., water at less than 10° C.) a diver is at risk of developing hypothermia. Current diving garments only allow a diver to stay in the water for less than an hour. In some cases, however, divers need to stay in the water for more than an hour, such as for deep-sea exploration or for military recognizance missions. Accordingly, there remains a need in the art for improved diving garments that reduce a diver's risk of hypothermia, especially during long dive times.
SUMMARYProvided herein are thermally insulating fabrics comprising a polymer infused with a high molecular weight gas. Also provided herein is a flexible garment comprising a neoprene foam infused with a high molecular weight gas. In some embodiments, the flexible garment is a dive suit, such as a wetsuit, a variable volume drysuit, a hot water wetsuit, or an active diver thermal protection system.
Also provided herein is a method for preparing the thermally insulating fabrics described herein comprising placing fabric in a sealed container; and filling the container with an insulating gas. In some embodiments, the fabric comprises a polymeric material (e.g., neoprene, polystyrene, or nitrile butadiene rubber). In some embodiments, the insulating gas is a high molecular weight gas, such as a noble gas (e.g., xenon, krypton, or argon).
Also provided herein are methods for protecting a diver in cold water environments, comprising providing a diver with a thermally insulating fabric (e.g., such as those used in dive suits) described herein. In some embodiments, the method further comprises reducing the diver's risk for hyperthermia. In other embodiments, the method further comprises allowing the diver to stay in the cold-water environment from about two hours to about three hours.
Thermally insulating fabrics are critical for human survival at low temperatures. This is especially true in water, where heat loss to the surroundings is much higher than in air, even at smaller temperature differences. High-performance thermally insulating garments (whose performance does not degrade in water) are becoming essential components for military divers, shipyard and underwater workers, and recreational open-water swimmers and triathletes. In general, foam insulation typically contains a low-thermal conductivity gas dispersed in a relatively low thermal conductivity matrix in an open or closed cell structure. The thermal conductivity of the composite is highly influenced by the thermal conductivities of the gas and matrix material; in addition, the cell size and type affect the effective thermal conductivity. (B. P. Jelle, Energy Build., 2011, 43, 2549-2563.)
Traditional thermal insulation materials comprise biopolymer-based materials, such as cork (thermal conductivity between 0.040-0.050 W/m-K) and cellulose (0.040-0.050 W/m-K), or fossil-fuel-derived polymeric foams, such as expanded polystyrene (0.030-0.040 W/m-K), extruded polystyrene (0.030-0.040 W/m-K), polyurethane (0.020-0.030 W/m-K), neoprene (0.050-0.060 W/m-K), and the like. Neoprene foams offer flexibility (capability of being shaped into a garment) and a closed cell nature (giving the material water resistance). (E. Bardy, J. Mollendorf and D. Pendergast, J. Phys. Appl. Phys., 2006, 39, 1908.)
In some embodiments, provided herein is a process for the non-destructive, repeatable fabrication of transient gas insulating materials (GIMs) from commercial closed-cell neoprene (also referred to as polychloroprene) foams.
In some embodiments, the methods disclosed herein are used to modify commercial neoprene in the form of a wetsuit. In some such embodiments, the methods disclosed herein reduce the thermal conductivity of the neoprene by up to about 40% (0.031 W/m-K), thereby achieving the lowest value for a flexible, water-resistant insulating material. As used herein, the term “flexible” refers to a material that can easily be used to form a garment that allows the user to move satisfactorily while underwater. In some embodiments, the thermal conductivity of the altered neoprene remains below the control value for more than 12 hours. Accordingly, the materials provided by the methods disclosed herein enhance insulation performance of foam neoprene-based garments, such as wetsuits.
The thermal conductivity of a gas scales linearly with its specific heat and inversely with the square root of its molecular weight. (G. Chen, Nanoscale Energy Transport and Conversion: A Parallel Treatment of Electrons, Molecules, Phonons, and Photons, Oxford University Press, 2005.) To this end, the insulating gas used in the methods disclosed herein must be a monatomic (low specific heat) and high-molecular-weight gas.
Earlier studies used krypton-xenon mixtures and argon as blowing agents for foam insulation. (See, e.g., U.S. Pat. No. 5,266,251A; K. Dey, C. Jacob and M. Xanthos, J. Vinyl Addit. Technol., 1996, 2, 48-52). These techniques were not widely adopted as a result of the significant leakage rate and replacement by ambient air that the foams experience following manufacturing. The methods disclosed herein overcome these issues. Indeed, the methods disclosed herein demonstrate that commercial, closed-cell foams can be infused with the high molecular weight, noble gases in a non-destructive and repeatable fashion at any point post-fabrication. In some embodiments, the methods disclosed herein are used with fabrics comprising neoprene foams. Such fabrics are critical for extending dive persistence in near 0° C. water.
Neoprene foam conducts thermal energy such that a wetsuit wearer can only spend less than one hour in near-freezing water before becoming susceptible to hypothermia. The ultra-low thermal conductivity garments produced by the methods disclosed herein are capable of drastically extending dive times by reducing the rate of heat loss of the wearer. Taken together, the methods disclosed herein provide a simple technique enhancing the insulating performance of foam composite materials. Further, the methods provided herein extend the possible duration of recreational, industrial and military activities in water.
Material SynthesisFoam neoprene is a closed-cell elastomeric foam consisting of gaseous cells dispersed within a solid neoprene rubber (polychloroprene) matrix (
Xenon (Xe), krypton (Kr) and argon (Ar) all possess lower thermal conductivities than air and are chemically inert, making them attractive candidates to replace air and enhance the insulating capabilities of neoprene foam. Accordingly, in some embodiments, the methods disclosed herein use Xe as an insulating gas. In other embodiments, the methods disclosed herein use Kr as an insulating gas. In still other embodiments, the methods disclosed herein use Ar as an insulating gas.
Here kr is the thermal conductivity of the rubber (which was estimated to be 0.228 W/m-K, see Supplemental Information), kg is the thermal conductivity of the gas (or gas mixture) in the cells, and ϕ is the porosity. Equation (1) assumes that the pores with volume fraction ϕ are roughly spherical and that there is no Kapitza resistance at the interface between gas and rubber. The absolute lower bound on the foam thermal conductivity is determined from setting kg=0 in equation (1) above to find kf,kg=0=0.0274 W/m-K. When air is present in the pores, the thermal conductivity roughly doubles, suggesting a 50% heat partitioning between air and rubber. The predicted effective thermal conductivities for neoprene foam filled with air, argon, xenon, and krypton are provided in
Eventually, equilibrium was attained such that the pressure of the insulating gas inside the cells was equal to the ambient gas pressure. Accordingly, in some embodiments, provided herein is a method for fabricating foamed neoprene samples with argon, xenon, and krypton filling gases by placing a bare neoprene sample in a sealed container; and filling the container with an insulating gas.
The thermal conductivities of charged and unmodified neoprene foams were measured using the Hot Disk method, which is an established ISO standard transient method for measuring the thermal conductivity of polymeric samples. The accuracy of the Hot Disk instrument is estimated to be approximately 7%, as quantified by measurements conducted on a NIST thermal conductivity standard material, specifically SRM 1453 (Expanded Polystyrene Board). The thermal conductivity measured immediately after removal from the pure-gas environment for argon-, krypton-, and xenon-infused neoprene foams, is shown in
The reduction in thermal conductivity due to infusion of a highly insulating gas is transient in nature, as the thermal conductivity returns to and/or surpasses the control value within approximately 12 hours or more (
The methods disclosed herein afford a thermally insulating fabric or flexible garment comprising a polymeric material infused with a high molecular weight gas. In some embodiments, the fabric is water compatible. In other embodiments, the fabric is substantially water resistant or waterproof. In some embodiments, the polymeric material comprises neoprene or polystyrene. In certain embodiments, the flexible garment is a dive suit. Exemplary dive suits include a wetsuit, a variable volume drysuit, a hot water wetsuit, and an active diver thermal protection system.
Material Performance as a Low Temperature WetsuitIn certain embodiments, the ultra-low thermal conductivity materials produced by the methods disclosed herein are useful for the production of a new class of low temperature dive suits. To determine whether the charging process is repeatable, two sets of samples were subjected to multiple charging steps, one set each in argon and xenon.
Further, modification of foamed neoprene in the form of a commercial wetsuit was investigated. To this end, three wetsuits were analyzed: a control, a krypton-infused wetsuit, and an argon-infused wetsuit.
As shown in
Materials: Foamed neoprene (thicknesses=1.6 mm & 6.4 mm) was purchased from Cleverbrand Inc. (Cheektowaga, N.Y., USA). Men's medium sized 4/3 mm neoprene wetsuits were purchased from O'Neill (Santa Cruz, Calif., USA). Xenon and Krypton gases were purchased from Concorde Specialty Gases (Eatontown, N.J., USA). Argon gas was obtained from Airgas.
Material Fabrication: The bare neoprene coupons and wetsuit were placed into a 1.9 L and 19 L sealed container, respectively, which was then filled with the insulating gas until the pressure inside the container reached 20 psi (gauge). The sealed tanks were attached to the appropriate gas cylinders via pressure regulators, which maintain the pressure for the desired number of days.
Thermal Characterization: Thermal conductivity was measured using the Hot Disk method, an ISO standard technique (ISO 22007-2:2015(en)). Thermal conductivity measurements were carried out using a Thermtest Hot Disk TPS 2500 S thermal conductivity meter (ThermTest Inc., Fredericton, NB, Canada). For all measurements, the HotDisk Kapton 5501 sensor (radius=6.4 mm) acted as both the heat source and temperature measurement sensor. The heating power for each experiment was 15 mW for a period of 80 seconds. Data points 40-200 were analyzed to determine the thermal conductivity. At least four neoprene or wetsuit samples were cut into circles (radius=2.5 cm) and stacked symmetrically on either side of the planar sensor for each measurement. A mild steel weight (0.3 kg; radius=2.5 cm; thickness=2 cm) was also placed on the top of the stacked neoprene samples to minimize the interfacial thermal resistance between samples and the sensor (
Microscopic Characterization: Thickness and radius versus time measurements were taken using captured images (analyzed using ImageJ) from a Deluxe Handheld Digital Microscope from Celestron. A single Argon-infused neoprene sample (radius=2.5 cm) with the mild stainless steel weight (0.3 kg; radius=2.5 cm; thickness=2 cm) was imaged over time directly after removal from the pressurized argon gas environment. The morphology of the neoprene foams was investigated with SEM 6010LA JEOL under high vacuum and operation voltage of 1 kV.
Permeation Experiments: The xenon and argon permeation test through neoprene was carried out in a homemade permeation cell, where the neoprene foam was clamped between two halves of stainless steel module. Pure xenon or argon gas at a gauge pressure of 445 Torr was fed to the neoprene foam. Nitrogen was used as the sweep gas to direct the permeated gas components to the mass spectrometer (MS, Agilent 5977A coupled with Diablo 5000A real-time gas analyzer). The MS was pre-calibrated with respect to the gas composition, yielding a proportional dependence of the MS signal versus the molar composition (mol %) of gas feed. The MS signal intensities were used to calculate the permeability of each gas species. The pressure on the permeate side was maintained near atmospheric pressure at 1.1 bar.
Simulations: Simulations were performed using the finite element software package COMSOL Multiphysics 5.1 (Burlington, Mass., USA) on a Sony VAIO personal computer.
Permeation Experiments to Measure Gas Diffusivity in Neoprene: To determine the effective gas diffusivities in the neoprene foam, the rate of Ar and Xe permeation through the neoprene using a custom-built gas permeation module was measured, as illustrated in
The results of these permeation experiments are shown in
Radius of Neoprene Foams versus Time:
Polystyrene: The thermal conductivity for unmodified expanded polystyrene was monitored with the Hot Disk device (P0=15 mW; t=80 seconds; 5501 sensor) for approximately three days (
All patents and published patent applications mentioned in the description above are incorporated by reference herein in their entirety.
EQUIVALENTSHaving now fully described the present invention in some detail by way of illustration and example for purposes of clarity of understanding, it will be obvious to one of ordinary skill in the art that the same can be performed by modifying or changing the invention within a wide and equivalent range of conditions, formulations and other parameters without affecting the scope of the invention or any specific embodiment thereof, and that such modifications or changes are intended to be encompassed within the scope of the appended claims.
Claims
1. A thermally insulating fabric comprising a polymeric material infused with a high molecular weight gas.
2. The thermally insulating fabric of claim 1, wherein the fabric is water compatible.
3. The thermally insulating fabric of claim 1, wherein the fabric is substantially water resistant or waterproof
4. The thermally insulating fabric of claim 1, wherein the polymeric material comprises neoprene foam, polystyrene, or nitrile butadiene rubber.
5. The thermally insulating fabric of claim 1, wherein the high molecular weight gas is a noble gas.
6. The thermally insulating fabric of claim 5, wherein the high molecular weight gas is selected from the group consisting of xenon, krypton, and argon.
7. The thermally insulating fabric of claim 6, wherein the high molecular weight gas is xenon.
8. The thermally insulating fabric of claim 6, wherein the high molecular weight gas is argon.
9. The thermally insulating fabric of claim 1, wherein the thermally insulting fabric has a thermal conductivity of about 0.031 W/m-K.
10. The thermally insulating fabric of claim 1, wherein the thermally insulting fabric provides thermal protection in harsh environments.
11. The thermally insulating fabric of claim 1, wherein the polymeric material comprises neoprene foam.
12. (canceled)
13. A flexible garment comprising the thermally insulating fabric of claim 1.
14.-25. (canceled)
26. A dive suit comprising the thermally insulating fabric of claim 1.
27.-36. (canceled)
37. A method of preparing a thermally insulating fabric of claim 1, comprising:
- placing a fabric in a sealed container; and
- filling the sealed container with an insulating gas;
- thereby forming the thermally insulating fabric of claim 1.
38.-45. (canceled)
46. The method of claim 37, wherein the container is filled with the insulating gas to a pressure of about 10-50 psi or about 20 psi.
47. The method of claim 37, wherein the method further comprises maintaining the pressure of the container from about 1 hour to about 100 hours.
48.-52. (canceled)
53. A method for protecting a diver in a cold-water environment, comprising clothing a diver in the dive suit of claim 26.
54.-56. (canceled)
57. The method of claim 53, wherein the method reduces the diver's risk for hyperthermia.
58. The method of claim 53, wherein the method allows the diver to stay in the cold water environment for at least about two hours, or about two hours to about three hours.
59. The method of claim 58, wherein the cold water has a temperature of 10° C. or less.
Type: Application
Filed: Nov 21, 2017
Publication Date: Sep 5, 2019
Inventors: Jacopo Buongiorno (Burlington, MA), Michael Strano (Lexington, MA), Jeffrey Moran (Jamaica Plain, MA), Matteo Brucci (Boston, MA), Anton Cottrill (Cambridge, MA)
Application Number: 16/462,470