U.S. patent application number 16/462470 was filed with the patent office on 2019-09-05 for ultra-low thermal conductivity diving suit material for enhanced persistence in cold water dives.
The applicant listed for this patent is Massachusetts Institute of Technology. Invention is credited to Matteo Brucci, Jacopo Buongiorno, Anton Cottrill, Jeffrey Moran, Michael Strano.
Application Number | 20190269187 16/462470 |
Document ID | / |
Family ID | 62145878 |
Filed Date | 2019-09-05 |
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United States Patent
Application |
20190269187 |
Kind Code |
A1 |
Buongiorno; Jacopo ; et
al. |
September 5, 2019 |
ULTRA-LOW THERMAL CONDUCTIVITY DIVING SUIT MATERIAL FOR ENHANCED
PERSISTENCE IN COLD WATER DIVES
Abstract
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.
Inventors: |
Buongiorno; Jacopo;
(Burlington, MA) ; Strano; Michael; (Lexington,
MA) ; Moran; Jeffrey; (Jamaica Plain, MA) ;
Brucci; Matteo; (Boston, MA) ; Cottrill; Anton;
(Cambridge, MA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Massachusetts Institute of Technology |
Cambridge |
MA |
US |
|
|
Family ID: |
62145878 |
Appl. No.: |
16/462470 |
Filed: |
November 21, 2017 |
PCT Filed: |
November 21, 2017 |
PCT NO: |
PCT/US17/62775 |
371 Date: |
May 20, 2019 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
62424828 |
Nov 21, 2016 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B63C 11/04 20130101;
A41D 13/012 20130101; A41D 31/06 20190201; A41D 13/002
20130101 |
International
Class: |
A41D 31/06 20060101
A41D031/06; A41D 13/012 20060101 A41D013/012; A41D 13/002 20060101
A41D013/002; B63C 11/04 20060101 B63C011/04 |
Goverment Interests
GOVERNMENT SUPPORT
[0002] This 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.
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.degree. C. or less.
Description
RELATED APPLICATIONS
[0001] This application claims the benefit of priority to U.S.
Provisional Patent Application Ser. No. 62/424,828, filed Nov. 21,
2016.
BACKGROUND
[0003] Underwater 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.degree. 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.
SUMMARY
[0004] Provided 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.
[0005] 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).
[0006] 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.
BRIEF DESCRIPTION OF THE DRAWINGS
[0007] FIG. 1A is an SEM image of unaltered neoprene foam. A
magnified SEM is shown in the inset.
[0008] FIG. 1B shows an exemplary process flow for infusing
insulating gases into neoprene foam.
[0009] FIG. 1C is a bar graph depicting thermal conductivities of
neoprene foams when infused with the indicated gases. The
experimental measurements are compared with those of the Maxwell's
model, equation (1). Thermal conductivities for the gases
considered in this work.sup.14: air (0.026 W/m-K), argon (0.018
W/m-K), krypton (0.0095 W/m-K), and xenon (0.0055 W/m-K). For
experiments, the plotted data represent the average of at least 3
measurements and error bars represent one standard deviation in
each direction. For the Maxwell data, error bars reflect
uncertainty in the estimate due to uncertainty in the estimate of
porosity from SEM images.
[0010] FIG. 1D is a line graph depicting the measured thermal
conductivity of neoprene versus time for the indicated filling
gases, as compared to the control (air). Gas discharge takes place
over a time scale that depends mainly on the insulating gas. All
measurements are estimated to be within 7% of the actual
values.
[0011] FIG. 2A is a schematic showing discharging simulations,
wherein the neoprene is filled with argon at 243 kPa at t=0.
[0012] FIG. 2B is a schematic showing a charging simulation,
wherein the neoprene is initially filled with nitrogen (to
approximate air) at atmospheric pressure and is placed in a pure
atmosphere of argon at t=0.
[0013] FIG. 3A is a photograph of a thermal conductivity
measurement apparatus, making use of the hot disk transient method.
A nickel wire protected by a kapton covering ("Sensor/Source"),
which acts as both the heat source and temperature sensor, is
sandwiched between neoprene samples. They are held in place by a
mild steel weight that provides light compressive stress
(.about.0.01 bar), which keeps air cavities from forming between
the sample and sensor (which would corrupt the measurement). The
neoprene coupons are cut to have the same diameter as the weight so
that the compressive stress is uniform on the sample surface.
[0014] FIG. 3B is a plot showing the thickness of argon-infused
neoprene coupon as a function of time during gas discharge, as
measured optically using a high-resolution USB camera. The solid
black curve is a fit of the form ae.sup.-bt+c, where a=0.2092 cm,
b=-0.058 hr.sup.-1, and c=0.4842 cm. In the simulations, the
thickness varies in time according to this exponential fit curve.
Each thickness measurement is the average of five individual
measurements performed using ImageJ, and error bars represent one
standard deviation in each direction.
[0015] FIG. 3C is a plot showing the thermal conductivity of
argon-infused neoprene as a function of time for the discharging
process compared with the predicted range from the finite-element
simulation, showing good agreement.
[0016] FIG. 3D is s graph showing simulation predictions (curve)
compared with experimental measurements of thermal conductivity as
a function of charging time for argon-infused neoprene.
Experimental data points represent the average of at least 3
measurements and error bars indicate one standard deviation in each
direction.
[0017] FIG. 4A is a graph showing reproducibility of Ar charging.
The two data sets show the thermal conductivity vs time for one set
of neoprene coupons, charged and then recharged with the gas.
[0018] FIG. 4B is a graph showing reproducibility of Xe charging.
The two data sets show the thermal conductivity vs time for one set
of neoprene coupons, charged and then recharged with the gas.
[0019] FIG. 4C is a plot showing thermal conductivity versus time
for bare neoprene charged with krypton compared with data for a
full wetsuit, also charged with krypton.
[0020] FIG. 4D is a graph showing predictions of equation (1) for
the time to hypothermia (i.e., time required for core body
temperature T.sub.core to decrease from the initial value,
37.degree. C., to T.sub.h=35.degree. C.) as a function of water
temperature for no wetsuit and for wetsuits with the indicated
gases. These data are compared to experimental data (shaded grey
region) reported by Aguilella-Arzo et al. (Am. J. Phys., 2003, 71,
333-337).
[0021] FIG. 5A shows a scanning electron micrograph (SEM) image of
unmodified neoprene.
[0022] FIG. 5B shows the SEM image from FIG. 5A converted to binary
in ImageJ in order to estimate the porosity of the neoprene foam.
The dashed lines indicate the six regions of interest used to
calculate six values of porosity for the foam.
[0023] FIG. 6A shows an SEM image of a neoprene foam sample
following charging with argon gas.
[0024] FIG. 6B shows an SEM image of a neoprene foam sample
following charging with xenon gas.
[0025] FIG. 7A shows an apparatus for measuring gas permeation
through neoprene foam. Active area of the neoprene membrane is 6
cm.sup.2 and the thickness of the neoprene membrane is 1.6 mm.
[0026] FIG. 7B is a graph showing the experimentally measured mass
spectrometer counts for argon as a function of time (symbols),
along with a best-fit of equation (S8). From this curve fitting, an
effective diffusivity of 1.9.times.10.sup.-10 m.sup.2/s is
extracted for argon in neoprene foam.
[0027] FIG. 7D is a graph showing the mass spectrometer counts for
xenon as a function of time (symbols). From this analysis, the
effective diffusivity for xenon in neoprene foam is determined to
be 3.967.times.10.sup.-10 m.sup.2/s.
[0028] FIG. 8 is a graph showing the thermal conductivity versus
time for bare neoprene charged with argon and stored in air
(points) and neoprene samples charged with argon and stored in
stagnant (triangles) and stirred water (circles) in between
measurements. This figure indicates that leakage of the insulating
gas from the neoprene occurs more slowly in stirred water
(simulating a swimming diver) than in air and is slowest in
stagnant water.
[0029] FIG. 9A is a graph showing the measured thermal conductivity
as a function of time for argon-charged neoprene samples stored in
stirred deionized water. The data are fitted to a linear
regression, and the linear fit for the data is shown in the plot.
The suspected outlier is circled.
[0030] FIG. 9B shows the standardized residuals for the linear fit
in FIG. 9A. The suspected outlier is circled, and occurs almost
three standard deviations from the fit.
[0031] FIG. 10 shows the radius of argon-infused neoprene disc
(measured using optical images captured with USB camera and image
analysis using ImageJ software) as a function of time after removal
from the gas environment. Circles are experimental measurements and
curve is a fit of the form r.sub.fit=ae.sup.-bt+c. Here the
constants a, b, and c are 0.0357 cm, -0.1897 hr.sup.-1, and 2.4605
cm, respectively.
[0032] FIG. 11A shows a schematic of simulation domain showing
dimensions, initial conditions, and boundary conditions assumed in
the simulation.
[0033] FIG. 11B shows a schematic of charging simulations showing
boundary and initial conditions. Gas flux through the bottom
surface is ignored because the neoprene disc is assumed to sit flat
on the bottom of the charging container.
[0034] FIG. 12 is a graph showing the thermal conductivity versus
time for argon-infused expanded polystyrene (EPS) (black) and
unmodified EPS (gray).
[0035] FIG. 13 is a graph showing the thermal conductivity versus
time for argon-infused nitrile butadiene rubber, and air-infused
nitrile butadiene rubber. (Control)
DETAILED DESCRIPTION
[0036] 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.)
[0037] 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.)
[0038] 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.
[0039] 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.
[0040] 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.
[0041] 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.degree. C.
water.
[0042] 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 Synthesis
[0043] Foam neoprene is a closed-cell elastomeric foam consisting
of gaseous cells dispersed within a solid neoprene rubber
(polychloroprene) matrix (FIG. 1A). The gaseous phase of neoprene
foam typically contains nitrogen or air, with thermal conductivity
k.sub.g=0.026 W/m-K (at 25.degree. C.). Due to the high volume
fraction of the gas (typically >70%) and heat partitioning
between the gas and rubber phases, the inclusion of the gas phase
leads to a reduction in the overall thermal conductivity of the
material. However, air is not the most effective insulator among
gases at room temperature.
[0044] 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.
[0045] FIG. 1A shows a scanning electron micrograph (SEM) of a
standard, commercial neoprene foam, which is characterized by
approximately spherical pores with diameters in the range of
100-200 .mu.m. The pores contain a mixture of nitrogen and oxygen
(air) as the filling gas, and the pores are dispersed within a
neoprene rubber matrix. The porosity (gas volume fraction) of the
neoprene foam was calculated at 83.+-.2% from image analysis of
SEMs of the neoprene foam. The thermal conductivities of the gases
were also considered, and measured at room temperature, at 0.026
W/m-K (air), 0.018 W/m-K (argon), 0.0095 W/m-K (krypton), and
0.0055 W/m-K (xenon). The effect of replacing the standard neoprene
filling gas with a lower-thermal-conductivity gas can be predicted
using Maxwell's homogeneous medium model, which has been shown to
capture the effective thermal conductivity of neoprene foams,
k.sub.f, reasonably well:
k f = k r k g + 2 k r + 2 ( k g - k r ) .phi. k g + 2 k r - ( k g -
k r ) .phi. . ( 1 ) ##EQU00001##
Here k.sub.r is the thermal conductivity of the rubber (which was
estimated to be 0.228 W/m-K, see Supplemental Information), k.sub.g
is the thermal conductivity of the gas (or gas mixture) in the
cells, and .PHI. is the porosity. Equation (1) assumes that the
pores with volume fraction .PHI. 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 k.sub.g=0 in equation (1) above to find
k.sub.f,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 FIG. 1C. A reduction in thermal
conductivity of up to .about.40% is predicted for neoprene foam
infused with xenon as compared with standard neoprene foam infused
with air.
[0046] FIG. 1B illustrates the process flow for fabricating
neoprene foams infused with high-molecular-weight, noble gases:
starting with standard neoprene consisting of gas cells containing
air (black), the neoprene is immersed in an atmosphere of the
insulating gas to be infused (gray) at an absolute pressure of 243
kPa (20 psi gauge). The process of gas infusion into a closed-cell
foam consists of multiple steps: the insulating gas adsorbs to the
outer surface of the neoprene and dissolves in the solid rubber,
the gas molecules diffuse through the solid rubber, and the gas
desorbs at the inner walls of the gas cells. Herein, this process
is referred to as "charging." With the gas infused at room
temperature and 243 kPa of pressure, significant reductions in
thermal conductivity can be seen in as little as 2 hours, and the
maximum possible reduction is attained after approximately 5 days.
Accordingly, in some embodiments, the methods disclosed herein
maintain pressure in the container from about 1 hour to about 100
hours, e.g., from about 2 hours to about 72 hours, e.g., from about
24 hours to about 72 hours. In certain embodiments, the pressure is
maintained in the container for about 2 hours, about 4 hours, about
6 hours, about 8 hours, about 10 hours, about 12 hours, about 14
hours, about 16 hours, about 18 hours, about 20 hours, about 24
hours, about 36 hours, about 48 hours, about 60 hours, or about 72
hours.
[0047] 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.
[0048] 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 FIG. 1C. A measurement of the thermal
conductivity of standard, unmodified neoprene was provided as a
control. A significant reduction in thermal conductivity of
neoprene foam, ranging from .about.25% with Ar to 40% with Xe, was
observed. Error bars indicate the standard deviation of at least
three individual measurements in each direction. Immediately after
removal, only the noble gas inhabits the pores of the neoprene
foam, i.e., the infused gas completely replaces the air in the
pores.
[0049] 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 (FIG. 1D), reaches a local maximum,
and eventually decays back to the control value as the air returns
to the pores. Herein, this process is referred to as "discharging."
Without being bound by any one particular theory, the increase in
thermal conductivity with time after the neoprene samples are
removed from the gas environment may be attributed to (i) gas
exchange between the neoprene sample and the ambient air, and/or
(ii) an associated pore shrinkage within the foam, which reduces
its porosity. The pore contraction may, in turn, reduce sample
thickness (FIG. 3B) and hence thermal resistance, since neoprene
rubber is incompressible to a good approximation.
[0050] 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 Wetsuit
[0051] In 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. FIGS. 3A and 3B show the results of these
recharging experiments for argon and xenon, respectively. In each
case, a set of four neoprene discs was charged with the indicated
gas (over 7 days) and their thermal conductivity was measured ("one
charge") using the apparatus shown in FIG. 3A. The same samples
were then placed in the same insulating gas a second time (again
for 7 days) and their thermal conductivities are measured again.
Each panel shows strong evidence that the gas charging process is
repeatable using either Ar or Xe as the charging gas. This suggests
that garments made from foam neoprene, such as wetsuits, are able
to be charged and recharged multiple times without any reduction in
insulation performance.
[0052] 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. FIG. 4C shows the thermal conductivities of
the modified (krypton) and unmodified wetsuits stored in air as a
function of time. The results for the wetsuit were also compared
with the results for the krypton-infused "bare" neoprene
samples.
[0053] As shown in FIG. 4D, the thermally insulating materials
provided herein enable dives lasting 2-3 hours in water below
10.degree. C., compared with <1 hour for the state-of-the-art.
This advance introduces the prospect of effectively wearing a
flexible air gap for thermal protection in harsh environments.
Exemplification
[0054] 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.
[0055] 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.
[0056] 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 (FIG. 2A). All
measurements were performed at ambient temperature (21.degree.
C.).
[0057] FIG. 2A shows the experimental setup for measurement of
thermal conductivity. As shown in FIG. 2A, a cylindrical metal
weight (mild steel, mass M.sub.s=0.312 kg, diameter D.sub.s=5 cm,
thickness H.sub.s=2 cm) was placed on top of the sample to ensure
that no air gaps form between the Hot Disk sensor and the neoprene
pieces it directly touches. If such gaps were present, heat
transfer through the air within them would contaminate the thermal
conductivity measurements. The weight imposed a compressive stress
of 4M.sub.sg/.pi.D.sub.s.sup.2=1.56 kPa, or about 0.015 atm, on the
neoprene. From a systematic study of neoprene's thermal
conductivity as a function of ambient hydrostatic pressure by Bardy
et al. (J. Phys. Appl. Phys., 2005, 38, 3832), the pressure imposed
by the steel weight is not enough to significantly alter the
thermal conductivity from its nominal value in the absence of
compression. The neoprene coupons were cut into circular discs with
diameters equal to that of the steel weight, so that the
compressive stress was uniform over the neoprene surface, and was
consistent for different experiments. A heating power of 15 mW was
applied and measurements were collected for 80 s for all data.
[0058] 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.
[0059] 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.
[0060] Simulations: Simulations were performed using the finite
element software package COMSOL Multiphysics 5.1 (Burlington,
Mass., USA) on a Sony VAIO personal computer.
[0061] 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 FIG. 7A. After the neoprene foam was sealed
inside the membrane module, a feed of pure Ar or Xe was flowed over
the upstream side of the membrane at a gauge pressure of 445 Torr,
while the downstream side of the membrane was continually swept
with N.sub.2 gas at near atmospheric pressure. Due to the pressure
differential across the neoprene, over time, the Ar and Xe gas
permeated through the foam, and the permeate gas was carried by the
N.sub.2 sweep gas into an on-line mass spectrometer configured for
real-time gas analysis.
[0062] The results of these permeation experiments are shown in
FIGS. 7B and 7C. The counts detected by the mass spectrometer are
directly proportional to the instantaneous flux of the Ar or Xe
through the neoprene. At the beginning of each measurement, the
flux is low and increasing as the Ar and Xe diffuse into the foam
and build up a concentration gradient. Eventually the flux reaches
a steady state value, as expected. The time required to reach the
steady state flux depends on the effective diffusivity of the gas
in the neoprene.
[0063] Radius of Neoprene Foams versus Time: FIG. 10 shows the
evolution of the radius of an argon-infused disc of neoprene foam
as a function of time after removal from the argon environment. The
radius was observed to decay slightly, from 2.50 to approximately
2.46 cm. The dynamics of gas leakage from the neoprene were not
affected significantly by the change in volume induced by the
change in radius. However, even a slight change in volume did
produce a noticeable change in the porosity of the neoprene, to
which the overall thermal conductivity is rather sensitive.
[0064] Polystyrene: The thermal conductivity for unmodified
expanded polystyrene was monitored with the Hot Disk device
(P.sub.0=15 mW; t=80 seconds; 5501 sensor) for approximately three
days (FIG. 12; gray). Two cylinders (diameter=3.5 cm; height=2 cm)
of EPS were exposed to argon in a 1.9 L tank at 20 psig for seven
days, and the thermal conductivity of the samples with respect to
time (FIG. 12; black) was monitored using the Hot Disk device
directly after removal from the tank (P.sub.0=10 mW; t=80 seconds;
5501 sensor). The thermal conductivity initially decreased by
approximately 15%; however, the thermal conductivity quickly
returned to the control value in approximately one hour, suggesting
a high diffusivity of argon with the expanded polystyrene.
INCORPORATION OF REFERENCE
[0065] All patents and published patent applications mentioned in
the description above are incorporated by reference herein in their
entirety.
EQUIVALENTS
[0066] Having 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.
* * * * *