Extreme Phase Change Materials for Soldier Microclimate Regulation

Microclimate systems are being developed to minimize the effects of extreme temperature on performance capability and enable functioning under conditions that would otherwise cause incapacitation. It is important that these systems be highly reliable, lightweight and durable, with the intention to be worn under armor materials, heavy chemical/biological protective suits, and other protective clothing. This work involves guest-host interactions in nanomaterials. The nanomaterials that we will be investigating are those that involve nanospheres, nanotubes and nanobowls. These nanomaterials will be assembled with a low cost assembly of p-sulfonatocalix[4]arene building blocks. The calixarenes can form a conical shape that supports a separate guest molecule in the center of the calixarene. These p-sulfonatocalix[4]arene building blocks have been previously shown to assemble into spherical structures by the addition of pyridine N-oxide and lanthanide ions. The amount of 'chemical space' enclosed by the spherical structure is about 1,000 cubic angstroms. This space houses 30 water molecules and two sodium ions. The contents of the capsule are rather completely ordered for the sphere (by the hydrogen bonds from the enclosed water to the phenolic oxygen atom hydrogen bond acceptors at the base of the p-sulfonatocalix[4]arene). The supramolecular forces used to hold the spherical calixarene together are a combination of van der Waals forces, pi-stacking forces, and metal ion coordinate covalent bonds. These conical calixarenes and spherical shaped bilayer calixarenes can house guest molecules in an ordered configuration. At certain temperatures these calixarenes can absorb enough thermal energy to cause the guest molecules to go into a disordered configuration, or the guest molecule absorbs enough energy to escape the calixarene host molecule. This energy needed to cause disorder of the guest molecules or the guest molecules escaping is between 500-1800J/g. This thermal energy needed is tremendous and could find uses in thermal energy storage applications.