Dry powder mixes comprising phase change materials

DETAILED DESCRIPTION The present invention provides a novel phase change material/silica dry powder composite.
When solid-to-liquid transitions are contemplated, the phase change material (PCM) may consist of one or more of the following compositions: water, salt hydrates, quaternary ammonium halide clathrates, linear alkyl hydrocarbons, fatty acids, alcohols and esters, glycerine, pentaerythritol, pentaglycerine, neopentylglycol, polyethylene glycol and like materials characterized by having thermal energy storage of 30 calories/gram or higher, and a narrow temperature range of melting and freezing.
When liquid-to-gas transitions are contemplated, the preferred phase change materials are water, ethylene glycol, combinations of water and ethylene glycol, glycerol, combinations of water/glycerol, water/ethylene glycol/glycerin, methanol, dimethylformamide, and like materials.
The silicas that are suitable include those made by the fumed or precipitated process, and having surface areas ranging from 50 to 500 square meters per gram, and primary particle sizes from 0.
005 to 0.
046 microns.
Preferred silicas are those having a surface area of 100 m.
sup.
2 per gram or more, and primary particle size of 0.
025 microns or less.
Further, the silicas prepared by either the fumed or precipitated process can be modified to make them less hydrophilic, or even hydrophobic by surface treating them with effective concentrations of silane coupling agents (e.
g.
, dimethyldichlorosilane) or silicone resins.
The silicone resin surface treatment can and usually is followed by heat treating at elevated temperature wherein the silicone resin is chemically reacted with hydroxyl groups on the surface of the silica particles.
Importantly, controlled degrees of hydrophobic character can be obtained by varying the amount of waterproofing agent.
This precisely tailored balance of hydrophobic/hydrophilic character is very important in the preparation of PCM/silica dry powders using quaternary ammonium halides, and salt hydrates in order to diminish the attraction of the hydroxyl and other polar groups on the silica for the water molecules in these types of PCMs