Oil-based rheology modifiers


The alkyl silicone surfactants that have been discussed until now have had a single alkyl group on the silicone backbone. A series of patent pending alkyl dimethicone polymers have been developed which contain two different alkyl groups, one liquid at ambient temperatures and another that is solid at ambient temperatures. The presence of the liquid portion of the molecule inhibits the products from becoming hard solids. Instead a soft, thixotropic gel forms. These polymers provide unique aesthetics to cosmetic formulations. 


A study was conducted on the above materials by Microtrace LLC, their results state: “Sample 1 and 2 are entirely different from one another. Sample 2 is an opaque, waxy, white, crystalline solid at room temperature. Its color and solid phase structure are a direct result of the fact that it is composed entirely of colorless, interlocking crystals. 


These crystals melt at 56°C (132.8 °F) when the solid becomes liquid. This transformation is entirely reversible. Sample 1 is, at room temperature, a translucent, gel that flows under pressure. It is composed of two phases. The liquid phase is liquid at room temperature. The solid phase is crystalline and the relatively large, elongated crystals scatter light just enough to make the product translucent instead of white and opaque like sample 1 or entirely transparent and colorless as would be the case if the crystals were absent. The crystalline phase melts entirely at 38°C (100.4 °F) but recrystallises when the temperature drops below this. 


It also appears that the crystals in sample 1 are liquid-crystals rather than ordinary crystals such as those that form the waxy solid comprising sample 2. This would take some time and effort to confirm but the initial observations seem to point in this direction. The most compelling evidence for this is the disappearance of most of the birefringent crystals in a thin film of sample 1 when pressure is applied to the cover slip and their immediate reappearance once the pressure is released.”  Figures 11 and 12 show the results. 

As seen from these figures, the blend of two silicone polymers is drastically different from the silicone polymer with two different alkyl groups.