Dynamics of Water in a Hydrophobic Elastomer and Its Beneficial Role in Preserving Skin Hydration

Although the elasticity of silicone is of great importance for skin and biomedical applications, its inherent incompatibility with water proves to be a challenge. To address this, we developed a silicone elastomer by introducing “silicate” moieties tethered with a few units of carboxylic acid (COOH) as cross-links (CLs) within a flexible polydimethylsiloxane (PDMS) network. In this design, the cooperativity of the carboxylic acid (COOH) can effectively drive high swelling (88.2 wt %) of the elastomer in water. The starting acid molecules, which alone do not have the ability to hold water, are now able to hold about ∼6400 water molecules per COOH group. The formation of unusually strong H-bonds and their role in holding such a significant amount of water inside the hydrophobic polymer were established by a number of complementary analytical techniques such as DSC, WAXD, rheology, FTIR, confocal Raman microscopy, etc. The hydrogel prepared using this strategy shows a substantial enhancement of skin hydration compared to the benchmark hydrogel available in the market. Our findings provide important insights into the dynamic of H-bonding interactions of water molecules inside the hydrophobic environment and are very useful for the preparation of efficient hydrogels with functions for healthy living.