Water solubilization in nonionic microemulsions stabilized by grafted siliconic emulsifiers

Microemulsions containing octanol, decanol, or dodecanol as the oil phase a nd oligomeric, grafted nonionic amphiphiles based on ethoxylated polymethyl siloxanes (Silwets) have been studied. It was demonstrated that significant amounts of water can be solubilized only when the hydrophobic siliconic ba ckbone is very short (trimers). The water solubilization was evaluated usin g SAXS, DSC, and conductivity measurements. It was found that up to 40 wt% of water can be solubilized in dodecanol and Silwet L-7607 (MW 1000 and 75 wt% ethylene oxide (EO)), Surprisingly, no free water was detected in the a ggregate core. All the solubilized water was confined in the vicinity of th e interphasal region and froze at -10 degreesC and below. Up to three molec ules of water can be associated with each EO headgroup. Based on SAXS measu rements, the structural units of the microemulsions were interpreted to be lamellar-like, a form previously found for the related monomeric microemuls ions. (C) 2001 Academic Press.