Physico-chemical properties of siloxane surfactants in water and their surface energy characteristics

A simple but efficient method has been followed for the synthesis of water soluble siloxane amphiphile by grafting poly(ethylene glycol) (PEG) onto the hydrophobic poly(hydromethyl siloxane) backbone. Systematic variations in the amount of PEG incorporations were carried out to get water soluble oligomers. The structural analysis of the systems was done by 1H NMR and GPC analysis. The solution behavior of these amphiphiles was studied. The presence of nonpolar microdomains was observed at concentrations ≥0.01 g/dL for all the systems. Interestingly, I3/I1 ratio of pyrene fluoroprobe solubilised in aqueous solution of amphiphile suggests greater nonpolarity of microdomains in the system containing a higher PEG graft. The oligomers were shown to be surface active wherein, critical aggregation concentration decreased systematically with the decrease in the hydrophilic PEG substitutions. However, the system with a higher PEG substitution shows the close packed aggregates in the solution as suggested from the viscosity and fluorescence measurements. The contribution of polar and dispersion component towards the total surface energy was studied by the contact angle measurement by the sessile drop method.