Self-assembly of an amphiphilic siloxane graft copolymer in water

The micelle formation and micelle structure of an amphiphilic poly(dimethylsiloxane)-graft-polyether copolymer in aqueous solution were investigated with a variety of experimental techniques. We measured the CMC by three different methods-DPH solubilization, methyl orange hypsochromic shift, and pyrene fluorescence I₁/I₃ ratio. The microviscosity was evaluated from DPH anisotropy values that were obtained by fluorescence polarization measurements. The microviscosity in the siloxane copolymer micelles was found lower than that in Pluronic block copolyether micelles. The micelle size and structure were obtained from small-angle neutron scattering (SANS) using the hard sphere model. The micelle hydrodynamic radius and the micelle size distribution were monitored by dynamic light scattering (DLS). The degree of hydration was estimated from a combination of DLS and SANS results. The temperature effect on CMC was found to be small; however, a structural transition of micelles from spheres to ellipsoids was observed by SANS at elevated temperature (60°C).