Blends of amphiphilic poly(dimethylsiloxane) and nonamphiphilic octaisobutyl-POSS at the air/water interface

Brewster angle microscopy (BAM) shows that a nonamphiphilic polyhedral oligomeric silsesquioxane (POSS) nanofiller, octaisobutyl-POSS, forms aggregates at all surface concentrations at the air/water interface. When amphiphilic poly(dimethylsiloxane) (PDMS) is blended with the octaisobutyl-POSS (>10 wt % PDMS), the degree of POSS aggregation dramatically decreases. Thermodynamic analyses and morphology studies through surface pressure-area per monomer isotherm data and BAM, respectively, exhibit three distinct composition regimes: (1) Blends with >70 wt % POSS have unstable isotherms whose shapes deviate from those of PDMS and form large rigid domains comparable to but smaller than pure, octaisobutyl-POSS films. (2) At compositions between approximately 40 and 70 wt % POSS, the isotherms' features are qualitatively similar to those of pure PDMS, and extensive nanofiller "networks" are observed by BAM. (3) For compositions < or = approximately 30 wt % POSS, the isotherms are essentially those of pure PDMS with small POSS domains dispersed in the PDMS matrix. These results provide further insight into nanofiller aggregation mechanisms and dispersion that may be present in thicker films and bulk systems.