(57g) Tuning the Morphology of Surfactant Aggregates at Nanoscale Solid/Liquid Interfaces

The adsorption and self‑assembly of nonionic surfactants at nanostructured surfaces plays an important and diverse role in many technological fields. Here we discuss a method for controlling the morphology of the surfactant aggregate in the presence of silica nanomaterials (Bharti et al., Soft Matter 2012). Addition of a surface modifier (lysine) to a dispersion of silica nanoparticles (20 nm) decorated with surface micelles leads to a complete desorption of the surfactant from the particle surface and conversion to wormlike micelles in the aqueous solution. A remarkable morphological transition of surfactant aggregates occurs when the surface modifier is added to SBA-15 silica decorated with patches of surfactant bilayer at the pore walls. In this case a transition to threadlike micelles located in the center of the pore and only loosely connected to the pore walls occurs when the surface modifier is added. This is a first proof of existence of such enrotpically unfavorable surfactant aggregates in the confined 8 nm pore space (Bharti et al. J. Am. Chem., Soc. 2012). The behavior of nonionic surfactants will be compared with cationic surfactants which are more strongly bound to the silica surface. We used neutron scattering as a tool for characterizing surfactant aggregate morphology on silica nanoparticles and in the nanopores of silica SBA-15 material.