Small-Angle Neutron Scattering Studies of an Adsorbed Non-Ionic Surfactant (C_(12)E_(24)) on Hydrophobised Silica Particles in Water

摘要

Small-angle neutron scattering (SANS) studies of aqueous dispersions of Stober silica particles (which have been hydrophobised by having 1-octadecanol grafted to their surface),carrying an adsorbed layer of the nonionic surfactant C_(12)E_(24),in water,have been performed as a function of temperature.Using mixtures of D_2O and H_2O,the composition of the continuous phase was adjusted to have the same scattering length density as the silica particles.Hence,only the scattering from the 1-octadecanol and C_(12)E_(24) layers was detected.The data have been analyzed using both a surface Guinier analysis and a two-layer structure model.It has been found that a step profile best describes the inner combined adsorbed layer (1-octadecanol grafted chains,plus the penetrating alkyl chains from the surfactant) and a semi-Gaussian profile the extended poly(ethylene oxide) outer layer.Both analyses demonstrated that the combined surface layer contracted with increasing temperature.