title: Evanescent-wave dynamic light scattering at an oil-water interface: diffusion of interface-adsorbed colloids.
abstract: A light-scattering goniometer for evanescent-wave dynamic light scattering (EWDLS) measurements at a liquid-fluid interface is introduced, and used for measurements on two charge-stabilized polystyrene colloid systems adsorbed to alkane-water interfaces. The goniometer allows an independent variation of the penetration depth and the scattering vector components parallel and perpendicular to a liquid-fluid interface. The possible illumination geometries are compared. Ellipsometry at the liquid-fluid interface is implemented as a complementary tool. In EWDLS measurements, the absence of diffusive motion perpendicular to the interface is demonstrated, which confirms the adsorption of the particles. The two-step decay of the autocorrelation function is interpreted in terms of diffusion within a two-dimensional interface lattice of colloidal particles, stabilized by repulsive electrostatic interactions, and a desorption process. A significant slowing down of the in-plane diffusion of the colloids as compared to the bulk diffusion is observed.
authors.affiliation: Max Planck Institute of Colloids and Interfaces, Golm, Germany.
authors.forename: Antonio
authors.initials: A
authors.lastname: Stocco
authors.forename: Tahereh
authors.initials: T
authors.lastname: Mokhtari
authors.forename: Günter
authors.initials: G
authors.lastname: Haseloff
authors.forename: Andreas
authors.initials: A
authors.lastname: Erbe
authors.forename: Reinhard
authors.initials: R
authors.lastname: Sigel