OPTICAL-PROPERTIES OF SURFACES COVERED WITH LATEX-PARTICLES - COMPARISON WITH THEORY

Scanning-angle reflectometry :around the Brewster angle has been used to investigate the optical properties of positively charged polystyren e particles with radii ranging from 50 to 500 nm, deposited on a silic a/water interface. A theory for inhomogeneous thin films may be used t o analyze the data for the smallest of these particles, but gives inco rrect results for the larger ones. A model based on Mie theory describ es the data well over the entire size range. This model ignores direct particle substrate interactions, which is justified for the small dif ferences in refractive indices in this system. It is shown that the Mi e-based model is equivalent to the thin film model in the long-wavelen gth limit. The analysis yields three parameters: particle size, refrac tive index, and coverage.