Influence of Line Tension on Spherical Colloidal Particles at Liquid-Vapor Interfaces

Atomic force microscopy (AFM) imaging of isolated submicron dodecyltrichlorosilane coated silica spheres, immobilized at the liquid polystyrene- (PS-) air interface at the PS glass transition temperature, T-g, allows for determination of the contact angle theta versus particle radius R. At T-g, all theta versus R measurements are well described by the modified Young's equation for a line tension tau = 0.93 nN. The AFM measurements are also consistent with a minimum contact angle theta(min) and minimum radius R-min, below which single isolated silica spheres cannot exist at the PS-air interface.