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 θ versus particle radius R. At T(g), all θ versus R measurements are well described by the modified Young's equation for a line tension τ = 0.93 nN. The AFM measurements are also consistent with a minimum contact angle θ(min) and minimum radius R(min), below which single isolated silica spheres cannot exist at the PS-air interface.