Eliminating Surface Pressure Gradient Effects in Contact Angle Determination of Nano- and Microparticles Using a Film Balance

The surface pressure vs surface area isotherms of monoparticulate layers determined using Langmuir and Wilhelmy film balances depend nontrivially on the amount of spread particles. It is inferred that a surface pressure gradient across the spread particle layers is responsible. An extrapolation procedure for determining correct values of the contact angles is described.