Observation of weak primary minima in the interaction of polystyrene particles with nylon fibres

Abstract

The deposition of sub-micron polystyrene particles onto dispersed nylon fibres has been studied as a function of pH and ionic strength in the vicinity of the iso-electric point of the nylon. The presence of weak primary minima is inferred from the reversibility of the deposition under conditions where the interacting surfaces are oppositely charged. The observed deposition rates can be described by a simple kinetic equation containing rate constants for particle capture by the surface and particle escape from it. The observed equilibrium deposition isotherms have an initial linear region and a plateau but deviate from Langmuirian behaviour in the direction of indicating lateral attractive interactions between deposited particles. Initial linear slopes have been related to surface excess integrals of the form [graphic omitted] {exp[–u(x)/kT]– 1}dx, where u(x) is the interaction potential between a particle and the surface (assumed flat) at a separation x. The interaction potentials so inferred are orders of magnitude lower than those predicted by existing theory of the dominant electrostatic interaction. It is suggested that absorption of water by the nylon (∼9 % by weight), rendering the surface diffuse, is a controlling factor.