Assessing short-range membrane–colloid interactions using surface energetics

The contribution of acid–base (AB) (polar) interactions to the total interaction energy between membranes and colloids was investigated. The surface energetics of several membranes and colloids were evaluated using the Lifshitz–van der Waals acid-base approach. This provides the van der Waals (LW) and polar interaction energies between various surfaces from measurements of contact angles of different probe liquids on these surfaces. In addition, the surface potentials of the membranes and colloids were determined using electrokinetic measurements, yielding the electrostatic (EL) interaction between these surfaces. The three interaction energy components (LW, EL, and AB) were combined according to the extended Derjaguin–Landau–Verwey–Overbeek (extended DLVO or XDLVO) approach to evaluate membrane–colloid interaction energies. Predictions of interaction energy based on the XDLVO approach were compared to the corresponding predictions from the classical DLVO theory. For all the membrane–colloid combinations studied, the DLVO potentials were quite similar. However, inclusion of AB interactions resulted in a substantially different (qualitative and quantitative) prediction of short-range (separation distances <5 nm) interaction energies for several of the membrane–colloid combinations investigated. Finally, all of the membranes studied were found to have substantially low surface energies compared to the colloids and the interaction energy between the membranes and colloids was primarily dictated by the surface energies of the colloids. Fouling experiments for a membrane and three colloids supported the fouling trends predicted by the XDLVO approach.