Membrane–Colloid Interactions: Comparison of Extended DLVO Predictions with AFM Force Measurements

Theoretical predictions of interaction energies for several membrane–colloid pairs were made using the classical DLVO theory and an extended DLVO (XDLVO) approach. The XDLVO approach accounts for acid-base (polar) interactions that are not considered in the classical DLVO theory. For all membranecolloid pairs studied, DLVO interactions were similar. However, inclusion of acid-base interactions resulted in substantially different predictions of short-range (separation distance ,10 nm) interaction energies for several of the membrane–colloid pairs investigated. Predicted interaction energies were compared with atomic force microscopy (AFM) force measurements. The colloid probe technique was used to directly measure the force of interaction between a single colloid and a membrane surface. It was found that for strongly hydrophilic systems where the XDLVO approach predicts substantially different interaction energies than the DLVO theory, the measured force curves agree with the interaction sequence predicted by the XDLVO approach. For strongly hydrophobic systems where the XDLVO approach predicts an interaction similar to that predicted by the DLVO theory, the measured force curves agree with the interaction sequence seen in both DLVO and XDLVO predictions. It was also found that because the membranes have much higher surface energies (primarily due to the acid-base component) than the colloids investigated, the membranes control the general behavior of the interactions.