On the Colloidal Stability of Association Colloids

Abstract

Using self-consistent field (SCF) calculations, we quantify the interactions between spherical diblock copolymer micelles following a bottom-up approach. From the equilibrium properties of self-assembling micelles at different separation distances, a simple yet insightful micelle–micelle interaction can be extracted. The SCF results match with an analytical model based upon closed expressions for the free energy change per diblock copolymer in the micelle. To gain insight on the colloidal stability of micelle solutions, the second virial coefficient normalised by the undistorted micelle volume $B_2^*$ is evaluated. For stable micelle solutions ($B_2^*\gtrsim -6$), we find a weak dependence of $B_2^*$ on solvophilic block length for varying core-forming block properties (core solvation and block length). The micelle suspension gets unstable ($B_2^*\lesssim -6$) when the corona-forming block crosses $\Theta$-solvent conditions towards poor solvency. In contrast with what is expected from models where the soft nature of the micelle is not taken into account, increasing the effective grafting density of solvophilic tails from the core then leads to colloidal destabilisation of the micelle suspension.