Athermal models for diblock copolymer self-assembly

Abstract

Recent work on coarse-grained representations of interacting homopolymers and diblock copolymers in solution is briefly reviewed. Long homopolymer chains are modelled as ‘ultrasoft colloids’, with the effective interaction between their centres of mass (CM) determined by averaging over polymer conformations for fixed CM–CM distances. Diblock copolymers are modelled as ‘ultrasoft dumbells’, with the CMs of the two strands tethered by an anharmonic intramolecular potential. Monte Carlo simulations of these coarse-grained models allow the self-assembly of model diblock copolymers into lamellar and micellar microphases to be investigated. We show that the onset of clustering of two athermal models of diblock copolymers can be predicted within the ‘reference interaction site model’ (RISM) integral equation theory for the pair structure, using the simple random phase closure assumption. This analytic formulation highlights the natural link between bulk phase separation of binary polymer mixtures and microphase separation of the corresponding diblock copolymer in the same selective solvent.

Keywords:

• Diblock copolymers
• Self-assembly
• Athermal models

Acknowledgements

The authors are grateful to Chris Addison, Vincent Krakoviack and Carlo Pierleoni for their assistance and collaboration, and to Anna Oleksy for her help in calculating the numerical Fourier transforms.