Cascades of unfolding transitions in amphiphilic molecular brushes.

Abstract

Using a combination of self-consistent field theory with coarse-grained Brownian dynamics simulations, we studied mechanical unfolding of an amphiphilic molecular brush in a solvent that was poor for the side chains but good for the main chain of the brush. In striking contrast to earlier theoretical predictions [O. V. Borisov and A. Halperin, Europhys. Lett. 34, 657 (1996)] made for amphiphilic graft copolymers, we discovered that in a partially unfolded molecular brush, a globular core co-exists, at equilibrium, with a necklace of smaller sized intra-molecular micelles, each comprising a few side chains connected by stretched main chain strands (bridges). A progressive increase in the main chain end-to-end distance of the brush triggers a sequence of discrete events of generation of new intramolecular micelles, giving rise to a sawtooth pattern in the restoring force-deformation curve.