(446c) Theory of Helix Formation In the Polymer Brush

Experimental observations of self-assembled systems capable of helix-coil transitions indicate a strong interplay between this transition and polymer brush properties. Although these effects are only qualitatively understood, helix formation can drive shape transformations in stimuli-responsive micelles while polymer brush formation can shift the helix-coil equilibrium to favor helices. In order to aid bottom-up design in these systems, this work presents a quantitative theoretical model of a helix-forming polymer brush. A simple model of protein folding is combined with a lattice model to account for interactions between helical and coil monomers as well as a self-consistent field approximation to describe how these effects stretch each chain in the brush. Consistent with experimental observation, brush formation at low-to-moderate tethering density is demonstrated to favor helix formation and to increase brush compressibility in directions parallel to the tethering surface. At high tethering density, monomer crowding causes helical unfolding, as chains are forced to stretch beyond the helical contour length to reduce unfavorable interactions. Interestingly, crowding-induced unfolding creates distinct layers of monomer density, a prediction that may be tested with neutron or x-ray reflectivity experiments.