Support: NSF MRSEC 0520020

From the steering wheel of a sports cars to a baseball bat, the forms around us are contoured not only for function but also for how they feel between our fingers. The degree to which molecules also sense such contours and respond by moving left or right, up or down is a question of major importance to many fields including the field of self-assembly. Amphiphilic polymers are composed of hydrophilic and hydrophobic polymer links and can assemble in water into surprisingly long and stable worm-like micelles, but the intrinsic polydispersity of polymers as well as polymer blending efforts and the increasing use of degradable chains all raise basic questions of curvature–composition coupling and morphological stability.

Curvy Contours and Molecular MotionsLoverde, S.M., Ortiz, V., Kamien, R.D., Klein, M.L., and Discher, D.E.

Large-scale, molecularly detailed simulations show that a systematic increase in the hydrophilic polymer, in both monodisperse and binary blends, induces budding and breakup into spherical and novel ‘dumbbell’ micelles — as seen experimentally in electron microscopy images of degradable worm-like micelles. Key aspects of average structure are surprisingly consistent with simple theory, but morphological transitions of mixtures are only crudely predicted by simple mixture rules, which motivates a new theory for how molecules sense curvature. The computational methods developed for assemblies of a polymer called ‘PEG’ – which is widely used in household products as well as sophisticated biomedical devices – should be useful for many high curvature nanosystems.

Soft Matter, 6, 1363, 2010 (cover)