Structure and composition effects on the magnetically-induced ordering of poloxamer solutions

Directing the self assembly of diamagnetic block copolymers (BCPs) via magnetic fields can induce a rich variety of physical phenomena, including the formation and enhancement of various morphologies. Previous work has shown that amphiphilic poloxamer micelle solutions exposed to low intensity magnetic fields (B ≥ 0.05 T) demonstrate a disorder-to-order transition driven by magnetically-induced change in polymer-solvent parameters. This study shows magnetically-induced structure formation across 11 poloxamers of varying molecular weight and block composition. Notably, the critical magnetization time prior to ordering, denoted as t_crit, correlates strongly to variables associated with the thermodynamics of micellization, such as hydrophobic block size. Remarkably, all 11 samples show an enhancement in modulus when processed magnetically vs thermally, with enhancement factor (G_mag/G_T) showing a strong molecular weight dependence. This increase in enhancement factor is explained in part by the slower transition kinetics of associated with lower molecular weight poloxamers, which was quantified via the Avrami model. Further insights into the role of poloxamer composition on the induced structure and ordering mechanism are discussed. This innovative approach to BCP processing enables discovery of structures and d-spacings inaccessible via traditional thermal processing routes, providing a platform for developing materials with precisely-controlled features at mild conditions.