Elastocapillary Deformation of "Glassy" Polymer Micelles at an Air-Water Interface.

We report direct in situ neutron reflectivity (NR) observations of elastocapillary deformation of nominally glassy polymer micelles at the air-water interface. Despite possessing glassy cores, adsorbed micelles undergo pronounced surface-tension-driven deformation, forming flattened structures. Core anisotropy changes sharply near the core glass-transition temperature (Tg), revealing a crossover from elastic elastocapillary deformation to relaxation-dominated surface micellization. Far below Tg, the deformation is fully reversible and yields an apparent Young's modulus that depends strongly on nanoscale core thickness, highlighting surface-induced mechanical gradients within the core.