Stimuli-Responsive Shape Switching of Polymer Colloids by Temperature-Sensitive Absorption of Solvent.

The dynamic manipulation of colloidal particle shape offers a novel design mechanism for the creation of advanced responsive materials. To this end, we introduce a versatile new strategy for shape control of anisotropic polymeric colloidal particles. The concept utilizes temperature-sensitive absorption of a suitable solvent from a binary mixture. Specifically, increasing the temperature in the vicinity of the demixing transition of a binary mixture causes more solvent to be absorbed into the polymeric colloidal particle, which, in turn, lowers the glass transition temperature of the polymer inside the particle, with a concomitant decrease in viscosity. The balance between the internal viscosity and surface tension of the particle is thus disrupted, and the anisotropic shape of the particle shifts to become more spherical. Subsequent rapid temperature quenching can halt the process, leaving the particle with an intermediate anisotropy. The resultant shape anisotropy control provides new routes for studies of the phase transitions of anisotropic colloids and enables the fabrication of unique particles for materials applications.