Cryogenic transmission electron microscopy for observation of monomer protrusions that emerge during formation of dumbbell-shaped polymer colloids

Abstract

Anisotropic particles exhibit directional interactions resulting in a rich phase behavior. Considerable efforts have thus been invested in guiding particle synthesis into an anisotropic direction. Dumbbell-shaped polymer particles are one of the most remarkable examples. They result from phase separation during seeded polymerization. The underlying mechanism and thermodynamic principles are understood from its proximal end. Segregation of monomer and seed particle results in a monomer protrusion attached to the seed. Polymerization of the protrusion finally yields particles with two bulb-shaped halves. Little attention has been paid to an investigation of transient states, namely the formation of liquid protrusions grown from monomer-swollen seeds. This study demonstrates that cryogenic transmission electron microscopy is an excellent tool for mapping transient states within colloidal objects. Swelling of polymer particles and formation of liquid protrusions mediated by a surface coating on the seeds is explored for styrene and methyl-methacrylate at different temperatures and monomer-to-seed volume ratios.