Dynamic transformations of self-assembled polymeric microspheres induced by AC voltage and shear flow

Abstract

AC voltage and shear flow are applied to self-assembled, multi-layered microspheres (MLMs) composed of a double hydrophilic block copolymer, poly(ethylene glycol)-block-poly(3-dimethyl(methacryloyloxyethyl) ammoniumpropane sulfonate), (PEG-SB) in order to control dynamic transformations in aqueous solution. Under application of AC voltage, the fusion of MLMs is accelerated by contact and the size grows from ∼1.5 μm to several tens of μm. The rate of growth is controllable by varying the frequency and the polymerization degree of the SB unit. Bursting of the fused MLMs is induced in a closed chamber and the average size of the bursting MLMs is 25 μm. On the other hand, MLMs are also fused under shear flow above 1.5 × 10³ s⁻¹. The fused MLMs grow to be a string-like structure with a length of more than 4 cm and the aspect ratio of >4000. The string-like structure splits into MLMs when the shear flow is removed. Such multiple dynamic transformations of MLMs can be applied to versatile droplets as microcargoes, microreactors, and microseparators in fully aqueous droplet microfluidics.