(450a) Scalable Fabrication of Anisotropic Polymer Particles and Nanofibers in Sheared Liquid-Liquid Systems
The antisolvent-induced polymer precipitation from solution into particles is a basic and simple laboratory process, whose vast potential to be engineered into a precise process for nanoparticles and nanomaterials fabrication appears to have escaped much attention. Under shear, the ultralow interfacial tension between the droplets and the medium enables the formation of high surface area liquid structures, which can serve as templates for the synthesis of diverse classes of polymer materials, at least one characteristic dimension of which may be on the nanoscale. As the sheared solution droplets become highly stretched, the solvent diffuses out of the polymer-containing liquid phase, while the antisolvent in the medium infuses it. As the composition of the liquid medium changes, the polymer precipitates into specific shapes. The interplay of these effects (which occur rapidly and mostly simultaneously) results in the formation of a surprisingly rich variety of structures. We distinguish multiple types of material morphology outcomes, including nanorods, nanofibers, nanoribbons, nanosheets and various types of anisotropic particles. Their morphologies are critically dependent on the interplay of polymer molecular entanglement and antisolvent infusion rate. We will discuss the fundamental influence of polymer concentration and molecular weight on the process and the ability to control the resulting morphologies and sizes via the antisolvent concentration. The technique was first used for the fabrication of polymer microrods that can serve as superstabilizers of foams and emulsions. We next introduced a “shear nanospinning” technique that allows scalable manufacture of nanofibers and nanorods (Adv. Mater., 27, 2642, 2015). The patented XanoShear™ technology can increase drastically the scale and scope of industrial nanofiber fabrication. We will now demonstrate how the liquid shear combined with antisolvent precipitation can be tuned for the large-scale synthesis of a range of new sheet-like and "hairy" nanoparticles with very interesting rheological and structure-building properties.