Solvent-Induced Shape Recovery of Anisotropic Polymer Particles Prepared by a Modified Thermal Stretching Method

Anisotropic polymer particles have attracted great attention because of their unique properties and potential applications in various areas, such as microelectronics, drug delivery, and medical imaging. The fabrication and morphology control, especially the shape recovery, of anisotropic polymer particles, however, remains a challenging task. In this work, we develop a novel strategy to fabricate anisotropic polymer particles by thermally stretching poly(vinyl alcohol) (PVA) films embedding polystyrene (PS) microspheres using a weight. Depending on the preannealing condition, anisotropic PS particles with two different shapes, sharp-headed and blunt-headed PS particles, can be obtained. The PVA films can be selectively removed by isopropanol/water, releasing the anisotropic PS particles. By adding tetrahydrofuran (THF), a good solvent for PS, into the PS particle-containing solutions, the anisotropic particles gradually transform back to spheres to reduce the total interfacial energies. The shape recovery rates of the polymer particles can be controlled by the amount of the added THF. This work not only provides a simple and feasible route to fabricate anisotropic polymer particles but also contributes to a deeper understanding in the solvent-induced shape recovery process from anisotropic polymer particles to polymer spheres.