Preparation of hemispherical polystyrene particles utilizing the solvent evaporation method in aqueous dispersed systems

Abstract

Various nonspherical polystyrene (PS) particles were prepared by slow evaporation of toluene (used common good solvent) from homogeneous PS/hexadecane (HD)/toluene droplets dispersed in surfactant aqueous solutions at room temperature, followed by the rapid removal of HD from PS/HD particles with various phase-separated morphologies. The morphology of PS/HD particles was controlled by tuning the interfacial tension with various types of surfactants. Hemispherical PS particles with flat surfaces were obtained from phase-separated PS/HD/toluene droplets having a Janus structure, when polyoxyethylene nonylphenyl ether with an average ethylene oxide chain length of 30.8 was used as the surfactant. Polymer Journal ( Keywords: nonspherical particles; hemisphere; solvent evaporation method; phase separation; interfacial tension; polystyrene INTRODUCTION Nonspherical polymer particles have attracted great attention because of their potential as materials with unique crystal structures, 1-3 light scattering properties 4 and external field-responsive properties (e.g., shear field 5 and electric field 6 ). In general, polymer particles synthesized by heterogeneous polymerizations under thermodynamic control have a spherical shape because of interfacial free energy minimization. However, nonspherical polymer particles have been synthesized under kinetic control utilizing various seeded polymerization methods, 7-24 microfluidic techniques, 25-28 deformation of spherical polymer particles by external force, 29-31 the stepwise heterocoagulation method 32,33 and the self-organized precipitation method. 34 In a previous work, we proposed a novel approach for the preparation of micrometer-sized, monodisperse, nonspherical (i.e., dimpled and hemispherical) polystyrene (PS) particles by successive heating and cooling of spherical PS particles dispersed in a methanol/ water medium in the presence of droplets of decane. 35 Decane was absorbed by the particles during heating, and the particles subsequently phase-separated into PS and decane phases during cooling. Eventually, nonspherical particles reflecting the morphology of phase-separated PS/decane particles were formed by rapid removal of the decane phase. The final particle shape could be controlled simply with the amount of absorbed decane.We have also recently demonstrated morphology control of PS/poly(methyl methacrylate) composite particles prepared by the slow release of toluene as a common good solvent from homogeneous PS/poly(methyl methacrylate)/toluene droplets dispersed in a surfactant aqueous solution at room temperature (the solvent evaporation method). [36][37][38] It was revealed that the particle morphology could be

pH-Responsive Capsule Polymer Particles Prepared by Interfacial Photo-Cross-Linking: Effect of the Alkyl Chain Length of the pH-Responsive Monomer

“…Photo-reactive spherical polymer particles possessing pH-responsive groups of different alkyl chain lengths were prepared by the solvent evaporation method, − wherein a chloroform solution of the polymer was homogenized in a phosphate buffer (pH 7.4) containing poly­(vinyl alcohol) as the stabilizer. After the solvent evaporation process, the afforded particles prepared from the three different polymers displayed spherical morphologies (Figure ).…”

Recent Advances in the Emulsion Solvent Evaporation Technique for the Preparation of Nanoparticles and Nanocapsules

“…Half-spherical structures are accessible by removing the liquid in acorn structures formed with a polymer and a liquid [40,61]. Onion-like structures are created from block copolymers, for which the phase separation into lamellae causes layered structures that follows the curvature of the particle where they are confined [37,40,62].…”

Synthetic advances of internally nanostructured polymer particles: From and beyond block copolymer

“…Changing the interfacial interactions between polymer particles and the surrounding medium is crucial in preparing nonspherical BCP particles. [47][48][49] Surfactants can adsorb to the interface between the immiscible oil and water phases and reduce the interfacial tension; thus, they play a critical role in stabilizing the emul-sions. Nowadays, various surfactants involving small molecules, polymers, inorganic particles and even mixed systems have been widely used to tune the interfacial interaction.…”