Adsorption of styrene on micron-sized, monodisperse, cross-linked polymer particles in a snowman-shaped state by utilizing the dynamic swelling method

Synthesis of dimpled polymer particles and polymer particles with protrusions - Past, present, and future

Since the development of emulsion polymerization techniques, polymer particles have become the epitome of standard colloids due to the exceptional control over size, size distribution, and composition the synthesis methods allow reaching. The exploration of different variations of the synthesis methods has led to the discovery of more advanced techniques, enabling control over their composition and shape. Many early investigations focused on forming particles with protrusions (with one protrusion, called dumbbell particles) and particles with concavities, also called dimpled particles. This paper reviews the literature covering the synthesis, functionalization, and applications of both types of particles. The focus has been on the rationalization of the various approaches used to prepare such particles and on the discussion of the mechanisms of formation not just from the experimental viewpoint but also from the standpoint of thermodynamics. The primary motivation to combine in a single review the preparation of both types of particles has been the observation of similarities among some of the methods developed to prepare dimpled particles, which sometimes include the formation of particles with protrusions and vice versa. The most common applications of these particles have been discussed as well. By looking at the different approaches developed in the literature under one general perspective, we hope to stimulate a more ample use of these particles and promote the development of even more effective synthetic protocols.

Current status and future developments in preparation and application of nonspherical polymer particles

Nonspherical polymer particles (NPPs) are nano/micro-particulates of macromolecules that are anisotropic in shape, and can be designed anisotropic in chemistry. Due to shape and surface anisotropies, NPPs bear many unique structures and fascinating properties which are distinctly different from those of spherical polymer particles (SPPs). In recent years, the research on NPPs has surprisingly blossomed in recent years, and many practical materials based on NPPs with potential applications in photonic device, material science and biomedical engineering have been generated. In this review, we give a systematic, balanced and comprehensive summary of the main aspects of NPPs related to their preparation and application, and propose perspectives for the future developments of NPPs.

Gas Bubbles Stabilized by Janus Particles with Varying Hydrophilic-Hydrophobic Surface Characteristics

Micrometer-sized polymer-grafted gold-silica (Au-SiO₂) Janus particles were fabricated by vacuum evaporation followed by polymer grafting. The Janus particle diameter, diameter distribution, morphology, surface chemistry, and water wettability were characterized by optical microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy, and contact angle measurements. The optical microscopy results showed that the polystyrene (PS)-grafted Au-SiO₂ Janus particles exhibited monolayer adsorption at the air-water interface and could stabilize bubbles, preventing their coalescence for more than 1 month. The hydrophobic PS-grafted Au and hydrophilic SiO₂ surfaces were exposed to the air and water phases, respectively. Bare Au-SiO₂ and poly(2-(perfluorobutyl)ethyl methacrylate) (PPFBEM)-grafted Au-SiO₂ Janus particles could also stabilize bubbles for up to 2 weeks. By contrast, bare silica particles did not stabilize bubbles and were dispersed in water. The bubbles that formed in the PS-grafted Janus particle system were more stable than those formed in the bare Au-SiO₂ Janus particles, PPFBEM-grafted Au-SiO₂ Janus particles, and SiO₂ particle systems because of the high adsorption energy of the PS-grafted particles at the air-water interface.

Preparation of Flattened Cross-Linked Hollow Particles by Suspension Polymerization in a Solid Dispersion Medium

Flattened cross-linked hollow poly(divinylbenzene) (PDVB) particles with encapsulated n-hexadecane (HD) were successfully prepared through suspension polymerization using the self-assembling of phase-separated polymer (SaPSeP) method, in which the solid dispersion medium was gelled by gellan gum and compressed. The solid phase induced by gellan gum can be easily changed to a liquid state by heating, allowing the obtained particles to be easily recovered after polymerization. When the polymerization was conducted in the solid dispersion medium without compression, spherical hollow PDVB/HD composite particles were obtained. In contrast, when the polymerization was conducted with the compression of the solid dispersion medium, flattened hollow PDVB/HD composite particles were obtained. The shape of the flattened hollow polymer particles was controlled by changing the compression ratio of the solid phase, and the size could also be controlled by changing the DVB/HD droplet size using the Shirasu porous glass membrane-emulsification technique. Furthermore, flattened hollow particles larger than 20 μm in size were obtained, but it was difficult to obtain spherical hollow particles of such large size using the SaPSeP method.

Micrometer-sized gold-silica Janus particles as particulate emulsifiers

Micrometer-sized gold-silica Janus particles act as an effective stabilizer of emulsions by adsorption at the oil-water interface. The Janus particles were adsorbed at the oil-water interface as a monolayer and stabilized near-spherical and nonspherical oil droplets that remained stable without coalescence for longer than one year. Gold and silica surfaces have hydrophobic and hydrophilic features; these surfaces were exposed to oil and water phases, respectively. In contrast, bare silica particles cannot stabilize stable emulsion, and completed demulsification occurred within 2 h. Greater stability of the emulsion for the Janus particle system compared to the silica particle system was achieved by using the adsorption energy of the Janus particles at the oil-water interface; the adsorption energy of the Janus particles is more than 3 orders of magnitude greater than that of silica particles. Suspension polymerization of Janus particle-stabilized vinyl monomer droplets in the absence of any molecular-level emulsifier in aqueous media led to nonspherical microspheres with Janus particles on their surface. Furthermore, polymer microspheres carrying Au femtoliter cups on their surfaces were successfully fabricated by removal of the silica component from the Janus-particle stabilized microspheres.