Formation of Monodisperse Polymer@SiO2 Core–Shell Nanoparticles via Polymerization in Emulsions Stabilized by Amphiphilic Silica Precursor Polymers: HLB Dictates the Reaction Mechanism and Particle Size

Aerogel-Like Material Based on PEGylated Hyperbranched Polymethylethoxysiloxane

Aerogels are a class of materials that have gained increasing attention over the past several decades due to their exceptional physical and chemical properties. These materials are highly porous, with a low density and high surface area, allowing for applications such as insulation, catalysis, and energy storage. However, traditional aerogels, such as pure silica aerogels, suffer from brittleness and fragility, which limit their usefulness in many applications. Herein, we have addressed this problem by using organosilicon compounds, namely polymethylsilsesquioxane derivatives, for the synthesis of aerogel-like materials. Specifically, we have developed a novel approach involving surfactant-free synthesis of microcapsules from partially PEGylated hyperbranched polymethylethoxysiloxane. Due to the highly diphilic nature of these compounds, they readily concentrate at the oil/water interface in aqueous emulsions encapsulating oil droplets. During the subsequent condensation, the organosilicon precursor is consumed for hexane encapsulation (yielding hollow microcapsules) followed by the formation of a continuous condensed phase. Concurrently, methyl groups ensure the hydrophobicity of the resulting materials, which eliminates the need of using additional reagents for their hydrophobization.

Facile and scalable synthesis of functional Janus nanosheets - A polyethoxysiloxane assisted surfactant-free high internal phase emulsion approach

HYPOTHESIS

Janus nanosheets, which have two surfaces of different functionalities, exhibit unique interfacial properties. In this work, we propose a facile and scalable technique for preparation of silica-based Janus nanosheets, which is based on formation of high internal phase water-in-oil emulsions stabilized solely by alkyl-substituted polyethoxysiloxanes due to their hydrolysis-induced interfacial activity.

EXPERIMENTS

Janus nanosheets are then obtained by crushing the silica foams converted from such emulsions. The morphology of Janus nanosheets is investigated by field-emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). The chemical structure of functional silica materials is characterized by Fourier transform infrared spectroscopy (FT-IR). The asymmetric structure of silica nanosheets is observed by confocal laser scanning microscopy.

FINDINGS

The resulting nanosheets have a rough hydrophobic surface and a smooth hydrophilic one, and are capable of stabilizing Pickering oil-in-water emulsions. Remarkably, pH-responsiveness of emulsions can be attained using the nanosheets whose hydrophilic surface is substituted with amino groups. Fast oil-water separation is achieved by the Janus nanosheets, which has been demonstrated by the nanosheets with a polystyrene-coated hydrophobic surface. This work paves a new avenue for large-scale production of functional silica-based Janus nanosheets suitable for numerous promising applications.

Inclusion of Hydrophobic Liquids in Silica Aerogel Microparticles in an Aqueous Process: Microencapsulation and Extra Pore Creation

Due to its extraordinary properties, silica aerogel has a high potential for a number of applications; however, the state-of-the-art technique of its production involves cost-intensive supercritical drying or solvent exchange with a nonpolar solvent. Here, we report on a pure aqueous process for the preparation of silica aerogel particles as well as silica hollow nanoparticles, which is based on the self-assembly of amphiphilic silica precursor polymers, PEGylated poly(ethoxysiloxanes) (PEG-PEOS), in water and subsequent conversion under basic conditions. Addition of a hydrophobic organic liquid to the aqueous dispersions of PEG-PEOS results in the spontaneous formation of oil-in-water emulsions, which resemble the self-assembled structures of PEG-PEOS in water swollen by the organic liquid. The products of basic conversion of the emulsions are silica aerogel particles as well as hollow nanocapsules loaded with organic liquid. Remarkably, the oil phase significantly increases the porosity of the aerogel particles by acting as a porogen; meanwhile, it only decreases the silica shell thickness of the hollow nanoparticles. During freeze-drying, the aerogel particles, acting as matrix-type microcapsules, can efficiently retain the encapsulated volatile hydrophobic liquid; at the same time, the liquid is completely evaporated from the hollow particles (core-shell-type microcapsules). The encapsulation efficiency of hydrophobic liquids in the aerogel particles can reach as high as 99% after drying. The barrier property of the aerogel particles is higher with PEG-PEOS of lower PEGylation degrees due to bigger particle size and higher meso- and microporosity. This work opens a new avenue to prepare particulate silica aerogel for different promising applications including microencapsulation.

Cross-Linker-Controlled Ostwald Ripening in Emulsion Polymerization of Hollow Copolymer Nanoparticles

We propose a synthesis method for hollow copolymer nanoparticles, in which the size is controllable by the wettability of the materials designed by relative energy difference (RED). We investigated the influence of cross-linkers in RED and the hollow polymer nanoparticle synthesis. The size of the nanoparticles was characterized by scanning electron microscopy and transmission electron microscopy images. The diameter size of the hollow copolymer (styrene-co-methyl methacrylate) changes from 400 to 141 nm and the average core-vacancy sizes changes from 330 to 71 nm as increasing the feed ratio of the cross-linker, divinyl benzene, from 0.07 to 0.43. Cross-linkers in polymerization precipitates a polymerization reaction to produce seed copolymer particles quickly. The seed copolymer is a more transferrable medium through the surfactants across emulsion droplets and inhibits emulsion growth by unstable concentration variations of seed copolymers in emulsions. Therefore, Ostwald ripening was reduced by a higher feeding ratio of the cross-linker in the copolymer, which tends to produce smaller sized hollow nanoparticles.