Novel Polymeric Organosilica Precursor and Emulsion Stabilizer: Toward Highly Elastic Hollow Organosilica Nanospheres.

The fabrication of hollow organosilica nanoparticles with high elasticity is greatly desirable but still challenging. Herein, we present a new and simple strategy to prepare such nanoparticles by using hyperbranched polyvinylpolytrimethoxysilane (PVPMS) via a soap-free oil in water (O/W) emulsion system. PVPMS was synthesized through the radical polymerization of vinyltrimethoxysilane (VMS) followed by the acid-catalyzed hydrolytic polycondensation of trimethoxysilyl groups, which works not only as an organosilica precursor but also as a sole emulsion stabilizer due to its hydrolysis-induced amphiphilicity at the oil/water interface. When styrene was used as the oil phase and initiated to polymerize, hybrid polystyrene (PS) core-organosilica shell (PS@organosilica) nanoparticles were obtained by controlling the reaction conditions. Furthermore, highly elastic hollow organosilica nanospheres with low Young's modulus (∼220 MPa) were yielded through solvent etching of the core. This study expands the scope of organosilica precursor from small molecule organosilane to polymeric macromolecule and provides useful guidance for application in other polyorganosilsesquioxane related hybrid organosilica particles and functional hollow nanoparticles.

Ultralight Silica Foams with a Hierarchical Pore Structure via a Surfactant-Free High Internal Phase Emulsion Process.

An ultralight silica aerogel is among the most versatile materials available for technical applications; however, it remains a huge challenge to reduce its manufacturing cost. Here, we report on a simple approach for the preparation of silica foam monoliths with ultrahigh porosity up to 99.5% and specific surface area as high as 755 m2 g-1, which are similar to those of an aerogel. Our strategy is based on the effective stabilization of water-in-oil high internal phase emulsions by a hydrophobic silica precursor polymer, hyperbranched polyethoxysiloxane because of its hydrolysis-induced amphiphilicity. After conversion of this precursor polymer to silica, the emulsions are solidified without significant volume shrinkage. Thus, mechanically strong macroporous silica monoliths are obtained after removal of its liquid components. According to nitrogen sorption data, the resulting silica foams exhibit a high specific surface area and a foam skeleton consisting of both micropores (<2 nm) and mesopores (2-50 nm). The pore size, porosity, and surface area can be regulated by varying pH as well as the concentration of the silica precursor in the oil phase. In addition, the pore size can be adjusted by controlling shear force during emulsification. This work opens a new avenue for producing ultralight porous materials amenable to numerous applications.

Pore Structure of Macroporous Polymers Using Polystyrene/Silica Composite Particles as Pickering Stabilizers.

A novel approach for the preparation of interconnected macroporous polymers with a controllable pore structure was reported. The method was based on the polymerization of water-in-oil Pickering high internal phase emulsion (HIPE) stabilized by polystyrene (PS)/silica composite particles. The composite Pickering stabilizers were facilely obtained by mixing positively charged PS microspheres and negatively charged silica nanoparticles, and their amphiphilicity could be delicately tailored by varying the ratio of PS and silica. The droplet size of Pickering HIPEs was characterized using an optical microscope. The pore structure of polymer foams was observed using a scanning electron microscope. The interconnectivity of macroporous polymers was evaluated upon their gas permeability, which was greatly improved after etching PS microspheres included in the Pickering stabilizers with tetrahydrofuran. As a result, fine tailoring of the pore structure of polymer foams could be realized by simply tuning the ratio of PS to silica particles in the composite stabilizer.

Novel Retroreflective Structural Color Films Based on Total Internal Reflection Interference.

Structural color materials have tremendous applications and been extensively investigated in the past decades. Most of them involve either nanoscale periodic photonic crystal structure or film interference mechanisms. Herein, we report a novel retroreflective structural color film (RSCF) based on a combined effect of interference and total internal reflection (TIR). The RSCF is consisted of a microscale polymer hemisphere array formed on the same polymer matrix. When exposed to white light illumination, the non-hemisphere-side of the film exhibits non-iridescent color under coaxial illumination and observation, and iridescent color under noncoaxial illumination and observation. In contrary, the hemisphere-side of the film does not show any colors regardless of coaxial or noncoaxial illumination and observation. Furthermore, an elastic polyurethane-based RSCF can exhibit dynamically and reversibly changing colors during uniaxial tensile/compressive deformation.

Robust porous organosilica monoliths via a surfactant-free high internal phase emulsion process for efficient oil-water separation.

Elastic porous organosilica monoliths (POMs) are successfully prepared by water in oil (w/o) high internal phase emulsions (HIPEs) with a novel silica precursor named polyethoxysiloxane (PEOS) as sole stabilizer. The stability of the HIPEs and the mechanical strength of the POMs are investigated as functions of PEOS and crosslinker contents in the oil phase. FESEM reveals that PEOS molecules play a significant role of in-situ growth into silica particles to strengthen the POMs, which enables the successful preparation of elastic POMs. Furthermore, oil-water separation behavior of the POMs is studied. Both the absorbent capacity and speed are considerably superior to the previously reported PDMS sponges.

Stable Perovskite Quantum Dots Coated with Superhydrophobic Organosilica Shells for White Light-Emitting Diodes.

Metalammonium lead perovskite (MAPbX3 , MA=CH3 NH3 + ; X=Cl, Br, I) quantum dots (QDs) have attracted tremendous attention due to their outstanding optical properties. However, they usually suffer from poor stability towards water or moisture, which seriously limits their practical applications. Here, we report a simple and effective approach to improve the stability of MAPbBr3 QDs by encapsulating them with superhydrophobic fluorinated organosilica (FSiO2 ) shells. The water-resistant stability of the superhydrophobic MAPbBr3 QDs/FSiO2 is significantly enhanced and they display strong fluorescence even after immersion in water for 12 hours. This method is readily extended to prepare superhydrophobic MAPbBr2.4 Cl0.6 QDs/FSiO2 and MAPbI3 QDs/FSiO2 powders. These superhydrophobic MAPbX3 QDs/FSiO2 can be further used to fabricate white light-emitting diodes (LEDs) with comparable color to pure white emission.

A simple and environment-friendly approach for synthesizing macroporous polymers from aqueous foams.

We propose a facile and environment-friendly approach for the preparation of macroporous polyacrylamide (PAM) via thermal-initiated polymerization of aqueous foams that are stabilized by surface-modified silica nanoparticles. Cetyltrimethylammonium bromide (CTAB) is used to delicately adjust the surface amphiphilicity of silica to stabilize aqueous foams. The air bubble size and size distribution is affected by the wettability of silica particles, solid content and air volume fraction in the foams. The morphology of macroporous polymers is observed by a scanning electron microscope (SEM). The pore and pore throat size can be tailored effectively by varying the silica content and air volume fraction. A high porosity of 83% is achieved when the air volume fraction of the aqueous foam is 65%. PAM hydrogels obtained via polymerizing aqueous foams show pronounced advantage over the ones prepared from oil-in-water (O/W) emulsions in wastewater treatment because of their unique pore structure. This strategy would also be extended to prepare other macroporous polymers with well-defined pore structures.