A new class of donor-acceptor Stenhouse adduct (DASA)-functionalized silica microspheres (SMs) is designed and described to formulate Pickering emulsions with inversion property and large polarity change upon visible light irradiation. By tuning the hydrophilicity of the functional SM particles with visible light, these Pickering emulsions can easily perform inversion from water-in-oil to oil-in-water. The inversion performance of the emulsions is ascribed to DASA photoisomerization from an extended, hydrophobic, and intensely purple-colored triene to a compact, zwitterionic, and colorless cyclopentenone upon irradiation with visible light. This unique inversion behavior has been applied to control encapsulation and the release of fluorescein sodium salt.
Photo-induced conductivity modulation of stimuli-responsive materials is of great importance from the viewpoint of fundamental research and technology. In this work, 5 new kinds of azobenzene-based photo-responsive ionic liquids were synthesized and characterized, and UV/vis light modulation of their conductivity was investigated in an aqueous solution. The factors affecting the conductivity modulation of the photo-responsive fluids, such as photo-isomerization efficiency, photo-regulation aggregation, concentration and chemical structure of the ionic liquids, were examined systematically. It was found that the conductivity of the ionic liquids in water exhibited a significant increase upon UV light irradiation and the ionic liquids with a shorter alkyl spacer in the cation showed a more remarkable photo-induced conductivity enhancement with a maximum increase of 150%. In addition, the solution conductivity was restored (or very close) to the initial value upon an alternative irradiation with visible light. Thus, the solution conductivity can be modulated using alternative irradiation with UV and visible light. Although the reversible photo-isomerization of the azobenzene group under UV/vis irradiation is the origin of the conductivity modulation, the photo-regulated aggregation of the ionic liquid in water is indispensable for the maximum degree of conductivity modulation because UV irradiation can weaken, even break the aggregated cis-isomers of the ionic liquids in an aqueous solution.
Emulsion inversion has great potential in applications such as materials science, chemical reactions, and drug delivery. Therefore, developing a simple and green approach to control emulsion inversion is highly desirable. Herein an octyl-and bis(2-hydroxyethyl)-3-amino-bifunctionalized silica microsphere (SM-O-BIS) is designed, prepared, and used to fabricate a Pickering emulsion. It is found for the first time that this Pickering emulsion can be easily and reversibly inverted from water-in-oil (w/o) to oil-in-water (o/w) by alternate bubbling of CO 2 and N 2 at room temperature and atmospheric pressure. The molar ratio of trimethoxyoctylsilane to bis(2-hydroxyethyl)-3-aminopropyltriethoxysilane on the surface of silica is important for the emulsion inversion. This unique inversion can be recycled multiple times without any deterioration. By utilizing the emulsion inversion strategy, encapsulation and release of curcumin molecules have been actualized on demand. The possible mechanism of emulsion inversion is also investigated by measuring zeta potential, water contact angle, 13 C NMR spectroscopy, and FT-IR spectroscopy. It is shown that a significant and reversible change in hydrophilicity/hydrophobicity of SM-O-BIS is the driving force for such a CO 2 /N 2 -triggered inversion.
In recent years, covalent organic frameworks (COFs) have attracted enormous interest as a new generation of proton-exchange membranes, chemical sensors and electronic devices. However, to design high proton conductivity COFs,...
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