Based On Cholesterol Derivatives Create New Gel Emulsion And Its Application In The Preparation Of Low-density Polymer Materials

Gel emulsion (also referred as High Internal Phase Emulsion) consisting of water, stabilizer (or emulsifier) and oil is a gel-like disperse system with its internal-phase volume fraction exceeding 0.74, a data for the most compact arrangement of uniform, spherical droplets. Stabilizers used in preparations of gel emulsions do include surfactants and solid particles of sizes between a few nanometers to micrometers mostly. Conventionally, gel emulsions are commonly stabilized by large amounts of surfactants, about 5-50 wt%and particle-stabilized emulsions commonly phase-invert between volume fractions of 0.65 to 0.70. Gel emulsion is widely used in practice in food, cosmetics, medicine, chemical industry and as a template for the preparation of materials with special structure or functions and so on. Among them, the use of gel emulsions as templates to prepare materials with special structure or function is of the most importance, which has attracted much attention during the last few decades. High internal phase emulsion used as templates for the fabrication of highly porous materials contains one or more monomers as its continuous phase which has been polymerized in the system. And after the removal of dispersed phase, such materials, commonly known as poly(merized)HIPEs are obtained, which have proven to be useful in a variety of applications, including filtration membranes for molten metal and hot gases, catalyst carriers, scaffolds for solid phase organic synthesis, tissue engineering and so on.As a continuation of the works conducted in our group earlier, we have prepared stable W/O gel emulsions stabilized by cholesterol-based organogelators with water as dispersed phase and styrene as continuous phase at room temperature. Further investigation, including the preparation methods of low-density polystyrene and adjustment to its structures has been carried out. Specifically, it is composed of following two parts:PartⅠ:Gel emulsion experiments were conducted with five cholesterol-based organogelators, which have been specially prepared in the present work, as stabilizers, three kinds of monomer as the continuous phase, water as the dispersed phase. The results show that compounds 1 and 2 can stabilize styrene and tertiary butyl methacrylate to form gel emulsions with water, respectively, in a simple surge, with the concentrations of compounds being 5 wt%considering to the continuous phase. The highest volume fraction of the dispersed phase is 92%, at least. The optical microscopy and confocal images show that the microstructure of gel emulsions is a typical foam structure (Figure 1). Compounds 3,4 and 5 cannot stabilize three monomers and water to form a gel emulsion, but compounds 5 can gel monomers in the water, selectively. Unlike traditional gel emulsion stabilized by surfactant, cholesterol derivatives can make the monomer form "microgel" region in which dispersed droplets are packaged and get immobility. The intermolecular forces increase with the length of spacer'increasing, so compound 5 can make three monomers form physical gels in the water, selectively. According to the literature, this is the first case of using cholesterol derivatives as stabilizers to carry out gel emulsions with polymers. This kind of gel emulsion can be achieved simply and does not need to add other substances such as CaCl2·2H2O to prevent the "Ostwald" effect (the smaller particles are inclined to be particle annihilation by the larger phenomenon in emulsion), being compared with traditional gel emulsions.PartⅡ:Different dispersed phase volume fractions of gel emulsion with styrene as continuous phase were prepared and polymerized to obtain polystyrene. Implementation results show that the addition of cholesterol derivatives does not affect the polymerization of styrene. The removal of stabilizers by Soxhlet extraction and the dryness of materials at room temperature did not cause material collapse (Figure 2). Thus, the cholesterol derivatives, not only as a stabilizer gel emulsion can be successfully prepared but gel emulsions prepared can be used as template to synthesis polymer materials with special structure. The purification of the materials is simple. Furthermore, by adding porogen into the gel emulsion, polystyrenes with different pore structure were prepared and the effect of porogen concentration to the pore structure and density of materials were investigated, accessing to the experimental conditions of the preparation and adjustment of porous low-density polystyrene.