Preparation Of Thermal Responsive Silica Composites And Its Application In Pickering Emulsion

Thermal responsive polymers have been widely applied to several different fields, such as extraction, controlled release and enzyme activity control etc. Though the thermal responsive polymers show remarkable changes in aqueous solution with a change in temperature, the poor mechanical properties limit their applications. The hybrids of polymer/inorganic nanoparticle have attracted great attention in recent years because of their excellent mechanical properties, thermal stability, biodegradation and abrasion resistance. The polymer/SiO2composites are concentrated on the research of the hybrids of polymer/inorganic nanoparticle. Several methods have been used to synthesize the polymer/SiO2composites, such as surface-initiated atom transfer radical polymerization, sol-gel method and emulsion polymerization. However, these methods have some disadvantages such as multiple synthetic steps, difficult control synthetic process. Even worse, the solvents used in the preparation process can lead to environment pollution. In this thesis, the thermal responsive nano-SiO2composites were prepared by the two simple and environmental friendly methods, and these composites were used in Pickering emulsion as a solid particle emulsifier.1. Synthesis and characterization of monodisperse thermal responsive SiO2/PNIPAAm composite microspheresA simple and effective method was used to synthesize the thermal responsive SiO2/PNIPAAm composite microspheres by molecular design. The influences of monomer concentration, reaction time, reaction temperature and initiator amount on water contact angel of the synthesized microspheres were investigated, and the optimum technology condition was obtained. The structure, morphology and surface composition were characterized by Fourier Transform Infrared Spectroscopy (FTIR), Transmission Electron Microscopy (TEM), and X-ray Photoelectron Spectroscopy (XPS). The thermal responsive properties in aqueous solution were further studied by dynamic light scatter (DLS). The results show that the low critical solution temperature (LCST) of Si02/PNIPAAmcomposites is around304K and the particle is monodisperse microsphere.2. Synthesis and characterization of thermal responsive SiO2/Poly-ether compositeNonionic organosilicone surfactant trisiloxane-modified oligo (propylene oxide-block-ethylene oxide) was selected as the typical modified agent to synthesize thermal responsive SiO2/poly-ether composite by hydrolyzation reaction. The optimum technology was determined by researching the water contact angel of the sample in different synthesis conditions. The samples were characterized by FT-IR, TEM, XPS, and the thermal responsive property was measured by contact angle measurement instrument and DLS. The results showed that the polymer chains have been linked with SiO2and the low critical solution temperature (LCST) of the composite is consistent with the cloud point of trisiloxane-modified oligo (propylene oxide-block-ethylene oxide). This work might provide a new sight for the synthesis of thermal responsive composites.3. Application of thermal responsive SiO2composites in Pickering emulsionComparing with the traditional emulsion, Pickering emulsions have a lot of natural merits, for example,(1) less dosage emulsifier and lower cost;(2) lower toxicity;(3) thermodynamics stable emulsion and little effect by exoteric environment;(4) environment friendly. Therefore, they have been widely applied to mineral flotation, wetting control, crude oil emulsified, etc.Pickering emulsions were prepared with thermal responsive SiO2composites as solid particle emulsifier and liquid paraffin as the oil phase. The effects of adding amount of solid particles, water, liquid paraffin, inorganic salt and charging sequence on emulsion properties were investgated. Emulsion performance were comprehensively analyzed through the separated water and oil value, optical micrographs, particle size distribution, viscosity, technological conditions of preparation were summarized. And changes of emulsion at20℃and60℃as a function of temperature were observed. (1) Thermal responsive SiO2/PNIPAAm composites as emulsifierWith the increase of solid particle content, the emulsion drop size decreases, viscosity increases, stability of emulsion is improved; with oil content increasing, emulsion drop size increases slightly. The different charging sequence leads to the different drop size and viscosity of the emulsion. If solid particle was firstly ultrasonically dispersed in water and then adding of paraffin, the emulsion of bigger drop size and less viscosity will be received, the other way round, the emulsion has smaller drop size, more viscosity and stronger stability. The addition of NaCl promotes the particle adsorption at the oil/water interface, the formation of network structure at the interface maks drop size smaller, interfacial film strength increasing, emulsion viscosity enhancing and stability stronger.(2) Thermal responsive SiO2/poly-ether composite as emulsifierAlong with the adding of solid particle content, the drop size of the emulsion decreases, the viscosity increases and the stability of the emulsion improves; Along with the adding of water increases, the opposite thing is happened; charging sequence and liquid paraffin content has no effect on emulsion drop size, but charging sequence can affect the emulsion viscosity. The emulsion formed by adding firstly water into the solid particle has more viscosity and stronger stability. The addition of NaCl improves the stability of emulsion coalescence and stratification stability, this is because the NaCl can promote particle adsorption and the formation of network structure at the oil/water interface, emulsion stability is increasing. The change of NaC1concentration had no effect on emulsion drop size and viscosity.Pickering emulsions have no phase transition phenomenon stabilized by the two thermal responsive SiO2composite, when the temperature exceeds LCST, just reducing emulsion stratification stability at elevated temperatures. This is probably due to less polymer is grafted on the surface of the composites.