Preparation And Properties Of Thermoresponsive Silica Nanoparticles With Varied LCST

Thermosensitive polymers exhibit a lower critical solution temperature(LCST) in aqueous solution. Above the LCST, such polymers undergo a phase transition process tending to water insoluble. The most extensively studied thermosensitive polymers are poly(N-isopropylacrylamide)(PNIPAM) exhibiting LCST around 32 oC closed to body temperature with a wide range of applications in drug delivery. Despite its widespread popularity in materials science, PNIPAM has narrow and low LCST, which limits its practical applications. So, the pursuit of tunable LCST is one of major objectives of those materials. Poly(ethylene glycol) methyl ether methacrylate(POEGMA) was recently proposed as an attractive alternative to PNIPAM, because the LCST of POEGMA can be finely tuned through modification of the length of the oligo(ethylene glycol) side chain. Stimulus response nanoparticles have been attracted much attention due to their fascinating optical, electronic, magnetic, biologic, pharmacal, and catalytic properties. Typically, hybrid nanoparticles incorporate polymer shells which mainly determine the chemical properties of nanoparticles and their responsiveness to external stimuli into inorganic nanoparticles. In this thesis, thermosensitive Si O2 nanoparticles were prepared with graft-on poly(ethylene glycol) methyl ether methacrylate(POEGMA, Mn~300 or 500 g/mol) via atom transfer radical polymerization with activators generated through electron transfer(AGET ATRP) with a high grafting density. Pickering emulsions were prepared using Si O2-POEGMA500 as an emulsifier. The thermosensitive properties were investigated for the efficient separation and recycling of catalysts in future.(1) Nano-SiO2 particles were prepared according to the St?ber method. Then 3-aminopropyltriethoxysilane(KH550) was grafted on the nano-Si O2 particles to obtain Si O2-NH2. Si O2-Br was got with graft-on initiator 2-bromoisobutyryl bromide to the Si O2-NH2. The thermosensitive Si O2-POEGMA500 composite microspheres were successfully prepared by AGET ATRP. The effects of the amount of ligand, catalyst, ascorbic acid and monomer as well as the reaction temperature and time weresystematically investigated and optimized to get a high grafting density. The structure and surface composition of Si O2-POEGMA500 were analyzed using FT-IR, XPS, TGA, TEM and SEM to confirm that the Si O2-POEGMA500 has been prepared successfully. Measurements of turbidity, Dynamic Light Scattering(DLS), and phase transfer were conducted to investigate the thermosensitive properties of Si O2-POEGMA500.(2) Thermosensitive Si O2 nanoparticles were prepared with graft-on poly(ethylene glycol) methyl ether methacrylate(POEGMA, Mn~300) and POEGMA500-300 via AGET ATRP in optimal reaction conditions, respectively. The structure and surface composition of our hybrid materials were analyzed using FT-IR, XPS, TEM and SEM to confirm that the Si O2-POEGMA300 has been prepared successfully. Measurements of turbidity, Dynamic Light Scattering(DLS), and phase transfer were conducted to investigate the thermosensitive properties of Si O2-POEGMA300 and Si O2-POEGMA500-300. The effects of Na Cl, ethanol and SDS on LCST of Si O2-POEGMA300 were systematically investigated.(3) Pickering emulsions were prepared using such hybrid Si O2-POEGMA500 as an emulsifier, deionized water as aqueous phase, liquid paraffin as oil phase. The effects of the amount of solid particles, water, liquid paraffin, charging sequence and inorganic salt on emulsion stability were systematically optimized. The thermosensitive property of the as-prepared Pickering emulsions was observed.