双敏性微凝胶的絮凝及聚沉行为

Flocculation and Aggregation Behavior of Doubly Responsive Microgel

用沉降聚合法制备了聚(N-异丙基丙烯酰胺-co-甲基丙烯酸)微凝胶,并用NMR,DLS分析测定了微凝胶结构及凝胶颗粒在不同离子强度下粒径和表面电势的变化.25℃时在pH=7的溶液中Zeta电位为-18mV,随离子强度增加,逐渐减小.当NaCl浓度达0.2mol/L时基本不变,表明微凝胶表面电荷受到屏蔽,浓度继续增加主要使凝胶颗粒收缩.加热引起微凝胶收缩,颗粒表面电荷密度增大,Zeta电位增大.在0.2mol/LNaCl溶液中,41℃时微凝胶的Zeta电位可达-12.4mV,使微凝胶稳定.较高离子强度时,Zeta电位随温度升高发生突变,微凝胶表面几乎为中性,其突变温度与临界絮凝温度(CFT)相当.CFT随离子强度增加向低温迁移,微凝胶聚集速率在高温时比低温时快.

Poly（N-isopropylacrylamide-co-methacrylic acid） microgel was prepared by the precipitation polymerization method. NMR and TEM were used to analyze microstructure and morphology of the microgel. The stability and zeta potential of the microgel were investigated as a function of electrolyte concentration by dynamic light scattering. Zeta potential was -18 mV in pH=7 solution at 25 ℃, which decreased gradually with increasing ionic strength and reached an equilibrium value at 0.2 mol/L NaCl concentration, indicating that the surface charge of the microgel had been screened out. Increasing in NaCl concentration caused mainly the microgel particles to shrink. For the microgel in certain electrolyte solution, the heating induced the particles to deswell. As a result, the surface charge density became greater gradually,resulting in the increase of zeta potential. For microgel in 0.2 mol/L NaCl solution, the zeta potential was -12.4 mV at 41℃, playing an important role in stabilizing the microgel. The potential of the microgel at higher ionic strength displayed an abrupt transition of trending to zero as increasing the temperature, and the relevant temperature was correspondent with the critical flocculation temperature （CFT）. The CFT of the microgel was shifted to lower temperature with the increase of NaC1 concentration. At a certain salt concentration, the aggregation rate of the particles at a higher temperature was faster than that at a lower temperature.