Temperature dependent phase behavior of PNIPAM microgels in mixed water/methanol solvents

Temperature dependent phase behavior of poly(N-isopropylacylamide) (PNIPAM) microgels in water/methanol mixtures of different composition was studied with dynamic light scattering (DLS) and small-angle neutron scattering (SANS). Using DLS, it is possible to measure the diffusion coefficient, and thus the size of particles exactly and directly; the variation of the phase transition temperature in the different solvents is also easy to detect by this method. With SANS measurements in D₂O/MeOD mixtures, some of the DLS results were confirmed. Moreover, SANS measurements give valuable information on the particle structure in different solvents. The experiments were compared with the theory of competitive hydration introduced by Tanaka et al. We found a good agreement of theory and experiment, and obtained the theoretical predictions: around the transition temperature, the composition of the bound methanol along the chains is higher than that of the outer solution, while the whole methanol composition inside the gel is lower. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym. Phys. 2013, 51, 1100–1111     

Electrical Properties and Stability of Poly(N-isopropylacylamide-co-methacrylic Acid) Core-Shell Microgel

Graphical Abstract: A doubly responsive microgel with core shell shape was prepared by seed polymerization. The electrical properties were characterized. The latex stability was evaluated and discussed according to the colloid theory.

A core-shell microgel of poly(N-isopropylacylamide-co-methacrylic acid) was prepared by seeded polymerization. Dynamic light scattering measurements indicated that the microgel had a narrow size distribution. Zeta potential decreased gradually with increasing ionic strength, and when salinity reached a certain concentration the surface charge was almost screened out. Further addition of salt led to the shrinking and final flocculation. For increasing temperature, the zeta potential under higher ionic strength exhibited an abrupt change for trending to zero. Total interaction energy between particles was calculated with colloid theory. Meanwhile, thermal stability was evaluated and interpreted the experimental phenomenons.     

浊度法表征温敏性微凝胶体积的相转变行为

以N-异丙基丙烯酰胺(NIPAM)、甲基丙烯酸(MAA)为单体,N,N-亚甲基双丙烯酰胺(MBA)为交联剂,制备了温敏性聚(N-异丙基丙烯酰胺)(PNIPAM)和具有温度、pH敏感性的聚(N-异丙基丙烯酰胺-co-甲基丙烯酸)(PNIPAM-MAA)微凝胶。通过测定不同温度和pH条件下微凝胶浊度变化,表征微凝胶的温度及pH敏感性,描述了NaCl浓度和pH对微凝胶体积相转变温度的影响。同时,测定了微凝胶的临界聚沉浓度及临界絮凝温度,表征了微凝胶的稳定性,讨论了影响微凝胶的稳定性因素。     

热响应性磁性复合微粒的制备及性质

滴定水解法制备的Fe3O4磁流体,与单体N-异丙基丙烯酰胺(NIPAM)和α-甲基丙烯酸(MAA),在一定的条件下沉降聚合,制备了Fe3O4/P(NIPAM-MAA)复合微粒.对其形态及性能进行研究表明,复合微粒呈现核壳结构的规则球形,溶胀态和收缩态的平均粒径分别为334.7nm和141.5nm.复合颗粒中的Fe3O4颗粒质量分数为1.9%,当外磁场为104Oe时,复合微粒的饱和磁化强度(Ms)为0.6306emu/g.分散在水溶液中的复合微粒在30℃～36℃之间发生了体积相转变,表现出温度敏感性.在低pH溶液中的体积相转变十分显著,随pH逐渐增大,其体积相转变温度(VPTT)显示向高温迁移.