Synthesis, Characterization, and Pickering Emulsifier Performance of Anisotropic Cross-Linked Block Copolymer Worms: Effect of Aspect Ratio on Emulsion Stability in the Presence of Surfactant
Synthesis, Characterization, and Pickering Emulsifier Performance of Anisotropic Cross-Linked Block Copolymer Worms: Effect of Aspect Ratio on Emulsion Stability in the Presence of Surfactant
复制标题
DOI：
10.1021/acs.langmuir.8b03727
复制
发表时间：
2019-01-08
期刊：
影响因子：
3.9
通讯作者：
Armes, Steven P.
中科院分区：
文献类型：
--
作者：
Hunter, Saul J.;Thompson, Kate L.;Armes, Steven P.
采用可逆加成-断裂链转移（RAFT）水分散聚合制备环氧官能团PGMA-P（HPMA-stat-GlyMA）二嵌段共聚物蠕虫，其中GMA、HPMA和GlyMA分别表示单甲基丙烯酸甘油酯、甲基丙烯酸2-羟丙酯和甲基丙烯酸缩水甘油酯。使用 3-氨基丙基三乙氧基硅烷 (APTES) 将 GlyMA 残基上的环氧基开环，以便通过一系列水解缩合反应交联蠕虫核。重要的是，可以根据为共价稳定选择的精确条件来调整蠕虫长宽比。相对较长的交联蠕虫是通过在 20 摄氏度下与 APTES 反应获得的，而具有基本相同共聚物组成的短得多的蠕虫是通过在添加 APTES 之前将线性蠕虫从 20 冷却到 4 摄氏度而形成的。小角 X 射线散射 (SAXS) 研究证实，长蠕虫的平均纵横比大约是短蠕虫的八倍。水性电泳研究表明，由于纳米颗粒核心内 APTES 衍生的仲胺基团质子化，两种类型的交联蠕虫在低 pH 下都获得了弱阳离子表面电荷。这些交联蠕虫被评估为通过在 20 摄氏度和 pH 8 下进行高剪切均质化来稳定水包正十二烷乳液的乳化剂。增加共聚物浓度导致平均液滴直径减小，表明 APTES 交联足以使纳米颗粒完整地吸附在油/水界面，从而产生真正的皮克林乳液，而不是进行原位解离形成表面活性二嵌段共聚物链。在表面活性剂挑战研究中，与短蠕虫相比，相对较长的蠕虫需要高浓度的 30 倍非离子表面活性剂（Tween 80）才能从正十二烷-水界面中排出。这表明前者的纳米粒子比后者的吸附力强得多，表明通过使用高度各向异性的蠕虫可以实现显着更高的皮克林乳液稳定性。相比之下，通过羟基官能吸附蠕虫与油溶性聚合二异氰酸酯反应制备的胶体体在暴露于高浓度吐温80时保持完整。
Reversible addition-fragmentation chain transfer (RAFT) aqueous dispersion polymerization is used to prepare epoxy-functional PGMA-P(HPMA-stat-GlyMA) diblock copolymer worms, where GMA, HPMA, and GlyMA denote glycerol monomethacrylate, 2-hydroxypropyl methacrylate, and glycidyl methacrylate, respectively. The epoxy groups on the GlyMA residues were ring-opened using 3-amino-propyltriethoxysilane (APTES) in order to cross-link the worm cores via a series of hydrolysis-condensation reactions. Importantly, the worm aspect ratio can be adjusted depending on the precise conditions selected for covalent stabilization. Relatively long cross-linked worms are obtained by reaction with APTES at 20 degrees C, whereas much shorter worms with essentially the same copolymer composition are formed by cooling the linear worms from 20 to 4 degrees C prior to APTES addition. Small-angle X-ray scattering (SAXS) studies confirmed that the mean aspect ratio for the long worms is approximately eight times greater than that for the short worms. Aqueous electrophoresis studies indicated that both types of cross-linked worms acquired weak cationic surface charge at low pH as a result of protonation of APTES-derived secondary amine groups within the nanoparticle cores. These cross-linked worms were evaluated as emulsifiers for the stabilization of n-dodecane-in-water emulsions via high-shear homogenization at 20 degrees C and pH 8. Increasing the copolymer concentration led to a reduction in mean droplet diameter, indicating that APTES cross-linking was sufficient to allow the nanoparticles to adsorb intact at the oil/water interface and hence produce genuine Pickering emulsions, rather than undergo in situ dissociation to form surface-active diblock copolymer chains. In surfactant challenge studies, the relatively long worms required a thirty-fold higher concentration of a nonionic surfactant (Tween 80) to be displaced from the n-dodecane-water interface compared to the short worms. This suggests that the former nanoparticles are much more strongly adsorbed than the latter, indicating that significantly greater Pickering emulsion stability can be achieved by using highly anisotropic worms. In contrast, colloidosomes prepared by reacting the hydroxyl-functional adsorbed worms with an oil-soluble polymeric diisocyanate remained intact when exposed to high concentrations of Tween 80.