Engineering School of Lorena - University of São Paulo, Laboratory of Polymers, 12602-810 Lorena/SP, Brazil.
Université Lyon, Université Claude Bernard Lyon 1, CPE Lyon, CNRS, UMR 5265, Chemistry, Catalysis, Polymers and Processes (C2P2), 43 Bvd. du 11 Novembre 1918, F-69616 Villeurbanne, France.
Langmuir. 2017 Sep 26;33(38):9598-9608. doi: 10.1021/acs.langmuir.7b01882. Epub 2017 Sep 7.
Recently, there has been significant interest in the use of the reversible addition-fragmentation chain-transfer (RAFT) technique to generate a variety of organic/inorganic colloidal composite particles in aqueous dispersed media using the so-called macroRAFT-assisted encapsulating emulsion polymerization (REEP) strategy. In this process, special attention should be paid to the adsorption of the macromolecular RAFT (macroRAFT) agent onto the inorganic particles, as it determines the final particle morphology and can also influence latex stability. In this work, different amphipathic macroRAFT agents were synthesized by RAFT, and their adsorption onto commercial Montmorillonite clay Cloisite Na (MMT) was studied by means of adsorption isotherms. Three types of macroRAFT agents were considered: a nonionic one based on poly(ethylene glycol) methyl ether acrylate (PEGA) and n-butyl acrylate (BA), anionic ones, including a block copolymer and random copolymers, based on acrylic acid (AA), BA and PEGA, and cationic ones based on 2-(dimethylamino)ethyl methacrylate (DMAEMA), BA and PEGA. Six adsorption isotherm models (Langmuir, Freundlich, Tempkin, Redlich-Peterson, Sips, and Brunauer-Emmett-Teller) were adjusted to the experimental isotherms. The nonionic macroRAFT agent formed a monolayer on the clay surface with a maximum adsorption capacity of 400 mg g at pH 8, as determined from the Sips adsorption model. Adsorption of the AA-based macroRAFT agents onto MMT was moderate at alkaline pH due to electrostatic repulsions, but increased with decreasing pH. The DMAEMA-based macroRAFT agents displayed a much stronger interaction with the oppositely charged MMT surface at acidic pH due to electrostatic interactions, and the concentration of adsorbed macroRAFT agent reached values as high as 800 mg g. The BET model fitted the experimental data relatively well indicating multilayer adsorption promoted by the presence of the hydrophobic BA units. In addition, the cationic macroRAFT agents afforded stable MMT/macroRAFT agent complexes as evaluated by dynamic light scattering and zeta potential analyses.
最近，人们对使用可逆加成-断裂链转移（RAFT）技术在水性分散介质中生成各种有机/无机胶体复合粒子产生了浓厚的兴趣，采用所谓的大分子 RAFT 辅助包封乳液聚合（REEP）策略。在这个过程中，应特别注意高分子 RAFT（macroRAFT）剂在无机粒子上的吸附，因为它决定了最终的粒子形态，也会影响乳胶的稳定性。在这项工作中，通过 RAFT 合成了不同的两亲性大分子 RAFT 剂，并通过吸附等温线研究了它们对商业蒙脱石粘土 Cloisite Na（MMT）的吸附。考虑了三种类型的大分子 RAFT 剂：基于聚（乙二醇）甲基醚丙烯酸酯（PEGA）和正丁基丙烯酸酯（BA）的非离子型、基于丙烯酸（AA）、BA 和 PEGA 的嵌段共聚物和无规共聚物的阴离子型，以及基于 2-（二甲氨基）乙基甲基丙烯酸酯（DMAEMA）、BA 和 PEGA 的阳离子型。六种吸附等温线模型（朗缪尔、弗伦德利希、坦金、Redlich-Peterson、Sips 和 Brunauer-Emmett-Teller）被调整到实验等温线。非离子型大分子 RAFT 剂在 pH 8 时在粘土表面形成单层，最大吸附量为 400mg g，这是从 Sips 吸附模型确定的。在碱性 pH 下，由于静电排斥，AA 基大分子 RAFT 剂对 MMT 的吸附适中，但随着 pH 值的降低而增加。在酸性 pH 下，带相反电荷的 MMT 表面由于静电相互作用，带正电荷的 DMAEMA 基大分子 RAFT 剂表现出更强的相互作用，吸附的大分子 RAFT 剂浓度高达 800mg g。BET 模型对实验数据的拟合相对较好，表明存在疏水性 BA 单元会促进多层吸附。此外，通过动态光散射和 Zeta 电位分析评估，阳离子大分子 RAFT 剂提供了稳定的 MMT/macroRAFT 剂复合物。
