Centre de Recherche Paul Pascal, UMR 5031, Université de Bordeaux, CNRS, 115 Avenue du Dr A. Schweitzer, 33600 Pessac, France; Université de Bordeaux, ISM, CNRS UMR 5255, Bordeaux INP, Site ENSCBP, 16 Avenue Pey Berland, 33607 Pessac Cedex, France.
Centre de Recherche Paul Pascal, UMR 5031, Université de Bordeaux, CNRS, 115 Avenue du Dr A. Schweitzer, 33600 Pessac, France.
J Colloid Interface Sci. 2019 Jul 15;548:1-11. doi: 10.1016/j.jcis.2019.04.020. Epub 2019 Apr 6.
The aim of the paper is to examine the adsorption kinetics of soft microgels and to understand the role of fundamental parameters such as electrostatics and deformability on the process. This knowledge is further exploited to produce microgel-stabilized emulsions using a co-flow microfluidic device. Uncharged microgels made of poly(N-isopropylacrylamide) are synthesized with variable cross-linker contents, and charged ones are produced by introducing pH sensitive co-monomers during the synthesis. The study is carried out by measuring the microgels adsorption kinetics by means of the pendant drop method. The surface pressure is derived from the previous results as a function of time and is measured as a function of the area compression using a Langmuir trough. Emulsions are produced using a microfluidic device varying the microgels concentration and their stability is visually assessed. The microgels deformability as well as higher particle concentrations favour their adsorption. The adsorption is not governed by diffusion, it is cooperative and irreversible. Conversely, the kinetics is slowed down for increasing cross-linking density. The presence of charges slows down the kinetics of adsorption. In the presence of electrolyte, the kinetics accelerates and becomes similar to the one of neutral microgels. The original features of microgel adsorption is highlighted and the differences with adsorption of polymers, star polymers, proteins, and polyelectrolytes are emphasized. Taking benefit from the adsorption kinetics, the required formulation conditions for producing microgel-stabilized emulsions using a co-flow microfluidic device are derived. There exists a critical concentration above which microgels spontaneously adsorb in a sufficient way to decrease the interfacial tension. This critical microgel concentration increases with the cross-linking density and is higher for charged microgels. Whatever the kinetics, the same surface pressure is finally reached. This peculiar behaviour is likely a consequence of the presence of dangling chains in the as-prepared microgels. Consequently, a microgel excess is required to produce emulsions using microfluidics where adsorption has to be spontaneous.
本文旨在研究软质微凝胶的吸附动力学，并深入了解静电和变形等基本参数对这一过程的作用。利用共流微流控装置，进一步将这一知识应用于制备微凝胶稳定乳液。我们合成了不带电荷的聚（N-异丙基丙烯酰胺）微凝胶，改变其交联剂含量；同时在合成过程中引入 pH 敏感共聚单体，合成带电荷的微凝胶。我们通过悬滴法测量微凝胶的吸附动力学，来研究这一课题。通过先前的结果得出表面压力与时间的函数关系，并使用 Langmuir 槽，根据面积压缩测量表面压力。我们使用微流控装置制备乳液，改变微凝胶浓度，并直观评估乳液稳定性。微凝胶的变形性和更高的颗粒浓度有利于其吸附。吸附不是由扩散控制，而是协作和不可逆的。相反，交联密度增加会减缓吸附动力学。带电荷会减缓吸附动力学。在电解质存在的情况下，动力学会加速，变得与中性微凝胶的动力学相似。突出了微凝胶吸附的原始特征，并强调了其与聚合物、星形聚合物、蛋白质和聚电解质吸附的区别。利用吸附动力学，我们推导出了使用共流微流控装置制备微凝胶稳定乳液所需的配方条件。存在一个临界浓度，超过这个浓度，微凝胶就会自发吸附，从而降低界面张力。这个临界微凝胶浓度随交联密度的增加而增加，对于带电荷的微凝胶则更高。无论动力学如何，最终都会达到相同的表面压力。这种特殊的行为可能是由于预制备的微凝胶中存在悬垂链。因此，使用微流控制备乳液需要微凝胶过量，以确保吸附是自发的。
