Department of Chemical and Pharmaceutical Engineering, Faculty of Chemistry and Pharmacy, Sofia University, 1 J. Bouchier Ave., 1164 Sofia, Bulgaria.
Saint-Gobain Recherche, 39 Quai Lucien Lefranc, 93300 Aubervilliers, France.
J Colloid Interface Sci. 2017 Oct 15;504:48-57. doi: 10.1016/j.jcis.2017.05.036. Epub 2017 May 12.
Foaming of particulate suspensions, followed by foam drying, is developed as an efficient method for production of highly porous materials with various applications. A key factor for success is the appropriate choice of surfactants which both modify the particle surface and stabilize the foam. Here we compare the efficiency of this method for silica suspensions containing two surfactants which lead to very different types of foam stabilization. Cationic TTAB leads to particle-stabilized foams (Pickering stabilization) whereas zwitterionic CAPB - to surfactant-stabilized foams. Thus we determined the general (common) features shared between the various surfactant systems: (1) The foaminess is controlled exclusively by the suspension viscosity under shearing conditions which mimic precisely the foaming process; (2) The foam stability to drainage and coarsening is controlled exclusively by the suspension yield stress; (3) The surfactant adsorption on the particle surface should occur in the time scale of seconds to minutes, thus ensuring appropriate rheological properties of the foaming suspension. Similar kinetic effects could be of high interest to other colloid systems and processes, e.g. for kinetic control of the internal structure and properties of aerogels produced from sheared suspensions, and for control of the transient rheological properties and non-Newtonian flow of particulate gels.
颗粒悬浮液的起泡，随后进行泡沫干燥，被开发为一种生产具有各种应用的高多孔材料的有效方法。成功的关键因素是适当选择表面活性剂，这些表面活性剂既能改变颗粒表面又能稳定泡沫。在这里，我们比较了两种表面活性剂在二氧化硅悬浮液中应用的效果，这两种表面活性剂导致了非常不同类型的泡沫稳定。阳离子 TTAB 导致颗粒稳定的泡沫（Pickering 稳定），而两性离子 CAPB 则导致表面活性剂稳定的泡沫。因此，我们确定了各种表面活性剂体系之间的共同（通用）特征：（1）在模拟起泡过程的剪切条件下，泡沫的丰富度仅由悬浮液的粘度控制；（2）泡沫对排水和粗化的稳定性仅由悬浮液屈服应力控制；（3）表面活性剂在颗粒表面上的吸附应在几秒钟到几分钟的时间尺度内发生，从而确保起泡悬浮液具有适当的流变性能。类似的动力学效应可能对其他胶体系统和过程具有很高的兴趣，例如，用于控制剪切悬浮液制备的气凝胶的内部结构和性质的动力学，以及用于控制颗粒凝胶的瞬变流变性质和非牛顿流动。
