Polymer Engineering and Colloid Science Laboratory, Department of Chemical Engineering , Indian Institute of Technology , Madras, Chennai 600036 , India.
Langmuir. 2018 May 1;34(17):5060-5071. doi: 10.1021/acs.langmuir.8b00795. Epub 2018 Apr 20.
We present a simple and modular approach to realize highly stable pH responsive Pickering emulsion from mixtures of commercially available oppositely charged nanoparticle and polyelectrolyte. While highly charged nanoparticles and polyelectrolytes when used solely do not stabilize emulsions, we show that the electrostatic attraction between oppositely charged nanoparticles and polyelectrolytes can be exploited to formulate emulsions with long-term stability of up to 8 months. The Ludox CL nanoparticles and poly(4-styrenesulfonate) sodium salt (PSS) when dispersed in aqueous solution at pH 2-11 form particle polyelectrolyte complexes (PPCs) due to heteroaggregation. These complexes are effective in stabilizing oil-in-water Pickering emulsions. We demonstrate that this is due to the formation of weakly charged complexes that are surface active and hence readily adsorbed to the oil-water interface created during emulsification. We show that the composition of nanoparticles and polyelectrolytes in the mixture as well as the pH can be tuned to control the average diameter of the emulsions droplets. Immediate destabilization and doubled responsiveness of the emulsions stabilized by particle polyelectrolyte complexes are illustrated by changing the pH of the stable emulsions formed at intermediate pH to either 1 or 13. The aggregation behavior of nanoparticle-polyelectrolyte mixtures and the effect of various parameters such as mixing fraction, pH, and energy input on the formation of Pickering emulsions is discussed. Furthermore, we show that the formation of near charge neutral aggregates that exhibit optimal wetting conditions is a requirement to accomplish emulsion formation. The visualization of particle polyelectrolyte complexes around the emulsion droplets, their morphology prior to emulsification, and their wetting properties are also investigated to elucidate the mechanism of emulsification.
我们提出了一种简单而模块化的方法，可从商业上可获得的带相反电荷的纳米颗粒和聚电解质的混合物中实现高度稳定的 pH 响应性 Pickering 乳液。虽然高电荷纳米颗粒和聚电解质单独使用时不能稳定乳液，但我们表明，带相反电荷的纳米颗粒和聚电解质之间的静电吸引力可用于配制具有长达 8 个月的长期稳定性的乳液。当 Ludox CL 纳米颗粒和聚（4-苯乙烯磺酸钠）钠盐（PSS）在 pH 2-11 的水溶液中分散时，由于异质聚集而形成粒子聚电解质复合物（PPC）。这些复合物有效地稳定油包水 Pickering 乳液。我们证明，这是由于形成了带弱电荷的复合物，这些复合物具有表面活性，因此易于吸附在乳化过程中形成的油水界面上。我们表明，可以通过调节混合物中纳米颗粒和聚电解质的组成以及 pH 值来控制乳液液滴的平均直径。通过将在中间 pH 值下形成的稳定乳液的 pH 值分别调节为 1 或 13，立即使由粒子聚电解质复合物稳定的乳液失稳，并使乳液的响应性提高一倍。讨论了纳米颗粒-聚电解质混合物的聚集行为以及各种参数（例如混合分数，pH 和能量输入）对 Pickering 乳液形成的影响。此外，我们表明，形成具有最佳润湿性条件的近电荷中性聚集体是实现乳液形成的要求。还研究了围绕乳液液滴的粒子聚电解质复合物的可视化，其在乳化之前的形态及其润湿性，以阐明乳化机理。
