Research Institute of Materials Science, South China University of Technology, Guangzhou 510640, China.
Langmuir. 2012 Jul 31;28(30):11017-24. doi: 10.1021/la3021113. Epub 2012 Jul 17.
Chitosan without hydrophobic modification is not a good emulsifier itself. However, it has a pH-tunable sol-gel transition due to free amino groups along its backbone. In the present work, a simple reversible Pickering emulsion system based on the pH-tunable sol-gel transition of chitosan was developed. At pH > 6.0, as adjusted by NaOH, chitosan was insoluble in water. Chitosan nanoparticles or micrometer-sized floccular precipitates were formed in situ. These chitosan aggregates could adsorb at the interface of oil and water to stabilize the o/w emulsions, so-called Pickering emulsions. At pH < 6.0, as adjusted by HCl, chitosan was soluble in water. Demulsification happened. Four organic solvents (liquid paraffin, n-hexane, toluene, and dichloromethane) were chosen as the oil phase. Reversible emulsions were formed for all four oils. Chitosan-based Pickering emulsions could undergo five cycles of emulsification-demulsification with only a slight increase in the emulsion droplet size. They also had good long-term stability for more than 2 months. Herein, we give an example of chitosan without any hydrophobic modification to act as an effective emulsifier for various oil-water systems. From the results, we have determined that natural polymers with a stimulus-responsive sol-gel transition should be a good particulate emulsifier. The method for in situ formation of pH-responsive Pickering emulsions based on chitosan will open up a new route to the preparation of a wide range of reversible emulsions.
未经疏水改性的壳聚糖本身不是一种良好的乳化剂。然而，由于其主链上的游离氨基，它具有 pH 可调的溶胶-凝胶转变。在本工作中，开发了一种基于壳聚糖 pH 可调溶胶-凝胶转变的简单可逆 Pickering 乳液体系。在 pH > 6.0 时，用 NaOH 调节，壳聚糖在水中不溶。壳聚糖纳米粒子或微米级絮状沉淀物原位形成。这些壳聚糖聚集体可以吸附在油水界面上，稳定 o/w 乳液，即 Pickering 乳液。在 pH < 6.0 时，用 HCl 调节，壳聚糖在水中溶解。发生破乳。选择四种有机溶剂（液体石蜡、正己烷、甲苯和二氯甲烷）作为油相。对于所有四种油，都形成了可逆乳液。基于壳聚糖的 Pickering 乳液可以经历五次乳化-破乳循环，乳液粒径仅略有增加。它们在 2 个月以上的时间内也具有良好的长期稳定性。在此，我们以未经任何疏水改性的壳聚糖为例，证明其可作为各种油水体系的有效乳化剂。从结果来看，我们已经确定具有刺激响应溶胶-凝胶转变的天然聚合物应该是一种良好的颗粒乳化剂。基于壳聚糖的 pH 响应 Pickering 乳液的原位形成方法将为制备各种可逆乳液开辟新途径。
