Key Laboratory for Colloid & Interface Chemistry of Education Ministry, Shandong University, Jinan, Shandong 250100, People's Republic of China.
J Colloid Interface Sci. 2011 Sep 15;361(2):565-72. doi: 10.1016/j.jcis.2011.05.011. Epub 2011 Jun 1.
The phase inversion temperature (PIT) method is generally used to prepare nonionic surfactant stabilized nano-emulsions because of its low energy and surfactant consumption. The emulsion droplets are usually negatively charged because of the selective adsorption of OH(-) onto the droplet surfaces. In this work, positively charged oil/water nano-emulsions were prepared by adding a cationic surfactant to the system. The cationic molecules change the spontaneous curvature of the surfactant layers and raise the PIT above 100 °C. The PIT can be depressed by addition of NaBr, as shown by conductivity measurements and equilibrium phase behavior. Therefore, these nano-emulsions can be prepared by the PIT method. We found that the formation of the nano-emulsions did not require a cross-PIT cycle. The mechanism of the emulsification is the formation of mixed swollen micelles that can solubilize all the oil above a "clearing boundary", followed by a stir-quench to a temperature where these droplets become metastable emulsions. The zeta potential of the emulsion droplets can be easily tuned by varying the cationic surfactant concentrations. Due to electrosteric stabilization, the resulting nano-emulsions are highly stable, thus could find significant applications in areas such as pharmaceuticals, cosmetics and food industries.
相转变温度（PIT）法通常用于制备非离子表面活性剂稳定的纳米乳液，因为它的能量和表面活性剂消耗都较低。由于 OH(-) 选择性吸附在液滴表面，乳液液滴通常带负电荷。在这项工作中，通过向体系中添加阳离子表面活性剂来制备带正电荷的油/水纳米乳液。阳离子分子改变了表面活性剂层的自发曲率，并将 PIT 提高到 100°C 以上。通过电导率测量和平衡相行为可以看出，添加 NaBr 可以降低 PIT。因此，可以通过 PIT 法制备这些纳米乳液。我们发现，纳米乳液的形成不需要交叉 PIT 循环。乳化的机制是形成混合溶胀胶束，这些胶束可以在“澄清边界”之上溶解所有的油，然后进行搅拌淬火，使这些液滴在一个温度下成为亚稳的乳液。通过改变阳离子表面活性剂的浓度，可以很容易地调节乳液液滴的 ζ 电位。由于空间稳定作用，得到的纳米乳液非常稳定，因此在制药、化妆品和食品工业等领域有很大的应用潜力。
