Xu Maodong, Zhang Wanqing, Jiang Jianzhong, Pei Xiaomei, Zhu Haiyan, Cui Zhenggang, Binks Bernard P
The Key Laboratory of Synthetic and Biological Colloids, Ministry of Education, School of Chemical and Material Engineering, Jiangnan University, 1800 Lihu Road, Wuxi, Jiangsu 214122, P. R. China.
School of Biological and Chemical Engineering, Anhui Polytechnic University, 8 Beijing Road, Wuhu 241000, P. R. China.
Langmuir. 2020 Dec 29;36(51):15543-15551. doi: 10.1021/acs.langmuir.0c02892. Epub 2020 Dec 17.
The transition between a novel oil-in-dispersion emulsion and an oil-in-water (O/W) Pickering emulsion triggered by pH was achieved using alumina nanoparticles in combination with a cationic surfactant. In acidic and neutral aqueous media, positively charged particles and the surfactant both at very low concentrations costabilize an oil-in-dispersion emulsion with the surfactant adsorbed at droplet interfaces and particles dispersed in the aqueous phase between the droplets. In alkaline media, however, particles become negatively charged and are hydrophobized by adsorption of the surfactant to become surface-active and stabilize an O/W Pickering emulsion. The transition between the two is also possible by lowering the pH. The transformation can be achieved several times in a mixture of 0.1 wt % nanoparticles and 0.01 mM surfactant. This transition is significant, since particles can be made to either adsorb at the oil-water interface, which is beneficial for applications like biphasic catalysis, or remain dispersed in the aqueous phase, which is favorable for their recovery and reuse.
通过将氧化铝纳米颗粒与阳离子表面活性剂结合使用，实现了由pH引发的新型分散油包乳液与水包油（O/W）Pickering乳液之间的转变。在酸性和中性水性介质中，极低浓度的带正电颗粒和表面活性剂共同稳定了分散油包乳液，表面活性剂吸附在液滴界面，颗粒分散在液滴之间的水相中。然而，在碱性介质中，颗粒带负电，并通过吸附表面活性剂而被疏水化，从而变得具有表面活性并稳定了O/W Pickering乳液。通过降低pH值也可以实现两者之间的转变。在含有0.1 wt%纳米颗粒和0.01 mM表面活性剂的混合物中，可以多次实现这种转变。这种转变意义重大，因为颗粒既可以吸附在油水界面，这有利于双相催化等应用，也可以保持分散在水相中，这有利于它们的回收和再利用。
