Key Laboratory of Colloid and Interface Chemistry, Ministry of Education , Shandong University , Jinan , Shandong 250100 , P. R. China.
College of Chemistry and Molecular Engineering , Qingdao University of Science & Technology , Qingdao 266042 , P. R. China.
Langmuir. 2018 May 22;34(20):5798-5806. doi: 10.1021/acs.langmuir.8b00757. Epub 2018 May 10.
Dynamic covalent surfactants have been recently reported for preparation of pH-switchable emulsions [ Sun , D. Langmuir , 2017 , 33 , 3040 ]. In this study, dynamic covalent silica (SiO-B) nanoparticles of switchable wettability were fabricated by a pH-responsive dynamic (covalent) imine bond between hydrophilic amino silica (SiO-NH) nanoparticles and hydrophobic benzaldehyde molecules. The properties of SiO-B were characterized by Fourier transform infrared spectroscopy, elemental analysis, contact angle measurement, and ζ potential measurement. The hydrophilicity and hydrophobicity of SiO-B were shown to be readily switchable by adjusting pH between 7.8 and 3.5. At pH 7.8, SiO-B was partially hydrophobic and adsorbed at oil-water interface to stabilize O/W Pickering emulsions, which were characterized by electrical conductivity, optical microscopy, and confocal laser scanning microscopy. Upon lowering the pH to 3.5, the dynamic covalent bond is dissociated to convert partially hydrophobic SiO-B into highly hydrophilic SiO-NH and surface-inactive benzaldehyde. Both of them desorb from oil-water interface, resulting in a rapid oil-water separation of the Pickering emulsions. Alternating stabilization and phase separation of the Pickering emulsions over 3 cycles were demonstrated by adjusting the pH. The pH-switchable Pickering emulsions show great potential in application to effective oil-water separation of emulsions.
动态共价表面活性剂最近被报道可用于制备 pH 响应型乳液[Sun, D. Langmuir, 2017, 33, 3040]。在本研究中，通过亲水性氨基硅纳米粒子（SiO-NH）与疏水性苯甲醛分子之间的 pH 响应动态（共价）亚胺键，制备了具有可切换润湿性的动态共价硅纳米粒子（SiO-B）。通过傅里叶变换红外光谱、元素分析、接触角测量和 ζ 电位测量对 SiO-B 的性质进行了表征。SiO-B 的亲水性和疏水性可通过在 7.8 和 3.5 之间调节 pH 值来轻松切换。在 pH 7.8 时，SiO-B 部分疏水性并吸附在油水界面上，以稳定 O/W Pickering 乳液，其通过电导率、光学显微镜和共聚焦激光扫描显微镜进行了表征。当 pH 降低至 3.5 时，动态共价键解离，将部分疏水性的 SiO-B 转化为高亲水性的 SiO-NH 和无表面活性的苯甲醛。它们都从油水界面解吸，导致 Pickering 乳液的油水快速分离。通过调节 pH 值，证明了 Pickering 乳液的稳定和相分离可以在 3 个循环中交替进行。pH 响应型 Pickering 乳液在乳液的有效油水分离方面具有很大的应用潜力。
