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    pH-responsive foams based on a transition between a bola surfactant and a traditional surfactant

    Year: 2020

    Journal: J. Mol. Liq., Volume 298, JAN 15

    Authors: Zhai, Zhaolan; Xu, Ji; Yan, Xinyan; Song, Zhanqian; Shang, Shibin; Rao, Xiaoping

    Organizations: National Natural Science Foundation of China, ChinaNational Natural Science Foundation of China (NSFC) [31622017]; Fundamental Research Foundation of the Central Common Wealth Institute of the Chinese Academy of Forestry, China [CAFYBB2018QC002]

    Keywords: Rosin; Surfactant; Totally rigid group; pH-responsive; Foams

    pH-responsive aqueous foams were prepared by using a totally rigid surfactant, sodium N-azobenzenemaleimidepimaric carboxylate (Na-MPA-AZO-Na), derived from rosin. When the pH of aqueous solution decreases from 12.35 to 9.31, a Bola surfactant converts into a traditional surfactant containing a hydrophilic group and a hydrophobic group (Na-MPA-AZO), which severely affects the foaming ability and foam stability. And such changes of molecular configuration were rare reported. When the pH of aqueous solution is 931, the Na-MPA-AZO molecule tends to be upright at the air/water interface, which results in a close surfactant arrangement. The original volume of foams at 2 mM is 72 mL, and its half-life is up to 2145 min, which are far larger than that of sodium dodecyl sulfate (SDS) at the same concentration as a reference. When the pH of aqueous solution is 12.35, the Bola surfactant Na-MPA-AZO-Na tends to lie at the air/water interface in a V configuration, which leads Na-MPA-AZO-Na easily to desorb from the interface. The original volume of foams at 2 mM is only 9.5 mL, and its half-life is only 2 min, the foams will completely disappear in 6 min. The stable and unstable foams can be reversed at least 3 times by alternating the pH between 931 and 1235. Besides, because of the fixed positions of carbon atoms in the totally rigid skeleton, the pH-responsive foams show highly pH-responsive efficiency. (C) 2019 Elsevier B.V. All rights reserved.
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