pH-responsive Pickering emulsions stabilized by silica nanoparticles in combination with a conventional zwitterionic surfactant
Liu, Kaihong; Jiang, Jianzhong; Cui, Zhenggang; Binks, Bernard P.
Professor Bernard P Binks B.P.Binks@hull.ac.uk
Professor of Physical Chemistry
pH-responsive oil-in-water Pickering emulsions were prepared simply by using negatively charged silica nanoparticles in combination with a trace amount of a zwitterionic carboxyl betaine surfactant as stabilizer. Emulsions are stable to coalescence at pH 5 but phase separate completely at pH > 8.5. In acidic solution, the carboxyl betaine molecules become cationic allowing them to adsorb on silica nanoparticles via electrostatic interactions, thus hydrophobizing and flocculating them enhancing their surface activity. Upon increasing the pH, surfactant molecules are converted to witterionic form and significantly desorb from particles surfaces triggering de-hydrophobization and coalescence of oil droplets within the emulsion. The pH-responsive emulsion can be cycled between stable and unstable many times upon alternating the pH of the aqueous phase. The average droplet size in re-stabilized emulsions at low pH however increases gradually after four cycles due to the accumulation of NaCl. Experimental evidence including adsorption isotherms, zeta potentials, microscopy and three-phase contact angles is given to support the postulated mechanisms.
|Publication Date||Mar 7, 2017|
|Publisher||American Chemical Society|
|Peer Reviewed||Peer Reviewed|
|APA6 Citation||Liu, K., Jiang, J., Cui, Z., & Binks, B. P. (2017). pH-responsive Pickering emulsions stabilized by silica nanoparticles in combination with a conventional zwitterionic surfactant. Langmuir : the ACS journal of surfaces and colloids, 33(9), 2296-2305. https://doi.org/10.1021/acs.langmuir.6b04459|
|Keywords||Pickering emulsions; Silica nanoparticles; Zwitterionic surfactant|
|Copyright Statement||©2018 University of Hull|
|Additional Information||This document is the Accepted Manuscript version of a Published Work that appeared in final form in Langmuir, copyright © American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see http://dx.doi.org/10.1021/acs.langmuir.6b04459|
©2018 University of Hull
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