pH-responsive Pickering emulsions stabilized by silica nanoparticles in combination with a conventional zwitterionic surfactant

Liu, Kaihong; Jiang, Jianzhong; Cui, Zhenggang; Binks, Bernard P.

Abstract

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.

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

• Acceptance Date: Feb 13, 2017
• Online Publication Date: Feb 13, 2017
• Publication Date: Mar 7, 2017
• Deposit Date: Feb 17, 2017
• Publicly Available Date: Feb 14, 2018
• Journal: Langmuir
• Print ISSN: 0743-7463
• Electronic ISSN: 1520-5827
• Publisher: American Chemical Society
• Peer Reviewed: Peer Reviewed
• Volume: 33
• Issue: 9
• Pages: 2296-2305
• DOI: https://doi.org/10.1021/acs.langmuir.6b04459
• Keywords: Pickering emulsions; Silica nanoparticles; Zwitterionic surfactant
• Public URL: https://hull-repository.worktribe.com/output/448509
• Publisher URL: http://pubs.acs.org/doi/abs/10.1021/acs.langmuir.6b04459
• 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