Properties of the micelles of sulfonated methyl esters determined from the stepwise thinning of foam films and by rheological measurements

Elka S Basheva; Krassimir D Danov; Gergana M Radulova; Peter A Kralchevsky; Hui Xu; Yee Wei Ung; Jordan T Petkov

doi:10.1016/j.jcis.2018.12.034

Properties of the micelles of sulfonated methyl esters determined from the stepwise thinning of foam films and by rheological measurements

J Colloid Interface Sci. 2019 Mar 7:538:660-670. doi: 10.1016/j.jcis.2018.12.034. Epub 2018 Dec 11.

Authors

Elka S Basheva¹, Krassimir D Danov¹, Gergana M Radulova¹, Peter A Kralchevsky², Hui Xu³, Yee Wei Ung³, Jordan T Petkov³

Affiliations

¹ Department of Chemical and Pharmaceutical Engineering, Faculty of Chemistry and Pharmacy, Sofia University, 1164 Sofia, Bulgaria.
² Department of Chemical and Pharmaceutical Engineering, Faculty of Chemistry and Pharmacy, Sofia University, 1164 Sofia, Bulgaria. Electronic address: pk@lcpe.uni-sofia.bg.
³ KLK Oleo, KL-Kepong Oleomas SDN BHD, Menara KLK, Jalan PJU 7/6, Mutiara Damansara, 47810 Petaling Jaya, Selangor Dalur Ehsan, Malaysia.

PMID: 30572230
DOI: 10.1016/j.jcis.2018.12.034

Abstract

Hypotheses: The micellar solutions of sulfonated methyl esters (SME) are expected to form stratifying foam films that exhibit stepwise thinning. From the height of the steps, which are engendered by micellar layers confined in the films, we could determine the micelle aggregation number, surface electric potential, and ionization degree. Moreover, addition of the zwitterionic surfactant cocamidopropyl betaine (CAPB) is expected to transform the small spherical micelles of SME into giant wormlike aggregates.

Experiments: Stratifying films from SME solutions are formed and the heights of the steps are recorded. The viscosity of mixed SME + CAPB solutions is measured at various concentrations and weight ratios of the two surfactants.

Findings: By theoretical analysis of the foam film data, we established that at 30-100 mM SME spherical micelles are formed and their aggregation number was determined. The addition of calcium ions, as in hard water, does not produce significant effect. However, SME and CAPB exhibit a strong synergism with respect to micelle growth as indicated by the high solution's viscosity. For this reason, the SME + CAPB mixtures represent a promising system for formulations in personal-care and house-hold detergency, having in mind also other useful properties of SME, such as high hard water tolerance, biodegradability and skin compatibility.

Keywords: Film thicknesses interpretation; Micelle aggregation number; Rheology of micellar solutions; Stratifying foam films; Sulfonated methyl esters; Wormlike micelles.