The impact of electrolyte on the adsorption of the anionic surfactant methyl ester sulfonate at the air-solution interface: Surface multilayer formation

H Xu; R K Thomas; J Penfold; P X Li; K Ma; R J L Welbourne; D W Roberts; J T Petkov

doi:10.1016/j.jcis.2017.10.064

The impact of electrolyte on the adsorption of the anionic surfactant methyl ester sulfonate at the air-solution interface: Surface multilayer formation

J Colloid Interface Sci. 2018 Feb 15:512:231-238. doi: 10.1016/j.jcis.2017.10.064. Epub 2017 Oct 18.

Authors

H Xu¹, R K Thomas², J Penfold³, P X Li⁴, K Ma⁴, R J L Welbourne⁴, D W Roberts⁵, J T Petkov¹

Affiliations

¹ KLK Oleo, SDN BHD, Menara KLK, Mutiara Damansara, 47810 Petaling Jaya, Selangor, Malaysia.
² Physical and Theoretical Chemistry Laboratory, Oxford University, South Parks Road, Oxford, UK.
³ Physical and Theoretical Chemistry Laboratory, Oxford University, South Parks Road, Oxford, UK; ISIS Facility, STFC, Rutherford Appleton Laboratory, Chilton, Didcot, OXON, UK. Electronic address: jeff.penfold@stfc.ac.uk.
⁴ ISIS Facility, STFC, Rutherford Appleton Laboratory, Chilton, Didcot, OXON, UK.
⁵ D W Roberts, School of Pharmacy and Biomolecular Sciences, Liverpool John Moores University, Byrom Street, Liverpool L3 3AF, UK.

PMID: 29073464
DOI: 10.1016/j.jcis.2017.10.064

Abstract

The methyl ester sulfonates represent a promising group of anionic surfactants which have the potential for improved performance and biocompatibility in a range of applications. Their solution properties, in particular their tolerance to hard water, suggests that surface ordering may occur in the presence of multi-valent counterion. Understanding their adsorption properties in a range of different circumstances is key to the exploitation of their potential. Neutron reflectivity and surface tension have been used to characterise the adsorption at the air-aqueous solution interface of the anionic surfactant sodium tetradecanoic 2-sulfo 1-methyl ester, C₁₄MES, in the absence of electrolyte and in the presence of mono, di, and tri-valent counterions, Na⁺, Ca²⁺, and Al³⁺. In particular the emphasis has been on exploring the tendency to form layered structures at the interface. In the absence of electrolyte and in the presence of NaCl and CaCl₂ and AlCl₃ at low concentrations monolayer adsorption is observed, and the addition of electrolyte results in enhanced adsorption. In the presence of NaCl and CaCl₂ only monolayer adsorption is observed. However at higher AlCl₃ concentrations surface multilayer formation is observed, in which the number of bilayers at the surface depends upon the surfactant and AlCl₃ concentrations.

Keywords: Air-water interface; Methyl ester sulfonate adsorption; Neutron reflectivity; Surface multilayers; Surface tension.