Impact of molecular structure, headgroup and alkyl chain geometry, on the adsorption of the anionic ester sulfonate surfactants at the air-solution interface, in the presence and absence of electrolyte

Zi Wang; Peixun Li; Kun Ma; Yao Chen; Mario Campana; Jeffrey Penfold; Robert K Thomas; David W Roberts; Hui Xu; Jordan T Petkov; Zifeng Yan

doi:10.1016/j.jcis.2019.03.011

Impact of molecular structure, headgroup and alkyl chain geometry, on the adsorption of the anionic ester sulfonate surfactants at the air-solution interface, in the presence and absence of electrolyte

J Colloid Interface Sci. 2019 May 15:544:293-302. doi: 10.1016/j.jcis.2019.03.011. Epub 2019 Mar 6.

Authors

Zi Wang¹, Peixun Li², Kun Ma², Yao Chen², Mario Campana², Jeffrey Penfold³, Robert K Thomas⁴, David W Roberts⁵, Hui Xu⁶, Jordan T Petkov⁷, Zifeng Yan⁸

Affiliations

¹ School of Science, State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580, China; ISIS Facility, Rutherford Appleton Laboratory, STFC, Didcot, OXON OX11 0QX, UK.
² ISIS Facility, Rutherford Appleton Laboratory, STFC, Didcot, OXON OX11 0QX, UK.
³ ISIS Facility, Rutherford Appleton Laboratory, STFC, Didcot, OXON OX11 0QX, UK; Physical and Theoretical Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QZ, UK. Electronic address: jeff.penfold@stfc.ac.uk.
⁴ Physical and Theoretical Chemistry Laboratory, Oxford University, South Parks Road, Oxford OX1 3QZ, UK.
⁵ School of Pharmacy and Biomolecular Sciences, Liverpool John Moores University, Liverpool L3 3AF, UK.
⁶ KLK Oleo, SDN BDH, Menara KLK, Muliara Damansara, 47810 Petaling, Jaya Selanger, Malaysia.
⁷ Lonza UK, GB-Blackley, Manchester, Lancs M9 8ES, UK.
⁸ School of Science, State Key Laboratory of Heavy Oil Processing, China University of Petroleum, Qingdao 266580, China. Electronic address: zfyancat@upc.edu.cn.

PMID: 30861434
DOI: 10.1016/j.jcis.2019.03.011

Abstract

The transition from monolayer to multilayer adsorption at the air-water interface in the presence of multivalent counterions has been demonstrated for a limited range of anionic surfactants which exhibit increased tolerance to precipitation in the presence of multivalent counterions. Understanding the role of molecular structure in determining the transition to surface ordering is an important aspect of the phenomenon. The focus of the paper is on the alkyl ester sulfonate, AES, surfactants; a promising group of anionic surfactants, with the potential for improved performance and biocompatibility. Neutron reflectivity measurements were made in aqueous solution and in the presence of NaCl, CaCl₂, MgCl₂ and AlCl₃, for a range of alkyl ester sulfonate surfactants, in which the headgroup and alkyl chain geometries were manipulated. In the regions of monolayer adsorption changing the AES headgroup and alkyl chain geometries results in an increased saturation adsorption and in a more gradual decrease in the adsorption at low concentrations, consistent with a greater adsorption efficiency. Changing the AES headgroup and alkyl chain geometries also results in changes in the transition from monolayer adsorption to more ordered surface structures with the addition of AlCl₃ and mixed multivalent electrolytes. A more limited surface layering is observed for the ethyl ester sulfonate, EES, with a C₁₄ alkyl chain. Replacing the C₁₄ alkyl chain with a C₁₈ isostearic chain results in only monolayer adsorption. The results demonstrate the role and importance of the surfactant molecular structure in determining the nature of the surface adsorption in the presence of different electrolytes, and in the tendency to form extended surface multilayer structures.

Keywords: Adsorption; Air-solution interface; Ester sulfonate anionic surfactants; Neutron reflectivity; Surface multilayers.