The effect of the headgroup and chain structure on surfactant behaviour at the surface
27 Oct 2020







Anionic surfactants are the major surface active ingredient in most home and personal care products. The ester sulfonate surfactants are a class of anionic surfactants that exhibit increased tolerance to hard water, with a reduced tendency to precipitation in the presence of multivalent counterions. However, the addition of multivalent counterions results in the formation of multilayer structures at the air-solution interface, and is accompanied by advantageous wetting properties. 

Changing the surfactant geometry, by altering the headgroup or the structure of the alkyl chain, can have a significant impact upon the nature of the surface adsorption induced by multivalent counter-ions. This study further investigated the impact of the changes in geometry by comparing surfactants with a branched isostearic alkyl chain to a linear saturated alkyl chain, and by modifying the headgroup from methyl- to ethyl-ester, in the MES (methyl ester sulfonate) surfactant. 

Using neutron reflectivity on the SURF reflectometer the researchers found that, for the surfactants studied; in contrast to MES, more limited surface multilayer formation is observed with the addition of Al3+ counter-ions. This implies that the original Na+ surfactant counter-ions are more strongly bound, and are therefore less readily displaced by the Al3+ ions.  

Their results provide a crucial insight into how these subtle changes in surfactant geometry and structure can be used to manipulate their interaction with cations, and their associated surface properties. 

Instrument: SURF, Deuteration Facility 

Related publication“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” Journal of Colloid and Interface Science 544 (2019) 293–302 


Funding: China Scholarship Council 

AuthorsZ Wang (China University of Petroleum, ISIS), P Li, K Ma, Y Chen, M Campana (ISIS), J Penfold (ISIS, University of Oxford), RK Thomas (University of Oxford), DW Roberts (Liverpool John Moores University), H Xu (KLK, OLEO), JT Petkov (Lonza UK), Z Yan (China University of Petroleum) ​

Contact: Gianchandani, Shikha (STFC,RAL,ISIS)