Original Article

Journal of Surfactants and Detergents

, Volume 15, Issue 2, pp 157-165

First online:

On the Characteristic Curvature of Alkyl-Polypropylene Oxide Sulfate Extended Surfactants

  • Charles E. HammondAffiliated withSasol North America Inc. Email author 
  • , Edgar J. AcostaAffiliated withDepartment of Chemical Engineering and Applied Chemistry, University of Toronto Email author 

Rent the article at a discount

Rent now

* Final gross prices may vary according to local VAT.

Get Access


The hydrophobicity of alkyl-polypropylene oxide sulfate surfactants was evaluated via their characteristic curvature (Cc) using the hydrophilic-lipophilic difference (HLD) framework. A close examination of the relationship between the molecular structure of the surfactants considered (structure of the alkyl group and the number of propylene oxide groups in each surfactant) and their Cc led to a group contribution model that, for the first time, takes into consideration the geometry of the alkyl tail group. Based on this group contribution model, branching at the C2 (beta-carbon) position of the alkyl group produces the largest increase in characteristic curvature. This observation is consistent with the notion that the Cc is associated with the packing factor for anionic surfactants. Branching at the C2 position tends to produce cylindrical or inverse cone shape packing, typical of more hydrophobic (positive Cc) surfactants. This study also confirms previous observations that, different from conventional anionic surfactants, the phase behavior of alkyl polypropylene oxide sulfates is less sensitive to electrolyte concentration and that these formulations turn hydrophobic with increasing temperature, akin to the behavior of nonionic surfactants.


Microemulsion Characteristic curvature Phase behavior HLD Optimal salinity Solubilization Interfacial tension