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Are Hydrotropes Distinct from Surfactants?

Authors :
Sarah E. Rogers
Richard K. Heenan
Robert Dyer
Marios Hopkins Hatzopoulos
Peter J. Dowding
Julian Eastoe
Source :
Langmuir. 27:12346-12353
Publication Year :
2011
Publisher :
American Chemical Society (ACS), 2011.

Abstract

The physicochemical properties of a homologous series of sodium p-n-alkylbenzoates have been investigated. The objective was to determine whether there is a clear transition point from hydrotropic to surfactant-like behavior with increasing alkyl chain length n, so as to shed clear light on the aggregation mechanism of so-called "hydrotropes". Electrical conductivity measurements were used for a first estimation of the critical aggregation concentrations (cac). As for classical surfactants, log(cac) depends on alkyl chain length n, but two branches of behavior were observed: one having a gradient typical of long chain fatty acid salts and the other with a more shallow dependence. Surface tension (γ) measurements of high purity aqueous solutions were used to generate limiting headgroup areas A(cac), which were in the range (40-50 Å(2)) being consistent with monolayer formation. Small-angle neutron scattering conclusively shows that the lower chain length homologues (classed as hydrotropes) exhibit sharp transitions in aggregation as a function of bulk concentration, typical of regular surfactants. As such, there is little to suggest from this study that hydrotropes differ in association behavior from regular surfactants.

Details

ISSN :
15205827 and 07437463
Volume :
27
Database :
OpenAIRE
Journal :
Langmuir
Accession number :
edsair.doi.dedup.....faf8eeb68c1b9f94da49a659902ddd5d
Full Text :
https://doi.org/10.1021/la2025846