title: Effects of structure variation on solution properties of hydrotropes: phenyl versus cyclohexyl chain tips.
abstract: The physicochemical behavior of the phenyl-n-alkanoate (PhenCx) and cyclohexyl-n-alkanoate (CyclohexCx) series has been investigated, supporting previous work on the understanding of hydrotropes (Hopkins Hatzopoulos, M.; Eastoe, J.; Dowding, P.J.; Rogers, S. E.; Heenan, R.; Dyer, R. Langmuir2011, 27, 12346-12353). Electrical conductivity, surface tension, (1)H NMR, and small-angle neutron scattering (SANS) were used to study adsorption and aggregation in terms of critical aggregation concentration (cac). The PhenCx series exhibited very similar d log(cac)/dn to n-alkylbenzoates (CnBenz), exhibiting two branches of behavior, with a common inflection point at four linear carbons, whereas the CyclohexCx series showed no break point. Electrical conductivity and (1)H NMR concentration scans indicate a difference in physicochemical behavior between higher and lower homologues in both the PhenCx and CyclohexCx series. Surface tension measurements with compounds belonging to either group gave typical Gibbs adsorption profiles, having d log(cac)/dn curves consistent with limiting headgroup areas in the region of (35-55 Å(2)) indicating monolayer formation. SANS profiles showed no evidence for aggregates below the electrical conductivity determined cac values, inferring an "on-off" mode of aggregation. Analyses of SANS profiles was consistent with charged ellipsoidal aggregates, persisting from lower through to higher homologues in both the PhenCx and CyclohexCx series.
authors.affiliation: School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, United Kingdom.
authors.forename: Marios
authors.initials: M
authors.lastname: Hopkins Hatzopoulos
authors.forename: Julian
authors.initials: J
authors.lastname: Eastoe
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Dowding
authors.forename: Isabelle
authors.initials: I
authors.lastname: Grillo
authors.forename: Bruno
authors.initials: B
authors.lastname: Demé
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Rogers
authors.forename: Richard
authors.initials: R
authors.lastname: Heenan
authors.forename: Robert
authors.initials: R
authors.lastname: Dyer