S. Milioto et al., THERMODYNAMIC PROPERTIES OF WATER BETA-CYCLODEXTRIN DODECYLSURFACTANTTERNARY-SYSTEMS, Journal of solution chemistry, 24(2), 1995, pp. 103-120
Densities, heat capacities and conductivities of water-surfactant-beta
-cyclodextrin (beta-CD) ternary systems were determined at 25-degrees-
C. The surfactants studied were sodium dodecylsulfate (NaDS) and dodec
yltrimethyl-ammonium bromide (DTAB). From conductivity data, apparent
critical micelle concentrations (cmc) and degree of ionization of mic
elles were obtained at a fixed beta-CD concentration (m(CD)). From the
cmc value and that in water (cmc) the stoichiometry of the surfactan
t-beta-CD complex was calculated. At a given m(CD), the apparent molar
volume V(phi,CD) and heat capacity C(phi,CD) of beta-CD in the two su
rfactants were calculated as functions of surfactant concentration m(S
). For both NaDS and DTAB, V(phi,CD) increases with m(S) up to about t
he cmc beyond which it decreases to a constant value at high m(S); the
opposite is observed for C(phi,CD). With NaDS, a jump in the C(phi,CD
) vs. m(S) trend was detected and ascribed to a structural NaDS micell
ar transition. The apparent molar volume V(phiS) and heat capacity C(p
hiS) of NaDS and DTAB in the water-beta-CD mixture 0.017m were also ob
tained. From these properties and those in pure water, the volume DELT
AV(S) and heat capacity DELTAC(S) of transfer of the surfactant from w
ater to water+beta-CD mixture as functions of m(S) were calculated. Fo
r both surfactants, the DELTAV(S) vs. m(S) trends increase to the cmc
and then decrease in a monotonic manner, whereas DELTAC(S) increases r
egularly with m(S) in the pre-micellar region and is essentially const
ant in the post-micellar region. The DELTAV(S) vs. m(S) trends were qu
alitatively explained in terms of dispersed, complexed and micellized
surfactant contributions.