Colloids and Surfaces
A: Physicochemical and Engineering Aspects 196 (2002) 259 – 267
Thermodynamic investigation of surfactant aggregation in
2-pyrrolidinone
S.K. Mehta *, Shweta Sharma, I.M. Joshi
Department of Chemistry, Punjab Uniersity, Chandigarh160 014, India
Received 19 December 2000; accepted 10 July 2001
Abstract
The partial molal volume (V
,s
) of several surfactants viz. sodium dodecylsulphate (SDS) and sodium tetradecylsul-
fate (STS), tetraethylammonium bromide (Tea-Br), Span-80, 60, 40, 20 in 2-pyrrolidinone have been determined at
concentration below 0.80 mol kg
-1
at 30 and 40 °C. The partial molal isentropic compressibility (K
,s
) of micellar
solutions of surfactants SDS, STS, Span-80, 60, 40, 20 have been calculated from ultrasonic velocity measurements at
30 °C. The infinite dilution values of V
,s
and K
,s
of the solubilizates in 2-pyrrolidinone are also estimated. The
critical micellization concentration (cmc) values for the systems are taken at a concentration where a clear and well
defined break is observed in the concentration dependence of the ultrasonic velocity. The cmc data has been utilized
to compute standard free energy of micellization (G
m
o
). The results have been interpreted in terms of transfer of
surfactant monomer from dispersed to aggregated state. Limiting parameters have been used to explain the solvation
of surfactant molecules. © 2002 Elsevier Science B.V. All rights reserved.
Keywords: Partial molal volume; Partial molal isentropic compressibility; Critical micelle concentration; 2-Pyrrolidinone
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1. Introduction
Direct studies of thermodynamic properties of
surfactants in solution as a function of concentra-
tion are best suited for quantitative envisage of
stability of the system [1–6]. Fundamental to the
knowledge of surfactant – solvent system is the
determination of surfactant tendency towards
ending up as micelles. Important terms associated
with such systems are: structural organization and
interactions among the head groups. Effect of
these surfactant – solvent interactions can be stud-
ied by looking into the concomitant structural
reorganization and counter ion binding [7]. Most
of the studies on surfactant have been restricted
to their aqueous solution [8–14]. But in some
reports interesting results have also been obtained
for surfactant in non-aqueous media [15–28].
Such system is appraised to be important because
non-aqueous solvents are used extensively not
only in chemistry but also in other fields to con-
trol the factors like solubility, reactivity and the
stability in relation to biological homeostasis. It is
well known that surfactant molecules in water
* Corresponding author. Tel.: +91-172-534423; fax: +91-
172-545459.
E-mail address: skmehta@pu.ac.in (S.K. Mehta).
0927-7757/02/$ - see front matter © 2002 Elsevier Science B.V. All rights reserved.
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