1070-4272/01/7402-0188 $25.00 C 2001 MAIK [Nauka/Interperiodica]
Russian Journal of Applied Chemistry, Vol. 74, No. 2, 2001, pp. 188!192. Translated from Zhurnal Prikladnoi Khimii, Vol. 74, No. 2, 2001,
Original Russian Text Copyright + 2001 by Chunsheng Mo, Kochurova.
OF SYSTEMS AND PROCESSES
Polymorphism of Micelles in Aqueous
Cetyltrimethylammonium Bromide Solutions
Chunsheng Mo and N. N. Kochurova
Research Institute of Chemistry, St. Petersburg State University, St. Petersburg, Russia
Received August 9, 1999; in final form, January 2000
Abstract-A viscometric study was made of the polymorphous transformation of micelles in an aqueous so-
lution of cetyltrimethylammonium bromide in the presence of NaBr and sodium methylbenzenesulfonate.
The effects of temperature and nature and concentration of additives on the second critical micelle con-
centration were studied. The thermodynamic characteristics of the micellar transition are estimated.
It is well known that inorganic electrolytes and
polar organic compounds have a considerable effect
on the physicochemical characteristics of aqueous
solutions of ionic surfactants. Most clearly this effect
is reflected in the viscosity of a micellar solution .
It has been demonstrated experimentally that small
spherical micelles formed at the first critical micelle
) may transform into cylindrical
micelles with increasing surfactant concentration or as
a result of addition of polar compounds. Such a trans-
formation results in higher viscosity of the so-
lution and changes other thermodynamic character-
istics. The use of certain organic electrolytes, such as
benzenesulfonates, salicylates, etc., as additives to
an aqueous surfactant solution allows preparation of
highly viscous fluids, semisolid pastes, or gels. This
phenomenon is widely used in pharmaceutical, food,
and cosmetics industries, environmental protection,
etc. Therefore, studying the indicated polymorphism
is of considerable practical importance.
The asymmetrization of spherical micelles and
the viscoelastic properties of aqueous solutions of
cetyltrimethylammonium bromide (CTAB) in the pres-
ence of various additives have been studied extensive-
ly . However, systems with low additive con-
centrations were considered in most of these works.
Data on the thermodynamic characteristics of such
systems are very scarce.
In this communication, we report the effects of
the CTAB concentration and temperature on the poly-
morphism in dilute aqueous solutions of CTAB at rel-
atively high NaBr concentrations (0.2 and 0.4 M) and
in the presence of an organic additive, sodium methyl-
benzenesulfonate (NaMBS). The activation energy of
viscous flow is estimated.
As a surfactant we used CTAB (analytically pure
grade) multiply recrystallized from a mixture of ace-
tone and methanol (19 : 1). As the criterion of high
quality served the absence of a minimum in the sur-
face tension isotherm.
Sodium bromide and p-methylbenzenesulfonate
(both of analytically pure grade) were used without
The viscosities at 30, 35, 40, 45, and 50oC were
measured by capillary viscometry with an Ubbelohde
viscometer on an experimental setup described
in . The dynamic viscosity h (Pa s) was deter-
mined from the outflow time of water and the solu-
tions, using reference data on the viscosity of water.
Fig. 1. Dynamic viscosity h of CTAB micellar solutions
vs. the CTAB concentration C
in the presence
of various additives. Additive (M): (1) 0.2 NaBr, (2) 0.4
NaBr, and (3) 0.025 NaMBS. Temperature (oC): (1) 30,
(2) 40, and (3) 50.