E. Kudryashov et al., THE COMPRESSIBILITY OF ALKYLTRIMETHYLAMMONIUM BROMIDE MICELLES, Journal of colloid and interface science (Print), 203(1), 1998, pp. 59-68
Ultrasonic measurements have been carried out for solutions of octyl-,
decyl-, dodecyl-, tetradecyl-, and hexadecyltrimethylammonium bromide
s (C(n)TAB) over a wide range of concentrations above and below their
critical micelle concentrations (CMC) at 25 degrees C. The apparent mo
lar adiabatic compressibilities of the surfactants in monomer, (Phi(ks
))(f), and in micellar forms, (Phi(ks))(mic), have been determined. Th
e values for (Phi(ks))(f) decrease with increasing chain length of the
surfactant by an increment of -0.87 x 10(-4) cm(3) mol(-1) bar(-1) pe
r -CH2- group. The opposite trend has been found for the value of (Phi
(ks))(mic), the compressibility of surfactants in the micelle, which i
s positive, and increases with increasing chain length of the surfacta
nt by 9.5 x 10(-4) cm(3) mol(-1) bar(-1) per -CH2- group. The coeffici
ent of adiabatic compressibility of the internal cores of micelles is
estimated to be 59.5 x 10(-6) bar(-1), which is close to, but slightly
lower than the coefficient of adiabatic compressibility of pure hydro
carbon liquids having the same number of -CH2- groups. (C) 1998 Academ
ic Press.