Effect of head group polarity and spacer chain length on the aggregation properties of gemini surfactants in an aquatic environment.
The aggregation behavior of cationic gemini surfactants with respect to variation in head group polarity and spacer length is studied through conductance, surface tension, viscosity, and small-angle neutron-scattering (SANS) measurements. The critical micellar concentration (cmc), average degree of micelle ionization (beta(ave)), minimum area per molecule of surfactant at the air-water interface (A(min)), surface excess concentration (gamma(max)), and Gibb's free energy of micellization (delta G(mic)) of the surfactants were determined from conductance and surface tension data. The aggregation numbers (N), dimensions of micelles (b/a), effective fractional charge per monomer (alpha), and hydration of micelles (h(E)) were determined from SANS and viscosity data, respectively. The increasing head group polarity of gemini surfactant with spacer chain length of 4 methylene units promotes micellar growth, leading to a decrease in cmc, beta(ave), and delta G(mic) and an increase in N and b/a. This is well supported by the observed increase in hydration (h(E)) of micelles with increase in aggregation number (N) and dimension (b/a) of micelle.
Borse
Mahendra
M
Department of Chemistry, Faculty of Science, Maharaja Sayajirao University of Baroda, Vadodara 390 002, India.
Sharma
Vikas
V
Aswal
V K
VK
Goyal
P S
PS
Devi
Surekha
S