of two-dimensional aggregates of long chain ions at the inter-The kinetics of adsorption of cationic surfactants (CTAB, face from their studies of the adsorption of alkyl ammonium MTAB and DTAB) at silica surface has been studied at various halides at silica-water interface. The microstructure of advalues of bulk surfactant concentration ( C t 2 ), pH, ionic strength, sorbed layer of surfactants and polymer films have been and temperature and in presence of different electrolytes and urea. unraveled by fluorescence probes, ESR, excited state reso-The adsorption process has been found to follow a two-step firstnance, Raman spectra, etc. (15). Using the spectral reflecorder kinetic rate equation with two different rate constants k 1 tion of neutrons, Rennie et al. (16) has shown that CTAB and k 2 . From the variation of k 1 and k 2 with temperature, values is adsorbed on silica as defective bilayer or as flattened of energies of activation E a1 and E a2 for both the kinetic steps have been evaluated. The corresponding values of enthalpies of micelle depending upon the bulk concentration of the surfacactivation ( DH # 1 and DH # 2 ), entropies of activation ( DS # 1 and tant. The adsorption of different types of surfactants onto DS # 2 ) have been evaluated using Eyring's equation for absolute the solid-liquid interfaces has been investigated using caloreaction rate. It has been found that for both the kinetic steps, rimetry (18-20). Using ellipsometric and other techniques, DH # 1 Γ΅ T av DS # 1 and DH # 2 Γ΅ T av DS # 2 , which means that activation Lindman and coworkers (20) have indicated the formation reaction is largely entropy controlled. Again, for both kinetic of micelles at solid-liquid interfaces, which may be similar steps, DH # varies linearly with T av DS # , and DG # 1 and DG # 2 vary in nature to that formed in the bulk media. Recently Chattoraj between 70 and 88 kJ/mole of surfactant, respectively. Thus there et al. (21) have studied the thermodynamics of adsorption is a entropy-enthalpy compensation effect in the adsorption pro-
of cationic surfactants at different solid-liquid interfaces.
cess.