SURFACE-ACTIVITY AND MICELLE FORMATION OF CHEMODEGRADABLE CATIONIC SURFACTANTS CONTAINING THE 1,3-DIOXOLANE MOIETY

Systematic studies of adsorption phenomena and micellization for several cationic acetal-type surfactants: [(2-alkyl-1,3-dioxolane-4-yl)methyl] trimethylammonium bromides (C-n-D-TAB; where C-n = C9H19, C11H23 or C13H27) and [(2,2-dialkyl-1,3-dioxolane-4-yl)methyl] trimethylammonium bromides (CnCm-D-TAB; where C-n = C8H17 or C10H21 and C-m = CH3, or C-n = C-m = C6H13) carried out using surface tension measurements. Because these surfactants contain a 1,3-dioxolane moiety (D), they can be applied as a new acid-hydrolyzable type of chemodegradable surfactant. The structural effects of both the alkyl substituents (structural isomerism), and the 1,3-dioxolane ring on the adsorption (i.e. on the surface excess concentration, the area per molecule at the surface, the standard free energy of adsorption) and the micellization parameters have been discussed and compared with respect to parameters of the ''classical'' alkyltrimethylammonium bromides (C-n-TAB) and alkyl trimethylammonium bromides containing oxyethylene (EO(1)) and dioxyethylene (EO(2)) units (C-n-EO(2)-TAB and C-n-EO(2)TAB, respectively) also. The C-n-D-TAB surfactants exhibit micellar properties similar to those of C-n-EO(2)-TAB. The values of the standard free energy contribution of the 1,3-dioxolane ring [-D-] in the C-n-D-TAB derivatives to the micellization and the adsorption processes (Delta(mic)(o)[-D-] = -5.7 kJ mol(-1) and Delta G(ads)(o)[-D-] = -21.5 kJ mol(-1), respectively) showed that the [-D-] moiety is approximately 1.7 times more hydrophobic than the methylene group of the alkyl chain in promoting micellization (Delta G(mic)(o)[-CH2-] = -3.5 kJ mol(-1)) and 6.3 times more effective in promoting adsorption (Delta G(ads)(o)[-CH2-] = -3.35 kJ mol(-1)). The difference Delta Delta G(o)[-D-](=Delta G(ads)(o)[-D-]-Delta G(mic)(o)[-D-]= -16 kJ mol(-1)) indicates a higher strength of adsorption of the five-membered 1,3-dioxolane ring at the finite dilution surface film than the tendency to micellization.