Properties of two polymerizable surfactants aqueous solutions: dodecylethylmethacrylatedimethylammonium bromide and hexadecylethylmethacrylatedimethylammonium bromide

MARÍA BELEN SIERRA; PABLO SCHULZ; DULCE P. DEL J. GUTIÉRREZ-HIJAR; F.BECERRA; J. E. PUIG; J. F. ARMANDO SOLTERO-MARTÍNEZ

Iguazú Paraná

Congreso; XI International Conference on Surface and Colloid Science; 2003

IACIS

The aggregation of two polymerisable surfactants: dodecylethylmethacrylatedimethylammonium bromide (C12PS) and hexadecylethylmethacrylatedimethylammonium bromide (C16PS) was studied with a battery of methods. C12PS shows a three-step aggregation at the concentrations: C1 = (7.78± 0.27)x10-4 mol.dm-3, (pre-micellar aggregates formation); C2 = (2.02±0.53)x10-3 mol.dm-3, (CMC) with spherical micelles having ionization degree C12PS = 0.306 and micellar conductivity dsph.mic = 86.5 S.cm2eq-1. The area per adsorbed molecule at the air/solution interface is a = 1.41 nm2. There is an energetic advantage of the adsorbed monolayer over the micelles, giving rise to an increase in adsorption above the CMC. The third concentration C3 = (6.94± 0.36)x10-3 mol.dm-3, reflects the sphere-to-cylinder micelle transformation with dmic.cil. = 26.4 S.cm2eq-1 and a = 0.592 nm2. Micelles become more energetically favored than the adsorbed monolayer. C16PS shows a four-step aggregation at: C1 =(4.2± 4.4)x10-5 mol.dm-3, (pre-micellar aggregates formation); C2 = (1.42±0.24)x10-4 mol.dm-3, (CMC) with spherical micelles having ionization degree C12PS = 0.373 and micellar conductivity dsph.mic = 89.5 S.cm2eq-1, C3 = (3.83± 0.56)x10-4 mol.dm-3, that reflects the sphere-to-cylinder micelle transformation with dmic.cil. = 36.3 S.cm2eq-1 and a = 0.778 nm2. Micelles become more energetically favored than the adsorbed monolayer. The fourth transition at C4 = (5.0 ± 0.5)x10-3 mol.dm-3 probably corresponds to an entanglement of the worm-like micelles. The partial molar volume (PMV) and hydration of both micellised polymerisable surfactants were also determined. The PVMs at the CMC are 381.18 ± 0.44 cm3.mol-1 for C12PS and 462.6 ± 5.4 cm3.mol-1 for C16PS. The contribution of the polar head group to the PVM is Vph = 146.1 ± 3.5 cm3.mol-1. At the concentration corresponding to the transformation spherical ?to- cylindrical micelles, VC12PS = 381.18 ± 0.44 cm3.mol-1 and VC16PS = 462.6 ± 5.4 cm3.mol-1, giving Vph = 138.5 ± 4.6 cm3.mol-1. The PVM reduction may be explained by the crowding of he polar head groups at the Stern micelle layer when spherical micelles become worm-like. Results marginally support the annular model of the polar head group proposed by Hamid and Sherrington.