Photopolymerization of monolayers prepared from surfactants containing styrene moieties

Abstract

Monolayers on aqueous surfaces have been prepared from positively and negatively charged synthetic surfactants: bis(2-(n-hexadecanoyloxy)ethyl)methyl(p-vinylbenzyl)ammonium chloride (1), di-n-octadecylmethyl(p-vinylbenzyl)ammonium chloride (2), di-n-octadecylmethyl(2-((4-vinylbenzoyl)oxy)ethyl)ammonium chloride (3), n-hexadecyl 11-(4-vinylbenzamido)undecyl hydrogen phosphate (4), and dioctadecyldimethylammonium bromide (5). Surface pressure-surface area, surface potential-surface area, and surface ellipsometry-surface area isotherms have led to values for collapse areas (A{sub c}) and collapse pressures (P{sub c}) of 35 {angstrom}{sup 2}/molecule and 67 mN/m, 55 {angstrom}{sup 2}/molecule and 40 mN/m, 70 {angstrom}{sup 2}/molecule and 42 mN/m, 33 {angstrom}{sup 2}/molecule and 54 mN/m, and 42 {angstrom}{sup 2}/molecule and 50 mN/m for monolayers prepared from 1-5, respectively. Ultraviolet irradiation of monolayers prepared from 1-4 resulted in their photopolymerization. The A{sub c} value decreased upon polymerization of monolayers prepared from 1 and 2, but it increased for monolayers prepared from 4. A similar trend was observed in the surface potential and ellipsometric measurements. Kinetics of photopolymerization of monolayers prepared from 1 have been investigated in detail. Rate constants for the photopolymerization, initiated by steady-state and pulsed-laser irradiations, have been determined at different surface pressures and irradiation energies. The obtained data have been analyzed in terms of a two-dimensional patch-polymerization model (PPM) and by the classical approach considering photoinitiation, propagation, and termination rates (CPM).more » Both models predict a first-order change of the monolayer surface area as a function of irradiation time.« less