Ordered polyelectrolyte multilayers. 5. Photo-cross-linking of hybrid films containing an unsaturated and hydrophobized poly(diallylammonium) salt and exfoliated clay

A simple synthetic route to a new poly(diallylammonium) salt functionalized by a styrene group is presented. This reactive polymer was employed for polyelectrolyte multilayer films using electrostatical layer-by-layer self-assembly, together with an inorganic polyanion, namely an exfoliated hectorite clay. To enhance their stability, the final hybrid multilayers were cross-linked by exposure to UV light, leading only to a minor shrinkage. Alternatively, the reactive polycation was cross-linked after each adsorption step. X-ray reflectometry revealed that the two types of films dispose of an internal order with a short length scale, that seems insensitive to the photo-cross-linking. Cross-linking after each adsorption step, however, results in more regular film growth, and reduces the films' roughness and the amount of polyanion deposited. Under these conditions, the films seem to grow by deposition of submonolayers with a combined vertical and lateral expansion, resulting in the self-healing of previously deposited, incomplete layers.