Environmentally Responsive Surface Coatings of Polyion-Surfactant Ion Complex Salts

Abstract: Complexes formed between oppositely charged polyions and surfactant ions are known to have very rich phase behaviour in bulk solution. The work in this thesis investigates the possibilites of using such complexes as surface coatings. Stoichiometric polyion-surfactant ion complexes “complex salts” (CS) consisting of alkyltrimethylammonium surfactant ions and polyacrylates are typically insoluble in water but fators like surfactant tail and polyion length, hydrophobicity and addition of excess surfactant can cause the complexes to “redissolve”. In this wok it was established that redissolution is promoted by having shorter surfactant and polyions, incorporating a neutral comonomer in the polyion sequence or having a small counterion that interacts less strongly with the surfactant aggregates. Though typically water-insoluble, CS are water-responsive, and can be dissolved in certain organic solvents. Casting an ethanolic solution of CS on a solid surface is a facile method to produce a surface coating that does not come off in water but respond to changes in hydration. The major part of this thesis is dedicated to exploring CS as surface coatings and in particular understanding their responsivness towards changes in hydration and additives, both directly incorporated in the film or as solutes in a contacting aqueous solution. SAXS measurements were used to investigate the phase behaviour and two new liquid crystalline structure, not previously found in bulk, were discovered, rectangular c2mm and 3D-hexagonal. Adding solutes in the contacting solution revealed that CS films respond to a number of additives; acid, base, salt, ionic surfactant and water soluble polymers, could all invoke a phase transition in the film. Washing the films proved to be a sufficient method to regain the structures originally found in water, given that the washing time was long enough. Additives with low self-diffusion coefficient, like some surfactants, took considerably longer time to wash off, giving some clues to transportation in, and between film and bulk. Sorption measurements were done to further addresse the kinetics of water transport between hydrated films and humid air and sorption isotherms for both hydration and dehydration were established