Co-adsorption of polyanions and esterquat surfactants; effect on formation and stability of micellar core nanocapsules

Abstract

We investigated the co-adsorption at water/air interface of soft cationic surfactants of the esterquat-type, fatty acid quaternary ammonium esters with hydrocarbon chain containing eleven carbons and the amino acid betaine esters with twelve carbons in the chain with polyanions: polysodium 4–styrenesulfonate (PSS), poly-l-glutamic acid sodium salt (PGA), alginic acid sodium salt (ALG) and λ-carrageenan (CAR). The effect of surfactants basic hydrolysis on formation of surfactant/polymer complexes in bulk and at interface was taken into account. We found that the surface charge of the water/air interface originating from the adsorption of fatty acid quaternary ammonium esters decreased as the result of hydrolysis that led to lower co-adsorption of polyanions than in the case of amino acid betaine esters. The optimal conditions for formation of surfactant micelles/polyelectrolyte aggregates were established. These negatively charged aggregates were further used as nanocores for encapsulation by the layer-by-layer (LbL) adsorption of synthetic and natural polyelectrolytes. The average size of nanocapsules was in range 100–200nm. We observed that stability of micellar cores were dependent on the rate of esterquat hydrolysis, ones formed with fast hydrolysable surfactant were stable under acidic but unstable under basic conditions.