From polymeric surfactants to colloidal systems (3): Neutral and anionic polymeric surfactants derived from dextran

Neutral and anionic amphiphilic polysaccharides have been prepared by chemical modification of a bacterial polysaccharide, dextran. A two-step modification procedure allows controlling the number and nature of hydrocarbon groups as well as the density of anionic charges along the polysaccharide backbone.The solution behaviour in water is examined by viscometry. The experimental results are interpreted in terms of attractive hydrophobic effect and repulsive electrostatic interactions, both being modulated by the ionic strength. The surface active properties of the polymers have been established and related to the polymer chemical structure as well as to the solution behaviour. Especially, the effect of backbone charge density on the kinetics of interfacial tension decrease is evidenced.Submicronic oil-in-water emulsions were prepared in the presence of macromolecular surfactants. Anionic groups have a strong influence on the initial size of the oil droplets especially for low concentrations of polymeric surfactant. The main effect comes from the modulation of electrostatic repulsions rather than from the rate of interfacial tension decrease. The variation of the initial droplet size with ionic strength is also influenced by the charge density of the chains.