Polymeric surfactants in disperse systems.
This overview starts with a section on general classification of polymeric surfactants. Both homopolymers, block and graft copolymers are described. The solution properties of polymeric surfactants is described by using the Flory-Huggins theory. Particular attention is given to the effect of solvency of the medium for the polymer chains. The adsorption and conformation of homopolymers, block and graft copolymers at the solid/liquid interface is described. The theories of polymer adsorption and their predictions are briefly described. This is followed by a description of the experimental techniques that can be applied to study polymeric surfactant adsorption. Examples of adsorption isotherms of non-ionic polymeric surfactants are given. The effect of solvency on the adsorption amount is also described. Results for the adsorbed layer thickness of polymeric surfactants are given with particular attention to the effect of molecular weight. The interaction between particles containing adsorbed layers is described in terms of the unfavorable mixing of the stabilizing chains when these are in good solvent conditions. The entropic, volume restriction or elastic interaction that occurs on considerable overlap is also described. Combination of these two effects forms the basis of the theory of steric stabilization. The energy-distance curve produced with these sterically stabilized systems is described with particular attention of the effect of the ratio of adsorbed layer thickness to droplet radius. Examples of oil-in-water (O/W) and water-in-oil (W/O) emulsions stabilized with polymeric surfactants are given. Of particular interest is the O/W emulsions stabilized using hydrophobically modified inulin (INUTEC((R))SP1). The emulsions produced are highly stable against coalescence both in water and high electrolyte concentrations. This is accounted for by the multipoint attachment of the polymeric surfactant to the oil droplets with several alkyl groups and the strongly hydrated loops and tails of linear polyfructose. Evidence of this high stability was obtained from disjoining pressure measurements. Stabilization of suspensions using INUTEC((R))SP1 was described with particular reference to latexes that were prepared using emulsion polymerization. The high stability of the latexes is attributed to the strong adsorption of the polymeric surfactant on the particle surfaces and the enhanced steric stabilization produced by the strongly hydrated polyfructose loops and tails. Evidence for such high stability was obtained using Atomic Force Microscopy (AFM) measurements. The last part of the overview described the preparation and stabilization of nano-emulsions using INUTEC((R))SP1. In particular the polymeric surfactant was very effective in reducing Ostwald ripening as a result of its strong adsorption and the Gibbs elasticity produced by the polymeric surfactant.
Tadros
Tharwat
T
89 Nash Grove Lane, Wokingham, Berkshire RG40 4HE, UK.
D000327:Adsorption; D010316:Particle Size; D011108:Polymers / Q000737:chemistry*; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry*
D011108:Polymers; D013501:Surface-Active Agents