Interactions between cationic starch and mixed anionic surfactants

The interactions of cationic starch (CS, degree of substitution = 0.8)/mixe d anionic surfactant/water systems were investigated. The surfactants inves tigated were sodium dodecyl sulphate (SDS), sodium octanoate (NaOct), sodiu m decanoate (NaDe), sodium dodecanoate (NaDod), sodium oleate (NaOl) and so dium erucate (NaEr). The concentration of CS varied from 0.001 to 10 wt.%. The effect of mixing on the micellisation of the binary surfactant solution s can be described to a good approximation by taking into account only the effects of the volume difference between the hydrocarbon chains. Mixed mice lle formation on CS depends on the chain-length difference in quite the sam e way as for free mixed micelles. Aggregation of the mixed micelles of the surfactants and the polymer coils produces a gel-like complex phase. The wa ter content of the gel phase in equilibrium with aqueous solution increases when the chain-length difference between the two surfactants increases. Th e more surface-active component is strongly enriched in the polymer complex es and gels. (C) 1999 Elsevier Science B.V. All rights reserved.