Structure of starch-ionic surfactant complexes studied by ternary phase, XRD and scanning electron microscopy

Abstract

The structure of lyotropic liquid crystallineorgel like phases formedin starch/surfactant (cationicoranionic)/water ternary phase systems in the temperature range of 25-85° Chas been investigated by XRD, SEM and FT-IR techniques. The ionic surfactants were cetyltrimethyl ammonium bromide (CTAB), sodiumd odecyl sulfate (SDS). The phases were in equilibrium with aqueous solutions at 60°C and contained 15-25wt% starch and 10-30wt % surfactant, depending on the charge density of the starch and the chain length of the surfactant. The phases consist of starch/surfactant aggregates arranged in long-range structures similar tolyotropicmeso phases formed by the pure ionic surfactant salone, but they separate from aqueous solutions at much lower surfactant concentrations. When the charge density of the starchis low or the surfactant hydrocarbon chain is short, the characteristic cubicor hexagonal phases are formed. As expected, the formation of lamellar phaseis promoted by increasing these parameters. Temperature affects the stability of the phases and their structure. At high temperatures the long-range order breaks down, and the phases are akin to concentrated micellar starch/ionic surfactant solutions.