Structure of Starch-Ionic Surfactant Complexes Studied by Ternary Phase, XRD and Scanning Electron Microscopy

Thestructureoflyotropicliquidcrystallineorgel like phasesformedin starch/surfactant (cationicoranionic)/waterternaryphasesystemsinthetemperature rangeof 25-85oChas beeninvestigatedbyXRD,SEMandFT-IRtechniques.The ionicsurfactantswerecetyltrimethylammonium bromide(CTAB),sodiumdodecylsulfate (SDS).Thephaseswereinequilibriumwithaqueoussolutionsat 60°Candcontained15-25wt%starchand10-30wt%surfactant,dependingonthechargedensityof thestarchand thechainlengthofthesurfactant.Thephasesconsistofstarch/surfactant aggregatesarranged in long-range structures similartolyotropicmesophasesformedbythepureionicsurfactantsalone, butthey separatefromaqueous solutionsat muchlowersurfactant concentrations.Whenthechargedensityofthe starchislow orthe surfactanthydrocarbonchainisshort,the characteristiccubicor hexagonal phasesare formed.As expected,the formation of lamellar phaseis promotedbyincreasingtheseparameters.Temperature affectsthestabilityofthe phasesand theirstructure.Athightemperaturesthelong-rangeorder breaks down,and thephasesareakin toconcentratedmicellarstarch/ionic surfactantsolutions.