The adsorption of two ionic surfactants CTAB（Cetyl trimethyl ammonium bromide） and SDS（Dodecyl sodium sulfate） onto two kinds of modified starches LS（phosphoryslate starch,a kind of anionic starch） and CS-8（Quaternary starch,a kind of cationic starch） were studied by means of micro-electrophoretic method.The results show that both ionic surfactants CTAB and SDs may alternate the surface charge of two starches LS and CS-8 respectively at low concentrations,and result in the change of the isoelectric point（I.E.P）,which is drifted from pH 3.3 to pH 8.7 for LS and from pH 3.7 to pH 2.4 for CS-8.The zero potential concentration（Z.P.C） of CTAB and SDS are 8×10-6 and 7×10-5mol·dm-3,respectively.These results indicate that there are a special adsorption interaction between LS and CTAB or CS-8 and SDS.The special sorption free energy（ΔGs） was calculated according to the Guy-Chapman-Stern’s electronic double layer model,which was-37.3 KJ·mol-1 for SDS and-44.2 KJ·mol-1 for CTAB.Meanwhile,the influence of these two surfactants on LS or CS-8 pasty’s viscosity was also discussed.
