Spectroscopic studies of the investigation of molecular interaction between Acid Red and cetyltrimethylammonium bromideAuthor(s): Syeda Tanzima Saad, Md. Anamul Hoque, Mohammed Abdullah Khan
Interactionof ananionic textiledye namely Acid Red 266 (AR) with cationic surfactant like cetyltrimethylammoniumbromide (CTAB)hasbeeninvestigated by means of UV-visible spectroscopy in premicellar concentration range.The aggregation between surfactant and dyewas found to be observed at surfactant concentration far belowthe criticalmicelle concentration of the surfactant.Aggregation is reflected bya significant change inëmax(bathochromic shift),with the appearance of two newband in the spectrumof the pure dye. The binding constant (Kb) of complexation was determined fromtheBenesi-Hildebrand plot.The values ofKb forAR-CTABcomplex increasedwith increase of dye concentrations. The values of binding constant forAR-CTABsystemincreased up to certain temperatures and then start to decreasewith temperature. Theeffect ofpolyelectrolyte, sodiumalginate (SA) onAR-CTAB interactions was studied and was observed that the binding constant (Kb) value in waterpolyelectrolyte systemwashigher inmagnitudethanthat in purewater system.The binding constant (Kb) gradually increases as the sodiumalginate concentration increased up to 0.01%and thenwith further increase othe sodiumalginate concentration, precipitation occurs. The values of Kb forAR-CTABsystemwere found to behigher inmagnitude inmixedsolvent (water-alcohol) compared to that of purewater.With increasing alkyl chainlengthof alcohol, the bindingconstant (Kb)ofARCTABcomplexwas found to be increased.The effect of pHonAR-CTAB interactionwas found that there was a significant increase in Kb valuewith increasing pH. In all the cases,ÄG0 values of the complexeswere negativewhichindicatedthat thecomplexformationwas thermodynamicallyspontaneous.The binding interaction between dye and CTAB was found to be hydrophobicinnature at lower temperaturewhereasbothelectrostaticandhydrophobicinteractionsexist athigher temperatures. Enthalpy-entropycompensation is observed from a linear relation between enthalpy and entropy changes in aqueous solution forAR-CTABcomplex.