Equilibrium Constant, Concentrations Study of p-Aminobenzoic Acid in Anionic, Cationic and Non-ionic Surfactants

p-aminobenzoic acid (pABA) was used as a probe to study the equilibrium constant in ground and excited state and concentrations of anionic surfactant, cationic surfactant and non-ionic surfactant. The absorption and fluorescence spectral characteristics of pABA were reported in aqueous micellar environments (SDS, CTAB and TW 80) at different pHs. The neutral and monoanion form of pABA is present at both pHs 3 and 7 respectively. The blue shifted fluorescence maximum was accompanied by a great raise in intensity at pH 3 whereas at pH 7 the emission intensity a little increase with increasing micelles concentration. In the acidic medium, the CMC value is increased when compared to neutral solution. The strength of interaction between pABA-micelles at both pHs was estimated using Hirose - Sepulveda equation and these calculated values was further used to estimate the free energy change of the interaction from the fluorescence data. These results from the absorption and fluorescence spectra of pABA well explained that the nature of force and location of probe in ionic micelles and non-ionic micelles at different pHs.