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Acid‐base equilibria of sulfonephthalein dyes in aqueous polymer‐surfactant media
Author(s) -
Saikia Palash M.,
Dutta Robin K.
Publication year - 2006
Publication title -
journal of surfactants and detergents
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.349
H-Index - 48
eISSN - 1558-9293
pISSN - 1097-3958
DOI - 10.1007/s11743-006-0372-0
Subject(s) - chemistry , bromothymol blue , aqueous solution , polyvinyl alcohol , pulmonary surfactant , sodium dodecyl sulfate , polymer , polyethylene glycol , micelle , ethylene glycol , polymer chemistry , critical micelle concentration , inorganic chemistry , chromatography , organic chemistry , biochemistry
The acid‐base equilibria of three anionic sulfonephthalein dyes, viz. , bromothymol blue (BTB), thymol blue (TB), and cresol red (CR), were studied spectroscopically in aqueous media containing the water‐soluble noninonic polymers polyvinyl alcohol (PVA) and polyethylene glycol (PEG) in the presence of an anionic surfactant, sodium dodecyl sulfate (SDS). A partition equilibrium method was used to determine the equilibrium constant of partition of the dyes between the micellar pseudo phase and aqueous phase in the presence of PVA and PEG. The critical aggregation concentrations (CAC) of the surfactants in buffered aqueous systems containing the neutral polymers were also determined. The CAC of the polymer‐surfactant systems were found to be lower than the critical micelle concentration of such systems in the absence of polymer, in otherwise identical conditions. The pH‐dependent association constants, K ass , of the sulfonephthalein dyes with the SDS‐PVA system increased with the increase in molecular weight of the polymer. The interactions of the dyes with the buffered aqueous SDS‐PVA and SDS‐PEG systems were found to be endothermic and entropy oriented. In the polymer domain, the head group region of the micelles was more exposed at lower concentrations of the polymer, but under excess polymer concentration they were increasingly shielded, which impaired their electrostatic interaction with the dyes.