Partition equilibrium of phenol red in aqueous polymer-surfactant system: Determination of critical aggregation concentration

Acid-base equilibrium of phenol red (PR), a sulphonephthalein dye, was studied spectrophotometrically in aqueous media containing water soluble nonionic polymers viz., polyvinyl alcohol (PVA) and polyethylene glycol (PEG) in the presence of an anionic surfactant. sodium dodecyl sulfate (SDS). A partition equilibrium method was utilized to determine the equilibrium constant of partition of the PR between micellar pseudo phase and aqueous phase and the critical aggregation concentration (CAC) of SDS in buffered aqueous systems containing the neutral polymers. The pH dependent association constants, K-ass of PR with SDS-PVA, and 5DS-PEG system increase in the order PEG 200