ORIGINAL ARTICLE Micellization and Clouding Behavior of EO–PO Block Copolymer in Aqueous Salt Solutions Keyur Patel Æ Bhavesh Bharatiya Æ Yogesh Kadam Æ Pratap Bahadur Received: 23 July 2008 / Accepted: 18 April 2009 / Published online: 21 May 2009 Ó AOCS 2009 Abstract Aqueous solution properties of polyethylene oxide–block-polypropylene oxide–block-polyethylene oxide TBP [(PEO) 103 (PPO) 39 (PEO) 103 ] were studied in the presence of sodium salts with different anions (NaI, NaBr, NaCl, NaF, Na 2 SO 4 , Na 3 PO 4 ) to investigate unimer-to- micelle transition [critical micelle concentration (CMC), critical micellization temperature (CMT)], micelle size and the phase separation (cloud point). This TBP, due to its very hydrophilic (80% PEO) nature does not form micelles at ambient temperatures. Micellization can be induced much below its CMT in water on addition of sodium salts having different anions. Analytical methods viz. fluorescence, FTIR and dynamic light scattering (DLS) were used to monitor the salt-induced micellization. The hydration of respective anion and resultant contribution to its salting-out effect was found to be the governing factor in promoting micellization. The presence of salt decreases the CMC, CMT and phase separation temperature. The salts affect the aggregation process in agreement with an order mentioned in Hofmeister series. Keywords CMT Á Micelles Á Cloud point Á Hydrodynamic diameter Introduction Pluronics are commercially important symmetrical poly- ethylene oxide–block-polypropylene oxide–block-polyeth- ylene oxide symmetrical triblock copolymers, PEO–PPO– PEO, and have been of intense academic interest from the view point of their micelle formation, surface activity and phase behavior in recent years [1–9]. These are available in different molecular characteristics (%PEO and PPO molecular weight). Their availability with variable molec- ular weight of the middle PPO block and % composition (10–80% PEO) lead to surface active agents with wide variations in hydrophilic hydrophobic balance (HLB) val- ues that meet the specific requirements of diverse appli- cations such as dispersion stabilizers, detergents, emulsifiers in controlling foam/lubricity, etc. Furthermore, their low toxicity and thermo reversible rheological behavior makes them useful in drug delivery systems. The dehydration of PEO and PPO with an increase in temperature favors micelle formation and micellar transi- tions. This strong temperature dependence on the aggre- gation characteristics of PEO–PPO–PEO is unique and therefore their functional properties can be optimized by proper adjustment of temperature. However, the tempera- ture variation is not often desirable for many surfactants applications. Another way to tune the micellar characteristics without varying the temperature is to add salt. The presence of inorganic salts [10–23] influences the micellar and phase behavior of nonionic surfactants. For certain copolymers unique changes in the aggregation pattern were observed that are not observed for other PEO-based nonionic sur- factants. Salt-induced micelle formation/transitions and improved solubilization in the presence of salt may provide useful applications to highly hydrophilic copolymers with a K. Patel (&) Á B. Bharatiya Á Y. Kadam Á P. Bahadur Department of Chemistry, Veer Narmad South Gujarat University, Surat 395007, India e-mail: keyurpatel81@rediffmail.com B. Bharatiya e-mail: bhaveshbharatia@yahoo.co.in 123 J Surfact Deterg (2010) 13:89–95 DOI 10.1007/s11743-009-1127-5