Journal of Colloid and Interface Science 292 (2005) 548–556 www.elsevier.com/locate/jcis Concentration, temperature, and salt-induced micellization of a triblock copolymer Pluronic L64 in aqueous media J.P. Mata a,∗ , P.R. Majhi b , C. Guo c , H.Z. Liu c , P. Bahadur a a Department of Chemistry, Veer Narmad South Gujarat University, Surat 395007, India b Department of Pharmaceutical Chemistry, School of Pharmacy, University of California, San Francisco, CA 94143, USA c Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100080, People’s Republic of China Received 18 March 2005; accepted 3 June 2005 Available online 15 July 2005 Abstract The effect of copolymer concentration, temperature, and sodium halides (NaI, NaBr, NaCl, and NaF) on micellization and micellar prop- erties of a poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) (PEO-PPO-PEO) amphiphilic copolymer (Pluronic L64: EO 13 PO 30 EO 13 ), was examined by different methods such as dye spectral change, Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), small angle neutron scattering (SANS), dynamic light scattering (DLS), viscosity, and cloud point (CP). Temperature/polymer concentration/salt dependent aggregation behavior of L64 was observed. The data on critical micelle concentra- tion (CMC), critical micelle temperature (CMT), (CP), micelle size, and shape are reported. The Fourier transform infrared (FTIR) showed temperature dependent changes in C–O–C stretching variation band towards higher wave numbers and broadening of band width during the micellization process; this was attributed to increase in proportion of the anhydrous methyl groups, while the proportion of the hydrated methyl groups was decreased. Differential scanning calorimetry (DSC) provides CMTs and CPs from the same experiment. CMC values de- rived from dye spectral change, decrease significantly with the addition of salt. The increases in salt/copolymer concentration lower the onset temperature of micellization (CMT). Halide anions influence both CMT and CP in the order of F − > Cl − > Br − > I − when total salt and copolymer concentration kept constant. SANS results show the increase of inter-micellar interaction due to the increase in temperature/salt concentration; this is supported by viscosity data.  2005 Elsevier Inc. All rights reserved. Keywords: Pluronics; Cloud points; Inter-micellar 1. Introduction Pluronics viz. poly(ethylene oxide)-b-poly(propylene ox- ide)-b-poly(ethylene oxide) (PEO-PPO-PEO) triblock co- polymers are commercially available in a variety of mole- cular weights and EO/PO ratios [1]. These polymeric sur- factants form micelles with hydrophobic core consisting of PPO blocks and these are surrounded by an outer shell of the hydrated PEO above critical micelle concentration (CMC) in water and salt solutions [2–7]. The formation of the copoly- * Corresponding author. Fax: +91 261 2256012. E-mail address: jitendramata@yahoo.com (J.P. Mata). mer micelles is an extremely temperature dependent process resulting in a dramatic decrease of the CMC upon a small increase in temperature. This arises because of the tem- perature dependent difference in the hydration of the EO and PO blocks. The hydrophobic/hydrophilic character of the copolymer in aqueous solution can be altered by vary- ing the solution temperature or modifying the properties of aqueous solvent. As a result, amphiphilic copolymers have found widespread application in emulsification, solubiliza- tion and controlled release and product formulation in indus- tries ranging from agriculture to pharmaceuticals [4,8–10]. Strongly concentration/temperature dependent micellar be- havior of PEO-PPO-PEO block copolymers in water has been reported [5–12]. Salts have profound effect on solu- 0021-9797/$ – see front matter  2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2005.06.013