Micellization behavior of an amphiphilic ethylene oxide-propylene oxide-ethylene oxide tri-block copolymer Pluronic P85 [(EO)(26)(PO)(39)(EO)(26)] in aqueous solution and in the presence of a hydrophobic C(14)diol (also known as Surfynol (R) 104) was examined by physico-chemical methods such as viscometry, cloud point (CP) and scattering techniques viz. dynamic light scattering (DLS) and small angle neutron scattering (SANS). The addition of diol decreases the cloud point and gelation temperature of aqueous Pluronic P85 copolymer solution. DLS and SANS measurements of the polymer in aqueous solution indicated micellar growth and sphere to rod transition in the presence of diol. Surfynol (R) 104 is a sparingly water soluble chol surfactant with a solubility of similar to 0.1 wt%. However, up on addition to Pluronic solution, diol gets incorporated in the block copolymer micelles and leads to structural transition of the micelles. An increase in the temperature and the presence of added sodium chloride in the solution further enhances this effect. The addition of hydrophobic C(14)diol increases the hydrodynamic size and aggregation numbers of the micellar system. The micellar parameters for the copolymer in the presence of C(14)diol are reported at different temperatures and added sodium chloride concentrations. (C) 2008 Elsevier Inc. All rights reserved.