The rheological properties of Pluronic F68 were dissolved in various water/organic liquid mixtures over a wide range of temperatures, all at a concentration of 20？mg/mL. We have considered the following binary mixtures: Pluronic F68/water, F68/p-xylene, and F68/phenol. Various conformational transitions were detected and interpreted. We have also shown that these mixtures retain a Newtonian behavior independently of temperature and conformational changes. For ternary F68/p-xylene/water, F68/phenol/water, and F68/water/phenol mixtures, the behaviour of the solution is intimately related to the temperature and the amount of water and organic solvent added. 1. Introduction The triblocks copolymers based on poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide), usually named Pluronics (manufactured by BASF) or Poloxamers (manufactured by ICI), are able to form direct micelles with PEO coronas and PPO cores or reverse micelles with PEO cores and PPO coronas under some conditions. The investigation of their association properties has had considerable ambiguity due to the fact that some of them are able to form direct micelles, reveres micelles, and various arrangements under several conditions, whereas some of them showed that the dimension of the structures formed was equal to the length of the hydrophobic stretched blocks [1–9]. In this regard, the critical micelle concentration, the critical micelle temperature, the aggregation number, and the polydispersity are usually given with a certain uncertainty [3]. These triblocks copolymers constitute an interesting class of surfactants which have attracted considerable attention due to their possible use in many specialized applications, for example, in the pharmaceutical industries [10] and bioprocessing [11]. In the last few years several experimental and theoretical works have been directed at the investigation of binary Pluronic/organic solvent and ternary Pluronic/water/organic solvents due to the profound changes observed in the solution properties and their wide domain of application [12–15]. Three topics characterizing these systems, namely, (i) the effect of the copolymer architecture on the association behavior [16, 17], (ii) the anomalous micellization and composition [18, 19], and (iii) the reverse micelles caused by the water presence [20], are the subject of numerous studies. For example, Ghaouar et al. [1] used dynamic light scattering and viscosity measurements for the Pluronics L64 and F68 dissolved in aqueous and organic solvent for various concentrations. To investigate their
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