A comparative study on the effect of structural variations of co-solvent on the Tetronic® micelles with widely different hydrophobicity

Abstract Here we report, a comparative study on the micellization and phase behavior of two commercially available ethylene oxide – propylene oxide (EO-PO) octablock copolymers, Tetronics ® 1304 and 1307 (hereafter written as T1304 and T1307), in the presence of 2,2,2‑trifluoroethanol (TFE) and ethanol (EtOH) using cloud point (CP), dynamic light scattering (DLS), high sensitivity differential scanning calorimetry (HSDSC), relative viscosity and Langmuir film balance. These copolymers fabricated with almost the same PO block length vary in their EO chain lengths and hence display different characteristics. T1304 shows a more hydrophobic character and forms micelles at ambient temperature while T1307, due to longer EO chain length, exhibits high hydrophilicity and faces difficulty in forming micelles which results into high polydispersity in the aqueous system. In the presence of co-solvents TFE and EtOH, however a more interesting behavior is noted. T1304, as evident from DLS and viscosity measurements, displays micellar growth in the presence of TFE, while the presence of EtOH induces micellar breakdown. Though, in case of T1307, presence of TFE improves micellization and a single micellar peak becomes evident in the DLS stacks, no micellar growth can be noticed both through DLS and relative viscosity, which is possibly due to its highly hydrophilic character. Likewise, presence of TFE depresses the CMT in both the copolymers while EtOH increases it. A similar trend is also justified by π-A isotherms form Langmuir monolayers.