Thermoresponsive phase behavior in normal and reverse Pluronic® and their mixed systems

Self-assembly generation in ethylene oxide (EO) - propylene oxide (PO) - based linear block copolymers (BCPs) in aqueous solution is examined by various techniques. Here, the aqueous solution behavior of normal Pluronics® viz. L31, L64, L35, P65 and reverse Pluronics® viz. 31R1, 17R4, 25R4, 10R5 with different molecular characteristics, hydrophilic-hydrophobic ratio was scrutinized in single and mixed systems. Solutions up to 10 %w/v as single and mixed systems remain clear transparent up to ambient temperature. On progressive heating these micellar solutions undergo phase separation (2ϕ) i.e. Cloud Point (CP) which was further complemented by scattering outline using dynamic light scattering (DLS) and small-angle light scattering (SANS). Normal Pluronic® L31 (low. mol. wt. PPO and 10 % PEO) essentially behaves like PPO homopolymer and phase separation at ~ 30 °C without any micelle formation. L64, L35 and P65 (increasingly hydrophilic) formed micelles at high temperatures with some growth close to CP. None of the reverse Pluronics® (31R1, 17R4, 25R4, 10R5) form micelles even at temperature close to CP. The proposed micellar scheme was also examined for mixed system (L31:31R1, L64:17R4, L35:10R5 and P65:25R4) in varying ratios (1:0, 0.25:0.75, 0.5:0.5, 0.75:0.25 and 0:1) giving an account to similar/ close details of molecular weight or hydrophobicity. Mixed micelles were formed and the results depicted the proper mixing of two BCPs in single geometry. For all BCPs as a single and mixed system, the hydrodynamic diameter (Dh) of unimers (~ 3-6 nm), spherical micelles (~ 8-16 nm), ellipsoidal/ rod-like micelles (> 30 nm) and clusters (> 1000 nm) as a function of temperature was evaluated from DLS and auxiliary reinforced by SANS are reported. Furthermore, these micellar aggregates were looked upon as potential nanocargos for anticancer (Curcumin) drug solubilization which was estimated using UV-vis spectroscopy. (author)