Su içinde PEO-PPO-PEO triblock kopolimerleri: Miselizasyonları ve fiber şeklindeki çökeltilere kendinden yapılanmaları

Physicochemical properties of aqueous poly (ethylene oxide)-poly (propylene oxide)-poly(ethylene oxide) (PEO-PPO-PEO) triblock copolymers, commonly known as Pluronics, have long been studied. The phase diagram of micellar structures is well-known and these structures were exploited in various applications ranging from drug delivery systems to mesoporous metal oxide synthesis. In this thesis, micellization and the self-assembly of Pluronic F127, (PEO)106-(PPO)70-(PEO)106 in dilute aqueous solutions have been investigated. Formation of fiberlike aggregates below the critical micelle temperature (Tcm) has been observed for the first time. To understand the factors affecting this unexpected self-assembly into fiberlike aggregates, micellization of Pluronic F127 has been systematically studied by Dynamic Light Scattering (DLS) as a function of polymer concentration and in the presence of five different sodium salts. Tcm decreased linearly with salt concentration in aqueous solutions containing kosmotropic anions CO3 2-, CH3COO- and Cl-. In the presence of chaotropic SCN- and I- anions, Tcm increased with salt concentration. Similar trends have also been observed for Pluronic F68, (PEO)80-(PPO)30-(PEO)80, which showed ~30 oC higher Tcm compared to Pluronic F127 due to its higher PEO content. The formation of water-insoluble self-assembled fiberlike aggregates of Pluronic F127 below Tcm is difficult to understand considering the facts that both PEO and PPO are water soluble. Unexpected clustering of PEO in aqueous solutions has previously been reported. To understand whether PEO clustering plays any role in the formation of fiberlike aggregates, aqueous solutions of PEO having five different molecular weights were also investigated by DLS. A transition from good solvent to theta solvent conditions with increasing temperature was observed at ~40-45 oC. In some experiments, aggregation of PEO was also observed in the same temperature range. Though it is not possible to relate these observations directly to self-assembly of fiberlike aggregates at 25 oC, the early stages of such PEO clustering may be inducing the seeds of self-assembly.