NMR relaxation and self-diffusion in aqueous micellar gels of pluronic F-127
M M Shaikhullina, Aliya V. Khaliullina, Rustam Gimatdinov, Anatoly Butakov, Vladimir M. Chernov, Andrei Filippov
Abstract
We studied the transverse NMR relaxation of protons of different chemical groups and diffusion of molecules in an aqueous pluronic F-127 system. The system was studied at concentrations of 15, 21 and 28 wt% and in the temperature range of 293–333 K. The dynamic peculiarities in different phases were analyzed based on the NMR relaxation and diffusion data. Our study demonstrated a correlation between phase states, T 2 relaxation times of “solid-like” and “liquid” protons of selected chemical groups of polypropylene oxide (PPO) and polyethylene oxide (PEO) blocks, and diffusion coefficients . Transverse NMR relaxation established that the presence of a “solid-like” component of CH 3 protons of PEO blocks is observed only at temperatures and concentrations corresponding to the rigid-gel phase, due to entanglements between micellar coronas. At all temperatures and concentrations, some CH 3 protons of PPO blocks and some CH 2 protons of PEO blocks show “liquid-like” transverse NMR relaxation. Under the conditions corresponding to formation of the rigid-gel phase of the pluronic , relaxation of the “liquid-like” protons additionally accelerates due to entanglements of micellar coronas. Transition of the system to the rigid-gel phase is accompanied by decrease of diffusion coefficients by a factor of 10–10 4 relative to the diffusivity of free-moving pluronic micelles in the sol phase. Diffusion measurements show that there are pre-transition phenomena, which are characteristic for temperatures and concentrations near sol-gel phase boundaries .