Rouse dynamics in PEO-PPO-PEO block-copolymers in aqueous solution as observed through fast field-cycling NMR relaxometry. (15th August 2018) - Fraenza, Carla C.
Abstract: We present a proton fast field-cycling (FFC) NMR relaxometry study of the molecular dynamics in three different deuterated water-dispersed triblock copolymers of ethylene oxide (EO) and propylene oxide (PO):EO80 PO27 EO80 (F68), EO141 PO44 EO141 (F108), and EO101 PO56 EO101 (F127). Independently of the phase and molecular arrangement, bi-exponential decays of the magnetization during the spin-lattice relaxation process could be observed for F127, while mono-exponential decays were measured for F68 and F108. This fact has been attributed to the relative ratio of PEO and PPO protons for each case. In F127, each component of the magnetization decay could be associated with a particular block of the co-polymer. A direct consequence of this fact is the independent characterization of the molecular dynamics of each block. It was found that the dominant relaxation mechanism can be attributed to the Rouse model, and it seems to be independent on whether the molecules are incorporated into a micelle, or as individual unimers in the aqueous solution. The experimental results and the provided explanation are consistent with entanglement-free self-assembled structures, and a fast exchange of unimers between the micellar structure and the solvent. This particular feature was also investigated in F68 and F108, although for these cases a mono-exponential decay of the magnetization was observed. NMR relaxometry results are complemented with other relaxation experiments in the rotating frame, NMR spectroscopy and atomic-force microscopy. Graphical abstract: Image 1 Highlights: Deuterated water-dispersed triblock copolymers where studied using proton fast field-cycling (FFC) NMR relaxometry. Copolymers composed of ethylene oxide (EO) and propylene oxide (PO) were considered: F68, F108 and F127. Nuclear magnetic relaxation properties of PEO and PPO blocks can be individually analyzed in the case of F127. The observed relaxation dispersions could be consistently explained with the Rouse model.