A PFG NMR self-diffusion investigation of probe diffusion in an ethyl(hydroxyethyl)cellulose matrix

The translational dynamics of poly(ethylene oxide) (PEO), in ethyl(hydroxye thyl)cellulose (EHEC) solution and in a chemically cross-linked gel of EHEC , is investigated by means of pulsed field gradient (PFG) NMR. Two differen t matrix concentrations of EHEC are studied, 1 and 6 wt % in which the PEO concentrations are 0.01 and 0.06 wt %, respectively. The molar mass of PEO is varied from 10(4) to 10(6), and they are fairly monodisperse (typically M-w/M-n < 1.1). The echo decays for the PEO in the 1% EHEC solution show Ga ussian diffusion behavior as indicated by straight lines when the echo inte nsities are plotted vs the relevant parameters. This is also the case for P EO diffusing in the 6% EHEC solution matrix. For PEO diffusing in the 1% EH EC gel, a more complex situation is at hand. This is indicated by the obser vation of nonlinear echo decays for the PEG. The molar mass dependence of t he mean-square displacement is compared to scaling relations ((z(2)) = KM-a lpha) and to computer simulations by Baumgartner and Muthukumar for heterog eneous systems. For the 1% EHEC solution and gel, the (z(2)) dependence on the molar mass shows power law scaling with alpha approximate to 1. For the case when the EHEC solution matrix is 6%, a more complex behavior is seen, as revealed by a different functional form for the (z(2)) dependence on th e molar mass. These observations are discussed in terms of polymer diffusio n inside a heterogeneous matrix.