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NMR imaging and relaxation study of polymer swelling and chain dynamics

1988; Elsevier BV; Volume: 38; Issue: 3-4 Linguagem: Inglês

10.1016/0167-7322(88)80017-5

1873-3166

Thomas H. Mareci, Sune Dønstrup, A. Rigamonti,

Rheology and Fluid Dynamics Studies

A Fourier NMR imaging sequence with T1 and T2 contrast, high-resolution spectra and spin-lattice relaxation measurements are used to study the swelling process of polymethylmetacrylate in chloroform and the dynamics of the swollen polymer chain, in real-time. It is shown that the swelling process occurs in a way similar to a surface melting, through a kind of first-order phase transition which generates a layer of mobile polymer chains around the solid, without divergent behavior of the spin-lattice relaxation rate. Insights into the dynamics of the polymer chains in the region being swollen is provided by local T1 measurements. The relaxation rates for the protons of the swollen polymer chains are related to the segmental dynamics on the basis of the semi-phenomenological “blob” model of de Gennes. For the decay rate of the long-wavelength fluctuations, a hydrodynamic-type behavior for wavevector q ≦ ξ−1 (ξ, concentration dependent characteristic length scale) has been considered. While for larger q, a simple q3-dependence has been assumed. Thus, the concentration and ωL-dependence (ωL, measuring frequency) of the relaxation rate is derived. It is argued that the decay rates for wavevectors in the range 106–107 cm−1 are the most effective in the spin-lattice relaxation process, thus pointing out a role for these NMR results, somewhat complementary to the recent light scattering measurements carried out for equilibrium solutions of polymers.