Microscale and macroscale diffusion of water in colloidal gels. A pulse field gradient and NMR imaging investigation

Article Abstract:

Water diffusion in Laponite gels was shown to occur with basically the same rate at short and long time and length scales, despite the complex hierarchical structure of the gel, using two nuclear magnetic resonance techniques, namely, pulsed-gradient spin-echo and magnetic resonance imaging. The water diffusion coefficient was also found to be only marginally smaller than that of bulk water, possibly due to the very open structure at all length scales of the gel made from small platelets. Results demonstrate the feasibility of measuring a macroscopic interdiffusion coefficient using an MRI-based technique.

Water, Colloids, Diffusion, Diffusion (Physics), Gelation

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Phase distribution during isothermal crystallization of polyethylene probed by solid-state proton NMR free induction decay

Article Abstract:

The use of the NMR free induction decay method to characterize the crystallization process of polyethylene is investigated. It is shown that the method allows the observation of the three different phases of crystallization. An extended Avrami model can be used to model the time development of different phases. Kinetic data on the crystallization process can also be determined via in situ NMR measurements.

Crystallization, Polyethylene

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