Investigation of swelling and diffusion in polymers by H-1 NMR imaging: LCP networks and hydrogels

The kinetics of diffusion in polymers ranges from simple Fickian diffusion to higher-order diffusion, such as Case II diffusion. The conventional meth od for determining the characteristics of the diffusion of solvents into po lymer matrices is by measuring the mass uptake of the polymer while the sol vent penetrates the matrix. However, since such measurements perform observ ations at a macroscopic level, little information has been obtained relatin g to the properties of the solvent inside the polymer matrix and the mechan isms of the processes that control the diffusion. Nuclear magnetic resonanc e (NMR) imaging (MRI) is used to monitor the transport of solvents into sol id systems in real-time. The method provides a one- or more-dimensional ima ge of the density and the mobility of the solvent in a material. Furthermor e, the mobility of network chains itself changes due to the softening influ ence of the solvent. The former (imaging of the solvent) can be used for a quantitative measurement of the diffusion coefficient whereas the observati on of the network gives information about changes in the network properties (mobility, decrystallization) during the swelling process. The potential a pplicability of the NMR imaging techniques to polymer gel systems is demons trated on the diffusion of organic solvents in polymeric materials like nat ural rubber, nematic-like networks, and hydrogels. (C) 2000 Elsevier Scienc e B.V. All rights reserved.