Pulsed Field Gradient NMR Studies of Diffusion in Polymer Gels

Abstract: Soft biomaterials, such as gels, play an important role in different kinds of products and applications, in particular in drug delivery systems, health care products, and food. Polymer gel's great ability to control mass transport is applied on e.g. the uptake of liquids in diapers. Diffusion is one of the most essential transport mechanism, e.g. for releasing active substances. In this work, pulsed field gradient nuclear magnetic resonance (PFG NMR) techniques have been used to study diffusion on different time and length scales. The polymer strand radius, an important microstructural feature, has been extracted from reduced diffusivity in various alginate gels. The results agree well with the polymer strand radii obtained from image analysis of the corresponding transmission electron microscopy (TEM) micrographs. Chemical shift imaging (CSI), another PFG NMR method, has been used to monitor gel formation initiated by adding water to a non-aqueous cellulose solution. Diffusion rates of water molecules and fluoride ions have been obtained from one-dimensional profiles.