Structure and dynamics of hydrogels and organogels: An NMR spectroscopy approach

Hydrogels and organogels are semi-solid systems, in which a liquid phase is immobilized by a three-dimensional network composed of self-assembled, intertwined polymer/gelator fibers. Investigations pertaining to these systems have only picked up speed in the last few decades. Consequently, many burning questions regarding these systems, such as the specific molecular requirements guaranteeing gelation, still await definite answers. Nonetheless, the application of different hydrogels and organogels to various areas of interest, i.e., as drug delivery devices, has been quick to follow their discoveries. The use of NMR spectroscopy for the characterization of polymer hydrogels and organogels has recently seen enormous growth. The NMR measurements involving magic angle spinning (MAS) in the solid-state NMR, spin relaxation times, nuclear Overhauser enhancements (NOE), or multiple-quantum (MQ) spectroscopy, the pulse field gradient (PFG) technique and magnetic resonance imaging (MR1) allow obtaining the detailed information on morphology, molecular organization, specific interactions and internal mobility of constituents. This review aims at providing a global view and capabilities all of these NMR methods in comprehensive studies of hydrogels and organogels, with special emphasis on the interplay between the morphology and molecular mobility of constituents and the intermolecular interactions. (C) 2011 Elsevier Ltd. All rights reserved.