Application of electric fields in NMR

Abstract

Anisotropic orientation states in materials such as liquid crystals, liquid crystalline polymers or polymeric electrets can be induced by the application of electric fields. This behaviour is exploited extensively in displays or sensors. Anisotropic optical properties induced by relatively high electric field strengths are used in the well known displays made from liquid crystalline materials. The anisotropy of electric properties in polymeric materials gives rise to properties such as the high piezoelectricity of fluorine containing electrets. Attempts have been made to investigate the orientational state induced by electric fields after poling using NMR techniques. However, there is only access to the irreversible part of the electrically induced orientation. In-situ application of (high) voltages during NMR experiments enables the investigation of the influence of the electric field on molecular orientational states or electrically-induced morphological changes. The NMR methods have been modified to investigate the dynamics of reorientation processes in electric fields and to extend the possible time range towards below1ms. The application of high voltages in NMR experiments requires experimental specifications. Some of our experiences are outlined in this paper.