A review of the use of simple time-domain NMR/MRI for material-science

Abstract

The intention of this discussion is as a simple introduction for general—non-nuclear magnetic resonance (NMR)-specialist—materials scientists, to make them aware as to how some of the materials science measurements that they need to make might possibly be addressed by simple physical measurements using low-cost time-domain NMR apparatus. The intention is to include a minimum of complex NMR detail, while enabling general material-scientists to see that simple easily understood time-domain NMR might be of use to them. That is how I have tried to structure this discussion. It seems to me be generally forgotten how much of materials science is actually physics, as opposed to chemistry, and the extent to which simple time-domain NMR may be used to make measurements of the physical properties of materials. There frequently seems to be an assumption that if NMR is mentioned that it is chemical analysis methods that are under discussion, or possibly magnetic resonance imaging (MRI). These are both extremely powerful techniques, but to forget about the physics that often governs the properties of the sample can be a significant mistake. Key material science properties are often described in different fields using the terms mobility/dynamics/stiffness/viscosity/rigidity of the sample. These properties are usually dependent on atomic and molecular motion in the sample. We will discuss a method, time-domain NMR, that appears often to be ignored, to obtain quantitative or comparative information on these properties. The intention of this paper is not to probe the material properties of some interesting system, but to discuss in as clear a manner as possible a particular technique, “low-field time-domain NMR”, to bring this technique and its advantages to the attention of other material scientists. Thus we discuss time-domain NMR and MRI, as methods of measuring the physical properties of liquid and solid materials. Time-domain NMR is also a good technique for measuring pore-size distributions from the nano-meter to microns, using a technique known as NMR cryoporometry (NMRC). Standard MRI protocols may be combined with NMRC, so that spatial resolution of pore dimensions may also be obtained. Low-field time-domain NMR is, at its fundamentals, a very approachable and easily comparative technique, where the material properties may often be extracted from the time-domain data much more simply than from say high-field high-resolution spectral data. In addition, low-field time-domain NMR apparatus is typically a factor of 10 to 100 times cheaper than high-field high-resolution solid-state NMR systems.