Complex systems time-domain spectroscopy

With this chapter, we have intended to provide an introduction to the basics of solid-state NMR in application to wirious, very diverse problems in polymer science As has hopefully become obvious, almost innumerable NMR technictues are at ilable and are further developed. The complexity of NMR methods, however, is needed to cope with the complexity of today s polymer systems, both stmcturally and in their dynamics. Simple ID high resolution H and MAS spectra may be sufficient to identify the chemical components and unravel some details about chain statistics, configuration, and conformations. Technically, even less-demanding low-resolution time-domain spectroscopy may help to charaaerize mesoscopic stmctures in terms of volumes or sizes of nanosized domains in simple multiphase systems. 

The electronic absorption spectra of complex molecules at elevated temperatures in condensed matter are generally very broad and virtually featureless. In contrast, vibrational spectra of complex molecules, even in room-temperature liquids, can display sharp, well-defined peaks, many of which can be assigned to specific vibrational modes. The inverse of the line width sets a time scale for the dynamics associated with a transition. The relatively narrow line widths associated with many vibrational transitions make it possible to use pulse durations with correspondingly narrow bandwidths to extract information. For a vibration with sufficiently large anharmonicity or a sufficiently narrow absorption line, the system behaves as a two-level transition coupled to its environment. In this respect, time domain vibrational spectroscopy of internal molecular modes is more akin to NMR than to electronic spectroscopy. The potential has already been demonstrated, as described in some of the chapters in this book, to perform pulse sequences that are, in many respects, analogous to those used in NMR. Commercial equipment is available that can produce the necessary infrared (IR) pulses for such experiments, and the equipment is rapidly becoming less expensive, more compact, and more reliable. It is possible, even likely, that coherent IR pulse-sequence vibrational spectrometers will... 

This chapter concentrates on the results of DS study of the structure, dynamics, and macroscopic behavior of complex materials. First, we present an introduction to the basic concepts of dielectric polarization in static and time-dependent fields, before the dielectric spectroscopy technique itself is reviewed for both frequency and time domains. This part has three sections, namely, broadband dielectric spectroscopy, time-domain dielectric spectroscopy, and a section where different aspects of data treatment and fitting routines are discussed in detail. Then, some examples of dielectric responses observed in various disordered materials are presented. Finally, we will consider the experimental evidence of non-Debye dielectric responses in several complex disordered systems such as microemulsions, porous glasses, porous silicon, H-bonding liquids, aqueous solutions of polymers, and composite materials. 

Yet, when it comes to the dynamics of such systems, one quickly needs to adapt the experiment, mostly in order to lift the ambiguities inherent to the different NMR interactions that are active at the same time. Then, advanced methods such as H time-domain MQ spectroscopy, this particular example still being limited in application to simple polymers with only a few chemically distina components, becomes a tool to quantitatively smdy the chain dynamits, which is complex and encompasses a vast timescale range. 

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