Orientation Distribution of Molecules: Characterization and Experimental Determination by Means of Magnetic Resonance
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Applied Magnetic Resonance
REVIEW
Orientation Distribution of Molecules: Characterization and Experimental Determination by Means of Magnetic Resonance Natalia A. Chumakova1 · Andrey Kh. Vorobiev1 Received: 25 June 2020 / Revised: 2 August 2020 © Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract The article presents a comparative review of experimental methods used for characterization of orientational ordering of the molecules in a partially aligned media. The optical, X-ray and magnetic resonance techniques are considered. The potential and limitations of different approaches are discussed. The magnetic resonance is concluded to be the most informative technique for detailed characterization of the molecular orientation distribution.
1 Introduction Interest on determination of the orientational molecular alignment is growing now in course of the extensive fundamental study of spatially organized media and the design of new applied materials. The properties of substances and materials organized at molecular level such as stretched polymers, liquid crystals, biological or synthetic membranes etc. are largely governed by the orientational ordering of molecules. In this regard, urgent problem for physical chemistry and chemical physics is the development of experimental methods for the quantitative structural characterization of the partially ordered soft matter. This review is devoted to the comparative description of various methods for study of the partially ordered materials. At present, the most common methods used for the experimental characterization of the molecular orientational ordering are birefringence, various types of optical spectroscopy, X-ray absorption and diffraction, as well as nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR). In the present review the comparative analysis of various approaches developed for characterization of the orientational ordering is presented. We will show that magnetic resonance spectroscopy is the most
* Natalia A. Chumakova [email protected] 1
Chemistry Department, Moscow State University, Leninskie Gory 1‑3, Moscow 119991, Russia
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N. A. Chumakova, A. K. Vorobiev
informative method for investigation of systems with sophisticated orientation distribution of molecules.
2 Quantitative Description of Molecular Orientational Ordering There are various ways to describe of the orientational ordering of molecules in a sample. The most frequently used characteristics of the molecular orientational alignment are the orientation distribution function, the Herman’s orientation factors, the elements of Saupe matrix and the White–Spruiell orientation factors. The detailed description of these functions is presented in [1–4]. The orientation of a molecule with the arbitrary symmetry relative to the sample coordinate system can be specified by the three Euler angles (α, β, γ) that transform the sample reference frame to the molecule reference frame. The most detailed characteristic of the orientati
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