A novel concept in vibrational spectroscopy called two-dimensional infrared (2D IR) spectroscopy is described. In 2D IR, a spectrum defined by two independent wavenumbers is generated by a cross-correlation analysis of dynamic fluctuations of IR signals induced by an external perturbation. 2D IR spectra are especially suited for elucidating various chemical interactions among functional groups. Notable features of the 2D IR approach are: simplification of complex spectra consisting of many overlapped peaks; enhancement of spectral resolution by spreading peaks over the second dimension; and establishment of unambiguous assignments through correlation analysis of bands selectively coupled by various interaction mechanisms. The procedure for generating 2D IR correlation spectra and the properties of the 2D spectra are discussed in detail. Examples of 2D IR spectra are presented for atactic polystyrene and the proteinacious component of human stratum corneum to demonstrate the utility of this technique.

Two-Dimensional Infrared (2D IR) Spectroscopy: Theory and Applications

Fabrication of aligned and molecularly oriented electrospun polyacrylonitrile nanofibers and the mechanical behavior of their twisted yarns

Publisher Summary This chapter describes the various aspects of the vibrational spectra of carbohydrates. Vibrational spectroscopy is one of the techniques most adapted techniques for the study of hydrogen bonding, which is the indicator of molecular interaction in the aqueous solutions of sugars. A polyatomic molecule, such as sugar, may be regarded as a system of masses joined by bonds having spring-like properties. The vibration of each of the masses (atoms) can be resolved into components parallel to the x, y, and z axis of a Cartesian system of coordinates. The harmonic approximation is applied in which any motion of the molecule is resolved in a sum of displacements parallel to the Cartesian coordinates and these are called “fundamental, normal modes of vibration.” The analysis of crystallographic results shows the important role played by anomeric center in the structure of sugars. Infrared dichroism in polysaccharides was applied to obtain information on the orientation of chemical groups in the crystalline structure. The computational calculation of the frequencies of carbohydrates' vibration is also elaborated in the chapter.

Vibrational spectra of carbohydrates.

The authors review the results of extensive studies that have been reported by the author and by other workers on the preparation and properties of the conjugated polymer poly(p-phenylenevinylene) (PPV). The use of the sulphonium polyelectrolyte precursor-route synthesis gives considerable flexibility for materials processing and it is shown that high-quality samples of controlled morphology, crystallinity, orientation and length of uninterrupted conjugated sequences can be obtained through a suitable choice of preparation conditions. Where applicable, the experimental results are compared with those obtained from theoretical calculations and any discrepancies are discussed.

https://iopscience.iop.org/article/10.1088/0022-3727/20/11/007/pdf

Precursor-route poly(p-phenylenevinylene): polymer characterisation and control of electronic properties

A spectrometer for detecting dynamic infrared linear dichroism (DIRLD) induced by a small-amplitude oscillatory strain is described. The strain-induced dynamic variations of absorbance and linear dichroism, as well as the normal static absorbance and dichroism, are measured simultaneously as functions of IR wavenumber, temperature, and strain frequency. The phase (temporal) relationships between the dynamic optical signals and the applied strain are also obtained. The instrument is sensitive enough to detect dynamic optical signals on the order of 10−4 absorbance units with a time resolution of about 14 μs. The dynamic dichroism signals arise from the strain-induced temporary reorientation of dipole-transition moments associated with the molecular vibrations of chemical functional groups. Both the rate and extent of reorientations are strongly influenced by the local molecular environment of the functional groups. Because of the specificity of IR absorbance bands to the individual submolecular structures, DIRLD spectroscopy is especially suited for the study of the intra- and intermolecular interactions and the detection of subtle changes in the local molecular environment. Example DIRLD spectra of atactic polystyrene are presented to demonstrate the potential utility of this spectroscopic technique.

A Spectrometer for Measuring Time-Resolved Infrared Linear Dichroism Induced by a Small-Amplitude Oscillatory Strain

The mechanical properties of polymers are strongly influenced not only by the structure of the material but by the magnitude of the molecular orientation. Thus a great deal of interest exists in information about the molecular orientation in samples introduced by drawing or other forming processes. Several techniques of evaluation of this orientation exist such as birefringence, x-ray diffraction, sonic modulus, and fluorescence measurements [l, 2]. Vibrational analysis of oriented polymers provides a method of determining independently the molecular orientation both in the crystalline and amorphous phases of polymers. By using vibrational techniques, a number of macromolecules have been studied in the solid state for a variety of different processes. It is the purpose of this review to summarize the recent theoretical and experimental results which have occurred since the review of Zbinden [3]. Infrared and Raman measurements will be reported since they are complementary to each other in their a...

B. Jasse

Papers

Orientational Measurements in Polymers Using Vibrational Spectroscopy