Dynamic IR linear dichroism

Figure 1-3 shows a schematic diagram of a dynamic IR linear dichroism (DIRLD) experiment [20-25] which provided the foundation for the 2D IR analysis of polymers. In DIRLD spectroscopy, a small-amplitude oscillatory strain (ca. 0.1% of the sample dimension) with an acoustic-range frequency is applied to a thin polymer film. The submolecular-level response of individual chemical constituents induced by the applied dynamic strain is then monitored by using a polarized IR probe as a function of deformation frequency and other variables such as temperature. The macroscopic stress response of the system may also be measured simultaneously. In short, a DIRLD experiment may be regarded as a combination of two well-established characterization techniques already used extensively for polymers dynamic mechanical analysis (DMA) [26, 27] and infrared dichroism (IRD) spectroscopy [10, 11]. 

Here the terms AA v) and AA v) are referred to as the in-phase spectrum and the quadrature spectrum of the dynamic IR linear dichroism, respectively. The two orthogonal spectra are related to the amplitude, AA(v), and loss angle, /S(v) by... 

Dynamic IR linear dichroism (DIRLD) studies have been made using a rapid-scan interferometer system. For dynamic strain frequencies achievable are between 0.1 Hz and 10 kHz step-scan interferometers are useful. 

No.21, 19th Oct.1999, p.7147-55 STATIC AND DYNAMIC FT-IR LINEAR DICHROISM STUDIES OF PLASTICIZATION EFFECTS IN A POLYURETHANE ELASTOMER... 

Figure 1-3. Schematic diagram of the dynamic infrared linear dichroism (DIRLDi experiment 23], A small-amplitude sinusoidal strain is applied to a sample, and submolecular level reorientation responses of chemical moieties are monitored with a polarized IR beam.

In this chapter, electrochemical properties of ET proteins at electrode interfaces studied by spectroelectrochem-ical techniques are described. In situ spectroelectrochemical techniques at well-defined electrode surfaces are sufficiently selective and sensitive to distinguish not only steady state structures and oxidation states of adsorbed species but also dynamics of reactants, products, and intermediates at electrode surfaces on a monolayer level. The spectroelectrochemical techniques used in studies of ET proteins include IR reflection-absorption, potential-modulated UV-vis reflectance (electroreflectance), surface-enhanced Raman scattering (SERS) and surface plasmon resonance, total internal reflection fluorescence, (TIRE) and absorbance linear dichroism spectroscopies. 

In dynamic IR dichroism experiments, a change of the dipole transition moments of functional groups is induced by a small external time-dependent mechanical perturbation. In order to ensure a linear viscoelastic response, the oscillatory strain amplitude is typically well below 1.0%. When the perturbation is small, the time-dependent IR /l(v, t) can be written as a sum of two independent absorptions ... 

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