Molecular dynamics aging effects

The general experimental approach used in 2D correlation spectroscopy is based on the detection of dynamic variations of spectroscopic signals induced by an external perturbation (Figure 7.43). Various molecular-level excitations may be induced by electrical, thermal, magnetic, chemical, acoustic, or mechanical stimulations. The effect of perturbation-induced changes in the local molecular environment may be manifested by time-dependent fluctuations of various spectra representing the system. Such transient fluctuations of spectra are referred to as dynamic spectra of the system. Apart from time, other physical variables in a generalised 2D correlation analysis may be temperature, pressure, age, composition, or even concentration. 

The Landmann-unit structure of intercellular lipid lamellae is illustrated in Figure 28.1. This structure is found throughout nearly all of the normal SC. Swartzendruber et al. proposed a plausible molecular model that accounts for the electron-lucent and electron-dense lamellar structure of the Landmann unit.10 These Landmann units are dynamic in nature. At least in the inner and middle SC they are altered by age,19 disease,8 11 20-22 and hormonal status23,24 by experimental solvent treatment25-27 and topical inhibitor treatment.28,29 They are known to reform spontaneously following solvent extraction,5,26 and topical application of certain lipids is also reported to effect lamellar repair and barrier improvement.29-33... 

Calncci et al. (2004) studied the effects of accelerated aging of wheat seeds on structural and dynamic properties of dry and hydrated (ca. 10 wt% H2O) flour at a molecular level using high- and low-resolution solid-state NMR techniqnes (Figure 8.16). 

Since the first age of molecular beam scattering there has been a constant interest in the dynamics of metal atom-molecule reactive collisions. The effect of relative translational energy of reagents on reaction dynamics has been extensively studied. However a great majority of experiments has been devoted to alkali and alkali-earth reactions. The insight into the reactivity of other metal elements is comparatively less rich and this can be easily connected with the technical constraints associated with the generation of beams of these atoms. 

For better understanding the diverse relaxation behavior of confined polymers, researchers have utilized models or simulation tools to capture the kinetic features of the material at the molecular level, aiming to represent the results observed in experiments. The FVHD model, which has been widely employed in characterizing physical aging in bulk polymers, is reformulated to describe the relaxation behavior of polymers under nanoconfinement. A dual mechanism combines the effect of vacancy diffusion and lattice contraction, and was recently applied with time-dependent internal length scales to characterize the free volume reduction in the aging process [169]. The dual mechanism model (DMM) fits the data of thin film permeability fairly well. The potential predictive capability of the DMM model depends on the accuracy of the relationship between the internal length and time scale on the description of complex material dynamics [161]. 

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