Dynamical processes in solids

Another technique that has been employed for studying certain types of changes in solids is infrared spectroscopy, in which the sample is contained in a cell that can be heated. By monitoring the infrared spectrum at several temperatures, it is possible to follow changes in bonding modes as the sample is heated. This technique is useful for observing phase transitions and isomerizations. When used in combination, techniques such as TGA, DSC, and variable-temperature spectroscopy make it possible to learn a great deal about dynamic processes in solids. 

Y. Toyozawa, Dynamical Processes in Solid State Optics, R. Kubo and H. Kamimura, Eds., Syokabo Tokyo, 1967, p. 90. 

Furthermore, neutron scattering techniques, viz. quasielastic neutron scattering, are a valuable tool for studying other dynamic processes in solid hydrate research, such as rotatory and translatory diffusion of water molecules and hydrogen atoms, respectively (see, for example. Refs. 10, 32, 33). 

Toyozawa, Y. Dynamical Processes in Solid Optics (Kubo, R., Kamimura, H., eds.), p. 90-115, Tokyo, Syokabo, 1967... 

Dynamical processes in solids, including vibrational properties and atomic diffusion are of obvious interest and importance, not only in a crystallographic context but in broader aspects of materials science. Chapter 4 therefore focuses on the application of molecular dynamics simulation techniques in the explicit modelling of the atomic dynamics of solids. 

H. Kuroda, in Dynamic Processes in Solid Surfaces" (ed. K. Tamaru), Plenum Press, New York, p.51, 1985... 

Braga. D. Dynamical processes in solid organometallic compounds. Chem. Rev. 1992. 92. 369-685. 

In [305,306,311,327], the effects of a static magnetic field (2 or 4 kOe) on creep processes at room temperature in linear and cross-linked glassy polymers (basically within or close to the p-relaxation region) were revealed and studied on the microscopic level. This became possible owing to using the LICRM setup and decrease in the relaxation times of dynamic processes in solid polymers under the action of mechanical forces. 

The solid phase presents some fundamental differences from liquid and gas phases. First, the effect the solid has on the electronic structure of a sorbate can be profound (e.g., H2 chemidissociation on metals). Thus new processes may be energetically accessible in solid-state systems that are not important in liquid or gas phases. Second, dynamical processes in solid-state systems can be significantly different from those in liquid or gas phases. The average environment that a solute molecule encounters in gas and liquid phases is translationally invariant. This is not true for the solid with well-defined lattice sites e.g., the average environment a solute molecule sees near a lattice site is very different from that near an interstitial site. Therefore, diffusion of sorbates in or on a solid can often be treated as isolated jumps between well-defined sorption sites, and the diffusion constant can be approximated from the rate constants for isolated jumps. 

The CP/MAS NMR technique is also useful for investigating dynamic processes in solids such as re-orientational processes and structural phase transitions an example of solid-state phase transition monitored by variable temperature Sn CP/MAS is given by Me3Sn-C=C-C=C-SnMe3, for which a structural phase change occurs in the temperature range 232-248K. 

Adsorption is a dynamic process in which some adsorbate molecules are transferring from the fluid phase onto the solid surface, while others are releasing from the surface back into the fluid. When the rate of these two processes becomes equal, adsorption equilibrium has been established. The equilibrium relationship between a speeific adsorbate and adsorbent is usually defined in terms of an adsorption isotherm, which expresses the amount of adsorbate adsorbed as a fimetion of the gas phase coneentration, at a eonstant temperature. 

In polymers one will often particularly be interested in very slow dynamic processes. The solid echo technique just described is still limited by the transverse relaxation time T being of the order of a few ps at most. The ultimate limitation in every NMR experiment however, is not T but the longitudinal relaxation time T, which for 2H in solid polymers typically is much longer, being in the range 10 ms to 10 s. The spin alignment technique (20) circumvents transverse relaxation and is limited by Tx only, thus ultraslow motions become accessible of experiment. 

For solid surfaces interacting in air, the adhesion forces mainly result from van der Waals interaction and capillary force, but the effects of electrostatic forces due to the formation of an electrical double-layer have to be included for analyzing adhesion in solutions. Besides, adhesion has to be studied as a dynamic process in which the approach and separation of two surfaces are always accompanied by unstable motions, jump in and out, attributing to the instability of sliding system. 

The most important experimental task in structural chemistry is the structure determination. It is mainly performed by X-ray diffraction from single crystals further methods include X-ray diffraction from crystalline powders and neutron diffraction from single crystals and powders. Structure determination is the analytical aspect of structural chemistry the usual result is a static model. The elucidation of the spatial rearrangements of atoms during a chemical reaction is much less accessible experimentally. Reaction mechanisms deal with this aspect of structural chemistry in the chemistry of molecules. Topotaxy is concerned with chemical processes in solids, in which structural relations exist between the orientation of educts and products. Neither dynamic aspects of this kind are subjects of this book, nor the experimental methods for the preparation of solids, to grow crystals or to determine structures. 

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