Dynamic processes investigated

More systematic study of the dynamics of radicals in solution should now be possible using CIDNP. Investigations so far reported have indicated that the rates of very rapid chemical reactions and other dynamic processes undergone by radicals can be measured in a crade way greater refinement should be possible. Special effects have been predicted for reactions in thin films (Deutch, 1972). Moreover the time-scale of polarization is such that the technique may prove capable of throwing new light on the dynamics of excited states. 

Anastasijevic NA, Baltruschat H, Heitbaum J. 1989. DBMS as a tool for the investigation of dynamic processes Galvanostatic formic acid oxidation on a Pt electrode. J Electroanal Chem272 89-100. 

The few examples of deliberate investigation of dynamic processes as reflected by compression/expansion hysteresis have involved monolayers of fatty acids (Munden and Swarbrick, 1973 Munden et al., 1969), lecithins (Bienkowski and Skolnick, 1974 Cook and Webb, 1966), polymer films (Townsend and Buck, 1988) and monolayers of fatty acids and their sodium sulfate salts on aqueous subphases of alkanolamines (Rosano et al., 1971). A few of these studies determined the amount of hysteresis as a function of the rate of compression and expansion. However, no quantitative analysis of the results was attempted. Historically, dynamic surface tension has been used to study the dynamic response of lung phosphatidylcholine surfactant monolayers to a sinusoidal compression/expansion rate in order to mimic the mechanical contraction and expansion of the lungs. 

Catalysis is a dynamic process, and deeper insights into its phenomenology are extractable from in situ measurements than from characterizations of catalysts before and after catalysis. A number of notable in situ experiments have relied on modifications of standard TEM operations under vacuum. The main functions of the EM depend on a high-vacuum environment, and the pressure in a TEM is usually of the order of 10-7-10-6 mbar. Because the influence of the reaction environment on the structure and activity of a catalyst is critical (3), the high-vacuum environment of a conventional EM is inappropriate for investigating a catalytic reaction, as are characterizations of catalysts in post-reaction environments (e.g., when the catalyst has been taken out of the reaction environment and cooled to room temperature). 

The discussion of the mechanisms and models of the relaxation process given in Section 2.5 shows that the application of time-resolved methods produces substantial advantages in accessing dynamical information, but it does not allow the complete pattern of the dynamic process to be obtained. The analysis of the experimental results requires that a particular dynamic model be assumed. Information on the dynamics is obtained from studies of the dependence of emission intensity on two parameters the frequency (or the wavelength) of emission and on time. The function 7(vem, t) may be investigated by two types of potentially equivalent experiments ... 

By variation of the contrast between the structural imits or molecular groups, complex systems may be selectively studied. In particular, the large contrast achieved by isotopic substitution of hydrogen - one of the main components of polymers - by deuterium constitutes the most powerful tool for deciphering complex structures and dynamic processes in these materials. Neutron reflectometry constitutes a imique technique for the investigation of surfaces and interfaces in polymeric systems. 

From this comparison it follows that the observation of the structural relaxation by standard relaxation techniques in general might be hampered by contributions of other dynamic processes. It is also noteworthy that the structural relaxation time at a given temperature is slower than the characteristic time determined for the a-relaxation by spectroscopic techniques [105]. An isolation of the structural relaxation and its direct microscopic study is only possible through investigation of the dynamic structure factor at the interchain peak - and NSE is essential for this purpose. 

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