Pressure jump techniques technique/time scales

Proton adsorption/desorption kinetics may be studied by pressure-jump type techniques. Protonation is usually very fast deprotonation may be slower but time scales of a few tens of seconds are not exceeded For practical purposes, the oxide surface charge can be considered as being instantaneously established on contact with the metal-containing solution. 

There have been very few studies on the kinetics of micellization in block copolymer solutions. Micellization in aqueous surfactant systems close to equilibrium occurs on a time-scale far below one second. Experimental results obtained by fast reaction techniques, such as temperature jumps or pressure jumps or steady-state methods such as ultrasonic absorption, NMR and ESR, show that at least... 

A number of soil chemical phenomena are characterized by rapid reaction rates that occur on millisecond and microsecond time scales. Batch and flow techniques cannot be used to measure such reaction rates. Moreover, kinetic studies that are conducted using these methods yield apparent rate coefficients and apparent rate laws since mass transfer and transport processes usually predominate. Relaxation methods enable one to measure reaction rates on millisecond and microsecond time scales and 10 determine mechanistic rate laws. In this chapter, theoretical aspects of chemical relaxation are presented. Transient relaxation methods such as temperature-jump, pressure-jump, concentration-jump, and electric field pulse techniques will be discussed and their application to the study of cation and anion adsorption/desorption phenomena, ion-exchange processes, and hydrolysis and complexation reactions will he covered. 

For reactions that occur on time scales < 15 s, none of the techniques given above is satisfactory. To measure these reactions, one can employ relaxation methods (Table 3-1), such as pressure-jump, temperature-jump, concentration-jump, and electric-field pulse (Bernasconi, 1976 Gettins and Wyn-Jones, 1979 Bernasconi, 1986 Sparks, 1989, 1990). 

Elucidation of the kinetics and mechanisms of mineral-fluid interactions requires high-resolution X-ray scattering measurements on rapid time scales. Time series analyses are desired for addressing the evolution of structure and composition at the interface, on time scales as small as milliseconds or less. The high brilliance of the third-generation synchrotron sources affords new opportunities for such time-resolved studies, because we can observe in real time the processes of adsorption/desorption and complex formation at mineral-fluid interfaces. For example, experiments using a pressure-jump relaxation techniques yield rates of adsorption and desorption of protons and hydroxide at the surface of metal oxides in the range of milliseconds to seconds (reviewed by Casey and... 

The steady-state and rapid equilibrium kinetics do not give detailed information on the existence of multiple intermediates or on their lifetimes. Such information is provided by fast (or transient) kinetics. The methods can be divided in two categories rapid-mixing techniques (stopped-flow, rapid-scanning stopped-flow, quenched flow) which operate in a millisecond time scale and relaxation techniques (temperature jump, pressure jump) which monitor a transient reaction in a microsecond time scale. Most of the transient kinetic methods rely on spectrophotomet-rically observable substrate changes during the course of enzyme catalysis. 

Polarographic data yield ki2 = 1.3 X lO W" sec, which agrees well with specific rates of similar reactions shown in Table II. The specific rate kn of the much slower dehydration reaction has been determined by both the temperature and pressure jump methods to be about 0.5 sec at pH 3 and 25 °C with some general acid-base catalysis. While the hydration-dehydration equilibrium itself involves no conductivity change, it is coupled to a protolytic reaction that does, and a pressure jump determination of 32 is therefore possible. In this particular case the measured relaxation time is about 1 sec. The pressure jump technique permits the measurement of chemical relaxation times in the range 50 sec to 50 tisec, and thus complements the temperature jump method on the long end of the relaxation time scale. 

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