Pressure-jump

Other properties of association colloids that have been studied include calorimetric measurements of the heat of micelle formation (about 6 kcal/mol for a nonionic species, see Ref. 188) and the effect of high pressure (which decreases the aggregation number [189], but may raise the CMC [190]). Fast relaxation methods (rapid flow mixing, pressure-jump, temperature-jump) tend to reveal two relaxation times t and f2, the interpretation of which has been subject to much disagreement—see Ref. 191. A fast process of fi - 1 msec may represent the rate of addition to or dissociation from a micelle of individual monomer units, and a slow process of ti < 100 msec may represent the rate of total dissociation of a micelle (192 see also Refs. 193-195). 

Fig. XV-7. Fluorescence micrographs showing morphology of crystalline L-a-dimyris-tolphosphatidylethanolamine domains following a t jump to the plateau region of the v-a plot (a) after 2 sec b) after 1 min (c) after 20 min (d) following a second pressure jump after condition (c). (From Ref. 40.)...

Strehlow H and Beoker M 1959 The pressure-jump method for the measurement of rates of ionio reaotions Z. Eiektrochem. 63 457-61... 

Knoche W and Wiese G 1976 Pressure-jump relaxation techniques with optical detection Rev. Sc/. Instrum.47 220-1... 

Quednau J and Schneider G M 1989 A new high-pressure cell for differential pressure-jump experiments using optical detection Rev. Sc/. Instnim. 60 3685-7... 

Other perturbations have been demonstrated. The pressure,, jump, similar to the T-jump in principle, is attractive for organic reactions where Joule heating may be impractical both because of the solvent being used and because concentrations might have to be measured by conductivity. Large (10 —10 kPa) pressures are needed to perturb equiUbrium constants. One approach involves pressurizing a Hquid solution until a membrane mptures and drops the pressure to ambient. Electric field perturbations affect some reactions and have also been used (2), but infrequentiy. 

Typical pressure and temperature histories computed are shown in Figs. 6.6 and 6.7. In Figs. 6.6, the pressure is shown as a function of position within the powder compact at various times. For the baratol explosive loading shown, an initial wave, whose pressure is 1.8 GPa, is shown moving slowly from right to left. Upon reflection from the rear interface with the copper, the pressure jumps to a much higher value and then quickly reverberates to a peak pressure of about 11.4 GPa. The shorter reverberation time reflects the higher wavespeed and the major reduction in thickness in the compressed powder. 

The pressure-jump (P-jump) method is based on the pressure dependence of the equilibrium constant, Eq. (4-28), where AV is the molar volume change of the reaction. 

In the pressure-jump method, the solution is pressurized, usually to several thousand atmospheres. At the desired moment a diaphragm is mechanically ruptured. The... 

The temperature distribution has a characteristic maximum within the liquid domain, which is located in the vicinity of the evaporation front. Such a maximum results from two opposite factors (1) heat transfer from the hot wall to the liquid, and (2) heat removal due to the liquid evaporation at the evaporation front. The pressure drops monotonically in both domains and there is a pressure jump at the evaporation front due to the surface tension and phase change effect on the liquid-vapor interface. 

He considered that the rapid flame propagation could be achieved with the same mechanism as vortex breakdown. Figure 4.2.2 schematically shows his vortex bursting mechanism [4,5]. When a combustible mixture rotates, Ihe pressure on the axis of rotation becomes lower than the ambient pressure. The amount of pressure decrease is equal to max in Rankine s combined vor-fex, in which p denotes fhe unburned gas density and Vg denotes the maximum tangential velocity of the vortex. However, when combustion occurs, the pressure on the axis of rofafion increases in the burned gas owing to the decrease in the density, and becomes close to the ambient pressure. Thus, there appears a pressure jump AP across the flame on fhe axis of rotation. This pressure jump may cause a rapid movement of the hot burned gas. By considering the momentum flux conservation across the flame, fhe following expression for the burned gas speed was derived ... 

Later, in 1987, Daneshyar and Hill [6] indicated that if the angular momentum conservation was assumed to be held across the flame front, then the pressure jump AP can be given as... 

That is, once combustion is preceded, a pressure jump is invoked on the axis of rotation owing to angular momentum conservation. By further considering the pressure jump AP to be converted into the kinetic energy of the burned gas p u /l, an expression for the axial velocity of the hot gas can be obtained as ... 

The second method for the study of relaxation in spin-state equilibria makes use of the rapid change of pressure. Single-step pressure-jump relaxation requires an observation time of about lO s which is too slow. However, the... 

Seddon, J.M., Squires, A.M., Conn, C.E., Ces, O., Heron, A.J., Mulet, X., Shearman, G.C. and Templer, R.H. (2006) Pressure-jump X-ray studies of liquid crystal transitions in lipids. The Royal Society of London. Philosophical Transactions. Series A. Mathematical, Physical and Engineering Sciences, 364 (1847), 2635—2655. 

For cryptands in which the molecular cavity is larger than in the case of the [l.l.l]-species [78], proton transfer in and out of the cavity can be observed more conveniently. Proton transfer from the inside-monoprotonated cryptands [2.1.1] [79], [2.2.1] [80], and [2.2.2] [81 ] to hydroxide ion in aqueous solution has been studied by the pressure-jump technique, using the conductance change accompanying the shift in equilibrium position after a pressure jump to follow the reaction (Cox et al., 1978). The temperature-jump technique has also been used to study the reactions. If an equilibrium, such as that given in equation (80), can be coupled with the faster acid-base equilibrium of an indicator, then proton transfer from the proton cryptate to hydroxide ion... 

Temperature jump studies were performed in combination with stopped-flow experiments94 in response to criticism as to the reliability of temperature jump experiments26,142 and divergent interpretation of the kinetics. In particular, the suggestion from pressure jump experiments that the association step is diffusive in nature... 

Table 8 Equilibrium constants and association and dissociation rate constants for derivatives 27 and 28 with a-CD determined by temperature jump (27, T — 14 °C, I — 0.5 M), stopped-flow (28, T = 25 °C, /= 0.1 M) and with pressure jump experiments (29, T = 25 °C, /= 0.15 M)...

Pivalaldehyde. See 2,2-Dimethylpropanal Pivalic acid, physical properties, 5 35t, 37t Pivaloylacetanilide couplers, 19 253-254 p-jump (pressure jump), 14 616, 617... 

Pressure filters, 76 658-659 horizontal belt, 77 379 thickening, 77 382-388 Pressure gauge, 20 645 Pressure gradients, flow caused by, 9 110 Pressure infiltration, of metal-matrix composites, 76 167-169 Pressure injection, moldings, 10 11 Pressure-jump method, 73 427-428... 

The Heterogeneous Case. Hachiya et al. (1984) and Hayes and Leckie (1986) used the pressure-jump relaxation method to study the adsorption kinetics of metal ions to oxide minerals. Their results support in essence the same adsorption mechanism as that given for homogeneous complex formation. 

The circles refer to the pressure jump experiments of Hachiya et al. The relationship is expressed by an almost linear correlation (slope 0.92) ... 

Linear-free energy relation between the rate constants for water exchange k w [s 1] and the intrinsic adsorption rate constants katjS(int) [M 1 s 1] from the pressure jump experiments of Hachiya et al. The intrinsic constants refer to an uncharged surface. The linear-free energy relations based on the experimental points are extended to some ions with lower H20 exchange rate in order to predict adsorption rates. 

Hayes and Leckie (1986) postulate on the basis of their pressure jump relaxation experiments on the adsorption-desorption of Pb2+ at the goethite-water interface the following mechanism ... 

A pressure perturbation results in the shifting of the equilibrium the return of the system to the original equilibrium state (i.e., the relaxation) is related to the rates of all elementary reaction steps. The relaxation time constant associated with the relaxation can be used to evaluate the mechanism of the reaction. During the shift in equilibrium (due to pressure-jump and relaxation) the composition of the solution changes and this change can be monitored, for example by conductivity. A description of the pressure-jump apparatus with conductivity detection and the method of data evaluation is given by Hayes and Leckie (1986). 

The simplest experiment we can visualise performing is the very rapid application of a small strain which is then maintained at a constant level. This is simply a strain-jump experiment and can be treated in an analogous fashion to a temperature or a pressure-jump experiment. The stress will follow the strain and increase to a maximum value. For an... 

Due to the fast kinetics of adsorption/desorption reactions of inorganic ions at the oxide/aqueous interface, few mechanistic studies have been completed that allow a description of the elementary processes occurring (half lives < 1 sec). Over the past five years, relaxation techniques have been utilized in studying fast reactions taking place at electrified interfaces (1-7). In this paper we illustrate the type of information that can be obtained by the pressure-jump method, using as an example a study of Pb2+ adsorption/desorption at the goethite/water interface. 

Based on the pressure-jump relaxation results reported here, the following mechanism is postulated for the adsorption/desorption of Pb2+ ion at the goethite/water interface (8) ... 

Kinetic experiments were conducted using a pressure-jump apparatus with conductivity detection. Details of the apparatus and its operation can be found in Appendix A. Sample equilibration time can have an effect on the kinetic results (e.g., slow processes (on the order of hours-days) occurring concurrently but not monitored in the time frame of the p-jump technique (milllseconds-seconds)) hence, it is important to run kinetic experiments on samples with similar equilibration history. All samples were equilibrated between 3 and 4 hours for the p-jump kinetic studies. The temperature of the p-jump apparatus, which includes sample and reference solution cells, was maintained at 25.0°C 0.1°C. 

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