Hydrostatic Pressure Effect

All the solid-state NMR investigations described provide a detailed description of the intramolecular motions performed in glassy BPA-PC. Unfortunately, they do not give any information on the intermolecular cooperativity that could be associated with some of them. 

To address this question, an interesting study has been carried out on the effect of hydrostatic pressure on the proton NMR fine width of BPA-PC [44]. Actually, the transverse relaxation time, XH T2, inversely proportional to the line width, is a more convenient parameter. 

The temperature dependence of XH T2 at various hydrostatic pressures is shown in Fig. 52 for BPA-PC (Fig. 52a) and for a BPA-PC deuterated at all positions except in aromatic position ortho to the isopropylidene group, BPA-dio-PC (Fig. 52b). 

The increase of T2 observed in BPA-PC between - 170 and - 120 °C does not exist in BPA-dio-PC, it is assigned to the occurrence of the methyl rotation around its C3 axis. Furthermore, the temperature dependence is unaffected by pressure, indicating a motion with zero or small activation volume, consistent with a methyl rotation. 

At higher temperatures, a pressure-dependent process occurs from - 100 to 60 °C, which is reversible. Such a broad temperature range indicates a site heterogeneity and a broad distribution of activation energies. By considering a thermally activated motion, an estimate of the mean activation energy leads to 38 kj mol 1 and for the activation volume to 25 cm3 mol 1 for the two types of polycarbonates. 

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Laverman and coworkers have reported activation parameters for the aqueous solution reactions of NO with the iron(II) and iron(III) complexes of the water soluble porphyrins TPPS andTMPS (21). These studies involved systematic measurements to determine on and kQ as functions of temperature (298—318 K) and hydrostatic pressure (0.1—250 MPa) to determine values of AH, AS and AV for the on and off reactions of the ferri-heme models and for the on reactions of the ferro-heme models (Table II). Figure 2 illustrates hydrostatic pressure effects on kOTL and kQff for Fem(TPPS). 

Prestamo, G. and Arroyo, G. (1998). High hydrostatic pressure effect on vegetable structure.. Pood Sci 63, 878-881. 

Boer, G., Dodge, A., Fluri, K., van der Schoot, B.H., Verpoorte, E., de Rooij, N.F., Studies of hydrostatic pressure effects in electrokinetically driven p l AS. Micro Total Analysis Systems 98, Proceedings pTAS 98 Workshop, Banff, Canada, 13-16 Oct. 1998, 53-56. 

Gervilla, R., Ferragut, V., Guamis, B. 2001. High hydrostatic pressure effects on colour and milk-fat globule of ewe s milk. J. Food Sci. 66, 880-885. 

Horsewill et al. (1994) examined the hydrostatic pressure effect on the proton transfer in crystals of a carboxylic acid dimer. Under a hydrostatic pressure, the distance of hydrogen bonds becomes shorter, and this is accompanied by a decrease in the potential barrier to proton transfer. The temperature dependence of the rate of the proton transfer turns out to be of a non-Arrhenius type. The influence of phonon-assisted tunnelling becomes evident as the external pressure increases, especially at lower temperatures. 

Samuels (1) has pointed out that plastic deformation occurs during abrasion of ionic salt crystals which are ordinarily considered brittle and that this has been attributed to a hydrostatic pressure effect. 

Figure 14.8 shows stress-strain curves for polycarbonate at 77 K obtained in tension and in uniaxial compression (12), where it can be seen that the yield stress differs in these two tests. In general, for polymers the compressive yield stress is higher than the tensile yield stress, as Figure 14.8 shows for polycarbonate. Also, yield stress increases significantly with hydrostatic pressure on polymers, though the Tresca and von Mises criteria predict that the yield stress measured in uniaxial tension is the same as that measured in compression. The differences observed between the behavior of polymers in uniaxial compression and in uniaxial tension are due to the fact that these materials are mostly van der Waals solids. Therefore it is not surprising that their mechanical properties are subject to hydrostatic pressure effects. It is possible to modify the yield criteria described in the previous section to take into account the pressure dependence. Thus, Xy in Eq. (14.10) can be expressed as a function of hydrostatic pressure P as... 

The Hydrostatic Pressure Effect. The particular hydroxy-terminated polybutadiene (HTPB) solid propellant employed here is a polybutadi-... 

This large increase in the solvent power of ethylene on compression to 100 bar cannot be attributed to a hydrostatic pressure effect on the vapor pressure of naphthalene, since the pressure effect is explicitly accounted for in the exponential term in equation 1.1. Instead, the large difference in experimental and calculated naphthalene solubility at high pressures is associated with the nonideal behavior of ethylene as it is compressed to liquid-like densities in its critical region. It is the strength of the interactions between solvent and solute molecules that fixes the solubility depending of course on whether the solvent molecules are in close enough proximity to interact. Chapters 3 and 5 delve more deeply into intermolecular interactions and solubility behavior. 

The situation is considerably different for the iron(III) analog (TPPS)Fe "(H20)2 which is hexacoordinate in aqueous solution. In this case the reaction with NO is considerably slower (kon = 4.5 x 10 s ) and kojr (500 s ) is sufficiently large to be measurable by the flash photolysis method as well [92]. Temperature and hydrostatic pressure effects were probed and AH, AS and AV values of 69 + 3 kj mol , 95 10 J mol K and +9+1 cm mol were determined for the "orf reaction and 76 + 6 kJ mol , 60 + 11 ) mol and 18 + 2 cm mol respectively, for the off reaction [93j. The activation parameters for the on reaction compare very favorably with those measured for exchange between coordinated and solvent water for aqueous solutions of (TPPS)Fe "(H20)2 [94] and indicate that kinetics for the reaction of NO with this complex are dominated by the lability of the coordinated water. Furthermore, the large and positive values of AVj and ASj point to a dissociative substitution mechanism as described in Eq. (6.43). 

ADA/BIL] Adam, A., Billerey, D., Terrier, C., Bartholin, H., Regnault, L. P., Rossat-Mignod, J., Hydrostatic pressure effect on the commensurate-incommensurate phase transition of NiBr2, Phys. Lett., 84A, (1981), 24-27. Cited on pages 132, 386. 

The first true mechanical study was made by Schadler et al. in 1998. They measured the stress-strain properties of a MWNT poxy composite during both tension and compression. In tension, the modulus increased from 3.1 GPa to 3.71 GPa on the addition of 5 -wt% nanotubes, a reinforcement of d I7d V( = 18 GPa. However, better results were seen in compression, with an increase in the modulus from 3.63 to 4.5 GPa, which corresponds to a reinforcement of 26 GPa. No significant increases in the strength of toughness were observed. The difference between tension and compression was explained by Raman studies which showed significantly better stress transfer to the nanotubes in compression than in tension. This can be explained by the fact that load transfer in compression can be thought of as a hydrostatic pressure effect, whereas load transfer in tension relies on the matrix-nanotube bond. However, it should be pointed out that later studies showed the reverse to be true, Le. load transfer in tension but none in eompression. In further contrast, work by Wood et al has shown that the mechanical response of SWNTs in tension and compression are identical. 

It is difficult to generalize with regard to vessel geometry but some observations are made on the use of cylindro-conical tanks (see pp. 659-668). Probably the most important dimension is depth because this affects not only (i) yeast sedimentation but also (//) carbon-dioxide bubble generation per unit area, (in) hydrostatic pressure effects on carbon-dioxide evolution and (/v) circulation currents in the vessel. 

Pease, D. C. 1941. Hydrostatic pressure effects upon the spindle fiber and chromosome movement. I. Experiments on the first meiotic division of Urechis eggs. J. Morph., 69 405 41. 

The carbon dioxide permeability for both mixtures was depressed below the pure carbon dioxide values, but the carbon dioxide permeability for the 50/50 mixture did not display a decreasing tendency with pressure as was observed for the 10/90 CO2/N2 mixture. Therefore, at the lower nitrogen partial pressures observed in the 50/50 mixture, the impact of the hydrostatic pressure effect is reduced by the swelling effect of CO2. Although the swelling effect of CO2 cannot completely overcome the hydrostatic pressure effect of CO2 nitrogen, it greatly offsets its influence. 

Except for supercritical extraction conditions, hydrostatic pressure effects are typically of negligible importance for simple solvent vapors diffusing in polymers, since the saturation vapor pressure is low, <101.3 kPa (1 atm), in most applications. The predictive power of the approach is indicated by the results for the mutual diffusion coefficient of toluene in a toluene-polystyrene system (Fig. 14) (35). 

Quality of the haemodynamic data is also affected by technical factors. Major factors to consider include the possibility of hydrostatic pressure effects (i.e. blood inside the vasculature or fluid-filled catheter systems that are utilized in recording methods), long-term stability of the pressure sensor (subject to possible drift with time), frequency response of the sensor and associated modem solid-state electronics (see Sarazan 2014 for a complete review of technological requirements and potential errors that can be encountered when measuring cardiovascular pressure in safety pharmacology studies). 

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