Pressure isotherm

D) CONSTANT-TEMPERATURE CONSTANT-PRESSURE (ISOTHERMAL-ISOBARIC) PROCESSES... 

Comparison of the proposed dynamic stability theory for the critical capillary pressure shows acceptable agreement to experimental data on 100-/im permeability sandpacks at reservoir rates and with a commercial a-olefin sulfonate surfactant. The importance of the conjoining/disjoining pressure isotherm and its implications on surfactant formulation (i.e., chemical structure, concentration, and physical properties) is discussed in terms of the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory of classic colloid science. 

Figure 4. A conjoining/disjoining pressure isotherm for the constant- potential and weak overlap electrostatic model.

We can conclude that the stability of static foam in porous media depends on the medium permeability and wetting-phase saturation (i.e., through the capillary pressure) in addition to the surfactant formulation. More importantly, these effects can be quantified once the conjoining/disjoining pressure isotherm is known either experimentally (8) or theoretically (9). Our focus... 

Figure 6. Evolution of the lamella thickness as it transports down the periodic pore for the conjoining/disjoining pressure isotherm of Figure 4. Three capillary pressures are considered in curves 1 through 3. These capillary-pressure values are also labelled in Figure 4. Curve 2 defines the critical or marginally...

ENORDET AOS 1618) in an 81- fjtm permeability sandpack. Using the parameters listed and the constant- charge electrostatic model for the conjoining/disjoining pressure isotherm, the data are rescaled A ... 

Figure 9.12 (a) Enthalpy of oxidation of Lai xAxB03, 5 as a function of x. Open symbols represents values deduced from non-stoichiometry versus partial pressure isotherms. Closed symbols represent calorimetric values, (b) Comparison of experimental and calculated non-stoichiometry versus partial pressure isotherms [23], Reproduced by permission of the Royal Society of Chemistry. 

The tentative equation summarized in Table V allows the calculation of the solubility at one atmosphere gas partial pressure which is numerically equal to the inverse of Henry s constant (equation 1). Although Henry s law may be adequate up to moderate pressures, it requires some corrections for the solubilities at higher pressures. Table VI summarizes some approaches that have been used to correlate solubility pressure isotherms. These have been discussed in many places including references [,21 and 22]. ... 

Using the a Function. A typical molar volume-pressure isotherm for a real gas is illustrated in Figure 10.6, together with the corresponding isotherm for an ideal gas. From Equation (10.34) we can write... 

Figure 10.6. Comparison of molar volume-pressure isotherms for a possible real gas and an ideal gas.

Duplessix et al. used water vapor pressure isotherm (i.e., water uptake vs external relative humidity) data combined with simultaneous isotherm differential microcalorimeter analysis to determine the average heat of absorption per water molecule for 1200 EW acid form samples. Hysteresis was seen between sorption and subsequent desorption curves at 25 °C, and nonzero water content remained at zero relative humidity, indicating the presence of tightly... 

We now introduce two new parameters that describe the changes in interionic distances and volume with pressure isothermal linear compression coefficient ft, and isothermal volumetric compression coefficient jiy ... 

Figure 8.15 Typical film pressure isotherm for a surfactant monolayer.

Fig. 8. Surface-area/surface-pressure isotherms for spreading 1,5, and mixtures of 1 + 5 at 0.2,0.4, 0.6, and 0.8 mole fractions of 1 on aqueous S.O mM NaCl. Areas (A,) and pressures (iq) associated with the transition to a compressed state were taken by projecting the intersection of straight lines drawn to the appropriate sections of the isotherm to the surface-area and surface-pressure axes. The collapse pressure (nc) and collapse area (Ac) were taken by treating that transition, similarly. The insert shows an expansion of the isotherms between 20-40 mN/m. Temperature = 24.0 + 0.5 °C [116]...

The gas pressure is next calculated from the concentration. The additional assumption is that the incremental gas pressure inside the sample is the same as the external gas pressure required to yield the same amount of dissolved gas within the polymer at equilibrium (from a solubility-external pressure isotherm). This procedure gives approxi-... 

Although the combined asymptotic density/linear temperature program is usually the best approach, such a gradient is difficult to achieve without computer control of the pump and oven. Even an asymptotic (or linear) density gradient alone is beyond the capability of some SFC pumps. When faced with such limitations, it is reasonable to use a linear pressure program instead. The curvature of the density pressure-isotherms for some supercritical fluids (e.g., pure CO2) is such that a linear increase in... 

G. Garofalakis and B. S. Murray, Surface pressure isotherms, dilatational rheology, and brewster angle microscopy of insoluble monolayers of sugar monoesters, Langmuir, 18 (2002) 4765-4774. 

Pressure. Isothermally increasing the pressure applied to a polymer also reduces molecular mobility, and consequently, free volume. Thus, the Tg will generally increase with increased pressure [approximately 20 °C increase in Tg per thousand atmosphere increase in pressure (Eisenberg, 1984)]. 

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