Apparent phase transition effect

Otherwise a slow transition from a mobile to a non-mobile state occurred below 0°C. This can be explained by super-cooling and slow-freezing or an apparent phase transition effect. (Depending on the validity and applicability of the model, this difference in freezing behavior could be used as a quick diagnostic tool to determine whether a membrane is suitable for desalination or not). At low coverages (2 layers), the water behaved very similarly on both pore-size glasses. For example T1/T2, f profiles and t. were all similar. ... 

For those systems near a phase transition, the apparent hydrodynamic diameter of the droplets (or the correlation length), as calculated using the Stokes-Einstein equation, appears to decrease as pressure increases [2,4,39]. For example, the apparent hydrodynamic diameter of a microemulsion droplet (for [surfactant] = 150 mM and 5) in supercritical xenon [2] decreases from 6.5 to 4.5 nm as pressure is increased from 350 to 550 bar (10 bar = 1 MPa). This effect is due to the change in the extent of micelle clustering rather than an actual change in the micelle size. 

Resing, H.A. and Davidson, D.W. 1975. Conunentary on the NMR apparent phase transition effect in natroUte, flnor-montmoriUionite and other systems Generalizations when the Arrhenius law applies. Can. J. Phys. 54 295-300. 

The small effects and the progressive evolutions observed seem to be in agreement with a second order phase transition. The lack of coexistence of the low- and high-temperature phases in the temperature range close to the transition temperature and the apparent lack of thermal hysteresis confirm this conclusion. 

For the reduction of NO with propene, the catalyst potential dependence of the apparent activation energies does not show a step change and is much less pronounced than it is for the CO+O2 and NO+CO systems. There is persuasive evidence [20] that the step change is associated with a surface phase transition - the formation or disruption of islands of CO. It is reasonable to assume that this phenomenon cannot occur in the NO+propene case, since there is no reason to expect that large amounts of chemisorbed CO can be present under any conditions. That there should be a difference in this respect between CO+O2/CO+NO on the one hand, and NO+propene on the other hand, is therefore understandable however, the chemical complexity of the adsorbed layer in the NO+-propene precludes any detailed analysis of the Ea(VwR> effect. 

A representative uptake experiment is shown in Figure 5, where the effect of temperature is apparent (80). For both vinorelbine and vincristine, little uptake is observed at 25°C, far below the gel-to-liquid crystalline phase transition temperature of egg SPM (about 44°C), whereas 80% uptake is observed at 60°C where the membrane is fluid. Interestingly, the uptake of vinblastine at 25°C yields an end point nearly identical to that obtained... 

Near the transition temperature, SMAs also exhibit the curious effect of pseudoelasticity, in which the metal recovers (apparently in the usual manner) from an isothermal bending deformation when the stress is removed. However, the elasticity is not due to the usual elastic modulus of a fixed crystalline form, but instead results from strain-induced solid-solid phase transition to a more deformable crystalline structure, which yields to the stress, then spontaneously returns to the original equilibrium crystal structure (restoring the original macroscopic shape) when the stress is removed. 

Knowledge of the effective molecular area is of particular importance when gas adsorption is used for the determination of surface area (see Chapter 6). It is often assumed that the completed monolayer is in a liquid close-packed state, but it is now apparent that we must question the soundness of this assumption. The recent studies of phase transitions and monolayer structures lead us to the conclusion that the degree of molecular packing is dependent on the adsorption system (both adsorbent and adsorptive) and the operational conditions of pressure and temperature (Steele, 1996). 

Zirconia also undergoes high pressure phase transitions from the monoclinic to two orthorhombic structures. A thermochemical study of these phases, combined with phase equilibrium observations (Ohtaka et al. 1991) suggests that surface energy changes the apparent position of phase boundaries, as well as enhances the kinetics of transformation. However Ohtaka et al. (1991) were unable to quantify these effects. 

It is also possible that the coupling coefficients can be temperature-dependent, in which case the apparent thermodynamic character of a phase transition might appear to vary with temperature. This effect would be detectable as an unusual evolution pattern for the order parameter, as shown, perhaps, by NaMgFs perovskite. In this perovskite, the orthorhombic structure appears to develop directly from the cubic structure according to a transition Pm3m < Pnma (Zhao et al. 1993a,b, 1994 Topor et al. 1997). The orthorhombic structure has q2t qA = and qi = q , = q = 0. Equation (32) yields... 

On the other hand, despite the information about long chain sulfates, sulfonates, phosphates, and carboxylates that indicates stronger interaction with Ca2+ than with Mg2+ (i.e., in apparent harmony with the sequence of the Hofmeister (44) series), several difficulties remain. For example, while Miyamoto s data for DS (10) indicate the interaction sequence Mg < Ca < Sr < Ba from solubility measurements (as well as from temperature/CMC measurements if one accepts the Mg—Ca sequence of the present paper), this sequence, with the exception of the position of Mg and Ca, is the opposite of that found by Deamer et al. (33) from condensation effects on the force/area curves of ionized fatty acids. At the same time, the ion sequence obtained by these authors from phase transition temperatures of spread fatty acids (33) differs from that deduced from the above-mentioned condensation effects, and the latter depended strongly on pH. Lastly, definite differences in ion sequence effects exist for the alkaline earth metals in their interaction with long... 

Local anesthetics. Anesthetics interact with membranes and increase the gel to liquid-crystalline transition of fully hydrated bilayers. They induce a volume expansion which has the opposite effect of HHP and so they antagonize the effect of HHP on membranes fluidity and volume, making membranes more fluid and expanded. The application of HHP to membrane-anesthetic systems may even result in the expulsion to the aqueous environment. The local anesthetic tetracaine (TTC) can be viewed as a model system for a large group of amphiphilic molecules. From volumetric measiuements on a sample containing e.g. 3 mol% TTC, it has been found that the main tansition at ambient pressure shifts to a lower temperature. The expansion coefficient a drastically increases relative to that of the pure lipid system in the gel phase, and the incorporation of the anesthetic into the DMPC bilayer causes an about 15 % decrease of relative to that of the pure lipid system. The addition of 3 mol% TTC shifts the pressure-induced liquid-crystalline to gel phase transition towards somewhat higher pressures. Larger values for the compressibilities are found for both lipid phases by addition of 3 mol% TTC, and there is no apparent difference in the coefficient of compressibility between the gel and liquid-crystalline phases. Comparison of the IR spectra of DMPC and DMPC/TTC mixtures at pH 5.5 as a function of pressure shows an abrupt... 

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