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Pretransitional regions

The signal contained an initial decay in the form of a spike. We may consider three possibilities as originally cansing the photocurrent decay in the pretransit region. [Pg.69]

Both PBLG and PBDG solution have the same chiral sense in the pretransition region. The signs of the optical rotations are predominantly negative. As the temperature is increased the solution behavior approaches that of the isotropic liquid. This effect is observed only in chloroform. [Pg.40]

In a very recent calculation by Markwick et al. targeted molecular dynamics methods were implemented in the framework of Car-Parinello molecular dynamics to study the nature of the double proton transfer [48]. They predict a concerted proton transfer reaction. In the very early stages of this reaction the system enters a vibrationally excited pretransitional state. Whereas in the global minima large amplitude fluctuations have been found in the pretransitional region, the frequency of these fluctuations is found to increase dramatically while the amplitude of the oscillation decreases when approaching the transition state. [Pg.44]

In the pretransitional region above the transition it has been shown that a stress-strain relation similar to that of common rubbers occurs [3]. From the behavior of stress-strain curves just below the phase transition, but above the transition to a monodomain state it has been demonstrated that one can linearly extrapolate to stress zero and extract the length /q of a corresponding monodomain sample [3]. When... [Pg.277]

As a rule, the phase transition from the isotropic phase into the nematic phase is a weak first-order transition [6] with a small jump in the order parameter 5 (Fig. 1.3 [7]) and other thermodynamic properties. The so-called clearing point corresponds to this first-order transition temperature Tni. At the same time, in the pretransitional region of the isotropic phase we can observe the temperature divergence in some physical parameters, such as heat capacity, dielectric permittivity, etc., according to the power law (T — T i) where T j is the other, virtual, second-order phase transition point, (Tni — T 0.1 K) and t) is an exponent, depending on the physical property under consideration. [Pg.3]

A considerable amount of experimental results on the free motion of bubbles and drops in quiescent non-Newtonian media is available in the literature. In most cases, the two-parameter power-law model has been used to model the ambient liquid rheology. It is worthwhile to mention here that in the bulk of the work dealing with the free fall of liquid drops in polymer solutions, the ratio of the viscosity of the dispersed phase to that of the continuous phase is in the range lO -lO" and, hence, these drops may effectively be treated as gas bubbles. At this juncture, it is also important to recall that bubbles in the pretransition region (prior to the abrupt change) behave more like solid spheres and, hence, the drag under these conditions is approximated... [Pg.104]

Solids are characterized by a nonzero static shear elastic constant, whereas a liquid will not support static shear. Conventional viscometric techniques (i.e., capillary flow and falling balls), which now seem rather crude considering the fragile nature of the blue phase lattice, initially showed a large viscosity peak at the helical-isotropic transition [89], [90], [91]. Viscosities and other transport coefficients associated with the pretransitional region of the isotropic phase were addressed by light scattering [92], [93], [94], [95]. [Pg.205]

STUDY OF THE SYSTEM ACETONITRILE-WATER IN THE ONE-PHASE PRETRANSITIONAL REGION... [Pg.105]

Figure 13. Magnitude of the nonlinear refractive index in the pretransitional region of MBBA [75], The solid line is a best fit of the form (T-T y ... Figure 13. Magnitude of the nonlinear refractive index in the pretransitional region of MBBA [75], The solid line is a best fit of the form (T-T y ...
Twisting of the helix is due to the formation of nuclei of the smectic mesophase in the pretransition region. The width of the pretransition region and the steepness of the dependence X(I) or P(7) are a function of the structure of the meshase to a great degree. ThCTe is not yet any theoretical dependence which correlates the course of P(J) near the pretransition region of temperatures with the parameters of the molecular and supermolecular structure. [Pg.256]

The prediction of two minima in the dependence of the free energy of the phase transition as a function of the order parameter (concentration) is a characteristic feature of the Doi theory. This makes the existence of a mixture of an isotropic andmetastable LC phase possible in the very narrow pretransition region. This situation is reflected by the system of equations... [Pg.349]

The dependence of the heat of activation of flow on the concentration of copolymer based on PPTA in sulfuric acid is shown in Fig. 9.25. An increase in the steepness in the pretransition region and a sharp decrease in for c> c are characteristic of this dependence. The value of E decreases by approximately 3 times in the range of concentrations of =1% in the region of the transition from the isotropic to the LC state. Not only the heat of activation but also generally the temperature dependence of the viscosity are the same for different concentrations for LC solutions. This can indicate the preservation of the same kinetic unit of flow on the segment of quasi-Newtonian flow (at the limit the molecule or segment), which is characteristic of systems with a continuous LC phase. [Pg.371]

Figure 13 Dipalmitoylphosphatidylcholine liposomes undergo a phase transition at 41 -42°C (curve b). This transition is characterized by a pretransition (region 1 in curve b) and a main transition (region 2 in curve b) and has been shown to be a solid gel-to-Uquid crystalline transition of the membrane phospholipids. This phase transition is abolished when cholesterol is incorporated in the membranes at 45 mol% (curve a). Cholesterol increases the order of membranes in the hquid crystalline phase and decrease the order of membranes in the solid gel phase. (Adapted from Ref. 3.)... [Pg.190]


See other pages where Pretransitional regions is mentioned: [Pg.64]    [Pg.140]    [Pg.48]    [Pg.37]    [Pg.40]    [Pg.40]    [Pg.41]    [Pg.50]    [Pg.97]    [Pg.285]    [Pg.333]    [Pg.241]    [Pg.95]    [Pg.266]    [Pg.267]    [Pg.547]    [Pg.130]    [Pg.637]    [Pg.261]    [Pg.374]    [Pg.740]    [Pg.855]    [Pg.2345]    [Pg.186]   
See also in sourсe #XX -- [ Pg.40 ]




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