Near-critical transition phenomenon

Generally, the metastability is a phenomenon associated with the persistence of the given phase well below the stability domain, bordered by the first order transition, for instance (/) the glass transition phenomenon, (//) metastable systems studies linked to spinodals - absolute stability limits, with particular attention towards the inherently metastable negative pressure domain (///) metastability near a critical point, (/v) the quest for the liquid - liquid near-critical transition in one component liquid, (v) the issue of liquid crystals where... 

It is often suggested that L-L transition in one component liquids is always "secret"", for instance hidden below the glass temperature, and then the evidence for its existence is non-direct. The most classical examples for this phenomenon are water or and triphenyl phosphite (TPP)." Recently clear evidence for the L-L near critical transition in the experimentally available domain for two novel liquids of vital technological and environmental significance have been given. They are nitrobenzene and trans-1,2-dichlorethylene. ... 

Let us consider now behaviour of the gas-liquid system near the critical point. It reveals rather interesting effect called the critical opalescence, that is strong increase of the light scattering. Its analogs are known also in other physical systems in the vicinity of phase transitions. In the beginning of our century Einstein and Smoluchowski expressed an idea, that the opalescence phenomenon is related to the density (order parameter) fluctuations in the system. More consistent theory was presented later by Omstein and Zemike [23], who for the first time introduced a concept of the intermediate order as the spatial correlation in the density fluctuations. Later Zemike [24] has applied this idea to the lattice systems. 

At low temperatures, rj will be unity because all of the Cu atoms will be localized on A sites. 1 But the degree of disorder increases as the temperature increases until the Cu and Zn atoms are mixed randomly on the two sublattices and 77 = 0. This process, called a positional (order + disorder) transition, is often described as a cooperative phenomenon because it becomes easier to produce additional disorder once some disorder is generated. In the vicinity of a critical temperature, the order parameter rj behaves like the density difference (pi — pg) near the gas-liquid critical point. Thus,... 

Family [9] considered the conformations of statistical branched fractals (which simulate branched polymers) formed in equilibrium processes in terms of the Flory theory. Using this approach, he found only three different states of statistical fractals, which were called uncoiled, compensated, and collapsed states. In particular, it was found that in thermally induced phase transitions, clusters occur in the compensated state and have nearly equal fractal dimensions ( 2.5). Recall that the value df = 2.5 in polymers corresponds to the gelation point this allows gelation to be classified as a critical phenomenon. 

In second-order or nearly second-order phase transitions, the dielectric dispersion is observed to show a critical slowing-down a phenomenon in which the response of the polarization to a change of the electric field becomes slower as the temperature approaches the Curie point. Critical slowing-down has been observed in the GHz region in several order-disorder ferroelectrics (e.g. Figs. 4.5-8 and 4.5-9) and displacive ferroelectrics (e.g. Fig. 4.5-10). The dielectric constants at the Curie point in the GHz region are very small in order-disorder... 

The effect of correlated molecular motions can be observed even in the isotropic phase of nematic liquid crystals near the phase transition temperature. This phenomenon was first studied by Wong and Shen and Frost and Lalanne. They found both a pretransitional increase of the Kerr coefficient and a critical slowing-down in the relaxation process. 

The application of the RG is the subject of a recent introductory review, which whilst couched in terms of criticality near to magnetic phase transitions, explains scaling, and also the importance of universality viz. that certain critical exponents, i.e. properties near a phase transition depend only upon for example the number of spatial dimensions and the range of interactions, and not upon the nature of the physical phenomenon itself (see also ref. 24). 

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