Phase transition vitrification

As opposed to the liquid-crystal transformation, the liquid-glass transformation is not a phase transition and therefore it can not be characterized by a certain transition temperature. Nevertheless, the term "the vitrification temperature , Tv, is widely used. It has the following physical meaning. As opposed to crystallization, vitrification occurs when the temperature changes continuously, i.e. over some temperature interval, rather than jump-wise. Inside this interval, the sample behaves as a liquid relative to some of the processes occurring in it, and as a solid relative to other processes occurring in it. The character of this behaviour is determined by the ratio between the characteristic time of the process, t, and the characteristic relaxation time of the matrix, x = t//G, where tj is the macroscopic viscosity and G is the matrix elasticity module. If t x, then the matrix should be considered as a solid relative to the process, and if t > x it should be considered as a liquid. The relation tjx = 1 can be considered as the condition of the matrix transition from the liquid to the solid (vitreous) state, and the temperature Tv at which this condition is realized as the temperature of vitrification. Evidently, Tv determined by such means will be somewhat different for the processes with different characteristic times t. However, due to the rapid (exponential) dependence of the viscosity rj on T, the dependence of Tw on t (i.e. on the kind of process) will be comparatively weak (logarith-... 

The kinetics of the mesophase transitions can be discussed by comparison with the crystallization-melting and the vitrification-devitrification transitions of the three limiting phases of Fig. 2. Except for the crystallization kinetics, the literature on the kinetics of phase transitions is limited. For the mesophases, information is scarce. 

Fig. 1. Second order phase transition versus the vitrification process. They have different temperature dependence of the volume (F) and enthalpy (H), and their derivatives a (thermal expansion) and C (specific heat)...

Liquids with two equilibrium states coexisting in a temperature interval [Jcl, rc2] with the cluster fractions x T) and x2(T), moreover, XttT), x2(T) < xg with Te Tcii Tc2l For this type of liquids the vitrification takes place near Tf or near T and can be preceded by the first-type phase transition liquid-liquid . 

Menczd J, Wunderlich B (1980) Phase transitions in mesophase macromolecules. I. Novel bdiavior in the vitrification of poly(ethylene terephthalate-co-p-oxybenzoate). J. Polymer Sd., Polymer Phys. Ed. 18 1433... 

The basis for the SME of temperature sensitive SMPs is the phase transition of their switching domains. These switching domains consist of polymer segments and can solidify either through crystallisation or vitrification. The general ability of semicrystalline polymers to form crystallites depends on the type of monomers used, but is also affected by other properties such as the three-dimensional architecture of the polymer network (see Sect. 3.3). 

The phase transition for N(2,3)—F—012 as determined by DSC analysis are summarized in Table 3. Each phase was assigned using both WAXD and POM analyses. No further peaks were observed below the smectic phases in either the cooling or second heating directions, except for a vitrification confirmed at 298 K by both WAXD and POM, although a crystal phase was obtained for the as-synthesized sample at 298 K prior to the first... 

Sun, W.Q., Irving, T.C., and Leopold, A.C., The role of sugar, vitrification and membrane phase transition in seed desiccation tolerance. Physiol. Plant, 90,621,1994. 

Partial vitrification may affect kinetic processes during the coil-globule transition. Thus, at very high dilution, macroscopic phase separation well above the LCST might be stopped by partial vitrification of the polymer-rich phase. At this point we can only speculate whether vitrification interferes with the coil-globule transition or not. This problem is open for discussion and needs experimental confirmation. 

The structure of block copolymer melts is usually trapped upon vitrification. The mechanisms underlying the glass transition are similar to those of the constituent homopolymers. Thus there is little distinct physics associated with the formation of solid phases by glassy block copolymers. 

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