Metastable regime

The occurrence of demixing morphologies characteristic for the metastable regime between the binodal and the spinodal can be understood from Fig. 17. The red dot marks the initial position of the sample with c = 0.3. Upon laser heating the temperature within the laser focus rises by AT and the distance to the binodal first increases. A stationary temperature distribution is rapidly reached and the Laplacian of the temperature field T(r,t) is obtained from the stationary solution of the heat equation (5) with the power absorbed from the laser as source term ... 

For example, iieai a critical point or at a spinodal (i.e., at the stability limit of a fluid phase in the metastable regime), the above is no longer true. However, it should also be noted that, at a discontinuous phase transition (i.e., before entering the metastable regime), Eq. (2.76) still holds. 

Fig. 40. Schematic description of unstable thermodynamic fluctuations in the two-phase regime of a binary mixture AB at a concentration cb (a) in the unstable regime inside the two branches tp of the spinodal curve and (b) in the metastable regime between the spinodal curve tp and the coexistence curve The local concentration c(r) at a point r = (x. y, z.) in space is schematically plotted against the spatial coordinate x at some time after the quench. In case (a), the concentration variation at three distinct times t, ti, u is indicated. In case (b) a critical droplet is indicated, of diameter 2R , the width of the interfacial regions being the correlation length Note that the concentration profile of the droplet reaches the other branch ini, of the coexistence curve in the droplet center only for weak supersaturations of the mixture, where cb -

Fig. 2.2. The entropy ofliquid and crystalline aluminum as function of temperature in the stable and metastable regime. AS, denotes the entropy of fusion...

Generally, it is agreed that two fundamentally different mechanisms of phase separation can occur, as shown in Fig, 20.1-7. The so-called binodal regions in the two-phase envelope mark metastable regimes in which a single phase can exist until a nucleus (homogeneous or heterogeneous) presents itself and initiates a precipitation process. This process is similar in many respects to classical crystallization from... 

Measurements of transport properties would provide another means to explore the metastable regime. In particular, studies based on simulation focused on the supercooled regime [104] correlate the breakdown of the Stokes-Einstein relation Dv = constant) with the Widom line w P), locus of the correlation length maxima emanating down from the proposed liquid-liquid critical point toward lower pressures (Fig. 3b). Measurements of diffusivity could be performed at negative pressure by NMR on static samples (e.g., via MVLE or inclusions) and viscosity could be measured by capillary rheometry with the MVLE method. 

Gartia, M.R., Pilkhwal, D.S., Vijayan, P.K., Saha, D., 2001. Analysis of metastable regimes in a parallel channel single phase natural circulation system with RELAP5/MOD3.2. International Journal of Thermal Sciences 46, 1064—1074. 

Aside Recently, it has been found that protein salt water solutions do have liquid-liquid phase separations with true critical points, albeit sometimes only in metastable regimes at temperatures and protein concentrations at which the protein solution is supersaturated(69-71). Near critical points, Eq. 10.16 may well become valid, but only with a f that is substantially larger than molecular dimensions.)... 

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