Liquid-to-glass

Consider a polymer is quenched from liquid to glass where the sample is annealed. During isothermal annealing, the number of holes is close to a conserved quantity. The local excess of number density of the quenched glass relaxes by spreading slowly over the entire region, and is governed by... 

Different paths of time integration describe different thermal history behavior of the glassy state relaxation and recovery kinetics. Some typical examples of thermal history paths for Eq. (15) were illustrated in Ref. [5J. In this review, we consider mainly that the polymer is cooled from liquid to glass, and is then followed by isothermal annealing. 

Figure 5, (a) ISLS sound speed data and corresponding calculations for supercritical methanol along a 250° C isotherm (b) Data and corresponding calculations for supercritical ethanol along a 250° C isotherm. The difference between MeOH and EtOH sound speeds is typically less than 3 % in this pressure/temperature regime. Raman spectra taken from MeOH at 6.51 GPa indicate that a liquid to glass transition occurred and accounts for the discontinuous increase in velocity compared to the fluid state. 

The entropy theory is the result of a statistical mechanical calculation based on a quasi-lattice model. The configurational entropy (S, ) of a polymeric material was calculated as a function of temperature by a direct evaluation of the partition function (Gibbs and Di Marzio (1958). The results of this calculation are that, (1) there is a thermodynamically second order liquid to glass transformation at a temperature T2, and 2), the configurational entropy in the glass is zero i.e. for T > T2, => 0 as T... 

With respect to the dynamics, both solid-state NMR and DS revealed a relatively immobile core within the crystalline phase. Perylene derivatives that do not crystallize undergo an isotropic liquid-to-glass transformation at a temperature that was found to depend on the number of methylene units in the alkyl chains. The phase transformation kinetics from the high temperature isotropic phase to the crystalline phase at lower temperatures revealed a long-lived metastable state as a result of the soft potential. The crystalline phase is formed via nucleation and growth. The transformation kinetics is controlled by the nucleation barriers. The existence of slow molecular dynamics and of very slow phase transformation suggests that care should be taken in establishing the equilibrium phases of discotic liquid crystals. 

Transition from liquid to glass and crystallization are both phenomena responsible for polymer solidification at the end of a processing operation. Since they are kinetic phenomena, they lead to an out-of-equilibrium thermodynamic state glassy polymers present an excess of unstable conformations and free volume semi-crystalline polymers are not totally crystallized, their melting point being largely lower (usually some dozens of degrees) than the equilibrium value. 

Figure 6.9 Volume-temperature cooling curves. Note the discontinuity at melting or liquidus temperature (T = fi.) when crystals form while liquid-to-glass path is continuous with lower contraction being observed once...

The MCT equations show bifurcations due to the nonlinear nature of the equations. A bifurcation point is identified with an idealized liquid-to-glass transition. The quantity of special interest is the glass form factor or Edwards-Anderson nonergodicity parameter,/. It describes the frozen-in structure of the glass and obeys... 

Figure 22 (Top) Relaxation times at maximum loss for the PBLG45 under isothermal and isobaric conditions plotted as a function of density. The filled data correspond to the relaxation times at 0.1 MPa. Solid and dashed lines are fits to the isobaric (Pfrom 0.1 to 220 MPa in steps of 20 MPa) and isothermal (T=297,308,333,353, and 373 K) times, respectively. (Bottom) Ratio of activation energies Ok/lOp plotted as a function of density. The high values of the ratio suggest intramolecular correlations and hydrogen bonding as being responsible for the liquid-to-glass transition in polypeptides. For details, see Papadopoulos, P. Floudas, G. Schnell, I. Klok, H. A. Aliferis, T. latrou, H. ...

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