Glass-to-liquid transition

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 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. ...

The solidity of gel electrolytes results from chain entanglements. At high temperatures they flow like liquids, but on cooling they show a small increase in the shear modulus at temperatures well above T. This is the liquid-to-rubber transition. The values of shear modulus and viscosity for rubbery solids are considerably lower than those for glass forming liquids at an equivalent structural relaxation time. The local or microscopic viscosity relaxation time of the rubbery material, which is reflected in the 7], obeys a VTF equation with a pre-exponential factor equivalent to that for small-molecule liquids. Above the liquid-to-rubber transition, the VTF equation is also obeyed but the pre-exponential term for viscosity is much larger than is typical for small-molecule liquids and is dependent on the polymer molecular weight. 

Thus we note that the memory kernel has a short-time and a long-time part. It is the long-time part which is not present in the viscoelastic model, becomes important in the supercooled-liquid-near-glass transition, and gives rise to the long-time tail of the dynamic structure factor. 

Hyperbranched polyethers can be synthesized via the A2+B3 approach, when diepoxides (3-24) are reacted with triols, such as TMP. Emrick et al. used 1,2,7,8-diepoxyoctane as the A2 monomer and TMP as the B3 monomer with tetra-n-butylam-monium chloride as the nucleophilic catalyst. Nucleophilic attack of the chloride ion on an epoxide at the less-hindered terminal carbon led to the formation of secondary alkoxide. Due to the equilibrium between primary and secondary alk-oxides via proton exchange, nucleophilic attack of primary alkoxides on the epoxide rings resulted in the formation of aliphatic hyperbranched polyether. As the feed ratio of the diepoxide and TMP was varied from 1.5 to 3, the resulting hb polyether contained two types of terminal units (T), one type of dendritic unit (D), and linear units (L) as shown in Scheme 4. The polydispersity index (PDI) of the polyether increased with the increase of molecular weight (from 1.5-1.8 at M = 1000 up to 5.0 at Mw = 7000). The products are viscous liquids with glass transition temperatures below room temperature. 

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. 

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