Glass temperature systems

A prerequisite of long-life sodium/sulfur batteries is that the cells contain suitable corrosion-resistant materials which withstand the aggressively corrosive environment of this high—temperature system. Stackpool and Maclachlan have reported on investigations in this field [17], The components in an Na/S cell are required to be corrosion-resistant towards sodium, sulfur and especially sodium polysulphides. Four cell components suffer particularly in the Na/S environment the glass seal, the anode seal, the cathode seal, and the current collector (in central sodium arrangements, the cell case). 

Kelley FN, Bueche F (1961) Viscosity and glass temperature relations for polymer-diluent systems. J Polym Sci 50(154) 549-556... 

Figure 2 Sketch of typical temperature dependencies of the viscosity r of glass-forming systems. The viscosimetric Tg of a material is defined by the viscosity reaching 1013 Poise. Strong glass formers show an Arrhenius temperature dependence, whereas fragile glass formers follow reasonably well a Vogel-Fulcher (VF) law predicting a diverging viscosity at some temperature T0.

Let us now turn to a discussion of the relation of the temperature dependence of the polymer melt s configurational entropy with its glass transition and address the famous paradox of the Kauzmann temperature of glass-forming systems.90 It had been found experimentally that the excess entropy of super-cooled liquids, compared with the crystalline state, seemed... 

Fig. 4.1 a Typical time evolution of a given correlation function in a glass-forming system for different temperatures (T >T2>...>T ), b Molecular dynamics simulation results [105] for the time decay of different correlation functions in polyisoprene at 363 K normalized dynamic structure factor at the first static structure factor maximum solid thick line)y intermediate incoherent scattering function of the hydrogens solid thin line), dipole-dipole correlation function dashed line) and second order orientational correlation function of three different C-H bonds measurable by NMR dashed-dotted lines)... 

Plasticized Polymers. As mentioned above the glass transition temperature Tg is lowered by adding certain organic liquids, the so called plasticizers. The illustration of polymers above T0 by means of a model remains valid also for plasticized systems. The configuration that is built up at the transition from the melt to the glass, in this case, remains below the glass temperature, too. Thus, we have an extended structure containing holes. ... 

With the method used here, the specimen is free to expand in only one direction, and this means that only a linear expansion can be determined. This is the same as volumetric expansion. If the system is above its glass temperature, 7g,... 

The condition for valid results in this work is the fact that the system is in the gel-state that is, it is in a state of inner equilibrium, and not in the glass state. Measurements of Hellwege, Knappe, and Lehmann (5) on pure PVC show the expected discontinuity in the compressibility vs. pressure curve at the melting point transition in the glass state. It is inferred from this study that the glass temperature for pure PVC and for the plasticized, gel-type PVC does not rise above 110° C. at pressures of 200 atm. (Figure 7). Our study showed that the system is always in a state of inner equilibrium. 

The idea that the fractional free-volume at glass temperature as found experimentally depends on the mode of molecular motions was put forward in 196746 47 as a result of calculating/g from data obtained from isothermal volume relaxation for some polymer systems. By estimating average relaxation time at different temperatures it was possible to find the fractional free-volume/g at Te according to WLF theory. If we accept the validity of the theory as regards the universal dependence of the reduction factor aT on (T - Tg), then on the basis of data on Aa and theoretical values aT calculated from universal values of the coefficients C and C, it is possible to make an estimate of/g. In this case the value found corresponds to the universal one. If, however, we use the experimental values aT, the fractional free-... 

At present it is well established that the existence of the phase border between a polymer and any solid leads to the appearance of different types of micro- and macroheterogeneities at the molecular, supermolecular, and chemical levels78. It is established that, due to adsorption interaction at the interface, an essential decrease in molecular mobility takes place as a result of which the glass temperature of such systems increases79. At the same time, due to retardation of the relaxation processes in the surface layers, some loosening of packing takes place, whereas in pure adsorption layers some increase in density is observed80. ... 

We believe that, as the very definition of free-volume characterizes the state of ordering in the system (especially for the cases when we consider the free-volume distribution), it may be preferable to apply the thermodynamic description of the processes at glass temperature. 

Miscible systems invariably form a single phase and are transparent. Their physical properties are directly related to the properties of the individual components and the mole fractions of these in the mixture, the glass temperature (Tg) composition diagram of such mixtures is Unear between the two Tg of the individual components. Since, however, the majority of would be interesting polymer combinations are immiscible, they separate into two phases and become practically uninteresting because of the relatively weak adhesion between the two phases. 

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