Volume Relaxation Time Research Articles

Effects of a Distribution of Volume Relaxation Times in the Annealing of BSC Glass.

The influence of a distribution of relaxation times is studied in annealing experiments. A two-relaxation time model is proposed, which permits the calculation of the distribution of relaxation times from the crossover data of Spinner and Napolitano as well as that of Ritland. This model also characterizes the structure of any glass in terms of two parameters. Thus, quenched equilibrium as well as nonequilibrium glass were compared with rate cooled glasses with respect to their behavior upon further annealing as well as their conductivity at low temperatures with excellent agreement. Borosilicate crown glass was found to have a narrow distribution of relaxation times which is particular to associated liquid monomers rather than polymers. The results can be explained in terms of a topological model for the distribution of relaxation times. The temperature dependence of the viscosity is due to a true activation energy rather than a free volume effect.

Comparison of Dielectric and Mechanical Relaxation in Associated Liquids

A comparison is made of existing dielectric and ultrasonic shear and compressional relaxation data in several associated liquids including glycerol, hexanetriol 1,2,6, butanediol 1,3, 2-methyl pentanediol 2,4, and n-propyl alcohol. The data show that the pressure and temperature dependences of the dielectric time τD and the volume relaxation times τv are very similar indicating a close connection between the two processes. It is proposed here that cooperative effects cause the distribution of mechanical relaxation times in these liquids as well as the non-Arrhenius behavior of the temperature dependence of the shear and volume viscosities. It is further suggested that structural relaxation is a rate-determining step in the dielectric relaxation process and that the origin of the distribution of dielectric times is the distribution of structural relaxation times.

高分子物質の粘弾性とガラス転移

The prevailing relaxation theory on the nature of the glass transition (the sharp bend occurring in specific volume vs. temperature curve measured under a constant rate of cooling) in high polymers and other glass-forming liquids is re-examined.It is pointed out that the glass transition is essentially a non-linear relaxational phenomenon in which volume relaxation time varies steeply with temperature change, the excitation variable in this case, and that this variation is the real cause for the transition. It is therefore emphasized that elucidation of the mechanism of the transition is essentially equivalent to that of the mechanism of the precipitous change of relaxation time or viscosity near the transition temperature, as described in most cases analytically by WLF Eq. or more ultimately by Doolittle type equation in terms of the concept of free volume.It is also pointed out that the transition manifests itself in many physical properties as sharp change of their temperature coefficients and the time-scale determining the transition temperature thus located is only the rate of cooling in any case. The transition or freezing-in of free volume occurs necessarily through a range of temperature owing to the nature of relaxational phenomenon and both ends of the range are to be determined by means of the manifestation of the transition in some appropriate physical properties. As a special example of such cases relation between viscosity and volume retardation is discussed. By using a simple kinetic equation of the first order reaction type for volume retardation and Doolittle type equation for viscosity, it is easily shown that WLF Eq. referred to some equilibrium state is derived so far as volume follows the equilibrium liquid line and further shown that viscosity begins to deviate from WLF curve in response to the commencement of volume retardation with decrease of temperature. The temperature where the deviation starts is the higher temperature end of the transition range and on the other hand the lower end can be determined as the temperature where relaxation effect becomes remarkable with increase of temperature.The above-mentioned considerations are experimentally verified on five polymeric substances by observing viscoelastic and thermal expansion behaviors.

Relation of Nuclear Spin Lattice Relaxation to Ultrasonic Relaxation in Liquids

A comparison of the data on nuclear spin relaxation and ultrasonic relaxation is made. It is suggested the correlation time, τc, used in explaining nuclear spin effects is related to the shear and volume relaxational processes occurring in a liquid. The results of comparing the nuclear and ultrasonic processes indicate the following. (1) The average shear relaxation time found for glycerol is close in value to τc (2) The value for τc for water is shown to be very close to the volume relaxation time calculated by Hall. (3) The variation in the nuclear relaxation times in going from water to glycerol are closely related to the variation in the volume relaxation times. (4) Setting τc, proportional to the average shear relaxation time offers an explanation as to why the pressure dependence of the nuclear relaxation time is not a simple function of the viscosity as predicted by present nuclear relaxation theory.

Sorptive properties of glasslike polymers

AbstractThe swelling and solution of elastic polymers, like the mixing of liquids, results in the formation of equilibrium systems. In the interaction of conventional glasses and liquids, however, quite different phenomena appear and cause nonequilibrium systems to form. The density of molecules in conventional glasses is similar t o that of tightly packed liquids, but the diffusion rates are very low. Such glasses sorb practically nothing at low vapor pressures. Sorption begins only when the vapor pressure and the concentration of sorbed liquid in the surface layer are sufficient to cause the glass to melt. It should be noted that in this case sorption shows a sharp rise and an equilibrium solution forms. The degree of tight packing of polymeric glasses varies considerably, decreasing with increasing molecular weight and rigidity of the chain molecules. This packing can be estimated by comparing the densities of the polymers with the volume of the molecular groups of which these polymers consist, the latter being obtained from x‐ray data, or by comparing the density of the monomer with that of the polymer. Cellulose, which unlike tightly packed glucose sorbs water over the whole range of vapor pressures, is a typical example of a loosely packed polymer. The effect of the density of packing on the sorbing properties of glasses can be more clearly demonstrated by the sorption of ethylbenzene by polystyrenes of different molecular weights. Low molecular weight polystyrenes dissolve in ethylbenzene without any heat production and sorb ethylbenzene from the vapor at high pressures only. This process results in the formation of a solution. High molecular weight polystyrenes, however, dissolve in ethylbenzene, producing heat, and sorb ethylbenzene a t all vapor pressures. The loose packing of polymers is the result of the long relaxation times existent in glasses. When the deformation time of the polymer is less than the volume relaxation time, the polymer becomes porous. Thus both the sorbing properties and the heats of solution of polystyrene become more pronounced during orientation. The degree of tight packing again increases at heats close to the glass point. Thus polymeric glasses hold an intermediate position between liquids and hard porous sorbents, such as silica gel, in regard to their sorbing properties. Unlike hard sorbents, however, they are apt to change their structure not only under external influence but also in the process of sorption.

Effect of Pressure on Dielectric Properties and Volume of 1-Propanol and Glycerol

Dielectric constants and loss have been measured to pressures of 1000 kg/cm2 at audio- and radio-frequencies from 212 to 240°K for glycerol and 124 to 210°K for 1-propanol. Compressions to 1000 kg/cm2 have been measured to room temperature. The increases in static dielectric constant are less than predicted from density increase alone, and the differences are discussed in terms of molecular compression and liquid structure effects. Larger increases of relaxation time with pressure are found at lower temperatures. Constant volume relaxation times do not conform to a simple rate law, and cannot be explained by activation energies depending only on volume. Glycerol shows small, temperature independent, percentage volume decrease with pressure over the whole range; 1-propanol becomes much less compressible at low temperatures.