Temperature Dependence Of Specific Volume Research Articles

Correlation between volumetric change and glass-forming ability of metallic glass-forming alloys

We draw attention to the relationship between volumetric change and glass-forming ability (GFA) in various metallic glass-forming alloys. The critical cooling rate can be expressed as Rc=2.5×10−5exp(5.0×102Vlg), where Vlg is defined as (Vl-Vg)∕Vl. We specifically plot the temperature dependence of specific volume for Ca65Mg15Zn20 alloy, and then demonstrate that the larger slope between Vl and Vg, closely related to thermal expansion coefficient, corresponds well to the GFA of the alloy. This insight can provide a clue if the correlations are to be used in the appreciation of glass formation and in the development of an alloy system with enhanced GFA.

Effect of aging time on the volumetric and enthalpic glass transition of a-PMMA upon heating

In this paper we model the volumetric and enthalpic response of a-PMMA during heating at constant rate through the glass transition region following an aging period of varying length. The modeling is based on a recently developed thermodynamically consistent non-linear viscoelastic theory of thermal and mechanical behaviors of glassy polymers in the glass transition range [Caruthers JM, Adolf DB, Chambers RS, Shrikhande P. Polymer 2004;45:4577–97. Adolf DB, Chambers RS, Caruthers JM. Polymer 2004;45:4599–621]. The original model is slightly modified by replacing the stretched exponential by a relaxation function based on a simplified cooperative model emulating the commonly observed linear variation of the relaxing quantity with logarithmic time. Good agreement is found with the observed temperature dependence of specific volume and enthalpy. Also the peaks in thermal expansivity and heat capacity are well described, both with regard to their intensity and position along the temperature axis.

Negative excess volume of mixing in polybutadiene/polyisoprene blends

AbstractThe temperature dependence of specific volume was measured for miscible polybutadiene/polyisoprene blends by dilatometry. The negative excess volume of mixing below the lower critical solution temperature was studied in terms of the Flory equation‐of‐state. In order to achieve a best‐fit of the calculated excess volume to the experimental excess volume, Flory's interaction parameter X12 was estimated to be negative for the blend. Thus, a stereo structural effect for mixing would be predicted, since only van der Waals dispersion forces are expected between blend components. Considering that one way to observe the stereo‐structural effect is to study conformational changes during mixing, solid‐state proton NMR measurements were conducted. Evidence of a conformational change was obtained for the blend. The occurrence of a structural effect was also suggested. © 1994 John Wiley & Sons, Inc.

Quantitative infrared methods for the measurement of crystallinity and its temperature dependence: polyethylene

Vibrational spectroscopic methods are widely used to characterize semicrystalline polymers in terms of crystallinity. The temperature coefficient of crystallinity, an important and fundamental quantity, is seldom determined for lack of a sensitive method. In this paper, we describe an infrared approach to the measurement of the temperature coefficient of crystallinity. We start from the well-known observation that the integrated intensities of the bands in the spectrum of a semicrystalline polymer change with temperature. It is also known, though less appreciated, that only part of the change is due to changes in crystallinity, the remaining part being due to changes in the intrinsic intensity of the bands. We outline a method for separating these overlapping effects. The method has been applied to a variety of semicrystalline polyethylene samples. The temperature coefficients are found to be highly dependent both on the temperature and on the morphology of the sample. In addition we report crystallinity measurements on a solution crystallized low molecular weight (A& = 13 600) sample, discuss the origin of an apparent anomalous temperature dependence of band intensity cited in the literature, and offer quantitative evidence that the temperature dependence of specific volume is, at temperatures above 0 C, largely determined by partial melting.

Temperature shift factor: Polymer mechanical properties above and below glass transition

A general relation between the temperature shift factor a T and reduced volume ṽ, based on the Doolittle viscosity-volume equation, is considered. The shift factor and the specific volume are assumed to be continuous functions of the temperature T above, at, as well as below the glass transition region. A specific a T(T) formula is obtained by using the Guggenheim-Lu-Ruether density equation; knowledge of the characteristic volume v ∗ is not needed. Precise a T(T) values for a structural adhesive obtained by Kenner, Knauss and Chai have been represented before by two W-L-F equations, one above and the other below the glass transition temperature. The same set of the shift factor values is now represented by a single equation with good accuracy. Accurate data on the temperature dependence of specific volume, v(T), have been obtained from a T(T) values.

Effect of crosslinking density on the viscoelastic properties of unsaturated polyesters

AbstractViscoelastic properties of unsaturated polyesters were investigated in the glass‐rubber transition region in relation to the temperature dependence of specific volume. Polyesters which are homologous with respect to crosslinking density were prepared by using mixtures of succinic and fumaric acid as the dibasic acid component. The temperature dependence of the specific volume was determined by refractive index measurement, the specific refractivity being assumed to be independent of temperature. The temperature dispersion of dynamic viscoelasticity was measured at a constant frequency. Results are summarized as follows. Specific volume and glass temperature are linearly related to the logarithm of crosslinking density. The thermal expansion coefficient and steepness of viscoelastic dispersion decrease with increasing crosslinking density. Fractional free volume and expansion coefficient of free volume, both of which were calculated by WLF equation, are in good agreement with the temperature dependence of specific volume. The results indicate that the effect of crosslinking is largely attributable to the change in amount and distribution of free volume in polymer networks.