Shear Viscosity Activation Energy Research Articles

Analysis of apparent activation energy of shear viscosity of PVC/ZnO nanocomposite, at its phase transition temperature

The present paper deals with analysis of apparent activation energy of shear viscosity of PVC/ZnO nanocomposite, at its phase transition temperature. In this approach storage modulus (E′), loss modulus (E″), shear viscosity (ƞ) and phase transition temperature (Tg) of the PVC and its ZnO nanocomposite are ascertained through Dynamic Mechanical Analyzer (DMA). The variation between log (ƞ) versus (Tg/T) indicates the fragile behavior of the specimen that further depicts the nature of Arrhenius behavior of the specimen near its Tg. The slope of the curve between log (ƞ) versus (Tg/T) characterizes as fragility that is numerically equals to apparent activation energy of shear viscosity, particularly at its phase transition temperature. The study reveals that the apparent activation energy of shear viscosity of PVC changes due to dispersion of ZnO nanofillers.

Integral equation for calculation of distribution function of activation energy of shear viscosity

A new technique of calculation of a distribution function of activation energy ( f ( E ) ) of shear viscosity based on a regularization procedure applied to the Fredholm integral equation of the first kind has been developed using the Baxter-Drayton and Brady model for concentrated and flocculated suspensions. This technique has been applied to the rheological data obtained at different shear rates for aqueous suspensions with fumed silica A-300 and low-molecular (3,4,5-trihydroxybenzoic acid and 1,5-dioxynaphthalene) or high-molecular (poly(vinyl pyrrolidone) of 12.7 kDa and ossein of 20–29 kDa) compounds over a wide concentration range (up to 25 wt% of both components) and at different temperatures. Monomodal f ( E ) distributions are observed for the suspensions with individual A-300 or A-300 with a low amount of adsorbed organics. In the case of larger amounts of nanosilica and organics the f ( E ) distributions are multimodal because of stronger structurization and coagulation of the systems that require a high energy to break the coagulation structures resisting to the shear flow.

Effect of chemical composition on viscosity of oxide glasses

The dependence of viscosity on composition of silicate melts is described by means of a structure based model. It distinguishes between network forming oxides, such as SiO 2, and network modifying ones, such as Na 2O. The structural assumption is that there are two different types of bonds in the system: rigid ones like Si–O–Si and floppy bonds like Si–O −Na +. The activation energy for shear viscosity is reduced in the presence of floppy bonds. Therefore, even low concentrations of modifying oxides reduce considerably the viscosity of the melt, a lubricant effect.

Correlation spectroscopy in molten and supercooled antimony trichloride.

Correlation spectroscopy measurements performed on molten and supercooled antimony trichloride with the homodyne technique show correlation functions that have a nonexponential behavior. Two well-defined distributions of correlation times can be observed in different temporal regions. This behavior is discussed in terms of a structural relaxation of clusters dynamically formed by intermolecular and interchain bonds. The Arrhenius plot of these correlation times shows a linear behavior with the same activation energy for both. In contrast, the activation energy of shear viscosity has a different value, showing that the processes determining the temperature behavior of \ensuremath{\tau} and ${\mathrm{\ensuremath{\eta}}}_{\mathit{s}}$ are different.

Crystallization kinetics and rheology of undercooled melts

It was found that the transport of molecules through the crystal/melt interface is controlled by self-diffusion into the crystal and not only by shear viscosity of the melt. This is done by comparing the temperature dependence of both the linear rate of crystallization and the shear viscosity of two substances (NaPO 3 and LiPO 3). A survey of the available literature data on crystallization and structural relaxation of other substances is also considered. A simple phenomenological approach is proposed, which describes quantitatively the crystallization kinetics by taking into account the fact that the activation energy for molecule transition through the interface depends on both the activation energy of shear viscosity and the activation energy of self-diffusion into the crystal.

Structural relaxation in two metaphosphate glasses

The results of an experimental study on the kinetics of structural relaxation of NaPO3- and LiPO3- glass are reported. Two types of experiments were performed. The dependence of the fictive temperature, Tf, on the cooling rate gives the activation energy, Δh, equal to the activation energy for shear viscosity. On the other hand, the value of the activation energy obtained from the dependence of the temperature of vitrification Tg on the heating rate is considerably lower. In this way the value x = 0.6 for the dimensionless factor proposed by Narayanaswamy is obtained for both substances. The results obtained by the method described in the present investigation are compared with previous findings