Bulk and shear rheology of silica/polystyrene nanocomposite: Reinforcement and dynamics

Bulk and shear rheological studies were performed on a 10 wt % silica nanoparticle‐filled polystyrene nanocomposite. The limiting moduli in glassy and rubbery states are higher for the nanocomposite than for the neat polymer; the increase is consistent with hydrodynamic reinforcement and is slightly higher than the lower bound of the rule of mixtures prediction. All evidence indicates that the presence of nanoparticles does not significantly change the polymer dynamics associated with glass transition, except to increase the T_g by 3 K. Comparison of the bulk and shear retardation spectra suggests that the underlying mechanisms for both responses are similar at short times and that the long‐time chain modes available to the shear are not available to the bulk, consistent with Plazek's earlier findings. In addition, T ? T_g and TV^γ scaling, along with the findings of thermorheological complexity, are discussed. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015 , 53, 621–632     

Conductivity and thermal expansion of the Ce<Subscript>0.8</Subscript>Gd<Subscript>0.2</Subscript>O<Subscript>1.9</Subscript> solid electrolyte in the oxidizing and reducing atmospheres

Highly compact (99%) solid electrolyte Ce_0.8Gd_0.2O_1.9 with submicron (0.3 μm) grains is synthesized. The dilatometric (20–850°C) and conductivity (180–350°C) measurements are performed on the electrolyte in air and as a function of the partial oxygen pressure \(p_{O_2 } \) (0.21?1×10^?25 atm) at 600, 700, and 800°C. An inflection is found in the temperature dependences of the thermal coefficient of linear expansion and conductivity (impedance measurements) at ～230°C, which is the evidence for a phase transition. The activation energies for conduction in the grain bulk and boundaries differ only slightly, indicating that the grain boundaries’ resistance is caused not by the precipitation of the second phase at the boundaries, but most probably by the presence of intergranular nanopores. The dilatometric measurements confirm a significant increase in the linear dimensions of Ce_0.8Gd_0.2O_1.9 in the reducing atmospheres with a parallel increase in its electron conductivity. The electron conductivity and specific elongation increase proportionally to \(p_{O_2 }^{ - 1/4} \) at all temperatures. The \(p_{O_2 } \) values, at which the transport numbers of ions t _i = 0.5, are determined. They are 10^?22.5, 10^?20, and 10^?18 atm at 600, 700, and 800°C, respectively.     

The effects of molecular orientation on the physical aging and mobility of polycarbonate—solid state NMR and dynamic mechanical analysis

Solid‐state NMR and dynamic mechanical (DMA) measurements were performed on a series of uniaxially hot‐drawn bisphenol‐A polycarbonate samples in order to determine the effects of stretching on the structure, mobility, and local orientation environment. Proton spin‐lattice relaxation times, ¹H T_1ρ, for the phenylene carbon protons were fitted to a biexponential decay function, and both the long and short relaxation times initially increased with stretching. Intensity data indicated an increase in the number of short relaxation time protons and a decrease in the number of long relaxation protons with orientation. Similarly, DMA spectra showed that the β‐relaxation strength also increased with drawing, which implied an increase in the number of localized segmental relaxations. It is theorized that the long and short ¹H T_1ρ relate to protons within tightly packed “cooperative domains,” and to those with greater localized free‐volume, respectively. Stretching is known to distort the free‐volume distribution, causing a decrease in the mean free‐volume but an increase in the number of larger, more elliptical holes. This is expected to cause a decrease in the α‐transition mobility (due to larger cooperative domains) and an increase in the β‐mobility (due to the increase in the number of β‐relaxing segments associated with the larger free‐volume holes). These predictions are consistent with results recently reported by Shelby and Wilkes on the physical aging and creep behavior of these samples (M. D. Shelby & G. L. Wilkes, Polymer 1998, 39, 6767; M. D. Shelby & G. L. Wilkes, J Polym Sci Part B: Polym Phys 1998, 36, 2111). © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 39: 32–46, 2001     

The thermal analysis of polymers at high pressures

The extension of two techniques of thermal analysis into the region high pressures (50–100 MPa) are discussed. One is the extension of dilatometry (thus becoming pressure-volume-temperature measurements, PVT). This technique has been well established over the past few years. Some results obtained on typical polymer systems are presented and discussed. The second is the extension of the differential thermal analysis (DTA) principle to high pressures, trying to maintain some of the advantages of the DTA technique when compared to the PVT method, such as small sample size and productivity. DTA determinations of the pressure dependence of the melting points of pure metals and polymers are presented and compared with results from the PVT technique. Satisfactory agreement is obtained. The advantages and limitations of our current high-pressure DTA method are discussed.We gratefully acknowledge the partial financial support of the high-pressure DTA development by Metler Instrumente AG, Switzerland.     

Phase Equilibria in the Binary System Lead Fluoride [PbF2]-Cadmium Fluoride [CdF2]

Phase dependences in the binary system lead fluoride [PbF₂]—cadmium fluoride [CdF₂] were examined and the phase diagram of this system was established. The occurrence of solid continuous solutions with a minimum melting point of 750°C and a CdF₂content of 35 mol% was confirmed. Thermal, dilatometric, microscopic and X-ray analytical methods were used during the investigations. This revised version was published online in July 2006 with corrections to the Cover Date.     

Comparison of Various Analytical Methods in the Study of the Reaction Between Zinc Oxide and Fe(III) Oxide

The paper deals with the possible application of various methods to follow the course of reaction between zinc oxide and Fe(III) oxide with respect to various kinds of Fe(III) oxides used (Fe(III) pigments - red, yellow and black). Differential thermal analysis and chemical analysis can be recommended as the most suitable methods for following reactions leading to spinel formation. The possibilities of determining the activation energy of the studied processes are discussed. When Fe(III) red pigment is used as a reactant and therefore no reaction occurs except spinel formation, conductometric thermal analysis was found to be suitable and more sensitive for the evaluation of differences in reactivities. It has also been observed that the kind of Fe(III) pigment, due to its individual reactivity significantly affects the colouring properties of the final product (e.g., of the ceramic stain). This revised version was published online in July 2006 with corrections to the Cover Date.     

Caracterisation physico-chimique de certaines argiles utilisees dans l'industrie ceramique

The physico-chemical characterization of three samples of clay used in Nabeul (TUNISIA) ceramic industry are studied by some methods: chemical analysis, X-ray diffraction, infrared spectroscopy, differential thermal and thermogravimetry analysis, dilatometry, measurement of surface areas and cation exchange capacities. The samples are kaolino-illitic clay, but they differ in cristallinity and in the rate of quartz and iron. A quantitative estimation of the ratio kaolinite/illite by three methods (X-ray diffraction, infrared spectroscopy, differential thermal analysis) are proposed.     

Thermogravimetric and dilatometric studies using Stepwise Isothermal Analysis and related techniques

The Stepwise Isothermal Analysis (SIA) technique, which was introduced by the author in the late seventies has proved to be very useful both in thermogravimetric and dilatometric studies. By this technique the heating and cooling programme is controlled by the rate of the reactions taking place in the sample, for instance thermal decompositions (TG) or sintering (dilatometry). By an advanced computer programme this control is achieved in the following way: The sample is heated at a constant heating rate until the reaction rate. i. e. the slope of the weight/length versus time curve, exceeds a preset limit at which point the heating is stopped. The reaction thereafter proceeds isothermally until the rate again becomes smaller than the limit where the heating is resumed. By this techniques the reactions thus characteristically take place in isothermal steps.This technique is especially useful in studies of thermal decompositions and it is believed that the decomposition températures determined by SIA is much more accurate than those determined by other techniques even for materials involving consecutive and close-lying reactions. One typical application of this technique is establishment of optimum conditions for removal of organic binders from ceramic powder compacts prepared for instance by dry pressing or injection moulding.The SIA technique is also very useful in kinetic studies and with the advanced computer systems available today rather sophisticated control and analysis of the data can be obtained. One example, which will also be discussed in the presentation, is a study of the decomposition of Ce-carbonate using first the standard technique described above by which the reaction mechanism could be established and then followed by the so-called Forced Stepwise Isothermal Analysis technique (FSIA) by which the activation energy could be obtained.Finally the SIA technique is also very useful in dilatometric sintering studies and to demonstrate this the result obtained both using SIA and the related constant shrinkage rate technique in a study of the initial sintering stage of CeO₂ will be presented.

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Zusammenfassung Das vom Autor Ende der siebziger Jahre eingeführte Verfahren der Stufenweisen Isothermischen Analyse (SIA) erwies sich sowohl bei thermogravimetrischen als auch bei dilatometrischen Untersuchungen als sehr nutzvoll. Bei diesem Verfahren wir das Heiz- und Kühlprogramm durch die Geschwindigkeit der in der Probe ablaufenden Reaktion- z.B. der thermischen Zersetzung (TG) oder des Sintern (Dilatometrie) — gesteuert. Diese Steuerung wird durch ein Computerprogramm auf folgende Weise erreicht: Die Probe wird mit einer konstanten Aufheizgeschwindigkeit aufgeheizt, bis die Reaktionsgeschwindigkeit, d.h. der Anstieg der Gewichts/Längen — Zeitkurve, einen gewissen Grenzwert überschreitet, wodurch der Aufheizvorgang gestoppt wird. Die Reaktion wird anschlie\end isotherm fortgesetzt, bis die Geschwindigkeit wieder kleiner als der Grenzwert wird, zu diesem Zeitpunkt setzt die Aufheizung wieder ein. Durch dieses Verfahren erfolgt die Reaktion somit in isothermen Stufen.Dieses Verfahren ist besonders bei der Untersuchung von thermischen Zersetzungen nutzvoll und man nimmt an, da\ die mittels SIA ermittelte Zersetzungstemperatur wesentlich genauer ist als im Falle von anderen Verfahren, besonders bei Substanzen mit konsekutiven und nahe beieinanderliegenden Reaktionen. Eine typische Anwendung dieses Verfahrens ist die Ermittlung der Optimumbedingungen für die Entfernung organischer Bindemittel aus Keramikpulverpre\lingen, die z.B. durch Trockenpressen oder Spritzgie\en hergestellt wurden. Ein Anwendungsbeispiel dafür wird hier diskutiert.Auch bei kinetischen Untersuchungen ist das SIA Verfahren sehr nutzvoll und mit den heute erhältlichen Computersystemen ist eine anspruchsvollere überwachung und Analyse der Angaben ist möglich. Ein ebenfalls in vorliegender Arbeit diskutiertes Beispiel ist die Untersuchung der Zersetzung von Ceriumkarbonat, wobei zuerst die obenbeschriebene Standardmethode angewendet wird, wodurch der Reaktionsmechanismus abgeschätzt werden kann. Im Anschlu\ erfolgt eine sogenannte Erzwungene Stufenweise Isotherme Analyse (FSIA), wodurch die Aktivierungsenergie ermittelt werden kann.Letztendlich ist das SIA Verfahren auch bei dilatometrischen Sinteruntersuchungen sehr nutzbringend. Um dies darzustellen, wird bei einer Untersuchung des ursprünglichen Sinterzustandes von CeO₂, sowohl das durch SIA als auch das durch das Verfahren der konstanten Abschreckgeschwindigkeit≓ erhaltene Ergebnis dargestellt.

     

Dilatometry and high temperature x-ray diffractometry study of LaCrO<Subscript>3</Subscript> prepared using microwave heating

The phase transitions in the LaCrO₃ were studied using bulk dilatometry and high temperature X-ray diffractometry from room temperature to 1050 and 1200°C, respectively. LaCrO₃ was prepared at 500°C from oxalate precursor employing microwave heating technique. Bulk shrinkage measurements on LaCrO₃ pellets were carried out using dilatometer designed and fabricated in our own laboratory. Dilatometric curves of LaCrO₃ showed two peaks in ΔL/L vs. temperature curves in the range 200–400 and 800–1000°C, respectively. These phase transitions have been confirmed using high temperature X-ray diffractometry. The role of simple technique like bulk dilatometry in detecting and monitoring the polymorphic transformations in solids is discussed for lanthanum chromates.