Dynamic mechanical analysis apparatus

Dynamic Mechanical Analysis (DMA) is a technique in which the elastic and viscous response of a sample under oscillating load, are monitored against temperature, time or frequency. This technique became well known by the impressive amount of information about the structure of polymers obtained with the torsion pendulum apparatus. The torsion pendulum DMA apparatus is a so-called resonant system i.e. the measuring frequency is not constant. The modern DMA systems are nearly always fixed frequency systems operating at frequencies between about 0.01 and 100 Hz. and in a temperature region ranging from about -150°C to 300°C. A survey of the DMA technique and the available commercial equipment was given by Wunderlich [1]. 

The dynamic mechanical properties of polymers are measured using various types of apparatus, as discussed in Chapter 2. By dynamic mechanical analysis, not only main chain motion but also the secondary relaxation can be detected. The mathematical structure of theories of dynamic viscoelastic properties has been presented [81,821 and application to polymers has been described [83]. 

DMA Measurements. Elastic tensile modulus, E of the standard polymers was measured by dynamic mechanical analysis, DMA, on a Rheometrics RSAII DMTA apparatus. Measurements were done at 1 Hz. The deformation amplitude was limited to 0.02% for the stiffer polymers and to 0.1% for the softer ones. 

Costeux etal. [97] developed a model to predict the distribution of the longest ethylene sequence in mLLDPE, and Anantawaraskul etal [98] proposed a model for the CCD of multicomponent copolymers. Westphal et al. [99] compared DSC and TREF and showed how additional information can be provided by dynamic mechanical analysis (DMA). Another technique closely related to TREF is solvated thermal analysis fractionation (STAF), which makes use of a DSC apparatus [100]. 

Dynamic mechanical analysis (DMA) Frequency response under oscillatory stress DMA apparatus... 

Dynamic mechanical analysis is used to determine the response of a polyethylene sample to an oscillating force. In its most general form a sample is attached to a pair of movable probes, one of which applies a sinusoidal oscillatory motion while the other measures the force transmitted by the sample. The temperature of the sample and the frequency of oscillation (to) can be varied independently. The sample may be in either its solid or molten state. In the case of molten polyethylene, the sample typically takes the form of a disk sandwiched between a metal drive plate and a torque transducer. Rotation of the drive plate induces shear deformation within the sample, which is measured by the transducer. The basic configuration of the apparatus is similar to that of the cone-and-plate rotational viscometer shown in Figure 9. With appropriate modifications the same equipment can be used for both types of analysis. 

An apparatus for measuring the dynamic modulus and hysteresis of elastomers. The stress-strain oscillogram is shown on a ground-glass screen by means of an optical system. Now superseded by modem computer controlled servo hydraulic and dynamic mechanical thermal analysis machines. Roll Bending... 

Detailed analysis of the isothermal dynamic mechanical data obtained as a function of frequency on the Rheometrics apparatus lends strong support to the tentative conclusions outlined above. It is important to note that heterophase (21) polymer systems are now known to be thermo-rheologically complex (22,23,24,25), resulting in the inapplicability of traditional time-temperature superposition (26) to isothermal sets of viscoelastic data limitations on the time or frequency range of the data may lead to the appearance of successful superposition in some ranges of temperature (25), but the approximate shift factors (26) thus obtained show clearly the transfer viscoelastic response... 

The basic theories of physics - classical mechanics and electromagnetism, relativity theory, quantum mechanics, statistical mechanics, quantum electrodynamics - support the theoretical apparatus which is used in molecular sciences. Quantum mechanics plays a particular role in theoretical chemistry, providing the basis for the valence theories which allow to interpret the structure of molecules and for the spectroscopic models employed in the determination of structural information from spectral patterns. Indeed, Quantum Chemistry often appears synonymous with Theoretical Chemistry it will, therefore, constitute a major part of this book series. However, the scope of the series will also include other areas of theoretical chemistry, such as mathematical chemistry (which involves the use of algebra and topology in the analysis of molecular structures and reactions) molecular mechanics, molecular dynamics and chemical thermodynamics, which play an important role in rationalizing the geometric and electronic structures of molecular assemblies and polymers, clusters and crystals surface, interface, solvent and solid-state effects excited-state dynamics, reactive collisions, and chemical reactions. 

To interpret new experimental chemical kinetic data characterized by complex dynamic behaviour (hysteresis, self-oscillations) proved to be vitally important for the adoption of new general scientific ideas. The methods of the qualitative theory of differential equations and of graph theory permitted us to perform the analysis for the effect of mechanism structures on the kinetic peculiarities of catalytic reactions [6,10,11]. This tendency will be deepened. To our mind, fast progress is to be expected in studying distributed systems. Despite the complexity of the processes observed (wave and autowave), their interpretation is ensured by a new apparatus that is both effective and simple. 

The resins were tested dynamically by thermomechanical analysis (TMA) on a Mettler apparatus. Triplicate samples of beech wood alone, and of two beech wood plies each 0.6 mm thick bonded with each resin system, for sample dimensions of 21 X 6 X 1.2 mm were tested in non-isothermal mode between 40°C and 220°C at a heating rate of 10°C/min with a Mettler 40 TMA apparatus in three-point bending on a span of 18 mm. A force varying continuosly between 0.1 N, 0.5 N and back to 0.1 N was appUed on the specimens with each force cycle of 12 s (6 s/6 s). The classical mechanics relation between force and deflection E = [L /(4fc/i )][ AF/( A/)] (where L is the sample length, b and h are the sample width and thickness, AF is... 

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