DMA Instrumentation

Low-force tabletop systems with maximum force capability up to 18 N 

Higher force tabletop or floor models these most frequently are load frame instruments with capacities up to 450 N (or possibly greater) 

Rotational rheometers that perform both rheology and DMA solids measurements in the torsional shear mode 

Low-force tabletop instruments are offered by the traditional thermal analysis vendors Mettler Toledo, Netzsch, Perkin-Elmer, and TA Instruments as well as Seiko Instruments. Higher-force tabletop and floor model instruments are offered by Bose and OldbMetrovib. Rotational rheometers that also perform torsional shear measurements on solid samples are marketed by Reologica 

Instruments AB, TA Instruments, and ThermoFisher Scientific (Haake Rheometers). 

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This final point is illustrated more clearly in Figure 4 where viscoelastic data from the DMA instrument are related on a nomograph plot to those from a Rheovibron DDV-II instrument. 

Figure 3. Reduced temperature nomograph for a fluorosilicone polymer. Data taken by both resonant beam and DMA instruments. Key upper curve, modulus and lower curve, loss tangent.

DMA instruments use different principles to study the viscoelastic response of a sample under oscillatory load ). They are (1) The sample may be driven in forced oscillation or allowed to resume its natural frequency ... 

Commercial DMA instruments vary in their design. One commercial instrument is shown in Fig. 16.36, set up for a three-point bend test under dynamic load. A different commercial instrument schematic. Fig. 16.37 shows a sample clamped between two arms that are free to move about the pivot points [Fig. 16.37(a)] the electromagnetic drive and arm/ sample assembly are shown in Fig. 16.37(b). The electromagnetic motor oscillates the arm/sample system and drives the arm/sample system to a preselected amplitude (strain). The sample undergoes a flexural deformation as seen in Fig. 16.37(a). An LVDT on the driver arm measures the sample s response to the applied stress, calculates the modulus (stiffness) and the damping properties (energy dissipation) of the material. 

DMA instruments have furnaces programmable from — 170°C to 600°C. Frequency ranges can be varied from 0.001 to 1000 Hz, depending on the manufacturer. Probe types are the same as those for TMA. 

Thermomechanical Analyses (TMA) were recorded on a DuPont thermal analyzer. Model 943 TMA fitted with a penetrating tip probe, at 2g load and 10°C/mln temperature rise. Vertical displacement and the first derivative of that displacement with respect to time were recorded as a function of temperature. Dynamic Mechanical Analyses (DMA) were obtained on a DuPont 981 DMA Instrument. 

Spain has become home to two mobility groups during the past decade. The Sociedad Europea de AnaUsis Diferencial de Movilidad SL (SEADM) in Boecillo was founded in February 2005 to develop DMAs based on the work of its technical consultant and cofounder Professor Juan Fernandez de la Mora of Yale University. Efforts are largely directed to DMA/MS methods. In contrast, stand-alone DMA instruments are produced by RAMEM, SA, in Madrid. A stand-alone mobility analyzer is commercially available with multivariate analysis software a default library includes standards and one of several nonradioactive ionization sources, including photoionization, corona discharge, and ESI. 

On the other hand, the DMA instrument, which operates similarly to the alMS, contains only one collector electrode. Ions are focused onto the Faraday plate as a function of scanning the orthogonal voltage through which the ions traverse. Spectra are plotted as the ion current on the Faraday plate as a function of UK, where K is the mobility of the ion. In the DMA literature, Z is used to denote ion mobility instead of K. As with the alMS, resolution power is low however, monomers can be separated from dimers. For example. Figure 8.4 shows a typical ion mobility spectrum of a 9.2-kDa polystyrene resin obtained from a DMA." ... 

Note Compression molded specimens were rapidly quenched to the specified quenching temperatures. Relaxation temperatures (tan 5 peaks) were obtained on a DMA instrument at a heating scan rate of l°Cmin . Crystal phase structures were obtained by Raman LAM. Tire degree of aystallinity was determined from the heat of fusion data obtained on a DSC instrument. 

Bending mode Configuration of TMA (or DMA) instrument, where a sample is fixed at both ends and a constant (or oscillating) stress is applied. 

Continuous scans of modulus versus temperature utilizing the DuPont Dynamic Mechanical Analyzer (DMA) has provided a comparison of the high temperature service capabilities of radiation-cured experimental formulations of a vinyl-modified epoxy resin. Shell Epocryl-12. These scans were compared to data obtained when the same materials were applied as adhesives on aluminum test panels, radiation-cured with an electron beam, and lap shear strength tested at discrete temperatures. The DMA instrument utilizes a thin rectangular specimen for the analysis, so specimens can be cut from blocks or from flat sheets. In this case the specimens were cured as sheets of resin-saturated graphite-fibers. The same order of high temperature stability was obtained by each method. However, the DMA method provided a more complete characterization of temperature performance in a much shorter test time and thus, it can be very useful for quick analyses of formulation and processing variables in many types of materials optimization studies. The paper will present details of this study with illustrations of the comparisons. 

Dynamic mechanical analyzer n. An instrument that can test in an oscillating-flexural mode over a range of temperature and frequency to provide estimates of the real , i.e., in-phase, and imaginary , i.e., out-of-phase parts of the complex modulus. The real part is the elastic component, the imaginary part is the loss component. The square root of the sum of their squares is the complex modulus. With polymers, the components and the modulus are usually dependent on both temperature and frequency. ASTM D 4065 spells out the standard practice for reporting dynamic mechanical properties of plastics. An example of a DMA thermogram of different Perkin-Elmer Inc., manufactures the Diamond DMA instrument. Polymer films is shown. Sepe MP (1998) Dynamic mechanical analysis. Plastics Design Library, Norwich, New York. 

TA Instruments dynamic mechanical analyzers are used over a temperature range from -150 to 600°C (-238 to 1112°F) to measure deformations for shear, tension, compression, three-point bending, and dual/single cantilever [3]. They include an optical encoder. DMA instrumentation is more sensitive than differential scanning calorimetry for measuring smaller transition regions. The company s DSC instruments measure heat... 

There are three fundamental test methods for characterization of the viscoelastic behavior of polymers creep, stress relaxation, and dynamic mechanical analysis. Although the primary focus for this chapter is DMA, it is useful first to discuss the fundamentals of creep and stress relaxation, not only because they are conceptually simpler but because most DMA instruments also are capable of operating in either a creep or stress relaxation mode. All three of the methods are related, and numerical techniques are available for calculating creep and stress relaxation data from dynamic mechanical data (Ferry 1980). 

We noted previously that most DMA instruments can measure in a stress relaxation or creep mode. The discussion above relates directly to this. When... 

An alternative to DMA rheology-mode experiments is the shear sandwich experiment carried out with a solids mode DMA instrument. This is done with a parallel-plate fixture subjecting the sample to simple shear as illustrated in Fig. 5.4. Shear-sandwich-mode DMA data are shown in Fig. 5.46 for the cure of an epoxy resin, at frequencies from O.I to 100 Hz (Wetton et al. 1987). 

Several sample test geometries are available with most DMA instruments. These include the following (see illustrations in Fig. 5.50) ... 

S.8.4.2. Errors Due to Machine Compliance Issues As noted above, DMA instruments have a measurable stiffness associated with them. When a strain is imposed on the sample, both the sample and the instrument (including... 

Actual Sample Temperature. Any polymer sample will take a finite time to reach thermal equilibrium, and this is frequently commensurate with the timescale of the experiment. Most polymers have poor thermal conductivities. Thus, the most accurate measurements are made isothermaUy in the step mode, since a soak period can be arranged so that the sample reaches thermal equilibrium. Poorly designed ovens can exacerbate the problem. The guideline of 2 °C/min as the maximum rate for temperature scanning in the ramp heating mode is a useful one for a DMA instrument. This is the rate specified in the various ASTM standards (e.g., ASTM E1640-07, ASTM E1867-06 see Appendix). Samples such as thermoset adhesives coated onto wire mesh, which are thin and have... 

Obviously, the autotension mode will influence the DMA curve, since it may lead to different levels of shrinkage, creep, and change in orientation. Almost all presently available commercial DMA instruments have special fiber and film fixtures sometimes the same fixture can be used for both types of measurements. 

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