Modulated temperature TMA

Traditionally, simple combinations of linear heating or cooling rates and isothermal segments have been employed. Modern methods, however, frequently impose cyclic temperature programs coupled with Fourier analyses to achieve particular advantages and added information. These approaches are referred to as modulated techniques, and temperature is the most commonly modulated parameter. Note that in DMA, stress or strain is the modulated parameter and that in DEA, the electric field is modulated, but in modulated temperature DSC and modulated temperature TMA, it is the temperature that is modulated. 

In a modulated temperature TMA (MTTMA) experiment, the sample is exposed to a sinusoidal temperature modulation overlaid on a linear underlying heating, cooling, or isothermal profile, similar to modulated temperature DSC (see Section 2.13). Of course, the dependent physical property measured is length for this technique, and the temperature modulation with its resulting modulated length can be noted in Rg. 4.5. 

TA Instruments provides the only commercial modulated temperature TMA (see TA Instruments Application Notes TA311 at www.tainstruments.com). 

SThM was carried out in the laboratory of H. Pollock and A. Hammiche in the Physics Department of the University of Lancaster, Lancaster, UK using a modified Topometrix Explorer SPM (Topometrix Corporation, Santa Clara, CA). The microscope uses a small Wollaston wire, bent and etched to form a contact mode AFM tip with a nominal radius of about 200 nm. The tip is used both as a heat source and a heat sensor. A second, reference, tip is held in air in close proximity to the sample for differential measurements. The heat to the tip can be modulated and the material response to the modulated heating can be monitored during imaging via lock-in techniques. For the work described here the microscope was operated in three imaging modes (1) constant deflection (for topography) (2) constant temperature (DC) and (3) modulated temperature (AC). In an unscanned mode, the tip can be positioned on the surface for local differential thermal analysis (DTA) or local modulated temperature-DTA and local thermomechanical (TMA) measurements (4,22). 

Apart from combined TA techniques (on-line or not) the actual trends in thermal analysis are the introduction of modulated and high-resolution techniques, hyphenated thermal analysis methods e.g. TG-FTIR, TG-MS, DSC-XRD, etc.), alternative heating modes, microthermal analysis methods, industrial standardisation and quality control. Modulation means a periodic perturbation of a temperature program. Temperature modulation finds application in DSC, TG, DETA, TMA and uTA. Temperature-modulated techniques, such as Modulated DSC (MDSC ) and Modulated TGA (MTGATM), broaden the insight into the material properties. The use of modulated temperature programs in thermal methods has been reviewed [37,37a]. 

Table 2.5 summarises the main applications of thermal analysis and combined techniques for polymeric materials. Of these, thermomechanical analysis (TMA) and dynamic mechanical analysis (DMA) provide only physical properties of a very specific nature and yield very little chemical information. DMA was used to study the interaction of fillers with rubber host systems [40]. Thermomechanical analysis (TMA) measures the dimensional changes of a sample as a function of temperature. Relevant applications are reported for on-line TMA-MS cfr. Chp. 2.1.5) uTMA offers opportunities cfr. Chp. 2.1.6.1). The primary TA techniques for certifying product quality are DSC and TG (Table 2.6). Specific tests for which these techniques are used in quality testing vary depending upon the type of material and industry. Applications of modulated temperature programme are (i) study of kinetics (ii) AC calorimetry (Hi) separation of sample responses (in conjunction with deconvolution algorithms) and (iv) microthermal analysis.

The Mettler TMA 40 thermomechanical analyzer is illustrated in Figure 11.3. A measuring sensor applies a user-definable force to the sample of -0.05-0.5 N. The position of the sensor is continuously monitored by a LVDT. TMA measurements can be made in the temperature range -100-1000 C. This module is part of the Mettler TA 3000 thermal analysis system. 

The Du Pont Model 943 TMA module is shown in Figure 11.4. The apparatus uses a LVDT to sense linear displacements of the sample probe. A thermocouple in direct contact with or in close proximity of the sample is used to detect the sample temperature. The sample and probe are surrounded by a temperature-controlled cylindrical heater and Dewar assembly. Various probe configurations allow the apparatus to be used in the expansion, compression, penetration, tension, stress relaxation, parallel plate rheometry, and fiber tension. The temperature range of the instrument is — 180-800°C an optional furnace can be used to extend the range to 1200 C. 

The study of elastic and viscoelastic materials under conditions of cyclic stress or strain is called dynamic mechanical analysis, DMA. The periodic changes in either stress or strain permits the analysis of the dynamic response of the sample in the other variable. The analysis has certain parallels to the temperature-modulated differential thermal analysis described in Sect 4.4, where the dynamic response of the heat-flow rate is caused by the cyclic temperature change. In fact, much of the description of TMDSC was initially modeled on the more fully developed DMA. The instruments which measure stress versus strain as a function of frequency and temperature are called dynamic mechanical analyzers. The DMA is easily recognized as a further development of TMA. Its importance lies in the direct link of the experiment to the mechanical behavior of the samples. The difficulty of the technique lies in understanding the macroscopic measurement in terms of the microscopic origin. The... 

Chapter 4 Thermal Analysis Tools contains a detailed description of thermometry, calorimetry, temperature-modulated calorimetry (TMC), dilatometry, thermomechanical analysis (TMA), d)mamic mechanical analysis (DMA), and thermogravimetry (TGA). 

Data handling and software options (a) 1020 series for DSC-7 and TGA-7 (b) PC series for DSC-7, TMA-7, and high temperature DTA-1700 (c) 7 series personal workstation selected options PL-ETA software supports DHTA, DSC, TGA modules IBM personal computer systems/2" -model 70386 computer ... 

Later developments by the Mettler Company include a desktop thermogravimetry apparatus, the TA 4000. This system consists of a computer processor (TCIO A) and the thermobalance, shown in schematic cross section in Fig. 7.4. The readability of the balance is 1 ng. The electrical range of mass compensation is from 0 to 150 mg, and the overall capacity of the balance is 3,050 mg. The temperature range is room temperature to 1,250 K with heating rates of 0 -100 K/min. The TA 4000 system also includes tabletop modules for DSC and TMA, all coupled to the same data processor. 

Allsop, et al.,f found that DMTA and modulated DSC (MDSC) could be used to identify usefiil secondary components for adhesive formulations. Thermal analysis techniques have been successfully applied by the Naval Aviation Depot, North Island, in the evaluation and repair of advance composite components. DifFeiential scanning calorimetry (DSC) has been used to detect a residual exotherm in undercured FM300 film adhesive and the amount of residual exotherm has been correlated to a reduction in the lap shear strength ofthe adhesive. A similar correlation has been obtained between lap shear strength and the reduction in the glass transition temperature (Tg) as measured by DMA. A reduction in the Tg of thermally exposed AS4/3501-6 laminates has been detected using TMA. The authors correlated the Tg to the reduction in the mechanical properties of the material. 

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