Liquids, dynamic mechanical analysis

Miura and Yoshida also investigated the changes in the microstructure of 1100 EW Nafion sulfonate membranes, in alkali, ammonium, and alkylammonium cation forms, that were induced by swelling in ethanol using DSC, dynamic mechanical analysis (DMA), SAXS, and electron probe microanalysis (EPMA). These studies were performed within the context of liquid pervaporation membranes that could potentially be used to separate ethanol from water... 

Dynamic mechanical analysis (DMA) or dynamic mechanical thermal analysis (DMTA) provides a method for determining elastic and loss moduli of polymers as a function of temperature, frequency or time, or both [1-13]. Viscoelasticity describes the time-dependent mechanical properties of polymers, which in limiting cases can behave as either elastic solids or viscous liquids (Fig. 23.2). Knowledge of the viscoelastic behavior of polymers and its relation to molecular structure is essential in the understanding of both processing and end-use properties. 

The complex sorption behavior of the water in amine-epoxy thermosets is discussed and related to depression of the mechanical properties. The hypothesized sorption modes and the corresponding mechanisms of plasticization are discussed on the basis of experimental vapor and liquid sorption tests, differential scanning calorimetry (DSC), thermomechanical analysis (TMA) and dynamic mechanical analysis. In particular, two different types of epoxy materials have been chosen low-performance systems of diglycidyl ether of bisphenol-A (DGEBA) cured with linear amines, and high-performance formulations based on aromatic amine-cured tetraglycidyldiamino diphenylmethane (TGDDM) which are commonly used as matrices for carbon fiber composites. 

For radicals in a liquid environment the excitation and relaxation processes are very fast, which results in a narrow line shape. However, in the solid state these processes are slower, which results in a much broader line shape. Spectra A and B are characteristic of very mobile radicals. These radicals are present in a concentration of about 10 f mol l 1, during the first 3 min of reaction. Spectrum E is characteristic of less-mobile radicals present in a solid environment. Similar spectra were obtained after this time. Then, it is inferred that at 6 min (macro)gelation takes place, which was confirmed by experiments performed with dynamic mechanical analysis. 

Hsieh et al [62] found that for a range of thermotropic liquid crystalline polymers, the greater the free volume measured by PAL the greater the chain mobility at Tg and the higher the value of tan S (damping strength) measured by dynamic mechanical analysis. 

Dynamic Mechanical Analysis and Stress Relaxation Behavior. Samples were compression molded into bars of the dimensions 38.xl2.5x0.78 0.007 mm and 65.x9.7xl.7 0.007 mm in a Carver laboratory hot press model C. A TA Instruments 983 DMA, which was operated in the fixed frequency mode, was used to characterize the storage and loss moduli as a function of temperature. Samples were scanned at fi-equencies from 0.05 to 10.0 Hz over a temperature range from -150 C to above the glass transition temperature. The displacement was 0.4 - 0.6 mm. Stress relaxation curves were determined for the same size samples at a constant strain. The sample was displaced for 10.0 minutes and then allowed to recover for 10.0 minutes. The stress data were taken in five degree increments. A microprocessor controlled Liquid Nitrogen Cooling Accessory (LNCA) was used for sub-ambient operations. 

In this study, IPMCs with various electrodes (Pt, Au, and Pd) and Pt electroded IPMCs with ionic liquid were compared to study their mechanical characteristics [Park et al. (2007)]. Universal testing machine was used to test the samples in the tensile mode and dynamic mechanical analysis (DMA) was used to test samples in the shear mode. Temperature scanning of DMA makes it possible to conveniently measure the accuracy of the glass transition temperature Tg. In order to confirm the thermal behavior results from DMA, differential scanning calorimetry (DSC) was also performed. SEM was used to investigate the electrode layer and deposited particles. 

Relaxation transitions in polymer EPDM samples before and after the introduction of CNF in alternating load was studied using dynamic mechanical analysis (DMA) on the instrument Netzsch DMA 242C in a temperature range from -140 to 150°C. We used the special cooler CC 200 L running on liquid nitrogen to obtain low temperatures... 

Dynamic mechanical analysis is not limited to just shear deformation it is also used with elongational deformation. Further, dynamic mechanical analysis is employed in the characterization of solids as well as liquids. In 1982, a new standard was established, ASTM D4065, to standardize procedures for testing all types of materials. 

Dynamic mechanical methods (typically oscillatory parallel plate rheometry) are commonly used to measure the dynamic mechanical properties from the liquid state to the solid state. By using small-amplitude oscillatory deformations (linear viscoelastic regime), the dynamic storage and loss moduli can be obtained. From these quantities, the viscosity and modulus can be calculated (71) (see Dynamic Mechanical Analysis). 

Abiad MG, CampaneUa OH, Carvajal MT (2010) Assessment of thermal transitions by dynamic mechanical analysis (DMA) using a novel disposable powder holder. Pharmaceutics 2 78-90 Adijanowicz K, WojnarowskaZ, WlodarczykP, Kaminski K, Paluch M, Mazgalski J (2009) Molecular mobUity in liquid and glassy states of Telmisartan (TEL) smdied by broadband dielectric spectroscopy. Eur J Pharm Sci 38 395-404... 

Thermal analysis methods can be broadly defined as analytical techniques that study the behaviour of materials as a function of temperature [1]. These are rapidly expanding in both breadth (number of thermal analysis-associated techniques) and in depth (increased applications). Conventional thermal analysis techniques include DSC, DTA, TGA, thermomechanical analysis, and dynamic mechanical analysis (DMA). Thermal analysis of a material can be either destructive or non-destructive, but in almost all cases subtle and dramatic changes accompany the introduction of thermal energy. Thermal analysis can offer advantages over other analytical techniques including variability with respect to application of thermal energy (step-wise, cyclic, continuous, etc.), small sample size, the material can be in any solid form - gel, liquid, glass, solid, ease of variability and control of sample preparation, ease and variability of atmosphere, it is relatively rapid, and instrumentation is moderately priced. Most often, thermal analysis data are used in conjunction with results from other techniques. 

Dynamic mechanical analysis measures changes in mechanical behavior, such as modulus and damping as a function of temperature, time, frequency, stress, or combinations of these parameters. The technique also measures the modulus (stiffness) and damping (energy dissipation) properties of materials as they are deformed under periodic stress. Such measurements provide quantitative and qualitative information about the performance of materials. The technique can be used to evaluate reinforced and unreinforced polymers, elastomers, viscous thermoset liquids, composite coating and adhesives, and materials that exhibit time, frequency, and temperature effects or mechanical properties because of their viscoelastic behavior. 

Polymers are viscoelastic materials, whose mechanical behavior exhibits characteristics of both solids and liquids. Thermal analysts are frequently called on to measure the mechanical properties of polymers for a number of purposes. Of the different methods for viscoelastic property characterization, dynamic mechanical techniques are the most popular, since they are readily adapted for studies of both polymeric solids and liquids. They are often referred to collectively as dynamic mechanical analysis (DMA). Thermal analysts often refer to the DMA measurements on liquids as rheology measurements. 

S.2.3.2. Dynamic Mechanical Analysis and Rheology The principles of DMA are equally applicable to liquids. In fact, dynamic mechanical methods are an important way to determine (to a first approximation) flow viscosity data for thermoplastics in the melt state, in lieu of using more expensive and... 

Gas chromatography (GC) and high-pressure liquid chromatography (HPLC) have been used to analyze the reaction mixtures. Thermal analysis and dynamic mechanical analysis is also an important analytical and control tool. Other analyses involve refractive index, viscosity, specific gravity, melting point and gel-time, to name a few. 

Tackifier resins are generally brittle amorphous materials with high softening temperatures (typically 40 -150 °C) [242], [243] and low molecular masses (some 10 to some 10 g/mol). Some are liquids that soften below ambient temperature. All should exhibit reasonable compatibility with the elastomer, which can be detected by the clearness of the mixtures or by dynamic mechanical analysis (see Chap. 2.2.2.). Corn-... 

Dynamic mechanical analysis is quite useful to observe the result of chemical reactions of polymer chains (e.g., transesterification) as evidenced by Figs. 3.12 and 3.13 [26]. The DMA method can be applied isothermally to determine crystallization kinetics (modulus versus time measurements) [13, 27] and reaction rate of thermosetting materials (e.g., epoxy) [28]. For reaction rate determination of liquid systems, the torsional braid analyzer is most appropriate as the braid can be saturated with the prepolymer liquid. A cellulose blotter could be used for the torsion pendulum, and a section of nylon hosiery could be used for forced vibration studies (both supports saturated with liquid prepolymer). 

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