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The DMA determines changes in sample properties resulting from changes in five experimental variables: temperature, time, frequency, force, and strain. The deformation can be applied sinusoidally, in a constant (or step fashion), or under a fixed rate. The DMA uses samples that can be in bulk solid, film, fiber, gel, or viscous liquid form. Interchangeable clamps are employed to allow you to measure many properties, including: modulus, damping, creep, stress relaxation, glass transitions, and softening points. The storage modulus ε’ (elastic response) and loss modulus ε’’ (viscous response) of polymers are measured as a function of temperature or time as the polymer is deformed under an oscillatory load (stress) at a controlled (isothermal or programmed) temperature in a specified atmosphere. The storage modulus is related to stiffness, and the loss modulus to damping and energy dissipation. Glassy, viscoelastic, elastic, and liquid polymers can be differentiated by DMA, and some details of polymer structure can be inferred from the results. DMA is particularly useful for evaluating viscoelastic polymers that have mechanical properties, which exhibit time, frequency, and/or temperature effect. DMA is the most sensitive of all thermal analytical techniques. In DMA the sample is clamped between the ends of two parallel arms. The distance between the arms is adjustable by means of a precision mechanical slide to accommodate a wide range a sample length from less than 1 mm up to 65 mm. An electromechanical motor attached to one arm drives the arm/sample system to a selected strain or amplitude. As the arm/sample system is displaced, the sample undergoes a flexural deformation. A linear variable differential transformer mounted on the driven arm measures the sample response, strain, and frequency, as a function of the applied stress, and it provides feedback control to the motor. The sample is positioned in a temperature-controlled chamber. This heating system is precise and gives accurate control of the sample temperature. There are two classes of clamps for the DMA 2980 – tensioning and non-tensioning. The 3-point bend, tension/film, tension/fiber, compression and penetration clamps are tensioning clamps, while the single/dual cantilever and shear sandwich clamps are non-tensioning. When using non-tensioning clamps, the specimen oscillates about zero stress point and no static (preload) force is required. When you use the tensioning clamps, such as 3-point bending clam, a static (or preload) force must be applied to pretension the sample before the oscillation can occur. The four modes of DMA operation are fixed-frequency, resonant frequency, and stress relaxation. In the fixed-frequency mode the sample is allowed to oscillate at its natural resonance frequency under set conditions. These modes provide higher damping sensitivity than the fixed-frequency mode. The creep mode is used to measure sample creep and strain as a function of time and temperature at a selected stress. Using an isothermal step, the sample is allowed to equilibrate to relaxed state at each selected temperature. After equilibration, the polymer is subjected to a constant stress. The resulting deformation strain is recorded as a function of time for a given period. The sample is then allowed to recover.
Please contact Krystyna Brzezinska (kbrzez@mrl.ucsb.edu) to schedule training. Before training starts please read MANUAL.
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