Rheometrics, RSA II

DMTA instrument (Rheometric solid analyser) applies a small oscillating deformation and record the sample oscillating force response. Elastic modulus is calculated from the elastic response, that is the sample response “in phase” with applied oscillatory strain. Viscous modulus is calculated from the viscous response, that is the sample force response “out of phase” with the applied oscillatory strain. The sample behaviour can be tested as a function of oscillating frequency and amplitude as well as a function of temperature.
Moduli values change with temperature occurs not only at the glass transition, but also in correspondence of other transitions in the glassy or rubbery plateau. DMTA is a very sensible technique that can record very small changes of the sample mechanical behaviour.