Measurement of the Mechanocaloric Effect in Rubber

An apparatus for measurement of mechanocaloric effect in rubber has been constructed and tested by measuring the thermal response of three rubber materials to mechanical strain. The results obtained were satisfactory. Detailed measurement has been performed on these materials. The entropy changes that accompany elongation were calculated from the experimental results and compared with those derived from literature data and statistical theory of the macromolecular chain. A dissipative effect was found to accompany the rapid deformation of rubber and attributed to viscoelastic irreversibility. An experimental procedure to eliminate this effect was identified. The apparatus, assembled with the readily available components, will be a useful device for introducing the entropy concept in thermodynamics courses.

(by T. Matsuo & T. Sato)

Fig. 1. Thermocouple output signal from natural rubber (I) undergoing small elongation and contraction.

Fig. 2. Thermal response of natural rubber (I) vs. elongation ratio λ showing a small systematic difference for elongation and contraction.

Photo 1. (Color online) The silicone rubber sample under the mechano-caloric measurement. The length scale is shown by the centimeter ruler.

Fig. 3. Entropy of elongation of natural rubber (I) and (II) showing the reproducibility of the measurement. The best-fit functions eq. (6) are also shown.