Why can stretching rubber change its temperature?

A rubber sample can warm during a rapid stretch even without rubbing against another object. This elastocaloric response couples mechanical deformation to temperature. Rubber contains long polymer chains connected into a network. Stretching changes which chain configurations are accessible, rather than simply stretching every chemical bond like a tiny metal spring.

A less extended chain has many possible coiled configurations. Greater extension restricts that set and can lower configurational entropy, the part of entropy associated with these arrangements. In an ideal reversible stretch with negligible heat exchange, thermal entropy can increase to compensate, raising temperature. The mechanical work supplies the increased internal energy; entropy is not an energy source.

The illustration uses a fictional ideal account starting at 300 K. At twice the reference length, its configurational entropy falls by 1 J/K. A fixed heat capacity of 20 J/K gives an insulated temperature of 300 × exp(1/20), about 315.38 K. These parameters demonstrate an entropy and energy balance, not the temperature of a real band.

If deformation instead maintains constant temperature through heat exchange, heat can leave while the configuration entropy falls. Rapid compared with heat exchange need not mean too rapid for internal equilibration in the model. Real rubber also has dissipation, interactions, and sometimes strain-induced crystallization; composition, deformation range, rate, and history matter. Removing stress can produce cooling under suitable conditions, but a useful cooling cycle also needs controlled heat exchange.