Thermally- and Phase Transformation-Induced Volume Changes of Polymers for Actuator Applications

The potential of using polymer volume changes as a source of actuating power was explored. Volume changes may be induced by allowing the polymer to undergo physical transitions such as glass transition, melting or crystallization, and solid-state phase transformation, or by simply heating or cooling the polymer. When constrained from changing the volume, a polymer can exert a great counteracting stress or pressure on the constraining body. When free to expand or con tract, the polymer may be prescribed to undergo a large change in volume or shape. The magnitudes of the counteracting stresses and the percentages of achievable volume changes were calculated for several commonly used polymers. Methods and procedures for making these calculations were es tablished. The actuating power of polymers was compared with that of metals.