Non-linear temperature-dependent curvature of a phase change composite bimorph beam
Bimorph films curl in response to temperature. The degree of curvature typically varies linearly with temperature and in proportion to the difference in thermal expansion of the individual layers. In many applications, such as controlling a thermostat, this gentle linear behavior is acceptable. In other cases, such as opening or closing a valve or latching a deployable column into place, an abrupt motion at a fixed temperature is preferred. To achieve this non-linear motion, we describe the fabrication and performance of a new bilayer structure we call 'Phase Change Composite Bimorph (PCBM)'. In a PCBM, one layer in the bimorph is a composite containing small inclusions of phase change materials. When the inclusions melt, their large (generally positive and >1%) expansion coefficient induces a strong, reversible step function jump in bimorph curvature. The measured jump amplitude and thermal response is consistent with theory.