Bioengineering a Reversible Thermal Conductivity Switch in Tandem Repeat Proteins

The reversible regulation of heat transport within a material provides the user the ability to control its temperature as well as that of its surroundings. To achieve this nanoscale regulation, a material must be able to switch between thermally conductive and insulative states. In recent years it has been shown that thin films of certain tandem repeat proteins can achieve this thermal switch by simply hydrating and dehydrating the film. One material that is able to serve as a thermal switch is a synthetic bio-polymer whose sequence is inspired by those found in squid ring teeth (SRT). These SRT bio-polymers consist of repeating amorphous and crystalline domains which rely on hydrogen bonding and other intermolecular forces to retain their folded conformation. The addition and removal of water to these films will enhance or disrupt the intermolecular forces, thus encouraging or inhibiting the transport of heat. <br/><br/>In these experiments, we used time-domain thermoreflectance (TDTR) to monitor the thermal conductivity switch of SRT thin films under varying hydrating conditions. TDTR is an optical pump-probe technique for measuring thermal conductivity of microscale material systems, where a low power “probe” beam monitors the change in reflectivity of a metal transducer on the sample surface in response to a modulated heating “pump” laser. By applying an analytical solution to the heat conduction equation, we calculate thermal conductivity and other thermal properties of the material. We show that by modifying the composition of the hydrating solution, we are able to obtain a thermal conductivity switch ratio of four between ambient and hydrated states.