Ultra-thin, thermal diodes incorporating surfaces of extreme wettability, for phase change, heat transfer applications

• Wickless, ultra-thin 310 μm, polymeric thermal diodes for phase-change heat transfer. • 200% improved performance compared to untreated devices. • Minimum thermal resistance of 0.17°C/W. • Stable heat transfer performance over successive operation cycles. The rapid development of portable and slim electronic devices has increased the requirements for heat flux management. The well-established metallic heat pipes can effectively transfer heat in one dimension, whereas vapor chambers can transfer heat in two dimensions. Most of the devices reported in the literature are relatively thick (>500 μm, with most of them thicker than 1 mm). Herein, the complete micro-fabrication approach of an ultra-thin (310 μm), “wickless”, polymeric thermal diode that enables phase-change heat transfer through capillary action and liquid spreading on the evaporator plate and dropwise condensation on the condenser plate is presented. Thermal diodes can be considered as a type of vapor chamber which enables phase-change heat transfer in a perpendicular plane and can yield higher thermal performance due to high latent heat. The device is one of the thinnest ever reported in the literature, it does not have a conventional wick, instead the two plates of the device are micro and nanotextured using plasma processing and subsequent chemical functionalization (e.g. superhydrophilic evaporator plate and superhydrophobic condenser plate). The proposed thermal diode exhibits 200 % improved performance compared to devices with untreated plates, stable performance and a heat transfer coefficient value of 3650 W/m 2 o C.