Teflon AF-Coated Nanotextured Aluminum Surfaces for Jumping Droplet Thermal Rectification

Jumping droplet thermal diodes (JDTDs) are promising candidates to achieve thermal rectification for next-generation thermal control. However, most prior demonstrations of JDTDs have relied on monolayer-coated copper-based superhydrophobic (SHPB) surfaces, while lower-cost aluminum JDTDs with more durable thin polymeric coatings have not been explored. In this work, a JDTD is constructed that employs SHPB aluminum surfaces coated with protective thin films of Teflon AF (amorphous fluoropolymer) 1601. Measurements for different heating orientations, gap heights (H), and fill ratios (phi) show that a maximum thermal rectification ratio of 7 can be achieved for H = 2.4 mm and phi = 10%. A thermal circuit is demonstrated that uses the JDTD to rectify time-periodic temperature profiles, achieving thermal circuit effectiveness values up to 30% of the ideal-diode limit. Coupon-level durability tests and device-level cycling show that dip coated Teflon AF enables stable operation of Al JDTDs over >20 cycles, improving on the performance of a monolayer-coated surface that fails after 5 cycles. The findings of this work signify that Teflon AF coated Al SHPB surfaces can be used for thermal rectification and motivate future research into Al JDTDs for advanced thermal management applications.