Printing and coating of graphene and related materials for advanced devices

Abstract

The global inks market is continuously growing, from \$17 billion in 2016 it is expected to reach \$24 billion by the end of 2022. Inks have the peculiar advantages of being: cheap, produced and deposited by inexpensive and scalable processes, compatible with large area applications and versatile. Indeed, they are the base of printed electronics, they are employed as functional coatings as well as added to matrices to create smart composites. Graphene and related materials inks combine all these characteristics with outstanding optical and electronical properties, flexibility, good mechanical properties and environmental stability. This dissertation focuses on the use of graphene and related materials inks for advanced devices, covering different aspects of material production and characterization, device fabrication and demonstration of proof of concept devices. I demonstrated the exfoliation of graphite by microfluidization to produce graphene inks with sheet resistance down to 2ohm/sq. They have been used to screen print antennas integrated in RFIDs tags with reading distance of 11.1m at 865-928MHz. I have also formulated high-k h-BN inks via microfluidization suitable to achieve pin-hole free h-BN films down to 100nm thick and with dielectric constant of $\sim$7. I combined these h-BN dielectric films with graphene channels in inkjet printed flexible thin film transistors (TFTs), which showed mobility up to $\sim$100cm$^2$V$^{−1}$s$^{−1}$. I inkjet printed also graphene strain sensors with gauge factors $>$100 on flexible substrates. They have been integrated with printed graphene photodetectors and interconnects to create a flexible multisensors platform. I developed graphene/polymer composites suitable for 3d printing. Printed prototypes showed doubled thermal conductivity, 15$\%$ increase of Young modulus and 12 order of magnitude higher electrical conductivity than the bare polymer matrix. I designed graphene functional coatings to enhance the performances of loop heat pipes (LHPs). I demonstrated an increase of 20$\%$ of the capillary pressure by coating LHPs wicks with RGO/SWNTs foams. LHPs have been tested on ground and in hypergravity and microgravity conditions during parabolic flights.