Superhydrophobic Encapsulants for FHE Devices

Flexible Hybrid Electronics (FHE) offer benefits for an enormous range of applications, such as in healthcare wearables, smart layer-based integrated sensor networks, soft robotics, and digital microcontroller circuits. It is critical to create flexible and stretchable encapsulation approaches for FHE devices to protect them from the elements. Encapsulation for advanced FHE devices requires new material sets and processes to ensure the physical protection of any microchips in the FHE devices without compromising the stretch or flex properties. This work focused on creating a superhydrophobic coating that can be spray-coated on an FHE device for encapsulation. One of the superhydrophobic coatings was based on a commercial conformal acrylic coating/resin that included silica nanoparticles to create the needed micro and nanoscale roughness for superhydrophobicity. The coating was used on two typical substrates: aluminum and polyimide (Kapton). The resulting coatings possess exceptional water repellency due to a sophisticated micro/nano tailored hierarchical structure. The mechanical stability and durability of the superhydrophobic coatings were investigated using peel, flexibility, scratch, and hardness testing. Experimental results indicated that the mechanical durability was improved by optimizing the stirring time and number of layers of the coating. The final coatings showed good durability and maintain the superhydrophobic properties after these tests. A stretchable coating was also created, providing an encapsulation approach for stretchable FHE devices.