UC San Diego

Piezoelectric ceramics, which have the ability to interconvert between mechanical and electrical energies, have been applied for decades in fields such as mechanical sensing, short range actuation, or charge generation. However, the brittle and inflexible nature of these bulk ceramics has made it challenging for these materials to be applied as wearable electronics or flexible sensing technologies. While conventional piezocomposites involve intricate machining, including ‘dice-and-filling’ methods, these materials still present significant mechanical disadvantages.

This dissertation discusses the creation and study of polymer-ceramic composite materials which are able to be carefully shaped, compressed, or flexed to fit a large range of sensing applications in the wearable sensors space. Several routes that were explored for creating and improving these materials include optically printed 3D structures with tuned surface and matrix chemistries, compressible foam composite materials, and electrospun nanofiber nonwoven mats.The optically printed piezoelectric composite materials discussed in Chapters 2 and 3 offer us some understanding of the importance in chemically controlling the interface between the piezoelectric components and the matrix. This allows us to innovate and improve a piezoelectric composite foam material by introducing covalent linking between its nanoparticle additives and polymer as discussed in Chapter 4. While the porous foam composites act as effective sensors of impacts and other high-strain events, measuring low-strain interactions, such as heart rate is challenging. Addressing the need for more accessible routes to experimentally assess these types of composite materials and the strains and strain-rates involved in events like breathing, walking, or impact detection, Chapter 5 demonstrates a more accessible, purpose-built characterization suite. Through creating a porous electrospun piezoelectric ceramic-polymer mat device as shown in Chapter 6, we're able to leverage the advantages of a porous, flexible composite while achieving a sensing threshold capable of direct biosensing.

Using these varied morphologies of structures, foams, and mats, we are able to tailor these materials for a given application and begin to understand and overcome the mechanical hurdles found in this emerging composite space.