Advanced Materials and Technologies in Flexible Electronics

Abstract

Flexible electronics (FE), once a futuristic concept, have become a transformative force in modern technology. Advances in materials, such as conductive polymers, nanocomposites, and stretchable substrates, along with innovative structural designs like origami, kirigami, and soft matter mechanics (e.g., buckling theory, thin film mechanics), combined with fabrication techniques such as 3D printing and laser patterning, have paved the way for adaptable and wearable technologies that are lightweight, portable, and mechanically resilient. While traditional rigid electronics remain vital, they are limited by their inability to conform to dynamic surfaces, reduced durability under stress, and challenges in integrating with non-planar structures. Flexible materials and manufacturing methods offer promising solutions but still face challenges in micron-scale design, programmable control, and limited strength.
This work introduces flexible materials with advanced fabrication techniques designed to overcome these challenges. It aims to expand the control strategy of mechanical behaviours and related applications of flexible electronics, opening new horizons for innovation in this rapidly evolving field. The details are summarised below:
• In Chapter 2, a comprehensive review of literature on advanced materials, mechanisms, fabrication techniques, and novel applications is presented to provide a better understanding of the current state of the art in FE.
• In Chapter 3, the primary methods, including both experimental and simulation approaches for subsequent chapters, are introduced, with detailed descriptions of specific materials, equipment, and parameters defined within the software.
• In Chapter 4, a typical bilayer thin film using the hyper elastic material polydimethylsiloxane (PDMS) was developed with micron-scale micropatterns. This study thoroughly examines the mechanical morphologies of flexible PDMS bilayer structure under the influence of elastic instabilities. Based on Finite Element Method (FEM), I give a valuable model to analyse the 3D buckling analysis of bilayer thin film with complex structure. Incorporating micropatterns provides predictive control over surface buckling and enables programmable behaviour, offering valuable insights into the development of smart surfaces. This work presents a feasible strategy for manipulating nanoscale morphologies through larger-scale geometric confinement at the microscale, leveraging elastic instabilities of bilayer thin film, offering valuable insights for smart surface programming.
•In Chapter 5, the potential of polyacrylamide (PAAm) hydrogel was investigated as a flexible actuator, focusing on its spontaneous morphogenesis during swelling. I further refined the swelling model and expanded the existing mechanics of swelling, applying it to structures with curvature which were also verified through experiments. This study explored the mechanical behaviour of PAAm hydrogels under swelling conditions and extended the approach to hydrogels with diverse structural configurations. Additionally, a highly entangled strategy was explored to enhance the mechanical strength of PAAm hydrogels. This work primarily introduces a method to influence macroscopic morphogenesis at the millimeter scale through smaller-scale phenomena driven by elastic instabilities of swollen multilayer configuration. Moreover, a similar strategy—controlling finer morphologies through larger geometric constraints, as discussed in Chapter 4—is also applied to the complex structure of hydrogels.
•In Chapter 6, a graphene oxide-based aerogel was fabricated using a facile method to forma regularly buckled microstructure with unique metamaterial-like features, enhancing strength, durability, and sensitivity as a directional pressure sensor. I demonstrated the forming of microstructure by post annealing of aerogel through the FEM and developed further applications. The aerogel also exhibits excellent compatibility as a pressure sensor for human body detection, enabling control of a robotic hand in a commercially available system. This work introduces a relatively simple and novel method for reconstructing microstructures at the same scale, based on tailored thermomechanical deformation.

Date of Award	22 May 2025
Original language	English
Awarding Institution	Northumbria University
Supervisor	Ben B. Xu (Supervisor) & Sherry Chen (Supervisor)