Abstract
As a burgeoning technology, wearable electronics has brought a transformative force in various applications, including healthcare monitoring, soft robotics, human-machine interfaces, and energy harvesting and storage. They require advanced materials that are not only flexible and lightweight but also possess specific functionalities to improve performance in applications. Considering that biological systems primarily use ions as charge carriers rather than electrons, flexible quasi-solid ionic conductors have received significant interest in wearable applications by virtue of their biomimetic features, such as softness and ionic conductivity. Currently, ionogels, consisting of ionic liquids (ILs) and polymeric matrices, are considered the most advantageous candidates for stretchable ionic conductors due to the combination of the advantages of flexible gels and ILs. Consequently, the excellent characteristics of ionogel make them an ideal substitute for hydrogels in a broad range of applications. Although substantial progress has been made in constructing ionogels and several strategies have been proposed to enhance the performance of ionogels, diverse applications have different requirements on the characteristics and functions of ionogels. Therefore, it is essential for expanding the scope of feasible applications of ionogels to optimize the mechanical and electrical performances of ionogels through tailoring their components and molecular interactions between ILs and polymer matrices.In this research, utilizing cellulose nanofibers (CNFs) as one of the building blocks, a series of ionogels with desired characteristics were developed from bio-inspired perspectives. Through designing the molecular interactions among multiple components, the ionogels were endowed with task-specific functionalities, such as ion-selective migration or conformal adhesion to skin. Leveraging these characteristics and functions, the ionogels have been applied in wearable technologies, including moisture-enabled electricity generation, sensing, and bio-interfaces. Specifically, there are three parts in this thesis.
In the first part, inspired by the mechanical reinforcement of natural biomaterials through non-covalent aggregates, a strategy was proposed to develop CNF-based ionogels through complex coacervation-induced assembly. CNFs can bundle together with poly(ionic liquid) (PIL) to create a super-strong nanofibrous network that retains IL, resulting in ionogels with high liquid inclusion and ionic percolation. The strength of the CNF-PIL-IL ionogels can be adjusted by varying the IL content over a wide range of up to 78 MPa. Their optical transparency, high strength, and hygroscopicity enabled them a promising candidate in moist-electricity generation and applications such as wearable power generators. Additionally, the ionogels are degradable, and the ionogel-based generators can be recycled through dehydrating.
In the second part, considering the excellent performance of CNF-based ionogel demonstrated in the first part, CNF-based ionogel is coated on a stretchable conductive liquid metal (LM) electrode through in-situ coacervation to construct a flexible monolithic integrated moisture-sorption electricity generator (MSEG), in which the dynamic interface between functional materials and electrodes is mediated by a poly(ionic liquid) (PIL) binder to enable tough adhesion and efficient conversion from ion current to electron current. The pre-programmed asymmetric moisture adsorption enables the flexible MSEG to achieve high-performance sustainable output. Moreover, MSEG can be easily patterned and scaled up, highlighting its potential for integrated wearable electronics.
In the third part, inspired by the remarkable characteristics of mucus, we propose a nanofiber strengthening and solvent synergy strategy to fabricate a biocompatible ionogel, which simultaneously integrates desirable properties for bio-interfaces, including tissue-like softness, excellent stretchability, decent tissue adhesion, biocompatibility, ionic conductivity, and self-healing capabilities. The ionogel consists of a bio-binary solvent comprising glycerol and a biocompatible IL as the continuous phase, and CNF-strengthened high-entangled polymer formed via one-step free radical polymerization as the matrix. As a latent solvent, glycerol coordinates the components through interactions and improves their compatibility. Furthermore, the ionogel was demonstrated to be applied in on-skin sensors for real-time motion monitoring, early diagnosis of peripheral neuropathy.
Overall, various CNF-strengthened ionogels with distinct properties were fabricated, in which multiple components synergistically interact through non-covalent interactions to impart the task-specific characteristics. This methodology not only offers novel insights for the development of high-performance ionogels but also significantly expands their applications, propelling their practical implementation in wearable technology.
| Date of Award | 1 Aug 2025 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Xi YAO (Supervisor) |
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