| dc.description.abstract | Wearable sensors, particularly strain sensors that adhere directly to human skin for precise and dynamic monitoring of human motion and physiological signals, have undergone rapid development and demonstrated significant utility in modern medical systems. The development of wearable sensors necessitates materials with exceptional flexibility, a requirement for which polymeric gels have shown significant potential. Polymer gels are defined as three-dimensional (3D) networks of cross-linked polymers that swell in solvents. The properties of gels depend highly on the solvent used, as it constitutes a major component. In this context, deep eutectic solvents (DESs) have emerged as conductive, biodegradable, cost-effective, and non-toxic alternatives to water, ionic liquids, and organic solvents for fabricating polymer gels.
By harnessing the advantageous properties of DESs, eutectogels—composites of polymers and DESs—have undergone extensive research for diverse applications, notably in strain sensors. Within this thesis, a diverse range of eutectogels, encompassing both chemical and physical types, each possessing unique properties, has been developed for implementation in strain sensing applications. This thesis encompasses four papers:
Chapter 1: Developing Sustainable and Cost-Effective Inks from Jammed Microgels in Deep Eutectic Solvents for 3D Printing of Strain Sensors with Auxetic Structures
A green and low-cost 3D printing ink suitable for the direct ink writing technique has been developed using microgels and DES. The 3D printing ink can be used to fabricate various structures, especially auxetic frameworks. In contrast to a thin-film structure, the eutectogel with auxetic structures serves effectively as a strain sensor, detecting human motion with enhanced skin comfort and breathability.
Chapter 2: Microgel-Induced Regulation of Crystalline Domains toward the One-step Fabrication of Physical Eutectogels with Excellent Recyclability
The physical eutectogel is obtained through a one-step fabrication process using only green and low-cost materials, which include Carbopol (microgel), polyvinyl alcohol (PVA), and DES. This is attributed to the uniform dispersion of PVA crystalline domains within the DES, facilitated by the hydrogen bonds and space restriction effects between PVA and Carbopol. Furthermore, the recyclable physical eutectogel can consistently generate electrical resistance signals, highlighting its potential as a reliable strain sensor.
Chapter 3: One-step, Additive-free Fabrication of Highly Stretchable and Ultra-Tough Physical Eutectogels
A highly stretchable and ultra-tough physical eutectogel is fabricated in a single step using partially hydrolyzed PVA instead of fully hydrolyzed PVA. The physical eutectogel, containg only PVA and DES, exhibits outstanding mechanical properties, including a tensile strength of 6.8 MPa, stretchability of up to 2420% strain, and ultra-high toughness of 122.3 MJ/m³. It also exhibits good ionic conductivity, at 0.15 S/m, and consistently produces reliable resistance signals over a variety of human movements, showcasing its effectiveness in strain sensing.
Chapter 4: Functional Eutectogel Based on Ultrahigh-Molecular-Weight Polymers: Physical Entanglements in Deep Eutectic Solvents
A physical eutectogel is developed based on the entanglements of ultra-high molecular weight polyvinylpyrrolidone (PVP) in DES. The entangled eutectogel showcases outstanding stretchability, reaching 1410% strain, and produces a dependable resistance signal, ideal for strain-sensing applications. Additionally, alongside its high adhesive strength, the entangled eutectogel demonstrates self-healing capabilities, enabled by the diffusion and re-entanglement of polymer chains. | en_US |