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Fabrication of Stretchable, Skin-like and Conductive Hydrogel Based on Cellulose Nanocrystal As a Strain Sensor Monitoring Human Motions

Rahmani, Pooria | 2023

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  1. Type of Document: Ph.D. Dissertation
  2. Language: Farsi
  3. Document No: 56874 (06)
  4. University: Sharif University of Technology
  5. Department: Chemical and Petroleum Engineering
  6. Advisor(s): Shojaei, Akbar
  7. Abstract:
  8. Hydrogels are of growing interest for fabrication of wearable strain sensors due to their intrinsic ionic conductivity, flexibility, and biocompatibility. Herein, to improve the mechanical properties of hydrogels, conventional covalent crosslinking is replaced with novel physical cross-linking. First, the microstructure and properties of pure hydrogel is optimized. Then, Cellulose nanocrystal (CNC) is added to the optimized gel to reinforce it. Finally, through a sequential strategy, aniline monomers are diffused into the gel network and are in-situ polymerized accordingly, providing high conductivity of 21.7 S/m. The resulting hydrogel has the stretchability of 2500% and the toughness of 1.5 MJ/m3. The hydrogel is able to accurately sense a wide range of strains (0-1000%) and can monitor human motions from large strains to minor ones (e.g., breathing). We also investigated the ability of CNCs for making tough hydrogels based on liquid metal particles (LMPs). To this end, LMPs are physically hybridized with CNCs (as stabilizer) to serve as fillers in PAA hydrogel. The results show that the LM-CNC nanohybrid dramatically improves the toughness of the gel without needing any chemical initiator and cross-linker thanks to presence of LM. The gel is immersed into the NaCl 1M aqueous solution, leading to improving its electrical conductivity up to 3.8 S/m. The resulting gel reveals stretchability of 1500% and toughness of 1.5 MJ/m3. Through adhering to human skin, the gel is able to detect minor (e.g., pulse beat) and large strains associated with human motions. Owing to piezoionic effect, the hydrogel sensor produces noticeable electrical current (≈ 30 µA) under a gentle touch, beneficial for self-powered touch sensing applications
  9. Keywords:
  10. Strain Sensor ; Hydrogel ; Cellulose Nanocrystalls ; Hydrophobic Associations ; Polyaniline ; Liquid Metal ; Polymer Nanocomposits ; Wearable Sensor ; Motion Sensor

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