Preparation Of Anti-freezing And Self-healing Nanocomposite Hydrogels Constructed By Phytic Acid And Sensing Performance

With the popularization of intelligent devices,flexible sensors with excellent sensitivity and stability have been extensively applied in fields such as motion monitoring and medical rehabilitation.In recent years,hydrogels have shown strong potential for applications in the field of flexible sensors thanks to their excellent biocompatibility,flexibility,and conductivity.However,traditional hydrogels have issues of poor cold resistance and vulnerability,which greatly limit the application range of flexible sensors and shorten their service life.Therefore,improving the anti-freezing and self-healing properties of hydrogels in low-temperature environments is of great significance.Inspired by the anti-freezing properties of biological organisms in nature,the introduction of biomass anti-freezing materials into self-healing hydrogels has become a research focus.Phytic acid（PA）obtained from plants is both abundant hydrogen bond donors and receptors.The strong hydrogen bond between PA and H₂O significantly weakens the hydrogen bond between H₂O molecules,thereby reducing the freezing point of gel system.In this paper,under the participation of PA,cellulose nanocrystals（CNCs）based nanocomposites and microcapsules were implanted into hydrogels,and a series of anti-freezing and self-healing nanocomposite hydrogels were successfully constructed.Furthermore,flexible sensors based on the hydrogels with a wide application temperature range and long service life were developed,which achieved high-sensitivity monitoring of human motion in low-temperature environments.The specific contents of this paper include the following three parts:1.The design and anti-freezing sensing performance study of self-healing nanocomposite hydrogels based on CNCs/poly（diallyldimethylammonium chloride）（PDDA）under the participation of PA.The functional PDDA was used to modify the surface of CNCs,and functionalized CNCs based nanocomposites（CNCs@PDDA）were prepared.CNCs@PDDA were implanted into the polyvinyl alcohol（PVA）network,and the anti-freezing and self-healing nanocomposite hydrogels were successfully designed through freeze-thaw cycles under the joint action of PA and glycerol.With the increase of PA content,the anti-freezing properties of the hydrogels were prominently enhanced,maintaining good self-healing property（self-healing efficiency 85.0%）.Flexible sensors based on the hydrogels had excellent sensitivity（GF=0.9）and fast response（310.0 ms）,which could stably monitor human movements such as smiling,finger bending and knee bending at-30℃.This work provides new ideas for the application of wearable flexible sensors in low-temperature environments.2.The design and low temperature sensing performance study of self-healing nanocomposite hydrogels based on CNCs/poly（pyrrole）（PPy）under the participation of PA.PPy was prepared using chemical oxidation and used for surface modification of CNCs,resulting in CNCs based nanocomposites（CNCs-g-PPy）.In the presence of PA,CNCs-g-PPy were implanted into a double network composed of PVA and PDDA to construct the anti-freezing and self-healing nanocomposite hydrogels.Due to the hydrogen bonding between PA and H₂O,the anti-freezing temperature of the hydrogels could reach to-15℃.With the hydrogen bonding and electrostatic interactions between PA,CNCs-g-PPy and the matrix,the self-healing efficiency of the hydrogels could reach to 92.9%at-15℃.Taking advantage of the hydrogels,the hydrogel based flexible sensors were successfully constructed,with a working range of 0～850%at-15℃,a sensitivity（GF）of 0.8.The sensor could detect human movement,voice and handwriting recognition in low temperature environments,which obtained regular and stable electrical signals.3.The design and sensing performance study of anti-freezing and self-healing nanocomposite hydrogels based on functional microcapsules under the participation of PA.Microporous activated carbon（MAC）was used as carrier for the healing agent-linseed oil（LO）.After loading LO onto MAC,functionalized microcapsules（LO@MAC@PDA）were prepared by modifying the MAC surface with polydopamine（PDA）based on mussel-inspired chemistry.In the presence of PA,LO@MAC@PDA were integrated into a network skeleton composed of guar gum（GG）and PVA,resulting in the successful design of the anti-freezing and self-healing nanocomposite hydrogels.Due to the dual self-healing effect of healing agent and reversible non-covalent bonds,the self-healing efficiency of the hydrogels was up to 93.5%at-20℃.After performance testing,the hydrogel based flexible sensors still exhibited excellent durability（800 cycles of stretching）,fast response（205.0 ms）,and high sensitivity（GF=1.0）.The hydrogel based flexible sensors sensitively captured signals such as smiling,blowing and bending of various human joints at-20℃.This work provides new insights for the research and application of anti-freezing and self-healing nanocomposite hydrogels in the field of flexible wearable sensors.