Preparation And Properties Of Polyvinyl Alcohol Based Eutectogel

Eutectogel is an emerging environment-friendly ionic flexible material with unique ionic conductivity,environmental stability,and low toxicity,possessing the potential to overcome some defects of hydrogels(narrow temperature window)and ionogels(toxicity and high manufacturing costs).Therefore,eutectogels are considered as ideal candidates for flexible and wearable strain sensors.However,the reported eutectogel sensors still suffer from poor mechanical properties and lack self-recovery capability,causing it difficult to maintain the stability of signal during long-term usage.To solve these issues,we developed two methods to fabricate high strength and anti-fatigue eutectogels based on crystalline polymer polyvinyl alcohol(PVA),where outstanding properties were realized by regulating the crystallization degree of PVA in specific deep eutectic solvents(DES s).And a series of investigations were performed to characterize strain sensing performance of the eutectogels and verify practical applications in human motion detection.In the second chapter of this thesis,a high-strength PVA eutectogel was synthesized by a strategy of solvent-induced microphase separation.Here,PVA is dissolved in water,and DES(choline chloride/glycerol)was introduced to induce PVA to undergo microphase separation,leading to poorly solvated domains and highly solvated domains.In poorly solvated domains,the PVA chain is folded and crystallized,and the formed crystal domains served as physical crosslinkers.Such crosslinking structures endowed the eutectogels with remarkable mechanical properties,showing a tensile strength of up to 1.2 MPa,an elongation at break of 405%,and a fracture toughness of 3.23 MJ m-3.Meanwhile,these obtained eutectogels possess plasticity and can be recycled through high temperature dissolution and recasting.In addition,the eutectogel also exhibits excellent frost resistance,and its ionic conductivity can still reach 0.62 mS cm-1 at40℃.Here,a flexible sensor based on the eutectogel was assembled,and it was able to maintain a stable signal output during 1000 stretching/releasing cycles at 50%strain,exhibiting outstanding long-term durability.And this sensor can detect the bending motion of various joints and distinguish the different bending angles of fingers,showing a certain application potential in human motion detection.In the third chapter,we prepared a tough,self-recovery,and transparent eutectogel with PVA/PAA binary polymer framework by UV-induced polymerization of acrylic acid(AA)monomer in PVA DES(choline chloride/ethylene glycol)solution.In this gel,the tight entanglements between PAA molecular chains and PVA molecular chains greatly improve the compatibility of PVA and DES,and promote the formation of uniformly distributed small-sized PVA crystalline domains.Such a eutectogel with high-density hydrogen bond interactions exhibits excellent mechanical properties and rapid self-recovery ability.Specifically,this eutectogel possesses a tensile strength of 2.6 MPa,an elongation at break of 680%,and a fracture toughness of 8.39 MJ m-3.During a cyclic tensile/release process with a fixed strain of 100%,the eutectogel can recover its mechanical properties within a resting time of 600 s.Based on this eutectogel,a reliable and flexible sensor was fabricated and it can exhibit good linearity,sensitivity,and signal stability in a wide strain range(1%～300%).More importantly,the flexible sensor can maintain a highly repeatable response signal in 1000 consecutive cyclic stretching/releasing tests with 100%strain,showing excellent long-term durability.And it has been verified that this sensor can monitor large-scale joint movements and even subtle movements of throat vibration.Thus,this flexible strain sensor possesses strong application potential in human motion detections.