Preparation And Functionalization Of Starch-based Ionic Conductive Hydrogel And Its Application In Flexible Sensors

Flexible wearable sensors have received widespread attentions due to their comfort in use,high sensitivity,rapid response,portability and other advantages,and have been used in many flexible electronic fields,such as personalized healthcare,artificial intelligence,human motion detection,and software robots.At present,most of the commercially available wearable sensors are based on elastomers.However,the low stretchability and poor biocompatibility of elastomers still severely restrict the development of flexible electronics.Hydrogels have widely been used in the field of flexible electronics due to their high water content and structural similarity with natural soft tissues.However,hydrogels also have shortcomings,such as weak mechanical properties,lack of adhesion and self-healability,narrow operating temperature range,and poor degradation.In this paper,a series of low-cost,environment-friendly,high-sensitivity,and fast-response multifunctional starch-based ionically conductive hydrogels are designed,assembled into flexible sensors and tested their sensing performance.The main contents are as follows:1.Using starch as the main body and prepared eco-friendly starch-based ionically conductive hydrogels by adding polyvinyl alcohol and borax.The hydrogel has improved mechanical toughness(50.5 k J/m³),ultrafast self-healing performance(10 s in air,120 s under water)and recyclability.The hydrogel-based resistive strain sensors showed high sensitivity(GF=1.02),rapid response(150 ms)and cyclic stability(20%strain,5000 cycles)and could detect large-deformed limb movements and small-deformed movements,such as swallowing and pronunciation.2.Using dialdehyde starch(DAS)and acrylamide(AM)as the main body,with Al₂O₃nanoparticles modified by polydopamine(PDA)as the dynamic crosslinking centers,nanocomposite ionically conductive hydrogels were prepared through the synergistic effect of multiple reversible interactions between the components.The adhesive hydrogels showed high fracture stress(84.0 kPa),strain(2800%)and strong mechanical toughness(1.33 MJ/m³),high UV shielding efficiency(99.8%),and degradability in alkaline solutions(p H=12)within 12 h.The hydrogel-based resistive strain sensors exhibitd high sensitivity(GF=13.90),rapid response(200 ms),wide range of strain windows(0.1-2500%),low detection limit(50 Pa)and cyclic stability(50%strain,1000cycles)under ultra-low working voltage(0.03 V),and could detect large-deformed limb movements and small movements,such as chewing,swallowing,speaking,and pulses.The hydrogel-based temperature sensors showed a high temperature coefficient of resistance and stability.3.Based on the second part,the solvent was changed to a water/1,2-propylene glycol binary solvent system.This part of work also took DAS and AM as the main body,and PDA-modified Al₂O₃ nanoparticles were used as the dynamic cross-linking centers.Highly transparent,self-adhesive,self-healing,anti-drying and anti-freezing organic ionically conductive hydrogels were prepared through the synergistic effect of multiple reversible interactions between the components.The adhesive hydrogels showed high fracture stress(80.8 kPa),strain(2680%),strong mechanical toughness(1.17 MJ/m³)and excellent anti-freezing and anti-drying performance.The hydrogel-based resistive strain sensors exhibitd high sensitivity(GF=11.27),rapid response(260 ms),wide range of strain windows(0.1-2680%),and cyclic stability(50%strain,4000 cycles)under ultra-low working voltage(0.02 V),and could detect large-deformed limb movements and small and complex mvements.In addition,the hydrogel-based contactless ionic sensors could distinguish the distance,angle and number of fingers,indicating their promising potentials in the fields of gesture recognition.4.Using DAS and AM as the main body,and PDA-modified montmorillonite(MMT)as the dynamic crosslinking points,single-sided adhesive,self-healing and degradable Janus double-layer ionically conductive hydrogels were prepared through multiple reversible interactions.The hydrogel showed high fracture stress(104.0 kPa),strain(2100%)and mechanical toughness(1.69 MJ/m³).The hydrogel could be completely degraded in alkaline solutions(p H=13)within 10 h.The hydrogel-based resistive strain sensors presentd high sensitivity(GF=6.51),rapid response(190 ms),wide range of strain windows(0.05-1800%)and cyclic stability(50%strain,5000 cycles),and could detect large limb movements of human body and small and complex movements.In addition,the hydrogel-based capacitive pressure sensors exhibitd high sensitivity(0.202 kPa^-1)and fast linear response.