Polyelectrolyte Complexes-based Self-healing Hydrogels With High Mechanical Strength

Polymeric materials with high mechanical strength and stretchability show great potential to be used in diverse areas fields including stretchable or wearable electronic devices,actuators,tissue engineering,and so forth.However,it is difficult to design polymeric materials with a combination of high mechanical strength and stretchability because these properties generally tend to be mutually exclusive.Furthermore,polymeric materials are readily damaged in practical usage,resulting in deteriorating their original functions and shortening their life time.Endowing polymeric materials with self-healing capability and recyclability can significantly extend the material lifetimes,decrease the raw material consumption,and reduce the environmental pollution.In this thesis,we demonstrate the rapid fabrication of high-performance polymeric hydrogels that not only integrate high tensile strength,stretchability and toughness,but also possess excellent self-healing and recycling capability by simple complexation process.1.We demonstrate the fabrication of self-healing and recyclable hydrogels with high tensile strength and stretchability by mixing positively charged polyelectrolyte mixture of poly(diallyldimethylammonium chloride)(PDDA)/branched poly(ethylenimine)(PEI)with negatively charged polyelectrolyte mixture of poly(sodium 4-styrenesulfonate)(PSS)/poly(acrylic acid)(PAA)in aqueous solution followed by molding,drying and rehydration.The(PDDA/PEI)-(PSS/PAA)hydrogels with in-situ formed PDDA-PSS nanoparticles have a tensile strength,strain at break and toughness of 1.26 ± 0.06 MPa,2434.2 ± 150.3% and 19.53 ± 0.48 MJ/m3,respectively,which are 2.4-,1.8-and 5.2-times higher than that of the PEI-PAA hydrogels.Benefiting from the high reversibility of the hydrogen-bonding and electrostatic interactions,the(PDDA/PEI)-(PSS/PAA)hydrogels can efficiently heal from physical damage to restore their original mechanical properties at room temperature in water.Moreover,the(PDDA/PEI)-(PSS/PAA)hydrogels after being dried and ground can be recycled at room temperature in the presence of water.2.We demonstrate the fabrication of hydrogels with integrated high mechanical strength,stretchability,and excellent self-healing and recycling properties by simply complexing of PAA and PEI-1-pyrenybutyric acid(PEI-PYA)complexes.The hierarchical PYA nanofibrils that in-situ assembled during the complexation can simultaneously enhance the tensile strength and stretchability of the as-prepared PAA/PEI-PYA hydrogels,leading to the hydrogels with a tensile strength of 1.13 ± 0.04 MPa,stretchability of 2969.9 ± 153.8% and toughness of 18.17 ± 0.86 MJ/m3,which are 2.2-,2.1-and 4.8-times higher than that of the PAA/PEI hydrogels.Meanwhile,the PAA/PEI-PYA hydrogels can efficiently heal from physical cut and be recycled at room temperature due to the reversibility of hydrogen-bonding and electrostatic interactions.This strategy is further extended to fabricate hydrogels comprising hierarchical 9-Anthracenecarboxylic acid(An)and N,N?-di(propanoic acid)-perylene-3,4,9,10-tetracarboxylic diimide(PBI)nanofibrils by complexing of PAA and PEI-An or PEI-PBI complexes,demonstrating its generality for fabricating hydrogels with enhanced mechanical properties.3.We demonstrate that the high-strength,highly stretchable,self-healing and recyclable hydrogels with conveniently tailored mechanical properties can be fabricated by complexing the mixtures of pyranine/PAA(PYR/PAA)and viologen-containing amphiphile/PEI(RV/PEI).The in-situ assembled PYR-RV nanostructures during the complexation can simultaneously enhance the tensile strength and stretchability of the as-prepared(PYR/PAA)-(RV/PEI)hydrogels.Variations of the PYR and RV ratios lead to hydrogels with different nanostructures,which have different effect on simultaneous enhancement of tensile strength and stretchability of hydrogels,thus conveniently tailoring the mechanical properties of hydrogels.Moreover,benefiting from the high reversibility of the hydrogen-bonding and electrostatic interactions as well as high mobility of polymer chains,the(PYR/PAA)-(RV/PEI)hydrogels with different mechanical properties can efficiently heal from physical damage and be recycled at room temperature in water.4.We demonstrate that self-healing hydrogels with high mechanical strength and excellent self-recovery can be fabricated via complexing of linear poly(ethylenimine)(LPEI)and benzaldehyde-2,4-disulfonic acid disodium salt(BADS)modified poly(vinyl alcohol)(SPVA).The strong electrostatic interactions between sulfonate groups of SPVA and protonated amine groups of LPEI,and the weak hydrogen-bonding interactions between sulfonate groups and hydroxyl groups of SPVA are the main driving forces for the formation of LPEI/SPVA hydrogels.The mechanical properties of LPEI/SPVA hydrogels can be tailored by varying the molar fraction of BADS and mass ratio of LPEI and SPVA.The LPEI/SPVA hydrogels with optimized mechanical properties have a tensile strength of 10.0 MPa.After being stretched of 200%,the hydrogels can completely recover to its initial state at room temperature within 1 h.Furthermore,the hydrogel can heal from physical cut at room temperature due to the reversibility of hydrogen-bonding and electrostatic interactions.