Polymer Complex-based Functional Hydrogels

Polymer hydrogels containing a large amount of water possess three-dimensional cross-linked networks.Polymer hydrogels not only exhibit mechanical properties similar to solids to bear external forces,but also possess flexible chain motility,which exhibits a dynamic structural or volume change in response to external stimulation.However,there are still challenges in application of polymer hydrogels like smart windows,information encryption and biomedical applications.For example,the weak solar modulation ability of hydrogel-based thermochromic smart windows,the complicated preparation method and simple functions of information encryption hydrogels,and the mismatch in mechanical properties between tissue engineered hydrogels and human tissue.Therefore,it is necessary to develop simple and effective methods for fabricating hydrogels with optimized functions and improved mechanical properties.In addition,hydrogels containing a lot of water suffer from mechanical damage,leading to their function loss and degraded mechanical properties.Therefore,endowing hydrogel with self-healing ability is one of the most effective ways to improve the functional reliability of hydrogel and extend its service life.This thesis aims to optimize the network crosslinking density,polymer chains motility and dynamic cross-linking states of hydrogels by adjusting the composition of polymer complexes,regulating the type and intensity of supramolecular interactions,and customizing polymer network microstructure.Therefore,the stimuli-responsive ability（such as thermochromic ability）and mechanical properties（such as mechanical strength,toughness and elasticity）of hydrogels can be significantly improved to ensure the functional reliability and the damage resistance.At the same time,the self-healing abilities endow the hydrogel with extended service life and is conductive to the fabrication of large-scale hydrogel materials.Furthermore,the thesis carries out exploration of the functionalization of polymer complex-based hydrogels,which was divided into the following three parts:1.The polyelectrolyte complex-based thermochromic hydrogels are conveniently fabricated by complexing polyallylamine hydrochloride（PAH）,polyacrylic acid（PAA）,and carbonized polymer dots（CPDs）in NaCl aqueous solution.The thermochromic hydrogel,which is denoted as PAH-PAA-10%CPDs,exhibits ultrahigh optical performance including luminous transmittance（Tlum）of～98.7%and solar modulation capacity（ΔTsol）of～89.3%.Benefiting from the incorporation of functional CPDs forming reversible anchoring with polyelectrolyte complexes in the hydrogels,the PAH-PAA-10%CPDs hydrogel-based smart window exhibits a suitableτc of～24.2℃ and rapid transition ability in～3 s.The loaded NaCl decreases the freezing point of water entrapped within the PAH-PAA-10%CPDs hydrogel to-22.5℃.Moreover,the PAH-PAA-10%CPDs hydrogel exhibits good mechanical compliant between hydrogel and substrates,superb self-healing capabilities without external stimulation and outstanding durability after being stored at least 147 days or undergoing 10000 heating and cooling cycles.The model house equipped with the PAH-PAA-CPDs smart window achieved a 9.2℃ temperature reduction,showing a strong indoor temperature control capability.2.Thermo-responsive polymer complex-based hydrogels are conveniently prepared by complexing polyacrylic acid（PAA）and polyacrylamide（PAAm）in LiCl solutions to achieve reversible information recording,muti-encryption/decryption.The hydrogel（denoted as PAA-PAAm/0.5Li）exhibits temperature-dependent optical transmittance that changes from 3.52%to 94.1%.By varying the type and content of inorganic salts in the PAA-PAAm/0.5Li hydrogels,the transition temperature of hydrogels between opaque and transparent states can be well-controlled in a wide range of 30-60℃.Furthermore,the cross-linking density of the hydrogel network can be adjusted by acidification/deacidification treatment.The steady and repeatable change in transition temperature was achieved in a given hydrogel region after ten repeated acidification/deacidification cycles.The PAA-PAAm/0.5Li hydrogel exhibits excellent self-healing ability,which is conducive to extend their lifetime and realize the preparation of large area information encryption materials.3.We demonstrate the fabication of hydrogel membranes（denoted as SPU-PAA/Zn）with excellent mechanical strength and elasticity by complexation of sulfonate-containing polyurethane（SPU）and poly（acrylic acid）（PAA）in the presence of Zn²⁺ions and swelling in water after solvent volatilization.The low density complementary supramolecular interactions between polymer chains contributes to homogeneous polymer complex-based solution,which is suitable for processing into hydrogel membranes with well-controlled thickness and large area.Benefiting from the synergy of the coordination and hydrogen-bonding interactions and the reinforcement effect of the in situ formed hydrophobic domains,the SPU-PAA/Zn hydrogel membrane exhibits a high tensile strength of～7.1 MPa and a toughness of～30.4 MJ m^-3.Futhermore,the hydrogel membrane possesses high elasticity,which can restore from an～500%strain within 40 min rest at room temperature without any external assistance.The noncovalent interactions and hydrophobic domains in the hydrogels are dynamic to allow the fractured hydrogel membrane to be healed and completely regain its original integrity and mechanical properties at room temperature.Satisfactory biocompatibility of the hydrogel membrane confirms its potential as a biological barrier membrane in surgical operations or artificial organs.