Construction Of Multi-dimensional Nanocomposite Hydrogels Based On Glycerol/Water System And Their Structural Properties

As one of the most important soft materials with a three-dimensional（3D）hydrophilic network,hydrogels show high water absorption,high elasticity and good biocompatibility.Currently,hydrogels are attractive in fields of biomedicine,household chemicals and environmental protection.In particular,nanocomposite hydrogels（NC gels）,crosslinked with nanoparticles like Laponite（clay）via non-covalent interactions,are more appealing because they combine the functions of nanomaterials（size stability,rigidity etc.）and features of hydrogels（softness and wetness,responsiveness）.As a result,NC gels have gradually become a focus of research due to their mechanical toughness,optical transparency and facile construction strategy.Nonetheless,limited by environmental susceptibility and monotonous structures,conventional hydrogels are still challenging to apply in complex environment.Therefore,this dissertation focuses on achieving nanocomposite hydrogels and their fibers with anti-freezing,anti-dehydration,intelligent response and anisotropy based on the design of glycerol/water co-solvent and polymer structures,as well as the regulation of condensed structures during gelation process.These materials were further investigated for their utilization in fields of smart windows,bio-mimic skin and artificial muscles.The specific research contents and main results are as follows:1.Design and preparation of clay/glycerol/water co-solvent dispersions with anti-freezing and anti-dehydration performance,as well as the investigation of dispersion mechanism of electronegative clay in glycerol/water co-solvent.Via UV-Vis transmittance and viscosity measurements,the effect of water and glycerol on dispersion and stability of clay nanosheets was analyzed.Furthermore,a mathematical model that correlates clay concentration and the maximum addition of glycerol in clay/glycerol/water dispersions was established based on the miscibility of glycerol in water.The anti-freezing and anti-dehydration performance of clay/glycerol/water dispersions was enhanced through regulation of the hydrogen bonding interaction among glycerol and water molecules.It demonstrated that increasing the glycerol content from 0 wt.%to 60 wt.%,the weight loss ratio and freezing point of such dispersions reduced from 91%to 18%and from0.62℃to-24.2℃,respectively.Besides,the electrical performance of these dispersions was tuned by the glycerol content due to its inhibition towards the movement of the exfoliated clay nanosheets and dissociated Na⁺.Consequently,conductivity of the dispersions varied between 3.857～8.313m S/cm.2.Construction of nanocomposite hydrogels in varied glycerol/water co-solvent（GW-gels）with anti-freezing,anti-dehydration and thermo-responsive properties,as well as the investigation on regulating their forming mechanism and structural performance in terms of co-solvent.In GW-gels,oligo（ethylene glycerol）methyl ether methacrylate（OEGMA）and 2-（2-methaoxyethoxy）ethyl methacrylate（MEO₂MA）polymerized to act as the organic phase,while glycerol/water and clay served as the solvent and inorganic phase,respectively.According to the results from XRD,FTIR and SEM that the chemical and physical structures of GW-gels remained undisrupted,irrespective of the glycerol content.The resultant GW-gels displayed excellent transparency over 86.2%,enhanced weight loss ratio at 49%and low freezing point at-21.8℃,with glycerol content in the range of 0-30 wt.%.Besides,phase transition temperatures and self-healing efficiency of GW-gels were tuned within a range of 41.9-57℃and 18.1-84.8%,respectively.Meanwhile,combining conductivity and elasticity,GW-gels effectively sensed human motions with a response time of 0.82 s,thus displaying good sensitivity and stability.Moreover,GW-gels exhibited temperature-dependent transmittance due to the use of thermo-responsive P（MEO₂MA-co-OEGMA）,which was investigated for possible application in fields of smart windows.3.Development of“dynamic polymerization-drawing”spinning method to achieve continuous fabrication of nanocomposite hydrogel fibers with anti-freezing,high anisotropy and high mechanical performance,and the investigation of condensed structure evolution in the fiber forming process.Spinning precursor solutions consisting of comonomers（OEGMA and N,N-dimethylacrylamide（DMAA））as well as clay/glycerol/water dispersions were obtained.The gelation process was monitored in real-time based on rheological and ¹HNMR techniques,with subsequent exertion of drawing process to fabricate continuous nanocomposite hydrogel fibers（GH-Fibers）.Additionally,effects of clay content,monomer ratio and winding speed on spinnability of GH-Fibers were studied in detail to ensure optimal spinning components.SEM,SAXS,WAXD results showed that condensed structures of GH-Fibers underwent changes from“porous→dense”and“random→oriented”during the fiber forming process.As a result,the corresponding universal structural model for such evolution was established.The model indicated that the tensile stress of GH-Fibers with oriented micro-structures reached 5.25 MPa,～67 higher than those without stretching.Furthermore,the tensile stress and elastic modulus of such GH-Fibers was also adjustable by clay content in the range of 1.16～7.20 MPa and 1.07～16.14 MPa,respectively.Besides,glycerol/water co-solvent in GH-Fibers endowed them with fantastic anti-freezing and anti-dehydration properties.When glycerol content was 20 wt.%,GH-Fibers displayed outstanding gel elasticity with ice-free phenomenon up to-20℃,and retained excellent stretchability of～169.4%strain within 30 days.4.Macroscopic assembly of hydrogel fibers to obtain fiber-based membranes with anti-dehydration,high orientation and anisotropy,as well as the investigation of fiber-based hydrogels actuators with macroscopic deformation behaviors.Here,gelation process for the spinning precursor solutions consisting of OEGMA,MEO₂MA,N-isopropyl acrylamide（NIPAM）,and clay/glycerol/water co-solvent dispersions,was monitored by rheological and NMR techniques.The self-healing property of adjacent pre-gels was utilized for macroscopic assembly of corresponding hydrogel fibers,with subsequent exertion of“dynamic polymerization-drawing”method for fabrication of fiber-based membranes in high anisotropy.The results showed that condensed oriented structures evolved in such fiber-based membranes along drawing direction,which endowed them high elastic modulus at 23.5 MPa.Furthermore,resultant fiber-based membranes displayed good anti-dehydration property,whose weight loss ratio was 53%within 60h when glycerol content was 20 wt.%.Multiple composite smart actuators containing fiber-based membranes/hydrogels with symmetric and asymmetric thermo-responsive actuation behaviors were constructed via the effect of oriented structures on anisotropic shape deformations.Besides,fiber-based“Petal-like”devices were developed by directional cutting and macroscopic assembly of such fiber-based membranes.Such devices operated“open-close”shape deformations similar to natural petals and were applicable in fields of biomimetic devices.