High-throughput Synthesis And Comprehensive Investigation Of Self-healing Polybetaine Hydrogels

As a dynamic physical bonding with relatively high binding energy and fast reconstruction ability,ionic interaction plays a role in maintaining the integrity of the gel structure and endowing zwitterionic polybetaine hydrogels with self-healing properties.Polysulfobetaine polymers possess a variety of intrinsic characteristics,including biofouling,anti-fogging,anti-frost,phase transition,anti-polyelectrolyte behavior,high transparency and stickiness,etc.,thus exhibiting potential application in many fields like biomedical,surface protection,oil-water separation,etc..However,as most synthetic hydrogels,polybetaine hydrogels also exhibit poor mechanical properties due to the swelling by water molecules,which limits their application under actual working conditions.In response to the problem above,we have selected sulfobetaine monomer: 3-dimethyl-2-（2-methylprop-2-enoxyoxy）ethylazapropylpropane-1-sulfonate（DMAPS）as the main monomer,with chemical crosslinking and hydrophobic modification,to synthesize a series of tough and self-healable polysulfobetaine hydrogels:Firstly,poly（ethylene glycol）diacrylates of different lengths（PEGDA200/400/600,where 200/400/600 represents mean molecular weight）were selected as crosslinking agents,and chemically crosslinked polysulfonate betaine hydrogels were prepared through free radical polymerization.The effects of the monomer concentration,crosslinker chain length and content on the mechanical properties of the gel were explored.For the next step of the preparation of the composite gel,D₁P_600-0.3 was selected to be the control hydrogel as its favorable elongation at break and fracture toughness,which is over 1000% and 1100 k J·m^-3,respectively.Moreover,the self-healing properties of the control gel was preliminary evaluated to be good.Then,based on chemical crosslinking,hydrophobic interaction was further introduced to promote energy dissipation.Result shows the toughness of the gel was optimized significantly.Use anionic（sodium dodecyl sulfate,SDS）,cationic（hexadecyl trimethyl ammonium chloride,CTAC）,zwitterionic（dodecyl dimethyl betaine,BS-12）surfactants as co-solvents,the hydrophobic monomer 2,2,2-Trifluoroethyl methacrylate（FMA）was copolymerized with DMAPS and 0.3 mol% PEGDA600,and hydrophobic association and ionic bonding cross-linked polysulfobetaine hydrogels was prepared through micellar polymerization.Results show that after 24 h waiting time,the self-healing efficiency of a small amount（6 w/v%）of single-ionic surfactant-assisted gel reached 94% and 91% for SDS and CTAC,respectively.At the same time,compared with the control group D1P600-0.3 gel,for PPSB-HA/SDS and PPSB-HA/CTAC hydrogels containing only a small amount of FMA（<5 mol%）,the fracture toughness can be increased to 2 times and 4.5 times of its original value,respectively,indicating favorable toughening effect.Unexpectedly,betaine surfactant BS-12 did not improve the mechanical properties of the gel.On the contrary,it greatly reduces the self-healing efficiency of the gel due to its damage to original ionic bonding within its control PPSB hydrogels.Importantly,we conducted all the above screening experiments with a homemade high-throughput direct writing device.Due to application of high-throughput synthesis method,it’s able to explore systematically how sulfobetaine monomer concentration,crosslinker chain length and content,hydrophobic monomer content,surfactant type and dosage affect the hydrogel structure,mechanical properties and self-healing properties.The experimental efficiency is improved from the very beginning,saving the experimental time and cost,and the advantages of high-throughput preparation in material research and development were fully described.