Super Tough Hydrogel Based On Interfacial Molecular Assembly And Applications

In nature,many strong interfacial bonds stem from cooperative assembly of weak interactions,including the formation of bacterial biofilm,the adhesion of barnacle by secreting cement proteins to the humid environment,and the climbing of ivy to the cliff through the cooperative effect of multiple suckers and microstructure.Yet,it remains challenging to engineer such strong noncovalent interactions in synthetic system.Using the weak interaction between 1-Pyrenecarboxylic acid and graphite as an example,here we show that this interaction can be greatly enhanced by interfacial peptide-selfassembly.Taking advantage of such strong interactions,we were able to exfoliate graphene nanosheets in aqueous media by ultrasonication and further use these graphene layers as building blocks to construct hydrogels.Unlike the weak and brittle hydrogels,the graphene hydrogel based on such strong self-assembly-enhanced interfacial interaction are tough,stretchable,self-healable and remodeled with a toughness of ~32.64 MJ m-3,break strain of ~8000%,and self-healing rate is in seconds.We suggest that such remarkable mechanical strength of the graphene hydrogel originates from the synergistic effect of strong reversible self-assembly-enhanced interfacial interactions and the layered structures with multiple parallel alignment.The tough and stretchable graphene hydrogel also has excellent electrical properties with quick response to strain so that it can be applied to capacitive strain sensors,which can be used as a wearable sensor to monitor the vibration of human motion or acoustic sensors.We expect that the principle of strong self-assembly-enhanced interfacial interaction can be used as a general route to tune the strength of weak bonds and expand the applications of weak bonds for strong and tough materials.We also hope that the development of strong and tough graphene hydrogel can promote the innovation of flexible electronic devices.In chapter 1,we briefly describe the background,research status and application of single molecule force spectroscopy,graphene materials,stretchable and tough hydrogel based on the strong self-assembly-enhanced interfacial interaction.In Chapter 2,we use the weak interaction between 1-Pyrenecarboxylic acid(PY)and graphite as an example,and show that this interaction can be greatly enhanced by interfacial peptide-self-assembly through AFM-based single molecular force spectroscopy.We design a polypeptide system(PY-GAGAGY)which can be formed by the combination of PY and polypeptide(GAGAGY).Through the cooperative effect of ?-? interaction between PY and highly oriented pyrolytic graphite(HOPG)and the self-assembly of PY-GAGAGY to form a stable structure like centipede,we find that the dissociation force between PY-GAGAGY and HOPG is stronger than that between PY and HOPG by single molecular force spectrum method,and using this strong selfassembly-enhanced interfacial interaction mechanism,we can develop bio-adhesive material and prepare two-dimensional materials in aqueous media by ultrasonication.In Chapter 3,we develop an ultrasonic exfoliation method of graphene nanosheets based on the strong self-assembly-enhanced interfacial interaction between polypeptide(PY-GAGAGY)and HOPG.In order to enhance the exfoliation effect,we use PYGAGAGY and m PEG modified PY-GAGAGY(PY-GAGAGY-m PEG)as the stabilizer,and we can control the drag force of assistant molecules on the surface of graphite by changing the relative molecular mass of PEG chain and the feed ratio.The morphology and yield of graphene products can be characterized by atomic force microscopy,transmission electron microscopy,Raman spectroscopy and UV spectroscopy.We find that the mixture of PY-GAGAGY and PY-GAGAGY-m PEG can be used as a biosurfactant to prepare the high-yield,large-size,low-layer,defect-free graphene nanosheets with stability stored under liquid phase condition for a long time.In addition,the method is also suitable for preparing other two-dimensional materials.In Chapter 4,we use graphene nanosheets based on the principle of strong selfassembly-enhanced interfacial interaction as building blocks to construct graphene hydrogels.In such graphene hydrogel,graphene act as a high functionality crosslinker and the polyacrylamide linked with peptide absorbed on the surface of graphene nanosheets by free radical polymerization.We use standard mechanical tensile test and rheometer to measure the mechanical properties of hydrogels.The experimental results show that graphene hydrogel is tough,stretchable,and self-healable,moreover it can be remolded into arbitrary shape to applied to flexible electronic devices.In Chapter 5,we report the application of tough and stretchable graphene hydrogel as capacitive strain sensor.We introduce the design of graphene hydrogel capacitive sensor device,discuss the direct application in the direction of wearable sensors and acoustic sensors,suggest the improvement of fatigue resistance of sensors by introducing polydimethylsiloxane(PDMS)as protective coating.We hope that the tough materials based on the strong self-assembly-enhanced interfacial interaction can be widely used in flexible electronic devices.In this paper,the weak interaction between PY and graphite is taken as an example to explain the mechanism of self-assembly-enhanced interfacial interaction,and graphene nanosheets are prepared by using this adsorption mechanism in aqueous media by ultrasonication method.Then graphene nanosheets were used as building blocks to prepare stretchable and tough graphene hydrogel,which can be applied to capacitive strain sensor based on the excellent electrical properties of graphene.