Study On Controllable Preparation And Superwettability Property Of Graphene-based Microcells With Micro–nanoscale Hierarchical Structure

Due to their special properties,the surfaces with superwettability have been applied widely in the areas of self-cleaning,microdroplet manipulation,oil/water separation,anti-fog,anti-icing,etc.With the development of superwettability research,complex environment requests multiple functions so that fabricating smart surface with multifunction has became a important research direction.As an emergent material,graphene has some advantages for fabricating smart superwettable surface.However,most of reported materials based on graphene need the chemical modification on surface to reach superwettability.This will inevitably affect the conductivity of graphene,and seriously hamper the development of smart superwettable surface.To solve the above problems,this dissertation designs and fabricates superwettable pure graphene-based close-cell and open-cell materials with micro-nanoscale hierarchical structure.And it studies the surface superwettability and demonstrates the wettability mechanism.By the properties of graphene,above materials can complete many functions such as sensing capability,superwettability transition,controllable adhesion behaviors,and the sensing mechanisms have been studied.These materials have large practical value in transport microdroplets,sense environment and so on.By means of the amphipathicity of graphene oxide(GO),this dissertation first fabricated the stable GO Pickering emulsion with controllable microsphere diameter by chosing the suitable oil phase,and studied the relationship between microsphere diameter and stirring speed.The formation mechanism of emulsion was also analysed.Then the inner oil phase was frozen so that the nanowrinkles was introduced on the shell of GO.Finally,superhydrophobic,closed-cell graphene film with micro-nanoscale hierarchical structure was obtained through filtering,freeze-drying and chemical reduction.Its wettability could be controlled by size of microsphere and its contact angle could be adjusted from 124.5oto 152.7o,and the influence of microsphere diameter on wettability was also analyzed.Besides,the adhesion of this material for water droplet was high,which was greater than 77.8 ?N,so that it could be used as a mechanical hand for microdroplet transportation.Owing to the pure graphene composition,this material exhibited an excellent electrical conductivity and could sense damage and external pressure.Moreover,it could also sense and tell the position of water droplet in the transportation process,which combined media and sensor together.This dissertation also explored the mechanism of above sensing functions.Next,in order to complete the transition of superwettability,the graphene microspheres were opened via a vapor ejection method,and an open-cell graphene network with micro-nanoscale hierarchical structure was prepared in this dissertation.After air plasma treatment of only 1 s,the surface could be rapidly transformed from superhydrophobic state to the superhydrophilic state,whose efficiency was improved by dozens of times.The mechanism was studied from physical and chemical aspect and the rule between wettability and plasma treatment time was also obtained.Besides,because of composition of pure graphene,the Joule heating property of this material was excellent.It could rise to 200 ? within 8 s under 20 V voltage.Based on this property,the superhydrophobicity of surface was recovered,and the reversible surface superwettability was obtained.Beside,the open-cell graphene network with superhydrophilicity showed superoleophobicity in water and its adhesion for oil droplet was controllable by plasma treatment time.The wettability mechanism of surfaces with different adhesion for oil droplet was also analyzed.Therefore,based on controllable adhesion,oil microdroplet transportation in an underwater environment was completed using this material.At last,for controlling adhesion behavior,a new boiling coating was used to prepare the polypropylene/graphene composite material with heterogeneous microstructure.The open-cell graphene network was immersed in boiling polypropylene-toluene solution so that chemical state of surface was changed,but the inner still had pure graphene.The adhesion of polypropylene/graphene material could be controlled by the coating amount.A lossless water microdroplet transportation was completed using this material and the change mechanism was also studied deeply.Besides,by means of heterogeneous microstructure,it possessed low adhesion and sense for water droplet so that it could be used to sense falling water droplet,even determine the size of water droplets.Additionally,a heterogeneous polydimethylsiloxane/graphene material was also fabricated via a more simple method of inversed drying.And it could detect the behavior of immersion and emersion,and the sensing mechanism was also explored.