Fabrication And Application Of Functional Superhydrophobic Materials

Superhydrophobic materials with unique wettability have shown great application value in the fields of self-cleaning of exterior glass,anti-corrosion of metals and buildings,anti-fouling and waterproofing of fabrics,oil-water separation of industrial wastewater and marine oil spill,anti-icing,drag reduction,anti-fog,and microfluidic devices.However,the methods for preparing superhydrophobic materials usually involve complicated processes or expensive instruments.Besides,most superhydrophobic materials only have the characteristic of superhydrophobicity,which are difficult to meet the requirements in some harsh environments and rising fields.Based on these facts,a variety of functional superhydrophobic materials were prepared using simple methods without special expensive equipment in this work.The as-fabricated superhydrophobic materials were applied in droplet transfer,oil-water separation,sensors,electrothermal ice melting,photothermal manipulation,wettability control,underwater vibration detection,display devices,biomimetic actuators,etc.The main research contents and results are listed as following:（1）1H,1H,2H,2H-perfluorooctyltriethoxysilane（PFOTES）was utilized to modifynanoparticles（NPs）.Then,the modifiedNPs were used to construct roughness,and polydimethylsiloxane（PDMS,Sylgard 184）was selected to endow the surface with low surface energy.Subsequently,a piece of textile was immersed and stirred in themixture.After being thermally cured under an external magnetic field,the asymmetricmagnetic superhydrophobic textile was prepared.Fourier transform infrared（FT-IR）spectroscopy,X-ray diffractometry（XRD）and hysteresis loop results confirmed the successful modification of magneticNPs.Atomic force microscopy（AFM）,scanning electron microscopy（SEM）,and contact angle（CA）meter were utilized to study the effects of the mass fraction of PDMS solution and content of modifiedNPs on the morphology and wettability of textile.The results showed that the low/high mass fraction of PDMS solution and content of modifiedNPs were both not beneficial to the asymmetry formation of superhydrophobic textile.When the mass ratio of modifiedNPs/PDMS was 0.25-0.4,and the mass fraction of PDMS solution was 8 wt%,the positive surface of textile was in Cassie state with water droplets easily rolling down,and the opposite surface was in Wenzel state with water droplets firmly adhered.Furthermore,the asymmetric roll-down/pinned states of the textile could be used in droplet transfer,and the superhydrophobic box and groove designed with the textile could be applied in efficient oil-water separation.（2）The synthesized silver nanoparticles（Ag NPs）were hydrophobically modified with octadecanethiol,and polystyrene-b-poly（ethylene-co-butylene）-b-polystyrene（SEBS）was used as elastic low-surface-energy chemical.Then,a spraying method was proposed to fabricate the stretchable and conductive superhydrophobic coating by spraying the dispersion of SEBS and modified Ag NPs onto a pre-stretched natural rubber substrate.FT-IR,XRD and thermogravimetric analyzer（TGA）results confirmed the successful modification of Ag NPs.SEM,CA and resistance measurements were utilized to study the effects of the pre-tension strainεof rubber on the morphology,wettability and conductivity of coating.The results showed that with the increase ofε,the surface roughness,CAs,and conductive pathways were gradually increased.Whenεwas 200%,the CA and resistance of the coating were respectively162^o and 10Ω.SEM and CA results showed that the generated small protuberances at low stretch ratio（1<λ≤3）and big protuberances at high stretch ratio（3<λ≤9）both contributed to maintain the hierarchical roughness and superhydrophobicity of the coating.Whenλwas 9,the CA and sliding angle（SA）of the coating were respectively 154.5^o and 8.9^o.Additionally,the resistance of the coating presented a good response to stretching and bending deformation,and the coating exhibited a good durability to heat,acid/alkali,and mechanical forces.（3）Carbon nanotubes（CNTs）were modified with mixed acid and ethylenediamine.By vacuum-assisted layer-by-layer assembly,a CNTs composite film was constructed with the modified CNTs.Then,the CNTs composite film was transferred onto a substrate coated with ethylene-vinyl acetate（EVA）by hot pressing.Followed by the modification with octadecylamine（ODA）,the conductive superhydrophobic CNTs composite film was obtained.FT-IR,XPS and TGA results confirmed the successful modification of CNTs.SEM,X-ray photoelectron spectroscopy（XPS）and energy dispersive X-ray spectroscopy（EDS）results proved that the layers of the CNTs composite film were connected with amide bonds,and the film surface was successfully grafted with ODA molecules.SEM,CA measurement,and four-point probe resistance tester were utilized to study the effects of the CNTs assembling layers n on the roughness,wettability,and conductivity of film.The results showed that with the increase of n,the CAs were nearly unchanged,and the sheet resistances were gradually improved.When n was 6,the CA and sheet resistance of the film were 165^o and 1.16 kΩ·sq^-1,respectively.Meanwhile,the film exhibited great electrothermal and photothermal effects,which could be applied in high-speed deicing and remote manipulation.（4）Using salt particles（Na Cl）as template,the dispersion of EVA,CNTs,Na Cl and benzoyl peroxide（BPO）in toluene were mechanically stirred until a sticky state difficult to flow was formed.Followed by thermal crosslinking of EVA and subsequent removing of Na Cl by water washing,the 3D porous conductive superhydrophobic CNTs/EVA composite was fabricated.SEM,CA and resistance measurements were adopted to study the morphology,wettability,and conductivity of the composite.The results showed that the composite possessed a sponge-like structure with a CA of 154^oand electrical conductivity of 1.6 S/m.Additionally,the compression test results with a universal testing machine confirmed the great resilience and compression stability of the composite.The height retention maintained 87.5%even at 80%strain after 50 compressing-recovering cycles.Besides,the effects of the content of CNTs and Na Cl on the surface morphology,CAs,conductivity,and mechanical compressibility of the composite were investigated.It was found that with the increase of the content of CNTs and Na Cl,the roughness,hydrophobicity,and conductivity were improved.However,with the adding of excessive CNTs and Na Cl,the 3D porous structure of the composite was destroyed,resulting in a decreased compression resilience.Moreover,the shape memory behavior of the composite was studied,which presented a great shape fixation and recovery ratio,and shape-memory repeatability.By reversibly changing the surface morphology,the wettability of the composite could be regulated from 110^o to 160^o.Furthermore,the resistance responding behavior of the composite in water was discussed.The results showed that the composite could be used to detect underwater vibrations caused by various movements,exhibiting good sensitivity,response repeatability,and long service life.（5）A reduced graphene oxide（r GO）film was prepared using hydrogen iodide/acetic acid,and then a poly（vinylidene fluoride-co-hexafluoropropylene）（PVDF-HFP）solution was casted on the positive surface of r GO film to serve as a bottom substrate.Next,the dispersions of PVDF-HFP and thermochromic microcapsules were sprayed on the negative surface of r GO film to obtain a multi-stage color-changing layer,and the thermochromic superhydrophobic film with healability was prepared.SEM and CA results confirmed the hierarchical roughness and superhydrophobicity of the film.Infrared imager was utilized to study the electrothermal effect of r GO and the relationship between film color and temperature.The results showed that the surface temperature of the film attained 52 ^oC within 40 s at an input power of 0.64 W,and the film exhibited reversible color conversions of blue-pink-yellow.Additionally,SEM,resistance meter,and universal testing machine were adopted to prove the good healing capability for mechanical damage and conductive pathways.By means of the temperature difference generated by the objects contacting as a stimulus,the film could be applied in tactile imaging and writing record board.（6）A porous polyvinylidene fluoride（PVDF）layer was prepared by a solution drying method,and then a crosslinked polyvinyl alcohol（c PVA）layer was formed on the PVDF surface.Next,PDMS was blade coated on the c PVA surface to create a semi-cured layer with strong adhesiveness.After transferring a CNTs/PDMS film based on filter membrane to the PDMS surface with imprint method,the solvent vapor-driven superhydrophobic film was obtained.SEM and CA measurements were adopted to study the surface morphology and wettability of the film.It was found that the film surface presented a micro/nanoscale rough structure with a CA of 163^o,and the film exhibited great resistance to acid/alkali,solvent vapors,temperatures,and water impacting.Furthermore,the solvent vapor-driven actuation behavior of the film was investigated.The results showed that the film directionally bent towards the superhydrophobic CNTs@PDMS surface,and the curvature was 0.65 mm^-1 at 10 s.The actuation presented advantages of large deformation,fast response,stable repeatability,and sensitivity to various solvent vapors.Importantly,the actuation behavior was not affected under wet environments.Taking advantage of the superhydrophobicity,conductivity and actuation behavior,the film was successfully applied in biomimetic devices,electrical switches and liquid flow control.