Fabrication Of Functional LDHs-based Films And Study On Their Gas Barrier And Ion Conductivity Property

As a class of typical two-dimensional(2D)inorganic materials,layered double hydroxides(LDHs)have shown great application prospect in the fields of adsorption/separation,catalysis,energy storage and biomedicine by virtue of their structural features,including a versatile tunability in chemical composition,structure and morphology.In recent years,fabrication of high-performance gas barrier films by incorporation of LDHs materials within polymer matrix has aroused widespread concern in both scientific and industrial field.However,some improtant issues remain unresolved in the preparation and application of LDHs/polymer gas barrier films:(1)how to tune the aspect ratio of LDHs materials so as to enhance gas barrier property;(2)how to improve the interface compatibility between LDHs and polymer and depress the free volume at the inorganic/organic interface;(3)how to achieve gas barrier and ion penetration property simultaneously for prospective application in electrolyte membrance of fuel cells.In order to solve the problems mentioned above,in this dissertation,a systematic research was performed as follows:(1)Ultrathin LDH nanoplatelets(U-LDH)were prepared by coprecipitation method,followed by suface modification with nonionic surfactant polyvinylpyrrolidone(PVP)to obtain the ultrathin modified LDH nanosheets(U-mLDH).Subsequently,U-mLDH nanosheets and nitrile butadiene rubber(NBR)were used as building blocks to fabricate film materials via spin-coating method.The resulting(U-mLDH/NBR)n film displays an excellent gas barrier property with oxygen transmission rate of 10-16 cm3 cm cm-2 s-1 Pa-1 and relative permeability of 0.08,which is superior to previously reported rubber-based materials.The excellent gas barrier performance is attributed to the extremely-large aspect ratio of U-mLDH nanoplatelets and good interfacial compatibility,which could prolong the diffusion path of gas molecules and decrease the free volume for gas permeation.Therefore,a facile and effective approach was provided for the preparation of LDH/rubber composites,which can be potentially used in tyre inner lining and packing materials.(2)CoA1-LDH was firstly prepared by a facile separate nucleation and aging steps method;polysulfone was sequentially chloromethylated and quaternized to obtain the quaternary ammonium grafted polysulfone(QCMPSF).Subsequently,CoAl-LDH and QCMPSF were employed as building blocks to fabricate(LDH/QCMPSF)n films via layer-by-layer assembly technique.The resulting hybrid film shows excellent oxygen barrier property with an oxygen transmission rate of?2.35 cm3 m-2 day-1 atm-1.Furthermore,the electrochemical impedance spectroscopy(EIS)was used to investigate the ion conductivity of the film,giving a satisfactory ion conductivity of 7.252 mS cm-1(increased by 169%compared with that of pure QCMPSF film).It is revealed that the incorporation of 2D inorganic platelet into ordered film can prolong the diffusion path of gas molecule,resulting in an enhanced gas barrier property.In addition,the ion-exchange capacity of the composite film is greatly enhanced upon hybridization with LDH,thus improving the ion conductivity of the(LDH/QCMPSF)n film.The obtained gas barrier/ion conductivity dual-functional film would show application prospect in the field of fuel cells.