Study On Preparation And Properties Of Liquid Crystalline Polymers And Graphene Composites

Graphene is a single-atom-thick nanomaterial,which exhibits exceptional thermal,mechanical,optical,and electrical properties,stimulating active investigation by chemists and physicists.The unique structure and excellent physical properties make graphene potential for applications in ultracapacitors,field-effect transistors,transparent conducting films,catalysis and sensors.In order to make the application of graphene being extensive,many methods for surface modification of graphene have been reported recently.Among them,the most effective method is covalent modification.The[4 + 2]cyclo-addition,i.e.,Diels-Alder(DA)reaction,is one of the most attractive way for graphene,because two-dimensional graphene is capable to act as both dienophile and diene,the facile reactivity of graphene in the DA reaction and diverse of functional groups can be introduced.Liquid crystalline polymers(LCP)have been used to disperse graphene and prepare functional nanocomposites owing to their special optical,mechanical and piezoelectric properties.Dispersed graphene in polymer matrix can improve the thermal,electrical and mechanical properties of liquid crystals greatly,meanwhile,LCP can give additional functionality to graphene.In this paper,the effective functionalization of RGO with Liquid crystalline polymers using DA cycloaddition is reported for the first time,the properties of the obtained composites are characterized and analyzed by various techniques.As the properties of materials should be determined by their structures,two novel liquid crystalline polymers are firstly designed and prepared.The polymers possessing reactivity with reduced graphene oxide(RGO)and can be used to modify RGO.The maleimide groups or conjugated diene structures can be grafted onto the RGO surface via DA reaction,the mesogenic units would enable polymer to have optical rotation and excellent liquid crystalline properties,the carboxyl groups are expected to improve the dispersibility of RGO in solvent and disperse more TiO2 on the surface of RGO in composites than pure RGO.Spectroscopic tools(Raman and XRD)are used to confirm the completion of the reaction.Fourier transform infrared imaging system is utilized to analyze the dispersibility of RGO in the composites.The differential scanning calorimetry(DSC)equipment and thermal gravimetric analyzer(TGA)are used to determine the thermal properties of the composites.The transmission spectra of the composites were obtained with an ultraviolet-visible-near infrared(UV-Vis-NIR)spectrometer he surface morphology of samples were observed using scanning electron microscopy(SEM).The photocatalytic degradation experiment was carried out with a UV-Vis-NIR spectrophotometer.Due to the excellent thermal property of RGO and the interactions between RGO and Polymer,the dispersed RGO can increase the decomposition activation energy and the glass transition of composites.RGO can enhance the photocatalytic degradation of TiO2 due to its high electron mobility and large specific surface area.By preventing the aggregation of TiO2 and RGO,improving the solubility and dispersion stability of the RGO and increasing the affinity of RGO to TiO2,the composite is better than pure RGO to enhance the photocatalytic degradation efficiency of TiO2.Besides the optical and orientation property of the liquid crystal,the liquid crystal elastomers(LCEs)also have excellent mechanical property and chemical stability of the network polymer.It has become a hot topic during the liquid crystal polymer research area.Study on cholesteric LCEs holds not only important theoretical purpose,but also potential applications in numerous areas,especially in the fields of piezoelectric materials and nonlinear optics etc.In this paper,a new type of liquid crystal elastomers(N1)is prepared by the polymerization of vinyl monomers,the new type of liquid crystal elastomers(N2)is firstly prepared by the method of DA reaction in the molecular chain.The chemical structures and properties of the obtained liquid crystalline monomers and LCEs are characterized and analyzed by various techniques including FT-IR spectroscopy,1H-NMR spectroscopy,polarizingoptical microscopy(POM),X-ray diffraction(XRD),differential scanningcalorimetry(DSC),thermogravimetric analyses(TGA),their structure-property relationships are discussed in detail.Especially,the fourier transform infrared imaging system is used to characterize the distribution of cross-linked structures in LCEs(N2).