Study On Preparation And Properties Of Fluorographene/fluorinated Polyimide Composite Film

Fluorinated polyimide（f-PI）has been proposed as a potential candidate dielectric material because of its low dielectric constant,good transparency,and excellent chemical and thermal stability.Recently,the incorporation of inorganic dielectric fillers in a polymer matrix has been shown to further improve the dielectric and mechanical properties of the composite material.Two-dimensional fluorographene（FG）,with tunable F/C ratio and number of C-F bonds,is one of the most promising dielectric nano-fillers,because of its extremely low dielectric constant（ca.1.2）,good transparency in the visible,and the presence of highly electronegative groups.Optimization of molecular interactions between filler materials and a polymer matrix is one of the key methods to improve the dispersion of the filler in the matrix.In this work,we describe a low dielectric constant FG/f-PI nanocomposite film obtainedbythepreparationoff-PIonexfoliatedFGgraftedwith2,2’-bis（trifluoromethyl）-[1,1’-biphenyl]-4,4’-diamine（t-FG）.The strong interfacial interaction between f-PI and t-FG promotes the dispersion of t-FG in the f-PI matrix.The effects of the addition of t-FG on the optical,mechanical,and dielectric properties of the composite film are investigated by incorporating different amounts of t-FG.As a dispersed nanofiller,few-layers t-FG nanosheets with a lateral dimension of more than 5μm were exfoliated by solvothermal intercalation with TFDB.When a t-FG content of 0.75 wt%is reached,t-FG shows good homogeneity within the f-PI matrix,owing to strong interfacial interactions.Highly transparent and flexible t-FG_0.75/f-PI composite films combine low dielectric constant（2.09）and tangent loss（0.0019）with high tensile strength（300.1 MPa）,low water absorption（0.1%）,and good thermal stability.Furthermore,OTFT devices fabricated using this films as a dielectric layer exhibit good transistor mobility(0.21 cm²V^-1s^-1)and ON/OFF ratio（4.2×10³）.Transparent and flexible t-FG_0.75/f-PI composite films with very low dielectric constant are therefore suitable for application in transparent flexible displays.