Synthesis And Dielectric Properties Of Organic Modified SiC Whisker/PVDF Composite Membranes

Nowadays,with the over consumption of energy,materials with high dielectric properties are a way to solve the shortage of energy.Therefore,preparing the composite made of the high dielectric polymer and inorganic dielectric filler has very important practical significance.In this paper,the organic matter modified silicon carbide whisker(Si C_w)and barium titanate(BT)was added to polyvinylidene fluoride(PVDF)matrix to prepare the composite membrane in order to improve the dielectric and physical properties.The dielectric and physical properties of the composite membrane were discussed by the content of SiC_w,the amount of modifier,the temperature and the particle size and doping amount of BT.SiC_w was modified by cetyltrimethylammonium bromide(CTAB)firstly,and then CTAB-SiC_w/PVDF composite membranes were prepared with being added different amounts of CTAB-SiC_w by solution casting.The results showed that CTAB successfully modified SiC_w from hydrophilic property to lipophilicity by visual analysis.There's no effect occurred on its crystal structure,and also it was beneficial to formation of?-PVDF according to XRD results.It showed that the organic matter modification could improve the dispersion of SiC_w in PVDF matrix.Moreover,the dielectric constant of the modified SiC_w/PVDF composite membranes increased firstly and then decreased with the addition of CTAB-SiC_w.The maximum was obtained with 15wt%of CTAB-SiC_w.The dielectric properties of high and low temperature indicated that the composite membranes still maintain good dielectric properties at different temperatures.It showed that the decomposition temperature of PVDF and the heat resistance of composite membranes were enhanced after introducing of CTAB-SiC_w by TG analysis.The effects of three different silane coupling agents on the dielectric properties of SiC_w/PVDF membranes were studied.XRD results proved that after being modified by silane coupling agents,the crystal structure of SiC_w did not change.TG results showed that grafting amount of KH792 was up to 6.37%.The dielectric properties of composite membranes at room temperature showed that the dielectric constant decreased with the addition of silane coupling agent,and the dielectric properties of the composite membranes obtained by adding 0.1wt%of KH792 modified Si C_w were the best.The results of dielectric properties at low temperature showed that the dielectric constant and dielectric loss increased gradually with the increase of temperature.When f=500 Hz,T=120?,the max dielectric constant and tan?was 55 and 1.1,respectively.Based on the above conclusion and our earlier work,15wt%of CTAB-SiC_w was chosen to be used at following study.BT particles with different sizes modified by KH550 were selected and the BT/SiC_w/PVDF composite membranes were prepared.The effect of particle size and addition content of BT on the dielectric properties of the composite membranes at different temperature were explored.The results showed that KH550 can successfully modify BT particles and could not change its crystal structure by FTIR and XRD analysis.SEM results showed that the modified BT could dispersed well in PVDF matrix.The results of dielectric properties at room temperature showed that the dielectric constant of the composite membranes increased firstly and then decreased with the addition of BT,and the maximum was obtained at 10wt%.In conclusion,the ternary composite membrane obtained with 100nm and 10wt%of BT had the best dielectric properties.