| With the continuous development of communication technology,and the large-scale commercial deployment of 5G,signal transmission continues to develop in the direction of high speed,high frequency and low delay.Polytetrafluoroethylene(PTFE)-based composites have stable microwave dielectric properties in the microwave frequency band and it is easy to machine,which can meet the increasing demand for high-frequency and integration of microwave circuits and microwave devices.In this experiment,PTFE is selected as the substrate,Ag@TiO2core-shell structure,ZnNb2O6ceramics are used as fillers,and LCP A950 fiber is used as the reinforcing phase.Two kinds of PTFE-based microwave composites with high permittivity and medium/low permittivity were studied.We also studied the effect of LCP on the modification and reinforcement of PTFE-based microwave composites.The main contents of this paper are as follows:First,Ag@TiO2core-shell structure was synthesized by sol-gel method,and it is used as a high dielectric constant filler to composite with PTFE.We used a variety of analytical methods to study the morphology and composition of the test samples.When the molar ratio of Ag/TiO2is 1:30 and the filling ratio is 60 vol.%in Ag@TiO2/PTFE composites,the samples have a high dielectric constant(25.22),low dielectric loss(5.2×10-3),high thermal conductivity(1.367 W/(m·K))and low coefficient of linear expansion(25.6ppm/?).Secondly,ZnNb2O6ceramic powder was prepared by solid-state sintering method as filler and was compounded with PTFE.The effects of sintering temperature and coupling agent compound on the properties of ZnNb2O6/PTFE composites were studied.The results show that the preferred sintering temperature of ZnNb2O6is 1000?.When the filling ratio is 50 vol.%,the microwave dielectric properties of the sample are:=6.45,th=7.4×10-4,=-5.8 ppm/?,meanwhile the thermal conductivity is 0.845 W/(m·K),and the linear expansion coefficient is 52.1 ppm/?.In addition,x OPA+(1-x)KH550 coupling agent(x=0,0.33,0.5,0.66,1)was prepared by compounding n-octylphosphonic acid(OPA)and silane coupling agent KH550.When x=0.66,the modified ZnNb2O6powder reaches a hydrophilic and lipophilic balance,and the composites have the lowest water absorption(0.06%)and microwave dielectric loss(6.61×10-4).Finally,this paper studies the reinforcement effect of LCP A950 fiber on PTFE and ZnNb2O6/PTFE composites.Through DSC,SEM,DMA,and other analysis methods,it is found that the incorporation of a small amount of LCP can promote the crystallization of PTFE,and improve the density and mechanical strength of composites.When the volume fraction of the ZnNb2O6/PTFE/LCP three-phase is 50/45/5,the composites has a medium dielectric constant(=6.47),extremely low loss(th=7.68×10-4)and a near-zero temperature coefficient of dielectric constant(=+2.25 ppm/?).At the same time,the linear expansion coefficient of the material is 46.4 ppm/?,which is 10.6%lower than before doping with LCP;the flexural strength is 37.8 MPa,which is an increase of 17%compared to the previous one.LCP reinforced composite has excellent comprehensive properties,but when LCP content is too high,its reinforcement effect on the composites is gradually weakened. |
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