Porous Polyimide Composite Film Prepared Via Microemulsion Method And Its Performance

With the development of electronics,low dielectric constant materials are urgently required to solve the problems such as energy consumption,power dissipation caused by the decreasing size of the device and the increasing density of the wire.The dielectric constant can be effectively reduced by the introduction of porous structure into polyimide(PI)matrix,however,most reported methods involve complex steps,for example,the template removing steps,the uncontrollable size,distribution and order of the pores,the increase of water resistance and the sacrifice of mechanical properties,which limit the application of PI films in broader fields.Therefore,it is urgent to develop a simple method for preparing low dielectric porous PI films with undamaged or even excellent water absorption and mechanical properties.This work provides a simple and inexpensive method for the preparation of low dielectric constant PI porous film,in which the water absorption and mechanical properties were optimized,to realize the improvement of the comprehensive properties of PI films.In this dissertation,a soluble fluorine-containing polyimide(FPI)was used as polymer,water droplets as templates to construct the ordered porous film on the top surface of PI film through the microemulsion method,to prepare the composite PI film with single-layer porous structure(S-PI).The properties of S-PI can be regulated through controlling the morphology of the porous structure by changing the concentration of FPI,temperature and humidity during film formation.The results showed that the dielectric constant of the PI film decreased to 2.36-2.81 due to the introduction of the porous structure,while the dielectric loss of the PI film showed a decreased in a certain frequency,besides,the water resistance of the PI film decreased to 0.72-0.95 %,The decreased of water absorption is caused by the increase of hydrophobic due to the introduction of porous structure,the maximum contact angle of S-PI was 121.4 °,furthermore,the dielectric constant of the S-PI shows 2.45-4.24 % of increase after exposing to 75 % R.H.for 12 h.Besides,due to the existence of dense FPI layer between porous structure and PI substrate,the excellent mechanical properties of PI film was not damaged upon the introduction of porous structure.In order to further improve the dielectric and water absorption properties of PI films,sandwich-type PI film with the porous structure on both sides of the flat PI films(D-PI)were prepared by casting the filtrate on the back surface of S-PI.The results showed that the dielectric constant and water absorption of the D-PI were further reduced as low as 32.38 % and 79.2 %,respectively.Fuethermore,the dielectric constant increase of D-PI upon high humidity is only 1.51 %.Besides,due to the uniform distribution of the porous structure in D-PI,the tensile strength shows an increase of 2.77 %.Thus,the introduction of porous structure improves the comprehensive properties of PI films.