Study On Preparations And Properties Of DAST-Based Flexible Composite Materials

Recently,new technologies for photoelectric materials have been rapidly developing.The traditional semiconductor electronic technologies are challengable to meet the requirements of many practical applications.In contrast,flexible electronics has attracted worldwide attention,owing to the unique flexibility and extension ability of flexible electronics,as well as their advantages of low cost and high sensitivity.4-N,N-dimethylamino-4?-N?-methyl-stilbazolium tosylate?DAST?is an important organic material with excellent nonlinear effects.DAST has been applied widely in the fields of terahertz radiation and detection,high-speed electro-optic modulation,etc.However,DAST is generally limited in practical applications because of its brittleness,long growth period and difficulty for growing high-quality crystals.In this thesis,DAST was first synthesized,and then the purified product was composed with polydimethylsiloxane?PDMS?to prepare a flexible composite material with low cost,short cycle,excellent optical and mechanical properties.Importantly,the excellent piezoelectric properties of the as-prepared composite material were discovered in this work.To the best of our knowledge,no any related result has been previously reported in the literatures at home and abroad.The main results are as follows:?1?Two methods,including first mixture and then film formation,and successive film formation and overlapping,were ultilized in composite preparation.Consequently,novel PDMS-DAST flexible composites were successfully prepared.If PDMS-DAST composite films with a DAST concentration of 0.8%-1%were prepared by the method of first mixture and then film formation,DAST crystals with lare sizes and wrapped in the composites are uniformly dispersed,and the as-prepared composite films exhibit high film quality.?2?The optical,mechanical,and electrical properties of the as-prepared composite films with different DAST concentrations were systematically investigated.The results show that if the DAST concentration in the composite film is increased,the light absoption in a broad region from UV to IR is increased,while the ultimate elongation and ultimate stress of the resulting materials were gradully decreased.When the content of DAST is 0.8%,the elastic modulus of the composite film reaches the maximum.At room temperature,the resistance of the composite film is at the magnitude of T?.The TCR of the composite film is positive,and it is increased with the increase of DAST concentration.It is worth noting that the as-prepared DAST-based flexible materials not only inherit the optical and electrical properties of DAST,but also exhibit excellent mechanical properties of PDMS.?3?We explored the polarization conditions of DAST composite films,including:electric field at 80 KV/cm,temperature at 80?,polarization for 4 h and along the thickness direction,and the whole polarization process need to be carried out in silicone oil.The piezoelectric coefficient d₃₃ of the polarizing PDMS-0.8%DAST composite film was measured to be 1.6 pC/N.This proves for the first time that the DAST–based composite films exhibit excellent piezoelectric properties,which has never be revealed previously.In addition,the open circuit voltage and short circuit current of the composite film before and after polarization were experimentally measured.The results show that the piezoelectric properties of the resulting DAST-based flexible composites are in the same level of those of barium titanate matrix composites and other common piezoelectric composites.Particularly,the electric energy produced by the DAST flexible composite membrane has been successfully lighted the commercial LED.