Study On The Structure And Mechanical Properties Of PPV And Modified PPV

Polyphenylene vinylene (PPV) and its derivatives are widely used in a variety ofelectronic devices, such as thin-film light-emitting diodes, thin-film solar cells and otherfields. The stability and structural changes induced by the external force of conjugatedpolymer films in electronic devices will directly affect electro-optical performance ofoptoelectronic devices. The structure and the micro-mechanical properties of PPV anddoped PPV films were studied, and the effect of photodegradation on the structure andmechanical properties of PPV thin films was also discussed.PPV which had different chemical structure,trans–cis conformation and crystallinitywas obtained by controlling the temperature and vacuum degree. The effects ofexperimental parameters on the mechanical properties of thin films were studied, and therelationships among different chemical structure, conformation, and crystallinity andmicro-mechanical properties of PPV films were compared by nanoindentation test.Furthermore, the chemical structure and micro-mechanical properties of PPV films beforeand after doping with FeCl₃were studied, and the relationships between the changes in itschemical structure and micro-mechanical properties were explored. Then, PPV/TiO₂nano-composite materials were prepared and its micro mechanical properties wereresearched. Finally, the effect of photo-oxidative on the stability and mechanicalproperties of PPV thin films was discussed.Through investigating the effect of experimental parameters on the mechanicalproperties of PPV thin films by nanoindentation experiment, the results showed that thechange of load could not change the elastic modulus and hardness of PPV thin films; theelastic modulus and hardness of PPV thin films reduced until they keep constant when theholding time was extended after achieving the maximum load. In addition, increasing theloading rate would lead to a little decrease of hardness values of PPV thin films,but theelastic modulus is independent of the loading rate.The results which were the nanoindentation test to PPV prepolymer thin films by heattreatment at different temperature showed that the elastic modulus and hardness of PPVprepolymer thin films processed under different temperature decreased at first, then increased to a maximum value and decreased to a certain value at last. The elastic modulusand hardness of PPV thin film were the largest at the temperature of125℃(the content ofcis-vinylene in PPV film is the highest under this temperature), but decreased to minimumvalue at about230℃(the structure of vinylene in PPV film was complete trans isomer).Two different types of doped and photo-oxidation PPV thin films were characterizedby nanoindentation test, and the results showes that (i) the elastic modulus and hardness ofFeCl₃-doped PPV film were higher than undoped PPV film;(ii) the elastic modulus andhardness of PPV/TiO₂composite film prepared by sol-gel method were far bigger thanpure PPV film; the elastic modulus and hardness of photo-oxidation PPV film decreasedslightly compared with pure PPV film, and there was a "patform" phenomenon in theload-displacement curve.