Study On The Structure And Mechanical Properties Of Amorphous Polymer Thin Films

Nano-micro polymer thin films are widely used in the package of miniaturization electronic devices and flexible displays devices. Their chemical structure, aggregation structure will affect the stability of the polymer films and the mechanical properties directly, it will become the new hot topic of polymer thin films application to investigate the relations between polymer structure and the mechanical properties.Amorphous polymer PMMA and poly [2-methoxy-5-(2'-ethyl hexyloxy) -phenylene vinylene] (MEH-PPV) are selected in this article, and the influence of the experimental parameters on the mechanical properties of thin films is researched by nano-indentation test, also the mechanical properties of rigid polymer thin film (MEH-PPV) and flexible polymer thin film (PMMA) are compared. In addition, we also discuss the mechanical properties of MEH-PPV thin films of different conformations that were prepared with different solvents and annealed in N2 with different temperature.Investigating the effect of experimental parameters on the mechanical properties of MEH-PPV thin film by nano-indentation experiment, the results show that the applied load can increase the elastic modulus and hardness of MEH-PPV thin film; it can reduce elastic modulus and hardness of the MEH-PPV thin film to extend hold time after achieving the maximum load. In addition, increasing the loading rates will lead to the increase of elastic modulus and hardness values of MEH-PPV thin film.The displacement of loading segment, the creep displacement of holding segment and the residual indentation displacement of unloading segment of MEH-PPV thin film are all higher than the PMMA thin film under same applied load, but elastic modulus and hardness are lower than the PMMA film. The creep displacement of MEH-PPV thin film decreases as the increased loading rates, while the creep displacement of PMMA thin film increased as the increased loading rates in the same loading rates. During the hold segment, the increased rate of creep displacement of MEH-PPV thin film is greater than PMMA thin film in the same hold time.The maximum indentation displacement of MEH-PPV thin film prepared from dichloromethane (coiled conformation) is lower than that of MEH-PPV thin film prepared from toluene (straight conformation), but the hardness and elastic modulus are higher than that of the MEH-PPV thin film prepared from toluene. For the same flexible substrate, the critical bending radius of MEH-PPV thin film prepared from toluene is small, which indicates the MEH-PPV thin film prepared from toluene can bear a large bending stress.MEH-PPV films annealed in different temperatures were characterized by nano-indentation test, the results show that the maximum indentation displacement of MEH-PPV film annealed near the glass transition temperature is small in loading segment; and elastic modulus decrease with the annealing temperature; the hardness increases as increased the annealing temperature before the glass transition temperature and decrease as increased annealing temperature after the glass transition temperature...