Research Of Structural And Kinetic Property In The Glass Transition Of Lennard-Jones Systems

Amorphous materials are popular by persons because of outstanding properties, and nowadays people have paid more attention to complex disordered amorphous systems. It is due to the internal specific characteristics of atomic structure of amorphous system. Therefore, investigation in atomic structure of the amorphous system will not only benefit a deep apprehension of the various properties of amorphous materials, but also deepen the understanding of glass transition phenomena. In this thesis, molecular dynamic simulations are used to research the changes of structures and kinetic properties during solidification process of the Lennard-Jones system at different cooling rates.A molecular dynamic simulation study is performed for the effects of cooling rates on structures and kinetic properties during solidification process of the Lennard-Jones system. The resulting structures are not the same by using different cooling rates from the melts of the Lennard-Jones system. Hence, it is essential to research the effects of cooling rates on structures and kinetic properties. The amorphous Lennard-Jones system is obtained by using rapid cooling methods, and it is studied the pressure and temperature dependence of diffusion coefficients in the process of glass transition. In some research areas, the glass transition is interpreted as a dynamic phenomenon, so we research diffusion phenomenon in the process of glass transition by the method of molecular dynamic simulations. Therefore, effects of pressure and temperature on diffusion coefficients are studied in this topic in order to promote an interpretation of glass transition phenomena.Some conclusions we have summarized through the above simulation and research.(i) The cooling rate plays a critical role on structures during solidification process of the Lennard-Jones system. As the cooling rate being smaller, the system will be crystallized, and the slower the cooling rate, the higher the crystallization temperature, and the higher the degree of crystallization; As the cooling rate being high enough, the system will be transferred into glass, and the greater the cooling rate, the higher the glass transition temperature.(ii) The relations between diffusion coefficients and temperature deviate from the Arrhenius lines significantly in glass forming liquid, and there is a process of slow change.(iii) When we research the pressure dependence of diffusion coefficients in glass forming liquid, we find the Arrhenius relationship between diffusion coefficients and the reciprocal of pressure in the pressure range studied, but the slope of Arrhenius line is influenced by temperature.