Microscopic dynamics, supercomputer

An understanding of both the microscopic structure and dynamics of matter is essentia] for a full description of its macroscopic properties. In this regard, recent studies of the internal dynamics of paraffin- and polyethylene-like crystals by simulation with supercomputers have established a link between microscopic motion and macroscopic effect [1-9]. It was shown that conformational, rotational, and diffusional motion can start considerably below the melting or disordering transition temperatures. These types of motion underlie much of the observed macroscopic properties of polymers, and thus it is essential to develop an understanding of how such motion occurs on the microscopic level (mechanisms) and the rates of changes it introduces (kinetics). 

Recently it has become possible to establish the link to the microscopic, thermal motion of macromolecules by simulation on supercomputers. By solving the equation of motion (Hamiltonian) for a system of thousands of atoms in a crystal, considering all intermolecular interactions and internal potentials, it was possible to produce a detailed movie of molecular motion in a polyethylene-like crystal. Figure 1.10 shows excerpts of this motion at low and high temperature. The lower 40 atoms of 7 dynamic chains are represented from a crystal that contained a total of 100 chain atoms. The (CH2-) groups are located at the corners of the indicated zig-zag lines at times zero. By comparison of the successive frames, various skeletal vibrations can be... 

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