Atomistic simulations of the structure and thermodynamic properties of poly(1, 2-vinyl-butadiene) surfaces

Computer simulations play an important role in the design of new polymers and in the prediction of the properties of existing polymers. Atomistic modeling of amorphous poly(1,2-vinyl butadiene) using molecular mechanics and molecular dynamics simulations was carried out in three-dimensionally periodic and effective two-dimensionally periodic condensed phases. Sets of sample structures of two different periodicity (box edge lengths of 23.982 and 30.042 Angstrom) were generated in order to explore the structural and energetic aspects as a function of the simulation cell size. The calculated surface energy for poly(1,2-vinyl-butadiene) compares very well with the experimental value reported in literature. The equilibrium structure of the films shows an interior region of mass density reasonably close to the value in the bulk state and an outer surface layer of approximately 20 Angstrom across which the density falls rapidly but smoothly to zero at the outer limit of the free surface. The overall characteristics of the atomistic simulation approach is found to be similar to those presented in previous investigations for flexible polymers. In order to create the surface from the bulk state, energetic changes as a result of changes in the states of torsions and bond angles are favored, and these are opposite to the changes in the energies originating from non-bonded interactions. The dominant molecular energetic contribution to the formation of the surface is from dispersion forces (van der Waals). (C) 2003 Elsevier Ltd. All rights reserved.