Influence of C28H58 on the structure and phase change of C28H58/C22H46 n-alkane mixtures

Abstract

This study adopted molecular dynamics to investigate the influence of C28H58 mass fraction on the structure and phase change of C28H58/C22H46 n-alkane mixtures at different temperatures; systematically analyzed the C–H and C–C bond lengths, changes in the H–C–H bond angle and C–C–C–C torsion angle, and energy conversions within the mixture during heating of C28H58/C22H46 n-alkane mixtures; calculated the self-diffusion coefficient (D) by combining the Einstein relation and mean squared displacement; and determined the phase change temperature of each mixture according to the relationship between D and temperature. The results show that, at 280 K, changing the mass fraction of C28H58 does not affect the C–H and C–C bond lengths and the H–C–H bond angle. At 350 K, the C–H bond length decreases with the increase in the mass fraction of C28H58, the C–C bond length increases slightly when the mass fraction is 65.2% and remains unchanged for other mass fractions, and the H–C–H bond angle slightly decreases. With an increase in temperature, the peak intensity of the stretched conformation at ±180° gradually decreases, while the peak of the twisted conformation appears around ±70°, and the degree of twist of the C–C–C–C dihedral angle in the mixture increases. The phase change temperature begins to increase slowly with the increase in the mass fraction of C28H58, and the phase change temperature increases rapidly when the mass fraction exceeds 65.2%. The kinetic and potential energies of the mixture tend to increase with the increasing mass fraction of C28H58.