Liquid crystal model for hydrocarbons under shock wave conditions

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Abstract
To interpret shock wave data on hydrocarbons, Ree has proposed a model in which carbon, having tetrahedral coordination, and molecular hydrogen separate. He then shows that the Hugoniot curves can be ordered according to their hydrogen:carbon ratio and that a quantitative fit of the high pressure data proves possible. In the present work, an alternative proposal is put forward, in which the C–H bonds are not dissociated. Instead, it is suggested that pressure can induce a π-electron transition in which the delocalized behavior parallel to the molecular plane can give way to localized behavior in which the π electrons can participate in intermolecular bonding. In this model, the Hugoniot curves can be ordered according to the π-electron densities. A natural explanation of the discontinuities in the Hugoniot curves is, on the present proposal, a transition from an isotropic liquid phase to a nematic liquid crystal phase. Again, the model leads to an approximate equation of state which can be compared with the available experimental data. The agreement at very high pressures lends support to the model as being useful at a semiquantitative level.