THE EQUILIBRIUM STATE OF SOLID LIQUID INTERFACES OF ALIPHATIC-COMPOUNDS

The ordering and orientation of fluid units at interfaces of the aliphatic crystal solution system are the theme of this paper. Based on the idea that the bulk phase and the interfacial phase are two different phases, appropriate relations between the interfacial bond energies and the bulk bond energies are developed by introducing a surface scaling factor C(l). As a description of the interfacial structure of aliphatic compounds, it is assumed that a high degree of ordering is stored in the interfacial fluid phase. Then the so-called alpha-molecule approach is used to estimate the values of bond energies in the interfacial phase. This leads to the result of C(l) < 1, meaning that the the interfaces of n-paraffin crystals and the solutions will be extra wetting. This is consistent with the experimental data obtained from the roughening transitions occurring in several n-paraffin-n-hexane solution systems. Finally, a roughening phase transition diagram of the n-C23H48-n-hexane system is presented, which indicates that the roughening temperature of a surface on a crystal is concentration dependent.