Temperature coefficients of the refractive index for hydrocarbons and binary mixtures

Temperature coefficients of the refractive index (dn/dT) for nine hydrocarbons and two sets of binary mixtures were investigated in this work. The measured −dn/dT values for the pure hydrocarbons were found to be inversely proportional to their molar volumes (Vm) and molecular weights (M). Experimental data for binary mixtures show that −dn/dT varies linearly with volume and mass fractions, consistent with theory derived from the linear relationships of −dn/dT with 1/Vm and 1/M for individual hydrocarbons. This study should aid the interpretation of the observed correlations of dn/dT with physical and combustion properties of diesel fuels.