Binary mixtures made from components of the four series of the molecular structure 4-CnH2n+1O-C6H4-COO-C10H6-N=N-C6H4-X, in which both components bear the same alkoxy group (n = 8, 10, 12, or 14) but of different substituent (X = CH3O, CH3, Cl, or NO2), were prepared and characterized for their phase behaviour. Transition temperatures of mixtures were measured by differential scanning calorimetry and identified by polarized-light microscopy. The dependence of the phase behaviour of mixed systems upon differences in the electronic nature of the terminal group, X, attached to both components as well as the length of the alkoxy group, was investigated from the phase diagrams constructed for the various binary combinations. The nematic order parameters are in accordance with the conclusions drawn. (c) 2006 Published by Elsevier B.V.