Mesophase behavior of binary and ternary mixtures of benzoic acids bearing terminal substituents of different polarity and chain-lengths

• Binary mixtures of homologues of 4-alkoxy benzoic acids bearing alkoxy groups with different chain lengths were prepared.
• Most of the mixtures are dimorphic exhibiting the SmC and N mesophases.
• In the mixture, the thermal stability of the SmC increases and that of the N phases decreases, as the alkoxy-chain length increases.
• The addition of either of 4-cyano- or 4-methoxybenzoic acids has led to the formation of supramolecular complex within the investigated ternary systems.

The thermal and mesophase behavior of all possible 1:1 mixtures (Im/In) formed from any two derivatives of 4-n-alkoxy benzoic acids bearing different alkoxy chains (m and n   vary between 6 and 16 carbons), were investigated by differential scanning calorimetry (DSC) and phases identified by polarized light microscopy (PLM). Phase transitions were investigated as a function of the average alkoxy-chain length (n¯=(m+n)/2) of the mixed acids. In order to investigate whether a supramolecular complex is formed between the mixed acids, phase diagrams were constructed for the binary mixtures of 4-n-hexyloxy benzoic acid (I6) with the two homologues bearing extreme alkoxy-chain lengths, namely, 8 and 16 carbons. Investigation of the mesophase behavior of ternary mixtures, made from the two eutectic mixtures (I6/I8 or I6/I16) with 4-methoxy or 4-cyano-benzoic acids revealed that the stability of the SmC and N mesophases of the eutectic mixtures is affected in a way that is dependent on both the polarity of the substituent and the difference in the alkoxy-chain lengths.