Supramolecular complexes based on 4-n-alkoxycinnamic acids and pyridine derivatives: Mesomorphic properties and prospects of applying to tribosystems

The processes of self-assembly by hydrogen-bonding in the system of 4-n-alkoxycinnamic acid molecules (n-AOCA) with short hydrocarbon fragments (n = 2, 3), 4,4′-bipyridine (BPy) and 1,2-bis (4-pyridyl) ethane (BPyE) have been considered. The formation of hydrogen bonded (HB) complexes n-AOCA···BPy/BPyE···n-AOCA was confirmed by IR spectroscopy and quantum-chemical calculations. The liquid crystal properties of HB-complexes were studied by differential scanning calorimetry and polarization thermomicroscopy. The interrelation of mesomorphic properties with the structure of the obtained supramolecules n-AOCA···BP/BPE···n-AOCA was analyzed. It is shown that the nematic mesophase of HB-complexes has less thermal stability and is formed at lower temperatures than mesophase of individual 4-n-alkoxycinnamic acids. These trends are more pronounced in systems with 1,2-bis(4-pyridyl)ethane than in systems with 4,4′-bipyridine. While testing the boundary friction, it was found that saturated solutions of HB-complexes in Vaseline oil slightly reduce the friction coefficient and significantly increase the lubricating film durability (6–7 times) under conditions of depleted lubrication compared to a base solvent. [Display omitted] •New supramolecular liquid crystals are reported.•1,2-Bis(4-pyridyl)ethane forms a stronger HB with carboxylic acid than 4,4′-bipyridine.•The isotropization temperature of HB-complexes is significantly lower than individual acids.•The additives (acids and their H-complexes) activity in tribosystems are considered.•H-complexes are significantly increase the lubricating film durability.