The Influence of Flexible Segments on Liquid Crystalline Properties in Terms of Solubility Parameters. An Attempt at Quantitative Interpretation

Abstract

The phase behavior of some rodlike block molecules has been reviewed with reference to the polarity of constituent segments. It was found that the ability of the mesophase formation is connected with differences in polar character between the flexible chains and rigid cores. Thus the polar poly(oxyethylene) group connected with the polar rigid core reduces mesophase stability but is advantageous when put together with some apolar building blocks. An attempt at quantitative estimation of the incompatibilities of different parts of molecules by means of Hansen solubility parameters delta and Flory interaction parameters chi has also been made. On the basis of chi parameters the Gibbs free energies of mixing of these segments were calculated. The changes of Gibbs free energy reflecting the compatibility of segments and their tendency to the phase separation and the volume fraction of mesogenic rigid core reflecting their ability to arrangement in one direction appear to be crucial in terms of type of the mesophase formation.

A quantitative assessment of chemical perturbations in thermotropic cyanobiphenyls

“…1 H-NMR (400 MHz, CDCl 3 ) d = 7.98 (d, 3 J = 8.7 Hz, 2H), 6.90 (d, 3 J = 8.7 Hz, 2H), 4.00 (t, 3 J = 6.5 Hz, 2H), 3.88 (s, 3H), 3.60 (t, 3 J = 6. 6 Preparation of compound 6. A solution of KOH (2.23 g, 39.74 mmol) in H 2 O (20 mL) was slowly added to a stirred solution of 5 (14.00 g, 33.11 mmol) in EtOH (60 mL).…”

“…Segregation is then lost at the order-disorder transition temperature, also assigned as the clearing temperature T clearing in liquid crystals. 8 Applied to the formation of nanostructured liquid crystals, 6 this thermodynamic approach was successfully used for rationalizing the micro-segregation occurring in mesogenic calamitic cyanobiphenyls, 9 cubic-phase-forming liquid crystalline molecules 10 and polycatenar pentaerythritol derivatives. 11 Whereas the high temperature limit of existence of a mesophase, i.e.…”

Microsegregation: From Basic Concepts to Complexity in Liquid Crystal Self‐Assembly

“…Attempts have also been made to correlate the stability of positionally ordered LC phases of rod‐like LCs with Hildebrand solubility parameters δ , Hansen solubility parameters δ t ,36 and the Flory‐Huggins parameters χ 33,34,37. In this case it is especially important to define the core and chain regions properly for each individual case.…”

Chemical Programming of the Domain of Existence of Liquid Crystals

“…The Flory and Huggins theory, in terms of solubility parameters, shows that the latter interaction factor depends on ( δ A − δ B ) 2 weighted by the thermal energy . Quantitative applications to mesogenic calamitic cyanobiphenyls, cubic‐phase‐forming liquid‐crystalline molecules, and polycatenar pentaerythritol derivatives successfully rationalized phase segregation, leading to specific mesomorphism. However, contrary to Trouton's rule for the vaporization of liquids, the entropy changes, Δ S tr , accompanying the melting process that transforms a solid into a liquid or a liquid crystal, or the isotropization process that transforms a liquid crystal into an isotropic liquid, are not constant.…”