Monte Carlo simulations of systems of rodlike molecules with semiflexible terminal groups

Abstract

SUMMARY:The results of Monte Carlo simulations of systems of rodlike molecules with semiflexible terminal groups are compared with those of systems with terminal groups at a fixed angle s with respect to the rigid core and with those of a system containing the rigid cores alone in the same total volume. The nematic/ isotropic transition temperature decreases with increasing flexibility or with increasing s. For semiflexible groups, the transition is coupled with a conformational change favouring more extended conformations in the nematic phase. The results of the simulations are discussed in connection with those obtained for similar models in the recent literature and with the predictions of the Maier-Saupe and Flory-Ronca-Irvine theories.

Order–Disorder Transitions in Model Liquids of Mesogenic Trimers

“…[35] In practice, the trimer molecules are constituted by three of the latter molecules connected in sequence. However, in order to investigate the principal factors responsible for the observed behavior of segmented-chain oligomers and polymers, four separate simulations are performed for trimers with different conformational characteristics.…”

“…[35] for system RC (the reference system of monomers), while those of systems T b and T 6 are substantially higher. In other words, the transition temperature is practically unchanged when the three rigid cores are linked in sequence by conformationally unrestricted links, while including the bending potential E s increases the transition temperature by approximately 20 K. Adding to E s the potential E u has opposite effects in systems T 5 and T 6 , since the transition temperature decreases 20 K in system T 5 and increases 10 K in system T 6 with respect to system T b .…”

“…For system T 5 , as well as for other systems with E s , the broad maximum is shifted at angles between 120 8 and 140 8, while the maximum at 60 8 is much less intense. The two maxima at higher angles are practically as expected, while the maximum at 60 8 is found for all liquids of chain molecules made up of isodiametric units of this nature, [35,44] and originates from packing effects (for a discussion, see ref. [35] ).…”

“…The two maxima at higher angles are practically as expected, while the maximum at 60 8 is found for all liquids of chain molecules made up of isodiametric units of this nature, [35,44] and originates from packing effects (for a discussion, see ref. [35] ). Overall, the distribution of s in the isotropic phase of trimers simulated with the bending potential E s is not too different from the distribution shown in Figure 2.…”

“…Segmented-chain mesogenic trimers are simulated here using a model and a set of parameters practically coincident with those of the system of rigid anisometric molecules studied in ref. [35] In practice, the trimer molecules are constituted by three of the latter molecules connected in sequence. However, in order to investigate the principal factors responsible for the observed behavior of segmented-chain oligomers and polymers, four separate simulations are performed for trimers with different conformational characteristics.…”