The smectic effect on solute order parameters rationalized by double Maier–Saupe Kobayashi–McMillan theory

Abstract

From the dipolar couplings obtained by NMR spectroscopy we have calculated the order parameters of a wide variety of solutes in the nematic and smectic A phases of the liquid crystals 8CB and 8OCB. These measurements are then rationalized with the previously tested two Maier-Saupe Kobayashi-McMillan interaction potential from which smectic order parameters are calculated.

Recent NMR Studies of Thermotropic Liquid Crystals

“…(99) in Eq. (101)) to the orientational order parameters for the twelve solutes at a single temperature in liquid crystals 1132, "MM", EBBA, and at three different temperatures of both 8CB and 8OCB spanning their N ranges [343]. The values obtained can be found in table 1 of a recent review [344].…”

“…After introducing the MSMS potential in a N phase, the smectic potential due to layering according to the Kobayashi-McMillan (KM) model is introduced [5,342]. As demonstrated in a recent study of solutes dissolved in 8OCB and 8CB [343], the orientational order parameters of the solutes can detect the N-SmA phase transition. However, in order to extract information about translational (positional) ordering in the smectic phase, the nematic contribution to the total potential in the SmA phase must first be found as only the observed dipolar couplings (order parameters) of solutes in SmA phase would not be sufficient to get information on the smectic potential.…”

“…With the β s,γγ (i)'s now fixed [343], one can proceed to fit the experimental order parameters for the solutes of interest at each temperature in both the N and SmA phases of 8CB (8OCB), using just the nematic potential by varying G L,ZZ (1) and G L,ZZ (2), and notice that the RMS of the fit increases significantly in the smectic phase. Attempt to fit the S s,γγ in the smectic A phase to the combined MSMS-KM Hamiltonian of Eq.…”

“…The G(i) were determined using the known β's from Ref. [343]. This method of extrapolation of G(i) for each solute(s) (where possible) was deemed safer than the extrapolation of MSMS model parameters as a function of temperature [348].…”

NMR of solutes in nematic and smectic A liquid crystals: the anisotropic intermolecular potential

“…The solute β parameters are now obtained from a least‐squares fit [using the potential of Eqn in Eqn ] to the orientational order parameters for the 12 solutes at a single temperature in liquid crystals 1132, MM and EBBA and at three different temperatures spanning the N ranges of 8CB and 8OCB . The values obtained are given in Table .…”