Stepwise Phase Transitions of Chain Molecules: Crystallization/Meltingvia a Nematic Liquid-Crystalline Phase

Spatial Configuration and Thermodynamic Characteristics of Main‐Chain Liquid Crystals

“…When the unit is converted to the entropy change per spacer, the magnitude of ∆S NI becomes nearly invariant over a wide range of DPs from the dimer (9-DDA-9) to polymers: ∆S NI /R = 4.0 to 4.3. The conclusion derived from the observation of Blumstein et al was later confirmed by comparing the conformational characteristics for a series of main-chain liquid crystals, including dimers, trimers, and polymers [Abe and Furuya, 1989;Abe et al, 1995aAbe et al, , 1999Abe et al, , 2003Abe et al, , 2005a.…”

“…In these studies, the conformational entropies calculated from the spectroscopic observations were shown to compare favorably with the constant-volume transition entropies estimated from PVT analysis [Abe and Nam, 1995;Abe et al, 1995aAbe et al, , 1999Abe et al, , 2003Maeda et al, 1996]. Accumulation of various evidence suggests that the spatial configuration of the flexible spacer and its thermodynamic role remain nearly identical, independent of DP from dimer to polymers [Abe et al, 2005a].…”

“…Emsley et al [1984] have reported formation of the LC phase by using PM-type spacers −O(CH 2 ) n O− with n as large as 12. Thermal behaviors of a series of dimer compounds (MBBE-x) involving POE-type spacers -(OCH 2 CH 2 ) xare illustrated in Figure 7.2 Abe et al, 2005aAbe et al, , 2007. With n = 9, the contour length of the spacer (3.2 nm) largely exceeds that (1.82 nm) of the mesogenic core, the dimer compound still exhibiting a stable nematic LC phase.…”

“…Studies on dimers were extended further to include the effect of the size and orientation of mesogenic units [Furuya et al, 1986], the effect due to the tilting angle at the junction joining the mesogenic unit with the spacer [Abe et al, 1995b], and the optical anisotropy of the partially ordered spacer and its contribution to the orientation-dependent attractive interactions [Furuya et al, 1995]. Efforts were made to elucidate the thermodynamics involved in formation of the LC state of mainchain compounds [Abe et al, 2005a]. In these studies, the conformational entropies calculated from the spectroscopic observations were shown to compare favorably with the constant-volume transition entropies estimated from PVT analysis [Abe and Nam, 1995;Abe et al, 1995aAbe et al, , 1999Abe et al, , 2003Maeda et al, 1996].…”

Nematic Conformation of Chain Molecules Predominating in the Ordered Mesophase

“…where (ΔS NI ) P is the NI transition entropy under constant pressure, γ ¼ (∂P/∂T ) V is the thermal-pressure coefficient, and ΔV NI represents the volume change at the NI transition [33][34][35]. Essentially the same procedure can be applicable for the estimation of the entropy change at constant volume (ΔS CN ) V for the CN transition.…”