Influence of hydrogen bonding on phase abundance in ferroelectric liquid crystals

Abstract

The synthesis and characterization of five hydrogen-bonded ferroelectric liquid crystal complexes (HBFLCs) prepared from mesogenic p-n-alkoxy benzoic acids and non-mesogenic propionic/butyric acids with different chiral centres are reported. Complementary intermolecular hydrogen bonding is confirmed through IR study. HBFLCs are found to exhibit chiral nematic (N*), smectic C* (SmC*) and smectic G* (monotropic) phases in their cooling profiles during polarizing thermal microscopy and differential scanning calorimetry. Phase coexistence regions are observed above the IN* transition. The chiral nematic to smectic C* transition is found to be of first order. The temperature variation of spontaneous polarization exhibited by these HBFLC complexes in their SmC* phase is presented. The effect of non-covalent interaction imparted by the soft hydrogen bonding in these LC complexes on enhanced or induced thermal stability of tilted LC phases is discussed.

Experimental evidence of an optical shutter in cholesteric phase of a double hydrogen bonded liquid crystal

“…This relaxation is identified [35] as Goldstone mode. The order of f r relevant to the GM in the present compounds are found to be comparable to that reported [36,22] in other FLCs and HBFLC compounds. It is further observed that GM relaxation is suppressed under different applied fields as depicted in figure 7, thus this experimental evidence conforms that GM is originated from the helix spread over the smectic layers of respective phase.…”

“…As reported [22] in HBFLC, Goldstone mode is observed at lower frequencies namely at around 950 Hz in LTA+11BA complex. The variation of the capacitance with corresponding dielectric loss at various temperature which are referred as Cole-Cole plots, in smectic C* for the LTA+11BA are shown in figure 6 and is interpreted as due to collective response originated due to the excitation of the coupled transverse dipole moment situated around the chiral centers over the layers in the form of polarization helix.…”

“…From the figure 4 it is observed that the tilt angle increases with decreasing temperature and attains a saturation value of 29 0 . The large magnitudes of the tilt angle are attributed [22] to the direction of the soft covalent hydrogen bond interaction which spreads along molecular long axis with finite inclination. Tilt angle is a primary order parameter [32,33] in tilted phases namely smectic C* The temperature variation is estimated by fitting the observed data of θ(T) to the relation…”

“…In the case of HBLCs the molecular frame possesses [10,[18][19][20][21][22] additional soft-covalent interaction. Further, in case of non-ferroelectric and ferroelectric HBLCs, the observed [13,21] variation in device relevant properties like thermal stability, spontaneous polarization, tilt angle, switching times etc., are addressed through dipolar and refined dipolar models to vouch the fact that soft-covalent interaction extends rather inclined to the long molecular dipole moment.…”

Design, synthesis and characterization of a linear hydrogen bonded homologous series exhibiting reentrant smectic C ordering

“…The commercial viabilities and applicational aspects [8][9][10][11][12][13] made many of the research groups to work on these soft materials. Even though HBLC materials are known since 1960s [2], much work has been done on these complexes [3][4][5][6][7][14][15][16][17] only in this present epoch. Hydrogen bond, a non covalent interaction, enables various mesogenic and non mesogenic compounds to form complexes exhibiting rich phase polymorphism.…”