Liquid crystals in the twist bend modulated nematic phase spontaneously form gratings when filled in planar cells. Such gratings transform the polarization properties of the incident light and as such can be used as low cost switchers because no surface patterning is required to obtain the grating. In addition, the polarization properties of the second order diffraction peak, combined with a theoretical modelling, can be used to determine the spatial variation of the optical axis in the cell. In this paper, we report on a generalized behavior of the polarization of the diffracted light in cells of various thicknesses and for different twist bend nematic materials.
Two antiferroelectric liquid crystals (S) 4-(1- methylheptyloxycarbonyl)phenyl 4'-(3-butanoyloxyprop-1- oxy)biphenyl-4-carboxylate and (S) 4-(1- methylheptyloxycarbonyl)phenyl 4'-(3- perfluorobutanoyloxyprop-1-oxy)biphenyl-4-carboxylate have been prepared and their phase situation investigated by DSC, XRD and dielectric methods.
New series of ferroelectric liquid crystals derived form alkoxycinnamic acid containing chiral alkyllactate group was synthesized. All compounds have a wide temperature range SmC<SUP>*</SUP> phase at temperatures above 100 degrees C and high spontaneous polarization. Some of homologues exhibit spontaneous helix twist unwinding in the SmC<SUP>*</SUP> phase accompanied with the helix twist inversion.
The liquid crystals with Cr-SmC-N phases were studied under high pressure by x-ray method. Also intercalated SmC and SmA phases were investigated, relatively strong compressibility of the smectic layers in both phases was found. The columnar mesophases under pressure were studied as well. In hexagonal Dh phase the columnar distance was nearly pressure independent while in rectangular Dr mesophase pressure increases interdigitation of the molecules from neighboring columns.
Two homologous series of enaminoketone mesogens terminated with F<SUB>3</SUB>C/OC<SUB>n</SUB>H<SUB>2n+1</SUB> (perfluoromethyl series) and F<SUB>3</SUB>CO/OC<SUB>n</SUB>H<SUB>2n+1</SUB> groups (perfluoromethoxyl series) were synthesized and examined by optical and DSC methods. For the perfluoromethyl series, Sm-A and Cry-B smectic phases were observed and additional tilted phases appeared for short homologues (n < 7). For the perfluoromethoxyl series, the phase sequence of Sm-A, Cry-B and tilted smectic phases exist even for long examined homoglogues (to n equals 18). The occurrence of inverted phase sequence Cry-G - Sm-F - Cry- B and the presence of new orthogonal biaxial phase has also been observed for the last series.
Two homologue series of mesogenic enantiomers with chiral semiflexible joint, - C<SUP>*</SUP>H(CH<SUB>3</SUB>)CH<SUB>2</SUB>COO-, are examined. High twist power and presence of blue phases with short lattice period are found for eleven examined compounds. Some effects of chirality in the re-entrant system are discussed. On the phase diagram of enantiomers the SmA<SUB>d</SUB> phase area is shifted toward longer homologues as compared to racemates. In result, an island of the SmA<SUB>d</SUB> phase in the cholesteric sea exists on binary phase diagrams of R- and S- enantiomers.
Studies of complexes: [R-C<SUB>6</SUB>H<SUB>4</SUB>-CO(CH)<SUB>2</SUB>N-Alk]<SUB>2</SUB>Cu, (I), [Alk-CO(CH)<SUB>2</SUB>N-C<SUB>6</SUB>H<SUB>4</SUB>-R]<SUB>2</SUB>Cu, (II), and [R<SUP>1</SUP>-C<SUB>6</SUB>H<SUB>4</SUB>-CO(CH)<SUB>2</SUB>N-C<SUB>6</SUB>H<SUB>4</SUB>-R<SUP>2</SUP>]<SUB>2</SUB>Cu, (III), for various terminal substituents R, R<SUP>1</SUP>, R<SUP>2</SUP>, are presented. For alkyl substituents R, complexes are low- melting and low-clearing nematics [group (I)] and smectics A [group (II)]. Mesophases are monotropic for pure compounds, enantiotropic for mixtures. Elongation of molecular core by introduction trans-cyclohexyl rings into R substituents leads to enantiotropic paramagnetic mesogens. Complexes of the group (III) are high-melting and high-clearing mesogens which usually undergo decomposition in the isotropic phase.
Homologous series of 4'-nitro- and 4'-cyano-derivatives of 1-(4'-alkoxyphenylamino)- 3-phenyl-1-propen-3-ones and a structurally similar series of 1-(4'- alkoxyphenylamino)-3-(4'-pyridyl-N-oxide)-1-propen-3-ones were synthesized and studied by DSC and optical methods. The compounds behave typically for strongly polar mesogens: the smectic A<SUB>d</SUB> phase exists above a critical chain length and the re-entrant nematic phase is observed in the vicinity of the critical double point. For pyridyl N-oxides, a second-order SmA<SUB>d</SUB> - SmC<SUB>d</SUB> phase transition line is observed.