Solid State Phenomena Vols. 181-182

Abstract: Rod-like liquid crystals N-(4-methoxybenzylidene)-4-n-alkoxybenzenamine (MBnBA, n = 1, 2, 10) were synthesized and then were investigated by differential scanning calorimetry, polarizing optical microscopy, ultraviolet-visible spectrophotometry and fluorescence spectroscopy. Our results demonstrated that the dilute tetrahydrofuran solutions of each member in the family of MBnBA could give off blue fluorescence under the 325 nm excitation. The calculated electronic structures revealed that the fluorescence recorded at 469 nm (2.65 eV) was the result of π* → n transitions in the molecules of the synthesized liquid crystals MBnBA.

Abstract: Refractive indices measurements are carried out in four alkoxy benzylidene anilines viz., N-(p-n-methoxy and ethoxy benzaldehyde)-p-n-dodecyl and tetra decyl anilines, 1O.12, 1O.14, 2O.12 and 2O.14. First three compounds exhibit monovariant nematic phase while the last compound exhibits nematic and SmA phases with variable thermal ranges. The molecular polarizabilities are calculated from the refractive indices and the density using the well known internal field models by Vuks and Neugebauer. The molecular polarizability anisotropy is estimated from the Lippincott δ-function model as well as molecular vibrational methods. The order parameter is estimated using a) from the Haller’s extrapolation from molecular polarizabilities, b) from the scaling factors obtained from the equations by Vuks and Neugbeaur and c) directly from the birefringence - a method developed by Kuczynski et al without considering any internal field model to the liquid crystal molecule. The results evaluated from these methods are compared from one another and the limitations of the methods used are discussed.

Abstract: In this paper, based on the optical rotation property of cholesteric liquid crystals, a new system for studying the optical readout infrared imaging was designed. The profile of hot object is imaged on the surface of liquid crystal cell through the infrared lens, as the uneven heating, the optical rotation is different in various parts of the cholesteric liquid crystals, especially in the imaging area and non-imaging area, the difference is larger. Through the optical system, the optical rotation signal is translated into the corresponding light intensity signal, then the light intensity signal is collected by the visible CCD, and the image of the hot object will be displayed on the screen.

Abstract: A liquid crystal (LC) N,N-(terephthalylidene) bis (4-octyloxyaniline) (TBO10A) was synthesized at room temperature. The LC TBO10A were investigated by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), ultraviolet-visible spectrophotometry, photoluminecence (PL) spectroscopy and electronic structure calculations. In tetrahydrofuran solutions, two optical absorption bands were recorded for TBO10A at about 298 and 379 nm, respectively. Under the 325 nm excitation, dilute tetrahydrofuran solutions of the TBO10A can give off weak blue PL. With Hückel tight-binding method, the electronic structures of the TBO10A were calculated. Our results demonstrated that two absorptions can be attributed to the π→π* and n → π* transitions in the rigid core of the TBO10A while the PL observed at about 481 nm (2.58 eV) can be assigned to the π* →n transition.

Abstract: The nature of the phase transitions across isotropic–nematic (IN) and nematic–smectic-A (N-SmA) are carried out using density measurements in N-(p-n-ethoxy benzylidene)-p-n-pentyl aniline, 2O.5, N-(p-n-methoxy benzylidene)-p-n-pentyloxy aniline, 1O.O5, N-(p-n-ethyl benzylidene)-p-n-dodecyl aniline, 2.12 and N-(p-n-butyl benzylidene)-p-n-dodecyl aniline, 4.12. The compounds exhibit IN, IN, IN and INSmA phase sequences respectively with varying thermal ranges suitable for the study of birefringence. The birefringence studies are carried out using Newton’s rings and wedge techniques which provide δn = (n_e - n_o) (the birefringence) n_e, and n_o respectively. The orientational order parameter, S is evaluated (i) directly from δn and Δn (the birefringence in perfect order), independent of the local field that the nematic molecule experiences and (ii) from molecular polarizabilities estimated from n_e, n_o and density values assuming isotropic as well as anisotropic field that the nematic molecule experiences. The estimated order parameter from the different techniques is compared with one another and with the literature data.

Abstract: Cholesteric liquid crystals elastomers have been extensively studied during the last two decades. They showed Bragg-reflection in visible, Infrared and even UV wavelength Range and a particular circular polarization. Their special helical structure and the adjustment of pitch made them suitable for using as optical thin films. In this study, two kinds of mesogenic monomers undecylenate cholesteryl ester (M₁) and p-phenylene di-4-(allyloxyl) benzoate (M₂) were synthesized. Then the two monomers were fixed onto poly- (methylsiloxane) backbone by grafting polymerization using Dicyclopentadienylplatinum (II) Chloride as catalyst. A series of side-chain polymers with different monomer densities produced by the reaction of hydropolysiloxane and M₁/M₂ with different molar ratios were obtained. The synthesized polymers were characterized by IR, H1NMR and GPC. The mesophases were characterized by using differential scanning calorimetry (DSC), polarizing optical microscopy (POM).

Abstract: Novel conjugated polythiophene derivatives with azobenzene moieties to attaching to the polymer backbone via a flexible alkyl spacer were synthesized by electrochemically direct anodic oxidation in boron trifluoride diethyletherate (BFEE). The physical, optical and fluorescent properties of the resulting polymers were characterized. As conducting and optical materials, the polymers can be promising in the field of photoelecrtonics area.

Abstract: The synthesis and free-radical polymerization of the acrylates monomer containing photosensitive chalcone group and the acrylates monomer containing mesogenic group are described in this paper. The monomers and polymers were characterized by FT-IR and 1 H NMR spectra. The thermal properties of polymers were measured by DSC and the liquid crystalline texture was measured by POM. And the results indicated that the polymers showed typical nematic phase and liquid crystal temperature range was 74 °C-103 °C.

Abstract: A rod-like liquid crystal (LC) N,N-(terephthalaldehyde) bis (4-n-hexadecyloxyaniline) (TBO16A) was synthesized and investigated by nuclear magnetic resonance (NMR), fourier transform infrared (FTIR), differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and ultraviolet-visible (UV-vis) spectrophotometry. The FTIR, ¹H NMR and UV-vis absorption data confirmed the molecular structure of TBO16A. Our results demonstrated that the TBO16A can form enantiotropic smectic A phase.

Abstract: A side chain triphenylene-based polysiloxane were synthesized from 2-hydroxy-3-Methoxy-6,7,10,11–tetrapentyloxy-triphenylene.2-hydroxy-3-Methoxy-6,7,10,11–tetrapentyloxy triphenylene was synthesized via the common synthisis route including the Williamson Etherification of catechol, the iodination of 1,2-dipentyloxybenzene, the Ullman Coupling and the coupling of 3,3'-4,4'–tetrapentyloxy diphenyl and methoxy-phenol; 2-allyloxyl-3-Methoxy-6, 7, 10, 11–tetrapentyloxytriphenylene was synthesized by the etherification of 2-hydroxy-3-Methoxy-6,7,10, 11–tetrapentyloxytriphenylene and allyl bromide; the polysiloxane was synthesized by addition of 2-allyloxyl-3-Methoxy-6,7,10,11–tetrapentyloxytriphenylene and polydimethylsiloxane. The structures of the compounds were determined by FTIR and 1HNMR. Mesophase and their structural orders were determined using a polarized optical microscope and a differential scanning calorimeter.