J. Chruściel

The phase behaviour of 4- n -pentylphenyl-4′- n -heptyloxythiobenzoate

New results of investigations of phase polymorphism for two substances, hydrogenous (7OS5-d0) and partially deuterated (7OS5-d26) have been presented. On the basis of measurements of the integrated “elastic window” intensity (EL), quasielastic neutron scattering (QNS) spectra and results obtained with the Transmitted Light Intensity (TLI) method, the metastable character of the SmC phase, that at constant temperature always transforms to the crystalline phase Cr2, has been confirmed. Variations of the EL show a very clear hysteresis effect in the nematic and SmC phases as well as in solid phases. It was confirmed by a phase polymorphism in both investigated substances. Convergence of the EL and TLI methods was shown. The new phase situation of both hydrogenous and partly deuterated liquid crystals is presented.

Molecular dynamics in the nematic, SA and SC phases of 8S5 and 9S5 as studied by dielectric methods

Abstract Two experimental techniques—time domain spectroscopy (TDS) and a steady state frequency method—have been used to study dielectric spectra for the isotropic, nematic, SA, SC and SY phases of two thioesters (4-n-pentylphenyl-4′-n-octyloxy-and 4′-n-nonyloxythiobenzoates (C n H2n+1 O‒C6 H4‒COS‒C6H4‒C5H11, where n = 8 and n = 9) known as 8S5 and 9S5, in the frequency range from 10 Hz to 10 GHz. In the case of 8S5 a deuteriated sample (8S5-d 28) has been used to study relaxation processes in the nematic and smectic phases.

The influence of terminal chlorine on the mesomorphic properties of new thiobenzoates containing two and three benzene rings

New liquid crystalline chloro‐substituted thioesters containing two and three benzene rings have been synthesized. 4‐Chlorophenyl 4‐n‐alkoxythiobenzoates and 4‐chlorophenyl 4‐n‐alkoxybenzoyloxy‐4′‐thiobenzoates are referred to as nO.SCl and nO.OSCl, respectively, where n varies from 4 to 16 for nO.SCl, from 4 to 10 for nO.OSCl and denotes the number of carbon atoms in the alkyl chain. Their mesomorphic properties were investigated by means of polarizing optical microscopy, differential scanning calorimetry, transmittance light intensity and X‐ray diffraction measurements. The nO.SCl homologous series possesses smectic A (SmA) and nematic (N) phases for n = 4, 5, 6 while higher homologues have only an enantiotropic SmA phase. Those from the nO.OSCl homologous series have enantiotropic N and SmA phases and higher transition temperatures. The range of the N phase decreases, and of the SmA increases, with the elongation of the alkoxy chain in the nO.OSCl homologous series. The effect on mesomorphic behaviour of terminal alkoxy chain lengthening and replacement by chlorine on the other side of the molecule is discussed.

Megahertz dielectric relaxation process in the nematic and smectic phases of two thiol esters (9S5 and 10S5)

Abstract We present the results of a dielectric investigation of two members of the 4-n-pentylphenyl-4′-n-alkyloxythiobenzoate ([nbar]S5) homologous series with n = 9 (9S5) and n = 10 (10S5), in the frequency range 0·1–10 MHz, and in the temperature range covering all of the liquid crystal phases. Some properties of the [nbar]S5 substances with n = 5 to 10 are discussed.

Quasielastic neutron scattering study of molecular reorientation in the nematic and smectic phases of 4-n-pentylphenyl-4′-n-octyloxythiobenzoate

Abstract We report QNS investigations of the eighth member of the 4-n-pentylphenyl-4′-n-alkyloxythiobenzoate homologous series (C n H2n+1O-φ-COS-φ-C5H11, n = 8 and φ denotes the benzene ring), known as 8S5. QNS measurements have been performed for a fully protonated sample as well as for the one with deuteriated terminal alkyl and alkoxy groups, in the phases: isotropic, nematic, smectic A and smectic C. The results obtained indicate the important role of fast reorientation within the terminal chains, including conformational changes.

Phase polymorphism and thermal stability of new cholesterol thioesters derivatives

We report the fundamental properties of a series of new mesogens with cholesteric esters, cholesteryl 4-(4-alkoxybenzoylothio)benzoates CnH2n+1OC6H4COSC6H4COOch, where ch = cholesteryl, for n = 7–10, nOSBch in short. They share a common feature, which is a high temperature cholesteric mesophase. In addition, the n = 10 compound has a monotropic ferroelectric smectic C* phase. The chemical structure and purity of nOSBch were confirmed by standard methods: 1H nuclear magnetic resonance (NMR), 13C NMR, Fourier transform infrared spectroscopy and elemental analysis. Differential scanning calorimetry (DSC), polarising optical microscopy and transmitted light intensity were used to study the polymorphism of these mesogens. The substances were proved stable up to 240–270°C (thermal stability deduced from DSC scans). The crystal structures were determined from X-ray diffraction data. Possible conformational disorder as well as nearest-neighbours intermolecular interactions were inferred from quantum chemical calculations.

Phase behaviour of novel liquid crystalline mixtures based on thiobenzoates

Five compounds from the 4-n-pentylphenyl-4′-n-alkoxythiobenzoates homologous series, 4-chlorophenyl-4-n-octyloxythiobenzoate and two chiral compounds (S)-(+)-1-methylheptylbiphenyl-(4-n-pentylphenyl)thiobenzoate and (S)-(+)-4-(4′-n-penthylbenzoyl-thiobenzoyloxy)benzoate 1-methylheptyl have been prepared and investigated for their mesophase behaviour in new binary and ternary mixtures. The compounds and mixtures were thermally characterized by differential scanning calorimetry, polarizing optical microscopy and transmitted light intensity. Phase diagrams were constructed for various binary mixtures and one ternary mixture. The results are discussed in terms of influence of the molecular structure of the liquid crystalline components upon thermal stability of mesophases in their mixtures, and in particular the importance of terminal substituent. The existence of the nematic N, smectic A and smectic C multicritical point, the NAC point was suggested for three thioester mixtures. †Dedicated to Prof. Dr Jerzy A. Janik on his 80th birthday.

Phase Behavior and Dynamics of Binary and Multicomponent Thioester Liquid Crystal Mixtures

The results of studies conducted by means of complementary methods, differential scanning calorimetry, transmitted light intensity measurements, polarized optical microscopy, the electro-optical method, as well as dielectric relaxation spectroscopy of two new liquid crystal mixtures are presented. The first mixture is an equimolecular binary mixture consisting of two ferroelectric chiral liquid crystals from the homologous series, abbreviated as (S)-MHOBSn. The second mixture is a multicomponent mixture and consists of four mesogens from the homologous series of nOS5 as the base of the mixture, abbreviated as 610712 and chiral MHOBS8. The binary MHOBS4 + MHOBS7 mixture has an enantiotropic phase sequence, as follows: Cr, SmG*, SmI*, SmC*, N*. The second mixture has the same phase sequence but a much wider temperature range of ferroelectric SmC* phase. The switching time changes from 50 to 90 μs in the SmC* phase of the binary MHOBS4 + MHOBS7 mixture, whereas in 610712 + MHOBS8, the change is more than an order of magnitude higher, ranging from 500 to 3500 μs. Numerical analysis of the dielectric spectra results point toward the complex dynamics of the MHOBS4 + MHOBS7 and 610712 + MHOBS8 mixtures. The relaxation processes in the crystalline, SmC*, SmI*, and SmG* subphases have been observed and described. The relaxation processes have been detected up to 12 °C. There is a very low intensity Goldstone mode in SmC* and a low-frequency noncancellation mode in the SmI* and SmG* phases.

Physical properties of 8OS5 thioester studied by complementary methods

ABSTRACT Properties of 4-n-pentylphenyl-4’-n-octyloxythiobenzoate (8OS5), belonging to the nOS5 homologous series, have been studied by complementary methods. The phase sequence, the phase transition temperatures, the thickness of molecular layers, the average distance between long axes of molecules and the correlation length were determined during cooling and heating. For the first time, simultaneous X-ray diffraction and differential scanning calorimetry measurements have been used to study mesomorphic properties. The results are compared with the ones obtained in standard measurements by means of differential scanning calorimetry, X-ray diffraction and polarizing optical microscopy. Meaning of experimental procedures applied in investigations of monotropic mesophases below a melting point is discussed.

Calorimetric and microscopic investigations of selected members from the thioester homologous series

DSC measurements and microscopic observations of three compounds from the thioester series (4-n-pentylphenyl-4′-n-alkoxythiobenzoates, abbreviated to nS5) have been performed. In addition to the nematic and smectic phases known previously from the literature, a new monotropic low-temperature phase has been detected by both methods for 9S5 and 10S5. This new phase exists below a highly ordered smectic J phase and a crystal phase. The nature of this new phase is discussed.