Maria Massalska-Arodź

X‐ray studies on the crystalline E phase of the 4‐n‐alkyl‐4′‐isothiocyanatobiphenyl homologous series (nBT, n = 2–10)

X‐ray diffraction measurements were carried out on nine members of the isothiocyanatobiphenyl homologous series (nBT) in their smectic E (SmE) phase, with the aim of estimating the layer thickness and deriving orthorhombic unit cell parameters for the SmE phase. The data obtained are discussed in relation to molecular reorientation motion around the short axis in that phase.

Pressure-temperature phase diagrams of smectogenic 4′-alkyl-4-cyanobiphenyls (9CB, 10CB, 11CB and 12CB)

The pressure-temperature (p - T) phase diagrams for four smectogenic members of the 4′-alkyl-4-cyanobiphenyl homologous series (nCB, n = 9, 10, 11 and 12) over the temperature range 320–410 K and pressure range 0.1–300 MPa (3 kbar) were constructed using DTA. At 1 atm 9CB exhibits nematic and smectic Ad phases, while the other members show only the smectic Ad phase. However, at elevated pressures the clearing line splits in the case of 10CB and 11CB which indicates the induction of a nematic phase. It was found that the triple point, where the isotropic, nematic and smectic phases coexist, is strongly shifted to higher pressures with increasing chain length. This was interpreted as being caused by a loss of the rod-like shape of the molecules containing longer alkyl tails which explore a range of conformations. The slope of the clearing line, dT /dp, depends strongly on the length of the alkyl chain for the nCB series, but does not show a step-wise change between the nematogenic and smectogenic members.

DSC studies of neohexanol and its isomers

DSC method has been used to establish a solid state polymorphism of four dimethyl butanols having CH3 side groups: 2,2-dimethyl-1-butanol [CH3CH2C(CH3)2CH2OH)], 3,3-dimethyl-1-butanol [(CH3)3CCH2CH2OH], 3,3-dimethyl-2-butanol [(CH3)3CCH(OH)CH3] and 2,3-dimethyl-2-butanol [(CH3)2CHCOH(CH3)2]. Three isomers appear to be glass formers. Glass of liquid phase has been observed for 3,3-DM-1-B while glass of plastic phase for 2,2-DM-1-B and 3,3-DM-2-B. For 2,3-DM-2-B on cooling only crystallization has been found. Influence of location of the OH group in molecule on polymorphism is discussed. IR-spectra, measured in the liquid phase, have revealed hydrogen bonds in all isomers.

Signatures of glass transition in partially ordered phases

Features of glass transition in liquid crystalline nematic and smectic E, B and IA phases of selected materials observed by means of the polarising microscopy and Fourier transform infrared spectroscopy (FTIR) are reported. Evolution of cracking in the glass and a coincidence of its disappearance temperature with the glass transition temperature (Tg) on heating is shown and discussed in the context of processes that occur in the glass. The shape of temperature dependencies of absorption bands is shown as the signature of the glass transition.

Molecular dynamics and morphology of confined 4-heptyl-4′-isothiocyanatobiphenyl liquid crystals

Molecular dynamics and orientational order of 4-heptyl-4′-isothiocyanatobiphenyl (7BT) in non-intersecting nano-pores of mean diameters from 4 nm to 10.5 nm are studied by a combination of Broadband Dielectric and Fourier-Transform Infrared Spectroscopy. The smectic E phase observed in bulk 7BT is replaced by short-range molecular order imposed by the surface potential within the pores. In contrast to bulk dielectric properties of 7BT, geometrical confinement leads to modification of the molecular dynamics. Two dielectric relaxation processes exhibiting Arrhenius-like thermal activation are detected for molecules in nanopores of mean diameters from 6 nm to 10.5 nm. The slower process is assigned to molecular reorientation around the short axis (δ-relaxation) whereas the faster dipolar relaxation process (β-process) is attributed to librational motion of the molecules close to the pore-walls. Infrared Transition Moment Orientational Analysis reveals different molecular arrangement in pores of diameters 10.5 nm compared to the molecules in 4 nm and 6 nm pores.

Rich polymorphism in 4‐propyl‐4′‐thiocyanato‐1,1′‐biphenyl (3TCB) revealed by adiabatic calorimetry

The thermal behaviour of 4‐propyl‐4′‐thiocyanatobiphenyl (3TCB) was studied by adiabatic calorimetry. In addition to the isotropic liquid and smectic E (SmE) phases, five crystalline phases were detected. Such a rich polymorphism was not observed for the other low‐n members of the nTCB homologous series (n = 2–5). The observed anomalies are analysed and the possible origin for their existence is suggested. The temperature quench of the SmE phase leads to a metastable crystalline state with a multiple‐stage relaxation process.

Studies of Polymorphism of Right Handed (S)-4-(2-Methylbutyl)-4′-Cyanobiphenyl

Abstract Basing on the results of polarizing microscopy, differential scanning calorimetry (DSC) and infrared spectroscopy (in the range 70–700 cm−1) in the temperature range from 100 K to 320 K the phase diagram of right handed (S) 4-(2-methylbutyl)-4′-cyanobiphenyl was established. On cooling an isotropic phase transforms at 246 K into a cholesteric phase which can be easily supercooled to a glass at ca. 210 K. On heating this sequence of transitions reverses. Further heating of the sample leads to crystallization of supercooled isotropic phase at about 250 K. The crystal phase melts at 276 K. It was clarified that process of nucleation starts on cooling below 240 K. The shape of the far infrared bands (lattice vibration range) suggests that the crystal phase is highly disordered.

Dynamics in ferro- and antiferroelectric phases of a liquid crystal with fluorinated molecules as studied by dielectric spectroscopy

For 1-[3-fluoro-4-(1-methylheptyloxycarbonyl)phenyl]-2-[4-2,2,3,3,4,4,4-heptafluorobutoxybutoxy)biphenyl-4-yl]ethane (1F7), built of chiral molecules, results of dielectric measurements of liquid-crystalline and solid phases are presented. Rich polymorphism of liquid-crystalline (SmC*, SmC*A and SmI*A) phases as well as of solid (Cr1 and Cr2) phases were observed down to –130°C. At a frequency range from 0.1 Hz to 3 MHz, the relaxation processes were detected in ferroelectric SmC*, antiferroelectric SmC*A and highly ordered SmI*A smectic phases. The mechanism of complex dynamics (moleculear and collective) was identified with the help of the bias field. Vitrification of conformationally disordered crystal phase Cr2 was found in accordance with calorimetric observations.

X-ray studies of the smectic B phase of the 4-bromobenzylidene-4′-alkoxyanilines

The results of X-ray studies of the nine members (4 ÷ 12) of the 4-bromobenzylidene-4′-alkyloxyaniline homologous series (nBBAA) in smectic B (SmB) and smectic A (SmA) phases are presented. Interestingly, no SmC phase was identified. The thickness of smectic layers in the SmA and SmB phases was estimated showing unexpectedly that in SmA it is bigger than in the SmB. For the SmB phase, orthorhombic unit cell parameters were determined as a function of temperature. The obtained data are discussed in relation to rotational dynamics.

Phase Transition and Structure Studies of a Liquid Crystalline Schiff-Base Compound (4O.8)

Calorimetric and X-ray powder diffraction studies of N-(4-n-butyloxybenzylidene)-4′-n′-octylaniline are presented. Heat capacity measurements have been performed by adiabatic calorimetry in the temperature range from 5 K to 375 K. Three liquid crystalline phases, i.e., nematic, smectic A and smectic B, and an ordered crystal of triclinic structure and two new metastable crystal phases were observed. In addition, the crystalline smectic B phase of different sequence of molecular layers than liquid crystalline smectic B, has been found. Both smectic B phases have been vitrified. For the smectic B phase a hexagonal unit cell has been identified by X-ray diffraction. The diffraction pattern of glass of crystalline smectic B phase is shown.