A series of 4‐decyloxy‐4′‐hydroxybiphenyl esters of α,ω‐alkanedicarboxylic acids containing two mesogenic units connected by a methylene spacer was synthesized. The mesogenic properties of the compounds were investigated by polarising optical microscopy, differential scanning calorimetry and X‐ray diffraction methods. A strong influence of the spacer length and its parity on the mesomorphic properties was found. A dramatic odd–even effect was observed for the clearing temperatures and entropies. Compounds with an even number of carbon atoms in the methylene spacer formed tilted smectic phases, whereas compounds with an odd number of carbon atoms in the spacer exhibited the B4 phase, characteristic of bent‐shaped molecules.

Two ferroelectric three‐ring chiral esters, one with a partially fluorinated alkyl chain and another with a cyano terminal group, were mixed with a structurally similar compound having an alkyl terminal chain. In their mixtures an antiferroelectric phase was induced. The phase behaviour, spontaneous polarisation, tilt angle, smectic layer spacing and helical pitch of both systems were determined. The mechanism of the induction of an antiferroelectric phase is different in both cases, with highly tilted phases in former system and less tilted phases in the latter.

DSC, polarizing optical microscopy and X-ray diffractometry were used to investigate the mesomorphic behaviour of 4-n-butyl-4′-acetyl-biphenyl, which resulted to exhibit a smectic E and, possibly, a smectic K phase. Additionally, 2H NMR spectroscopy was applied on a selectively deuterated sample to study the properties of alignment of the mesophases within a magnetic field, as well as to characterize molecular dynamics. Two motional processes were found to be active in the smectic E phase, namely fast π-flips of the benzene rings and molecular self-diffusion about the herringbone bidimensional lattice of the layers. No molecular overall diffusional motions were observed by either 2H NMR spectroscopy or dielectric relaxation measurements.

Several substances of different chemical structures exhibiting the smectic B polymorphism in a wide temperature range [accompanied by the nematic (N) phase in few cases] were studied with the aid of the dielectric relaxation and Xray methods. The dielectric relaxation time tau(parallel to) connected with the end-over-end rotations of molecules was determined. It elongates considerably at the N-B transition whereas the activation barrier hindering the flip-flop motion decreases. The parameters of the hexagonal unit cell were determined as functions of temperature. The packing parameter, p = ZV(mol)/V-u.c., was calculated which exceeds value of c. 0.6, thus is typical for the plastic crystals. The dynamical properties of molecules are discussed in relation to their packing in the smectic layers. The applicability of the Arrhenius equation to calculation of the activation barrier from the temperature dependence Of tau(parallel to) in the B phase seems to be doubtful in view of the experimental data collected. It was concluded that all examined substances have rather the hexatic than the crystalline B phase.

Three ring chiral esters, substituted laterally or not with a fluorine atom, having chiral terminal chain of the structure –COOC*H(CH3)C6H13, and achiral terminal chain alkylated CnH2n+1COO(CH2)mO– or partially fluorinated CnF2n+1COO(CH2)mO– (n = 1–7, m = 3–6) were measured by small angle X-ray scattering technique. Most of the fluorinated homologues have high tilted an orthoconic antiferroelectric phase (angle in neighbouring layers is around 90°), which is followed by a SmA phase of like de Vries type. The following parameters are compared: temperature function of d, dA, d/l, dA/l, (d-layer thickness, dA-layer thickness of SmA phase, l-molecular length) upon temperature and relation with the structure is discussed. The preferred structure for formation of the orthoconic antiferroelectric structure is partially fluorinated terminal alkyl chain and biphenylyl benzoate rigid core. The strongest de Vriesation of SmA phase is observed for longer fluorinated terminal alkyl chain (n > 4, m = 6) and phenyl biphenylate rigid core substituted by a fluorine atom in the 2 position of the phenyl ring.

The series of cyclic oligosiloxanes having different attached mesogenic rigid cores and the polar end groups have been reported. The novel oligomers exhibit smectic A and E phases. The effects of the various central linking units and end terminal groups on mesomorphic properties are discussed. Mesophases were characterised by differential scanning calorimetry, polarizing optical microscope and X-ray diffraction.

Several new ester imide derivatives with different N‐substituents in the imide ring were synthesized and their mesogenic properties investigated by thermal analysis, optical microscopy and X‐ray diffraction. All the esters of N‐4‐[(4′‐decyloxybiphenyl‐4‐yl)oxycarbonyl]phthalimideacetic acid and aliphatic alcohols exhibited monolayer SmA and SmC phases. In addition, for the ethyl and propyl esters a monotropic hexatic (F or I) phase was observed. The introduction of additional substituents at the carbon atom in the methylenemethoxycarbonyl group (in the vicinity of the nitrogen atom) substantially influenced liquid crystalline properties: the compounds with a flexible chain exhibited monotropic SmA–SmB dimorphism, but liquid crystalline properties vanished for the substituent containing the more rigid phenyl ring.

X-ray investigations of nine smectogenic substances exhibiting the smectic A(d), A(1) and crystalline E phases were performed at various temperatures. X-ray patterns yielded the layer thickness d (A(d), A(1) phases) and orthorhombic unit cell parameters (E phase). The layer thickness of the A(d) phase in 4'-n-alkyl-4-cyanobiphenyls (nCBs) has different temperature coefficients for shorter (n = 8-10) and longer (n = 12-14) members, which is explained as resulting from two competing effects: a weakening with temperature of the intermolecular association energy that favours an increase in d, and the increasing number of conformers which reduces the molecular length. A small anisotropy of the thermal expansivity in the smectic phases was found by comparing the linear quantity d(T) with the linearized bulk characteristic of the system, V-3(T), where V = 1/ρ is the specific volume, ρ is the density. Differences between the slopes of the two quantities are less in the case of the A1 phase of two nDBTs (5-n-alkyl-2-(4'-isothiocyanatophenyl)-1,3-dioxanes). The present X-ray data and recent results of studies of the low frequency relaxation process in these compounds (under atmospheric as well as elevated pressures) give a consistent picture of molecular reorientations around the short axes in the smectic phases.

A series of new liquid crystalline cyclic siloxane oligomers was prepared to investigate the influence of the long alkyl chain as an end substituent on their mesomorphic behaviour. Liquid crystalline properties of the new cyclosiloxanes were examined by DSC, polarized optical micoscopy and X-ray diffraction methods.

Three homologous series of (4′-octyloxybiphenyl-4-yloxymethyl)benzoic acid derivatives were synthesised and studied. The compounds, substituted by n-alkyl esters, reveal strong discrimination of the tilted phases formation upon elongation of the alkyl group. In compounds with 2 methylalkyl chains, tilted phases were exclusively observed with both ferroelectric and antiferroelectric properties. It has been observed that for chiral derivatives an elongation of the chiral chain leads to odd-even effect on the polar properties. Also elongation of non-chiral alkoxy terminal chains affects the polar properties. For short homologues the antiferroelectric phases dominate, while for long homologues only ferroelectric behaviour is observed. The influence of strongly polar lateral groups (Cl, Br, NO 2 ) attached to the biphenyl ring on LC phase properties was also determined. It was detected that mono-substituted compounds have lower mesogenic stability then their disubtituted counterparts. The effect is probably related to restricted rotation around the phenyl-O bond that leads to a more rigid core structure.

The relation between molecular structure of enaminoketone derivatives and their mesomorphic properties is discussed. It has been observed that the electron accepting terminal groups (F,Cl,Br,CN) promote formation of orthogonal phases while strongly electron donating groups (OCnH2n+1) favour tilted phases. Among the synthesised compounds, materials useful for structural studies of two dimensional (2D) melting in orthogonal, as well as the tilted systems, were found. It has been determined that the heat effects in the melting process from crystalline smectic into liquid-like smectic, through the hexatic state, are correlated to the density changes.

Par une methode thermomicroscopique nous avons obtenu les diagrammes de phases des melanges de deux composants : l'un choisi dans la serie de composes homologues nCBB de telle sorte que ces composes aient une phase nematique et smectique A 1 (n = 4, 5, 6, 7) et l'autre appartenant a la serie de composes homologues nCB (n = 0-8). Dans le melange nCBB-nCB on observe une forte augmentation de la stabilite des phases A d lorsqu'un compose smectique de nCB (n = 8) est utilise, et une phase smectique est induite lorsque des composes nematiques de nCB (n = 0-7) sont utilises. Dans la majorite des cas, la surface de la phase smectique A d induite a la forme d'une ile entouree d'une phase nematique. La taille et la forme de la phase A d induite dependent de la longueur de la chaine alkyl des deux composants. L'intervalle entre les couches smectiques est sensible a la longueur du dimere de la molecule nCBB et augmente legerement avec la temperature et la concentration du nCB. Le remplacement d'un compose a chaine alkyl lineaire par un compose a chaine ramifiee favorise l'apparition de la phase A d .

Phase diagrams of binary systems containing liquid crystalline components with smectic C phases have been investigated. It has been shown that the difference of tilt angles of components is important but not the decisive factor which determines the thermostability of the smectic C phase of the mixtures.

The smectic I, F, J and G phases of the chiral ferroelectric compound (+)-(4-(2′-methylbutyl)phenyl 4′-n-octylbiphenyl-4-carboxylate) (+ 2M4P8BC) were studied by means of optical microscopy and X-ray diffraction. The free-standing film method was used. The films were additionally ordered with a d. c. electric field and true monodomain samples were prepared and examined.

C-203therefore the boundary serves as a source for dislocations.andmicrotwins.Planar faults, identified as micro twins are observed to emerge from the boundary area between the tungsten fibres and the matrix penetrating through the Ni 4 W phase.The diffraction pattern analysis identified them as having the (ll1)11i habit plane.No 'systematic dislocation substructures have been observed in the matrix because of the high temperature at which the creep specimen was left after failure had occurred.07.9-5 INVESTIGATION