SA Phase Research Articles

A comparative study of the molecular motions in the three smectic phases of isobutyl 4(4′ phenylbenzylideneamino) cinnamate using incoherent neutron scattering

Incoherent quasi-elastic neutron scattering results from aligned samples of isobutyl 4(4′ phenylbenzylideneamino) cinnamate in its smectic E, B and A phases are presented. The main results of a detailed analysis in conjunction with results from other techniques are as follows. Translational diffusion parallel to the layer normal is hindered in the SA phase by a weak temperature dependent barrier (5 to 15 kJ mol-1) but this is much stronger in the SB and SE phase (at least 30 kJ mol-1). However a feature of all three phases is that the molecules have the freedom to move diffusively on a time scale of 10-11 s by ∼ 1–4 A parallel to the layer normal. The molecules appear to undergo uniaxial rotational diffusion about their long axes in the SA and SB phases although it is not possible to discount some weak orientational ordering into six equivalent sites in the SB . In the SE phase there is a clear onset of orientational ordering into two sites separated by π. Dynamic fluctuation of the long molecular axes oc...

Evidence of tilted monolayer cybotactic groups in a partially bilayer SA phase

A study using X-ray diffraction for 4 nonanoate 4' cyanobiphenyl (8 COO CB) shows that the SA phase has a partially bilayer structure with layer thickness d = 1.4 L (L : molecular length). It also shows monolayer fluctuations inside this phase. Moreover, it points out that there exist skewed cybotactic groups of single molecules in the partially bilayer S A phase in the supercooled range of the SA phase. The size of these groups is about 500 molecules, the tilt angle is about 35°. A study using dielectric relaxation for this compound has also been performed. It shows that the activation energy for reorientational movement of the molecule has unusual behaviour. With decreasing temperature, this energy decreases to the N-SA transition but it increases in smectic supercooled range. Variations obtained are in agreement with information obtained from X-ray experiments.

X‐ray Studies on the Liquid Crystalline Phases of the 4‐[4‐n‐Heptyloxy‐Benzylidene‐Amino]4'‐cyanobiphenyl

AbstractBy means of X‐ray diffraction studies of oriented and non‐oriented samples the lattice parameters of the orthorhombic cell of the SE phase as well as of the hexagonal cell of the SB phase were determined. By packing considerations a bimolecular building unit with oppositely arranged cyano‐groups was assumed in the case of the SE phase.The SB phase is characterized by an ABAB sequence of the smectic layers in which the molecules are hexagonal arranged. The increasing mobility of the molecules at increasing temperature offers the possibility for a part of the molecules to slide in a more stable dimerized form. In the NR and SA phase the existence of monomers as well as of dimers is assumed.In this way a conception of the phase transitions SE → SB → NR → SA is given on the base of a decrease by steps of the dipole‐dipole repulsion.

ChemInform Abstract: NMR STUDY OF ALLOYS EXHIBITING A REENTRANT NEMATIC PHASE

Proton T1 was measured at 30 MHz as a function of temperature in three binary mixtures (27.7, 25.2, and 22.9 wt. % 60CB in 80CB) exhibiting a reentrant nematic phase. Proton T1 and T1D were also measured at 7.07 and 30 MHz, respectively, in 27.6 wt. % 60CB. The angular dependence of T1 was studied in the SA phase of 22.9 wt. % 60CB at 30 MHz and in the SA phase of 27.6 wt. % 60CB at 7.07 MHz. It was found that T1 and T1D show different behavior in the high temperature nematic and reentrant nematic phases. Nematic orientational order director fluctuation (ODF) and/or molecular self‐diffusion are used to account for the relaxation rates in various mesophases. ODF seems to be an important relaxation mechanism in the reentrant nematic phase, while molecular self‐diffusion appears to be responsible for spin relaxation in the high temperature nematic phase. It would appear that molecular dynamics for nematic and reentrant nematic phases are tied closely to the viscosity of the sample.

NMR study of alloys exhibiting a reentrant nematic phase

Proton T1 was measured at 30 MHz as a function of temperature in three binary mixtures (27.7, 25.2, and 22.9 wt. % 60CB in 80CB) exhibiting a reentrant nematic phase. Proton T1 and T1D were also measured at 7.07 and 30 MHz, respectively, in 27.6 wt. % 60CB. The angular dependence of T1 was studied in the SA phase of 22.9 wt. % 60CB at 30 MHz and in the SA phase of 27.6 wt. % 60CB at 7.07 MHz. It was found that T1 and T1D show different behavior in the high temperature nematic and reentrant nematic phases. Nematic orientational order director fluctuation (ODF) and/or molecular self-diffusion are used to account for the relaxation rates in various mesophases. ODF seems to be an important relaxation mechanism in the reentrant nematic phase, while molecular self-diffusion appears to be responsible for spin relaxation in the high temperature nematic phase. It would appear that molecular dynamics for nematic and reentrant nematic phases are tied closely to the viscosity of the sample.

Ultrasonic Studies in N-(p-n-butoxybenzylidene)-p-n-butylaniline

Abstract The ultrasonic velocity in the SG(SH), SB, SA, Nc , N0 and isotropic liquid phases of N-(p-n-butoxybenzylidene)-p-n-butylaniline (BBBA) has been measured as a function of temperature. A transition in the nematic phase seems to indicate the existence of an ordinary nematic and a cybotactic nematic phase. The transition SG-SB has been found for the first time with the ultra-sonic velocity method. The adiabatic compressibility βad and the molar sound velocity Rn (Rao number) have been determined using the experimental density and ultrasonic velocity.

Induced Smectic Phases I. Polymorphism in Binary Mixtures of Alkyloxybenzylidene-alkylanilines with Alkyl- and Alkyloxy- cyanobiphenyls

The diagrams of state of mixtures of 4-n-alkyloxybenzylidene-4'-n-butylanilines with 4-n- alkyl- and 4-n-alkyloxy-4'-cyanobiphenyls are studied. The mixtures form induced smectic phases of type SA, SB and SE. In all three smectic phases the thickness of the smectic layers agrees with the mean values of the molecular lengths. In most cases the induced SA phases do not show uninterrupted miscibility with the SA phases of the pure components. For instance, the system 40 • 4/8 CBP exhibits three separate SA phase areas. The maximum transition temperatures of the induced smectic phases increase with increasing chain length of the azomethines, but remain constant in case of the SA and SB phases or even decrease in case of the SE phases with increasing chain length of the cyanobiphenyls

Brillouin scattering in SA and SB phases of butyloxy-benzilidene octylaniline

Brillouin scattering in SA and SB phases of butyloxy-benzilidene octylaniline

Higher‐mode surface waves and structure of the Great Basin of Nevada and western Utah

Observed seismograms and dispersion data for crust and mantle higher mode surface waves in the Great Basin are compared with theoretical seismograms and dispersion curves computed for the Great Basin model of Priestley and Brune [1978]. This structure was originally derived from fundamental mode surface wave and refraction data. Phases identified as Sa [T∼13 s] are observed to have a phase velocity of 4.50±0.03 km s−1. Crustal second Rayleigh mode (first shear mode) waves have predominant periods varying from about 5 s on some paths to about 8 s on others. The observed excitation and phase velocity of the Sa phase are in agreement with theoretical seismograms and computed phase velocities for a modified Great Basin model. The agreement provides added support, in an unexpected way, for the existence of a mantle lid of velocity about 4.5 km s−1 in the Great Basin. The crustal higher mode group velocity observations, i.e., the predominant periods of the second Rayleigh mode along various paths, reflect variations in crustal thickness within the Great Basin. Crustal thicknesses of approximately 25 km are indicated for some paths in northwestern Nevada and southeastern Oregon, whereas crustal thicknesses of greater than 35 km are indicated for east central Nevada. The crustal thickness of 35 km in the Great Basin model is probably most appropriate for the central part of the Great Basin.

4(4-Alkyloxybenzoyloxy)-4' -cyanoazobenzole: Eine homologe Reihe flüssigkristalliner Verbindungen mit der ungewöhnlichen Phasenfolge smektisch A-nematisch-smektisch A / 4(4-Alkyloxybenzoyloxy)-4'-cyanoazobenzenes: A Homologous Series of Liquid Crystals Exhibiting the Unusual Phase Sequence Smectic A -Nematic -Smectic A

The synthesis and the phase transition temperatures of homologous liquid crystalline 4(4-alkyloxybenzoyloxy)-4'-cyanoazobenzenes with alkyl chain length n = 1-12 and n = 16 are reported. All compounds exhibit smectic A phases; the SA phase region being interrupted by a "re-entrant" nematic phase for alkyl chain lengath n ≥ 9.

Dielectric relaxation in nematic, smectic A and C phases in the MHz region

AbstractThe dielectric properties of four 4‐n‐alkyloxyphenyl 4‐n‐alkyloxybenzoates with nematic, smectic C and partly additional SA phases were investigated. In 2 substances for ϵ′ reproducible values also in the smectic phases resulted allowing to conclude on a good orientation in the samples. In all 4 substances the dielectric relaxation in the MHz region was measured and the respective activation energies were determined. The molecular mobility in the SC phases is higher than in the SA phases, however comparable with that of the nematic phases. In all 3 phase types a single relaxation mechanism exists, which is explained as rotation of the molecules around a short axis.

Polymorphism and X-Ray Diffraction of Some Cyano Biphenyl-Substituted Benzoates Exhibiting Reentrant Nematic Phases

Abstract The polymorphism of the 4 cyanobiphenyl-4′-n-alkoxy benzoate esters is investigated and a reentrant nematic phase is observed for the n = 8 and n = 9 homologues. X-Ray studies confirm this fact and show that in the reentrant phase the cybotactic groups are SA-like at high temperature near the SA phase while they appear SC-like at lower temperatures.

ULTRASOUND INSTABILITIES IN SMECTIC A

Some defect patterns induced by ultrasounds in SA phase are presented. The similarity of the results with the ones obtained with hydrodynamic flow indicates that the main origin of instabilities is due to the velocity field connected with the acoustic streaming.

A SA-SChTransition—The Problems of Phase Assignment

Abstract Re-examination of the smectic polymorphism of certain n-alkyl esters of some 4′-n-alkoxybiphenyl-4-carboxylic acids, by X-ray and miscibility techniques has shown a further phase to be present. This extra phase is proved to be a tilted smectic B (SH) phase. One of the esters, n-butyl 4′-n-octyloxybiphenyl-4-carboxylate, is shown to exhibit SA, Sc and SbC (SH) phases, but the Sc phase is so extremely short-lived that the impression is that the ester exhibits a SA-SCH transition.

The Liquid Crystal Properties of Some Aromatic Esters Derived From Naphthalene

Abstract Abstract The 2,6-naphthylene ring system has been used to replace each of the 1,4-phenylene rings in various 4-substituted-phenyl 4-substituted-benzoates, where the substituents were alkyl and/or alkoxy. For the dialkyl esters, the N-I temperatures were increased by 60–80° compared with the simpler, analogous phenyl benzoates, irrespective of the position of the 2,6-naphthylene ring. For the esters with one alkyl and one alkoxy substituent, the N-I temperatures were again higher than those of the corresponding phenyl benzoates (∼60°); SA properties were quite pronounced in the 6-alkyl-2-naphthyl 4-alkoxybenzoates. When both substituents were alkoxy groups, SC phases of quite wide thermal range were exhibited, usually preceded on cooling by a nematic and a SA phase.

Induced smectic phases

Mixtures of terminal polar with terminal non-polar nematic liquid crystals usually produce induced smectic phases (ISP). This is shown by the investigation of a great number of systems using the contact method.In general, SA phases are induced. By means of X-ray investigations SB and SE phases were also established. No solid molecular complex was found. The layer spacing for the induced smectic phases becomes minimal for mixtures about 1 : 1 at which the maximum thermal stability of the induced smectic phases was found as well. The effects observed indicate a close relation between the induction of smectic phases and the formation of the double layer structure in the smectic phases of terminal polar liquid crystals.

MOLECULAR STRUCTURE AND THE POLYMORPHISM OF SMECTIC LIQUID CRYSTALS

The smectic properties of four series of esters — the methyl to n-decyl esters of the 4'-n-hexyloxy, 4'-n-heptyloxy-, 4'-n-octyloxy- and 4'-n-nonyloxy-biphenyl-4-carboxylic acids — are discussed. The effects on the smectic phases of increasing the alkyl chain lengths are quite striking, particularly in the last three of these series, where SC properties are introduced for the midde members. The SC-SA transition temperatures in each series lie on two parabolae with the result that the earlier homologues exhibit A, B, E sequences and the higher homologues form only SA phases. Thus, the tendency of these series to exhibit SC phases is a function of alkyl chain length and is not determined simply by the more rigid central part of the molecule containing the permanent dipole moments. Evidence for the SC properties of these esters is given in detail. Other cases in which increasing the alkyl chain length leads to marked changes in smectic polymorphic behaviour, including the sudden injection of different smectic polymorphic phases into particular sequences of smectic phases, are reviewed.

NOVEL SMECTIC POLYMORPHIC BEHAVIOUR IN HOMOLOGOUS SERIES OF MESOGENS

The high alternation of nematic thermal stabilities found in the series of o-phenyl- alkyl4-(4'-phenylbenzylideneamino) cinnamates as the homologous series was ascended has been further exaggerated by substituting the terminal phenyl ester ring with methyl or chloro substi- tuents in the 3- or 4-positions. Nematic phases were found only when an even number (n) of methylene units occurred in the alkylene chain. Srnectic thermal stabilities also alternated as each of the four series of esters was ascended. Howe- ver, the srnectic A thermal stabilities decreased and the smectic B thermal stabilities increased on passing from even to odd values of n. In some cases this caused the thermal stabilities of the smectic A and B phases to coincide for odd values of n. When this occurred, a unique texture was observed microscopically at the I-S transition. Although no SA-SB transition could be detected microscopi- cally or by D. T. A., miscibility studies indicated that a transitional SA phase still existed. This suggests that it is necessary to form a transitional SA phase intermediate between the amorphous liquid and a SB phase, both on heating and cooling. This transition has been called SAB-I. Smectic E phases were also found for many of the sixteen new esters, and the thermal stabilities of SE phases, like those of SB phases, increased for odd values of n. The relative effects of 3- and 4-methyl- and chloro-substituents on N, SA, Sn and SR thermal stabilities are discussed.

New type of smectic mesophase?

4-Cyano-4′-octylbiphenyl (NC.C6H4.C6H4.C8H17) is a biphenyl derivative of considerable technological interest since it forms a colourless, stable smectic phase which exists at room temperature (21° C to 32.5° C). The corresponding ether 4-cyano-4′-octyloxybiphenyl (NC.C6H4.C6H4.OC8H17) forms a similar smectic phase at a higher temperature range (54.5° C to 67° C). Preliminary studies suggested that the smectic phases of these compounds are not miscible with any recognised type of smectic phase. Subsequent investigations (unpublished work by G.W.G.) have shown, however, that they are both miscible with a number of ‘authentic’ SA phases.

Rayleigh waves in southern New Guinea

abstract A shear velocity structure having features similar to the Gutenberg model for the upper 200 km of the mantle is consistent with features of higher mode Rayleighwave group-velocity dispersion curves in the period range 4 to 30 seconds, for paths across southern New Guinea. Pronounced discontinuities appear to be absent within the crust where shear velocities are expected to gradually increase with depth. Clearly dispersive second mode (M21) Rayleigh waves, well separated in time from the fundamental mode, are shown for path lengths less than 2000 km. Frequencies excited show some dependence on focal depth. Stationary wave groups of period 10-20 seconds, very like the Sa phase, and generated by earthquakes of focal depth between 100 and 160 km coincide with expected normal mode group arrivals.