Report on the 11th Annual British Liquid Crystal Society Meeting, 1–3 April 1996

Abstract

This year's meeting was held at the University of Central Lancashire in Preston and was attended by 185 delegates. The meeting was organized jointly by Professor Mike Holmes and Dr Richard McCabe and took place in the recently completed Harrington conference facilities. It provided a lively interchange of information on a wide variety of topics, led by the invited speakers who covered four important areas of interest. The Ben Sturgeon Memorial Lecture was delivered Professor Bill Doane from Kent State University. His up-to-the-minute presentation dealt with reflective cholesteric liquid crystal displays and the progress that has been made in developing low cost, low power and high-resolution displays capable of delivering the type of switching rates that will make them serious rivals to the printed page. He provided his audience with both the scientific background and the challenges remaining before commercial displays of this type are available.     

Microstructure of Milled Mesophase Pitch-Based Carbon Fibers as an Anode Material for Li-ion Batteries

Abstract

The microstructure of milled mesophase pitch-based carbon fibers (mMPCFs) that have been developed as an anode material for Li ion batteries have been studied as a function of heat treatment temperature (HTT), by SEM, X-ray diffraction, and Raman spectroscopy. And the results obtained are compared with those by X-ray diffraction (XRD) and SEM observations, for the characterization of specific structural features of mMPCFs as a promising anode material.     

Guest Editor's Preface

Abstract

The Korea-Japan Joint Forum (KJF) was held on September 9–11, 1999, in Kyongju, Korea, and celebrated its 10th anniversary with 170 participants from both countries. In the early days of KJF, the number of participants was around 50, mostly the invited lectures and a small number of poster presentations. However, the numbers have increased year by year, and at the same time, the quality of posters has a shown rapidly remarkable improvement. On this point the contribution from young Korean scientists was greatly appreciated. Since almost all the proceedings of KJF have been published as special issues of Molecular Crystals and Liquid Crystals, readers can catch up with the history of KJF easily: MCLC 189 (KJF'89), 217 (KJF'90), 224 (KJF'91), 227 (KFJ'92), 247 (KJF'93), 267 (KJF'94), 280 (KJF'95), 294–295 (KJF'96 as the 1st Asian Symposium on Organized Molecular Films (ASOMF'1)), 316 (KJF'97) and 322 (KJF'98). KJF covers the research field of “Organic Materials for Electronics and Photonics” since 1992, because this field has been most promising for industrial development in both Korea and Japan. Topics in KJF'99 are (i) Optical materials and related topics (nonlinear optics, photorefractive materials, liquid crystals), (ii) LB films, self-assembled monolayers and nanostructure control, (iii) Conducting polymers, (iv) Electroluminescent materials and devices, and (v) Device applications (photonic devices, rechargeable batteries, thin film transistors). Among these, the electroluminescent materials are the hottest topics for the coming display technology innovation. About two-thirds of the presented papers are collected in this proceedings after the peer review.     

Inverted SiC nanoneedles grown on carbon fibers by a two-crucible method without catalyst

Inverted single crystalline SiC nanoneedles with hexagonal cross-sections were grown on the surface of carbon fibers by high-frequency induction heating two-crucibles without using any catalysts. we employ a carbothermal reduction method of silicon monoxide with coke fibers to synthesize SiC nanoneedles within 5 min. The as-grown SiC nanoneedles shows bright blue color on carbon fibers in the [1 1 1] orientation of 3C-SiC structure. The needle-like structures grew on the substrate while the spindle portion was sticked into the carbon fibers which were different from other nanoneedles. Finally, the growth mechanism of SiC nanoneedles is proposed to be an axial direction growth with a driving force of screw dislocation and a radial direction growth with vapor–solid mechanism meanwhile.     

Thermal variation of attenuation for optical fibers

Thermal variation of attenuation for multi-component and high-silica glass fibers has been measured at 0.63 μm wavelength in a temperature range from 20°C to 600°C. The multicomponent glass fibers have shown no increase in loss below 400°C, whereas the high-silica glass fibers have shown a drastic, exponential increase in loss with increasing temperature. The observed change of attenuation has been explained on the basis of the shift of the ultra-violet absorption band calculated from temperature change of refractive index. The increase in optical loss, calculated from the obtained data of refractive index and dispersion parameters at each temperature, shows good agreement with the observed increase in loss.     

Molecular structure,vibrational spectroscopic and chemical reactivity of nematogenic p-n-alkylbenzoic acids: A comparative computational analysis

Molecular structure and vibrational spectroscopic studies of higher homologous series nematogenic p-n-alkylbenzoic acids (nBAC) that have 6 (6BAC) and 7 (7BAC) carbon atoms in the alkyl chain have been investigated using the Density Functional Becke3-Lee-Yang-Parr (B3LYP) level with the basis set 6-31++G (d.p) and Hartree Fock (HF) with the same basis set. The observed vibrational spectra has been resolved and assigned in detail for comparision with both the molecules. These results indicate that DFT and HF values are slightly different at both the levels. A comparision of chemical reactivity such as HOMO (E_H), LUMO (E_L) energies, energy gap (E_g), ionization energy (I), electron affinity (A), electro negativity (χ), chemical hardness (η), electronic chemical potential (μ), electrophilicity index (ω), and softness (S) has been made. It has been observed that the decrement has occurred in the energy band gap value of isolated molecule with increment in alkyl chain length. This provides valuable information regarding enhancing the stability of liquid crystal materials by maintaining the conductivity.     

Carbon nanotubes: Novel architecture in nanometer space

I describe here the basic structure of nanometer size tubules of graphitic carbon with the aid of high resolution transmission electron microscopy. The distribution of pentagons and heptagons on the hexagonal lattice of curved graphene sheets results in numerous morphologies in the closed cylindrical geometry of the tubules. The arrangement of hexagons on the tube surfaces follow helical patterns and the band structure is reported to change accordingly resulting in interesting electronic properties. The defect free structure of these nanotubules have been predicted to result in mechanically one of the strongest material in nature. All the more, the internal cavities of the tubules have been recently utilized for filling in different inorganic materials creating unique nano-composites. I review the recent developments on carbon nanotubes and discuss what potential awaits this material for possible future applications, considering the fact that bulk amounts of purified material is now available.     

Controllable mineralization of calcium carbonate on regenerated cellulose fibers

Gel–forming fibers (GF fibers) can serve as nucleation sites to prepare calcium carbonate (CaCO₃) because they can adsorb large amounts of Ca²⁺ due to their porous structure. In this paper, mineralization behavior of CaCO₃ on GF fibers in ethanol–water mixed solvents without any additives has been investigated. The results showed that some crystals covered the fibers, while others were embedded in fibers. Twin–sphere based vaterite, zonary and rodlike calcite with large aspect ratio could be prepared successfully. The effect of ethanol content inside GF fibers, concentration of Ca²⁺ and CO₃^2‐, mineralization time, miscibility between alcohol and water, and temperature were studied. Lastly, a possible mineralization mode was suggested. This work could provide a new method to prepare inorganic/polymer hybrid materials. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Vibrational spectra,electronic properties and effect of alkyl chain length on chemical stability of nematogens – A comparision using DFT and HF methods

The vibrational spectra of lower homologous series of nematogenic p-n-alkylbenzoic acids (nBAC) with 4 (4BAC) and 5 (5BAC) carbon atoms in the alkyl chain have been investigated using the Density Functional Becke3-Lee-Yang-Parr (B3LYP) level with the basis set 6–31++G(d.p) and Hartree Fock (HF) with the same basis set. The observed vibrational spectra has been resolved and assigned in detail for comparision with both the molecules. These results indicate that DFT and HF values are slightly different at both the level. A comparision of electronic properties such as HOMO (E_HOMO), LUMO (E_LUMO) energies, energy gap (E_g), ionization potential (I), electron affinity (A), electro negativity (χ), chemical hardness (η), electronic chemical potential (μ), electrophilicity index (ω), and softness (S) has been made. It has been observed that decrement occurred in the energy band gap value of isolated molecule with increment in alkyl chain length. This provides valuable information regarding the stability of liquid crystal materials.     

Normal coordinate analysis of tantalum(I) and niobium(I) hexahalide anions

Urey-Bradley force field (UBFF) and orbital valence force field (OVFF) techniques have been applied to the hexachloride and the hexabromide anions (O _h symmetry) of tantalum(I) and niobium(I). Trends in stretching force constants have been discussed on the basis of (i) the periodic position of the central metal atom and (ii) the nature of the halide ligands. Comments have been made also on the suitability of the force fields used.     

4-(2-Methylphenyl)-1,2,3,4,5,6,7,8-octahydroquinazoline-2,5-dione (I) and 4-(4chlorophenyl)-1,2,3,4,5,6,7,8-octahydroquinazoline-2,5-dione (II)

The crystal and molecular structures of the title compounds have been determined by x-ray structure analysis. The compounds (I) and (II) crystallize in space groups P2₁2₁2₁ and 12/a respectively. The structures were solved by direct methods and refined to R = 0.058 and R = 0.046. The saturated pyrimidine-2-one ring in both structures deviates from the planarity. There are two intermolecular hydrogen bonds in (I) and (II). The configuration at C4 in (I) is S.     

Field and Frequency Effects in a Nematic Mixture of Negative and Positive Dielectric Anisotropy

The molecular alignment in the nematic liquid crystal mixture of p-ethoxy benzylidene p′-n-butyl aniline (EBBA) and p-ethoxy benzylidene p′-cyano aniline (EBCA) has been investigated by measuring the dielectric constant at 1 MHz. Detailed investigation has been carried out for a composition of 2.74%, of EBCA in EBBA for different electric and magnetic field strengths and at different frequencies of the applied electric field. Both parallel and perpendicular electric and magnetic field configurations have been employed. Temperature and frequency dependence of the dielectric anisotropy have been studied.

Two interesting features have been observed. I) In the crossed field configuration complete molecular alignment could be observed by suitably changing the electric field strength. The range of electric field strength required to change the molecular ordering, is frequency dependent. This range shows a minimum in the neighbourhood of 2 kHz. 2) It has also been observed that in the parallel field configuration minimum dielectric constant change is observed apparently independent of frequency and electric field strength. Detailed results of the field and frequency effects and of optical studies in this mixture are reported.     

Mechanochemical synthesis of nonstoichiometric nanocrystals La1 ? yCayF3 ? y with a tysonite structure and nanoceramic materials from CaF2 and LaF3 crystals

The nonstoichiometric phases La_{1 − y} Ca _y F_{3 − y} (y = 0.15, 0.20) with a tysonite (LaF₃) structure have been prepared for the first time by the mechanochemical synthesis from CaF₂ and LaF₃ crystals. The average size of coherent scattering regions is approximately equal to 10–30 nm. It has been shown that the compositions of the phases prepared by the mechanochemical synthesis are inconsistent with the phase diagram of the CaF₂-LaF₃ system. The “mechanohydrolysis” of the La_{1 − y} Ca _y F_{3 − y} phase has been observed for the first time. Under these conditions, the La_{1 − y} Ca _y F_{3 − y} phase partially transforms into lanthanum calcium oxyfluoride for a milling time of 180 min with intermediate sampling. The La_{1 − y} Ca _y F_{3 − y} nanoceramic materials have been prepared from a powder of the mechanochemical synthesis product by pressing under a pressure of (2–6) × 10⁸ Pa at room temperature. The electrical conductivity of the synthesized materials at a temperature of 200°C is equal to 4.9(6) × 10⁻⁴ S/cm, and the activation energy of electrical conduction is 0.46(2) eV. These data for the nanoceramic materials coincide with those obtained for migration of fluorine vacancies in single-crystal tysonite fluoride materials. Original Russian Text ? B.P. Sobolev, I.A. Sviridov, V.I. Fadeeva, S.N. Sul’yanov, N.I. Sorokin, Z.I. Zhmurova, I.I. Khodos, A.S. Avilov, M.A. Zaporozhets, 2008, published in Kristallografiya, 2008, Vol. 53, No. 5, pp. 919–929.     

Mesomorphism in chloro substituted isomeric series including chalconyl central bridge

A novel homologous series of thermotropic liquid crystals α-4-(4′-n-alkoxy benzoyloxy phenyl) β-2″-chloro benzoyl ethylenes have been synthesized and studied with a view to understand and establish the effect of molecular structure on liquid crystal (LC) properties with reference to molecular flexibility in isomeric series with differing positional status of same functional group. Novel homologues series consist of 12 homologues C₁ to C_16. C₁, C₂, and C₃ homologues are nonliquid crystals (NLC) and rest of the homologues are liquid crystals. C₁₀ to C₁₆ homologues are enantiotropically smectogenic plus nematogenic and C₄ to C₈ homologues are enantiotropic nematic. The texture of nematogenic derivatives is threaded or schlieren and that of the smectic mesophase are focal conic of the type smectic A or C. Analytical, thermal and spectral data supported molecular structures of novel homologues. Transition temperatures as determine by a hot stage polarizing optical microscopy (POM) were plotted against number of carbon atom present in n-alkyl chain ‘R’ of left n-alkoxy (-OR) group and the phase transition curves Cr–I/M, Sm–N, N–I were obtained on linking like or related points. The odd–even effect is observed for the N–I transition curve and thus transition curves behaved in normal manner. The even-membered nematic transition curve occupied higher position than the odd-membered transition curve. Present series is predominantly nematogenic and partly smectogenic with middle-ordered melting type.     

Effects of carbon structure orientation on the performance of glucose sensors fabricated from electrospun carbon fibers

High-performance enzyme-based glucose sensors were prepared by electrospinning carbon fibers. The efficiency of the glucose sensor was assessed based on efficient enzyme immobilization and electrical resistance transfer by examining improved porosity and electrical properties, respectively. The porosity of the electrospun carbon fiber electrode was improved by physical activation to increase the immobilization sites of the glucose oxidase enzyme. The electrical properties were improved by a thermal treatment, which caused carbon orientation effects because of the high thermal energy. The glucose oxidase enzyme immobilization was developed based on improved specific surface area and pore volume, which were studied by pore structure and image analyzers. The glucose sensor was evaluated by amperometric measurements and cyclic voltammetry. The measured current increased with higher glucose concentrations based on the effects of the developed pore structure and the electrical properties. The enzymatic kinetics were also studied using the Lineweaver–Burk equation. The sensitivity of the glucose sensor was improved significantly with increased maximum current, whereas the GOD enzyme activity was diminished by efficient GOD immobilization. It is concluded that a high-performance glucose sensor was obtained using electrospun carbon fibers based on the effects of efficient GOD enzyme immobilization and electrical resistance transfer.     

On the Phase Transition Behaviour of Binary Systems: Various Non-Nematic Solutes in Nematic Solvent (EBBA)

Phase transition behaviour of the systems of EBBA with methyl alcohol (MeOH), 1.2-dibromo-ethylene (DBE), o-xylene, m-xylene, and p-xylene has been studied. The phase diagrams for each system have been determined by the polarizing microscope. The slopes, β_n and B_i, of the nematic and the isotropic phase boundary lines in each system have been qualitatively described by the molecular field treatment proposed by Humphries. The order parameters for both cis-and trans-DBE in EBBA have been obtained from analyses of ¹H-NMR spectra. In the nematic phase, they decrease with increase in temperature. In the nematic/isotropic coexisting phase (N/I phase), the order parameter for CIS-DBE is almost independent of temperature. The proton spin-lattice relaxation times (T₁) in the MeOH/EBBA system have been measured by a pulse NM R technique. Little temperature dependence of T¹ has been found in the N/1 phase region.c     

Chalcogenide infrared As2−xSe3+x glass fibers

Chalcogenide glasses As_2?xSe_3+x have been prepared. A new technique of preparing the raw material and subsequently drawing fibers has been developed in order to avoid the formation of oxygen compounds. The fibers have been drawn by the crucible and rod method from oxygen free raw material inside an Ar atmosphere glove box. The fibers drawn to date have a diameter of 50–500 μm and lengths of several meters. Preliminary attenuation measurements indicate that the attenuation is better than 0.1 dB/cm at 10.6 μm. The attenuation is not affected even when the fiber is bent to a circular radius of 2 cm. By improving the preparation of materials and the drawing technique, we expect to achieve a better transmission.     

Variation in Mesomorphic Characteristics with Certain Alterations in Molecular Structure: Homologous Series iso-Propyl p-(p'-n-Alkoxy CinnamoyIoxy) Benzoates and iso-Propyl p-(p'-n-AIkoxy Benzoyloxy) Benzoates

Mesomorphic characteristics of homologous series n-propyl p-(p'-n-alkoxy cinnamoyloxy)benzoates (I)¹ are quite in keeping with the general molecular structure and molecular forces accruing therefrom. Continuing the work further, the right hand terminal group of the series (I) has been replaced by a branched group with iso disposition of the alkylchain but having the same number of carbon atoms. Thus the new homologous series iso-propyl p-(p'-n-alkoxy cinnamoyloxy)benzoates (II) with all other molecular geometry the same, gets mesomorphic characteristics changed considerably. The first few members become non-mesogenic, nematic orientation is altogether eliminates and the smectic mesophase range is reduced to about one third of that of the series (I). Another new homologous series (III) with all the molecular geometry of the series (II). but with a shorter central bridge —COO— than —CH=CH—COO—receives a further jolt in its exhibition of mesomorphic characteristics. The first seven members and the last member of the series (III) become non-mesomorphic; however, some middle members exhibit monotropic smectic mesophase. The effect of the branching of the terminal substituent and shortening of the central bridge are thus quite evident and arouse good interest. The smectic texture as determined by optical microscopy and by the study of mixtures² is of fan shaped focal conic smectic A variety.     

Spectroscopy of smooth deuterated carbon films redeposited from plasma discharge in the tokamak T-10

Smooth deuterated carbon films redeposited from a deuterium plasma discharge in the tokamak T-10 vacuum chamber have been investigated by different spectroscopic methods and temperature measurements. The photoluminescence excitation spectra of sp ³-sp ² nanostructures of tokamak films and sp ² nanostructures of fullerite C60 films are compared. The effect of defect states on the photoluminescence and its temperature quenching is discussed. It is concluded that the mechanism of thermal luminescence quenching for smooth deuterated tokamak films is close to the corresponding mechanism for amorphous a-C:H films.

     

An X – Ray Study of the p-n-Alkoxycinnamic Acids. Part III.1

The effect upon molecular packing of increasing chain length in a homologous series of mesogens has been examined in the case of the p-n-alkoxycinnamic acids by determination of the crystal structures of the four nematogenic acids having two, four, six, and eight carbon atoms in the alkyl chain. The chains have the all-trans extended conformation, and the molecules exist in the crystal as planar hydrogen-bonded dimers. The dimers are arranged in end-to end fashion in parallel rows. Similar side-to-side packing of pairs of dimmers is found in each crystal structure giving a good fit between adjacent aromatic cores, but the amplitudes of thermal vibration of the chain carbon atoms increase markedly with increasing chain length, indicating a low packing efficiency for these moieties.