Calorimetric study on two biphenyl liquid crystals

The molar heat capacities of the two biphenyl liquid crystals, 3BmFF and 3BmFFXF3, with a purity of 99.7 mol% have been precisely measured by a fully automated precision adiabatic calorimeter in the temperature range between T = 80 and 350 K. Nematic phase-liquid phase transitions were found between T = 297 K and 300 K with a peak temperature of T-peak = (298.071 +/- 0.089) K for 3BmFF, and between T = 316 and 319 K with a peak temperature of T-peak = (315.543 +/- 0.043) K for 3BmFFXF3. The molar enthalpy (Delta(trs)H(m)) and entropy (Delta(trs)S(m)) corresponding to these phase transitions have been determined by means of the analysis of the heat capacity curves, which are (15.261 +/- 0.023) U mol(-1) and (51.202 +/- 0.076) J K-1 mol(-1) for 3BmFF, (31.624 +/- 0.066) kJ mol(-1) and (100.249 +/- 0.212) J K-1 mol(-1) for 3BmFFXF3, respectively. The real melting points (TI) and the ideal melting points (TO) with no impurities of the two compounds have been obtained from the fractional melting method to be (298.056 +/- 0.018) K and (298.165 +/- 0.038) K for 3BmFF, (315.585 +/- 0.043) K and (315.661 +/- 0.044) K for 3BmFFXF3, respectively. In addition, the transitions of these two biphenyl liquid crystals from nematic phase to liquid phase have further been investigated by differential scanning calorimeter (DSC) technique; the repeatability and reliability for these phase transitions were verified. (C) 2004 Elsevier B.V. All rights reserved.

Early Embryonic Exposure to Polychlorinated Biphenyls Disrupts Heat-Shock Protein 70 Cognate Expression in Zebrafish

Polychlorinated biphenyls (PCBs) are persistent environmental contaminants that have documented neurological effects in children exposed in utero. To better define neuronally linked molecular targets during early development, zebrafish embryos were exposed to Aroclor 1254, a mixture of PCB congeners that are common environmental contaminants. Microarray analysis of the zebrafish genome revealed consistent significant changes in 38 genes. Of these genes, 55% (21) are neuronally related. One gene that showed a consistent 50% reduction in expression in PCB-treated embryos was heat-shock protein 70 cognate (Hsc70). The reduction in Hsc70 expression was confirmed by real-time polymerase chain reaction (PCR), revealing a consistent 30% reduction in expression in PCB-treated embryos. Early embryonic exposure to PCBs also induced structural changes in the ventro-rostral cluster as detected by immunocytochemistry. In addition, there was a significant reduction in dorso-rostral neurite outgrowth emanating from the RoL1 cell cluster following PCB exposure. The serotonergic neurons in the developing diencephalon showed a 34% reduction in fluorescence when labeled with a serotonin antibody following PCB exposure, corresponding to a reduction in serotonin concentration in the neurons. The total size of the labeled neurons was not significantly different between treated and control embryos, indicating that the development of the neurons was not affected, only the production of serotonin within the neurons. The structural and biochemical changes in the developing central nervous system following early embryonic exposure to Aroclor 1254 may lead to alterations in the function of the affected regions.

Polyamide thin film composite membranes prepared from isomeric biphenyl tetraacyl chloride and m-phenylenediamine

Three novel of isomeric tetra-functional biphenyl acid chloride: 3,3',5,5'-biphenyl tetraacyl chloride (mm-BTEC), 2,2',4,4'-biphenyl tetraacyl chloride (om-BTEC), and 2,2',5,5'-biphenyl tetraacyl chloride (op-BTEC) were synthesized, and used as new monomers for the preparation of the thin film composite (TFC) reverse osmosis (RO) membranes through interfacial polymerization with m-phenylenediamine (MPDA). The results of membrane performance test showed that membranes prepared from om-BTEC and op-BTEC had higher flux at the expanse of rejection compared with membranes prepared from mm-BTEC.

Vertical structure p-type permeable metal-base organic transistors based on N,N '-diphentyl-N,N '-bis(1-naphthylphenyl)-1,1 '-biphenyl-4,4 '-diamine

In this article, vertical structure p-type permeable-base organic transistors were proposed and demonstrated. A hole-type organic semiconductor N,N-'-diphentyl-N,N-'-bis(1-naphthylphenyl)-1,1(')-biphenyl-4,4(')-diamine was used as emitter and collector. In the permeable-base transistors, the metal base was formed by firstly coevaporating Al and Ca in vacuum and then annealing at 120 degrees C for 5 min in air, followed by a thin Al deposition. These devices show a common-base current gain of near 1.0 and a common-emitter current gain of similar to 270.

Preparation and characterization of poly(piperazineamide) composite nanofiltration membrane by interfacial polymerization of 3,3 ',5,5 '-biphenyl tetraacyl chloride and piperazine

Most nanofiltration (NF) membranes are composite and have a polyamide thin film prepared by interfacial polymerization. Their performances mainly correlate the structure of the thin film and monomers used for its preparation. In this work, a novel thin-film composite (TFC) nanofiltration membrane was successfully prepared from 3,3',5,5'-biphenyl tetraacyl chloride (mm-BTEC) and piperazine (PIP) through interfacial polymerization. Attenuated reflectance infrared (ATR-IR) and X-ray photoelectronic spectroscopy (XPS) were used to characterize the chemical composition of the membrane surface. The membrane performance was optimized by studying preparation parameters including monomer concentration, reaction time, and pH of aqueous phase.

Diarylmethylene-bridged 4,4 '-(bis(9-carbazolyl))biphenyl: morphological stable host material for highly efficient electrophosphorescence

novel compound (BCBP) based on the modification of a well-known host material 4,4'-(bis(9-carbazolyl))biphenyl (CBP) through arylmethylene bridge linkage was synthesized, and fully characterized. Its thermal, electrochemical, electronic absorption and photoluminescent properties were studied. A high glass transition temperature (T-g) of 173 degrees C is observed for BCBP due to the introduction of the bridged structure, remarkably contrasting with a low T-g of 62 degrees C for CBP. Furthermore, the bridged structure enhances the conjugation and raises the HOMO energy, thus facilitating hole-injection and leading to a low turn-on voltage in an electroluminescent device. With the device structure of ITO/MoO3/NPB/Ir complex: BCBP/BCP/Alq(3)/LiF/Al, maximum power efficiencies of 41.3 lm/W and 6.3 lm/W for green- and blue-emitting OLED were achieved, respectively.

Polyamide thin film composite membranes prepared from 3,4',5-biphenyl triacyl chloride, 3,3',5,5'-biphenyl tetraacyl chloride and m-phenylenediamine

Two novel of tri- and tetra-functional biphenyl acid chloride: 3,4',5-biphenyl triacyl chloride (BTRC) and 3,3',5,5'-biphenyl tetraacyl chloride (BTEC), were synthesized, and used as new monomers for the preparations of the thin film composite (TFC) reverse osmosis (RO) membranes. The TFC RO membranes were prepared on a polysulfone supporting film through interfacial polymerization with the two new monomers and m-phenylenediamine (MPD). The membranes were characterized for the permeation properties, chemical composition, d-space between polymer chains, hydrophilicity, membrane morphology including top surface and cross-section. Permeation experiment was employed to evaluate the membranes performance including salt rejection and water flux. The surface structure and chemical composition of membranes were analyzed by attenuated total reflectance infrared (ATR-IR) and X-ray photoelectronic spectroscopy (XPS). The results revealed that the active layer of membranes was composed of highly cross-linked aromatic polyamide with the functional acylamide (-CONH-) bonds. The TFC membranes prepared from biphenyl acid chloride exhibit higher salt rejection compared with that prepared from trimesoyl chloride (TMC) at the expanse of some flux.

Electric-field-induced molecular alignment of side-chain liquid-crystalline polyacetylenes containing biphenyl mesogens

Electric-field-induced molecular alignments of side-chain liquid-crystalline polyacetylenes [-{HC=C[(CH2)(m)OCO-biph-OC7H15]}-, where biph is 4,4'-biphenylyl and m is 3 (PA3EO7) or 9 (PA9EO7)] were studied with X-ray diffraction and polarized optical microscopy. An orientation as high as 0.84 was obtained for PA9EO7. Furthermore, the molecular orientation of]PA9EO7 was achieved within a temperature range between the isotropic-to-smectic A transition temperature and 115 degreesC, and this suggested that the orientational packing was affected by the thermal fluctuation of the isotropic liquid and the mobility of the mesogenic moieties. The maximum achievable orientation for PA9EO7 was much greater than that for PA3EO7. This was the first time that the electric-field-induced molecular orientation of a side-chain liquid-crystalline polymer with a stiff backbone was studied.

Syntheses and properties of soluble biphenyl-based polyimides from asymmetric bis(chlorophthalimide)s

A novel synthesis of asymmetric bis(chlorophthalimide)s (3,4-BCPIs) has been established. The polymerizations of them produced higher molecular weight (0.38-0.51 dL/g) polyimides containing biphenyl units than those of isomeric polymers derived from symmetric bis(chlorophthalimide)s (4,4'-BCPIs) and 3,3'-BCPIs. The distribution of the formed biphenyl units of head to tail, head to head, and tail to tail in the chain of the polymers was about 58.0:21.0:21.0, determined by C-13 NMR spectra of the polymers. The composition of model compounds, determined by HPLC, was well consistent with the 13C NMR spectrum result. Comparing with polymers derived from 4,4'-BCPIs and 3,3'-BCPIs, the polymers derived from 3,4-BCPIs showed better solubilities in N,N-dimethylacetamide (DMAc), N,N-dimethyl-formamide (DMF), and N-methylpyrrolinone (NMP). Flexible films could be cast from the polymer solution with the inherent viscosities of above 0.35 dL/g. The polymer derived from asymmetric bis(chlorophthimide)s gave the highest T-g among the isomeric polymers.

Thermal mechanical and dynamic mechanical property of biphenyl polyimide fibers

High-performance polyimide fibers possess man), excellent properties, e.g., outstanding thermal stability and mechanical properties and excellent radiation resistant and electrical properties. However, the preparation of fibers with good mechanical properties is very difficult. In this report, a biphenvl polyimide from 3,3',4,4'-biphenyltetracarboxylic dianhydride and 4,4'-oxydianiline is synthesized in p-chlorophenol by one-step polymerization. The solution is spun into a coagulation bath of water and alcohol via dry-jet wet-spinning technology. Then, the fibers are drawn in two heating tubes. Thermal gravimetric analysis, thermal mechanical analysis, and dynamic mechanical analysis (DMA) are performed to study the properties of the fibers. The results show that the fibers have a good thermal stability at a temperature of more than 400degreesC. The linear coefficient of thermal expansion is negative in the solid state and the glass transition temperature is about 265degreesC. DMA spectra indicate that the tandelta of the fibers has three transition peaks, namely, alpha, beta, and gamma transition. The alpha and gamma transition temperature, corresponding to the end-group motion and glass transition, respectively, extensively depends on the applied frequency, while the beta transition does not.

Phase transition behavior and structure of the thermotropic liquid crystal 6-{[(4 '-{[(undecyl)carbonyl]oxy}biphenyl-4yl)carbonyl]oxy}-1-hexyne

The phase transition behaviors and corresponding structures of 6-{[(4'-([(undecyl)carbonyl]oxy)biphenyl-4yl)carbonyl]oxyl-l-hexyne (A4EE11) were investigated using differential scanning calorimetry (DSC), polarizing optical microscopy (POM) and wide angle X-ray diffraction (WAXD). In comparison with the published homologues, 5- [(4'-heptoxy-biphenyl-4-yl)carbonyl]oxyl-1-pentyne (A3EO7) which shows a monotropic smectic A (SmA) phase and a metastable monotropic smectic C (SmC) phase; 5-{ [(4'-heptoxybiphenyl-4-yl)oxy]carbonyl)- I-pentyne (A3E'O7) that exhibits three enantiotropic stable liquid crystalline (LC) phases, SmA phase, SmC phase and smectic X (SmX) phase; 5-{[(4'-heptoxy-biphenyl-4-yl)carbonyl]oxy}-1-undecyne (A9EO7) which has a monotropic SmA phase and a metastable crystal phase, A4EE11 integrates the enantiotropy, monotropy and metastability of the LC phases of those three compounds. Upon cooling from isotropic state to room temperature, in the temperature range of 62.0 to 58.5 degrees C, A4EE11 shows an enantiotropic smectic A (SmA) phase with a layer spacing d=32.69 angstrom.