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11.
Liquid-crystalline rigid-core semiconductor oligothiophenes: influence of molecular structure on phase behaviour and thin-film properties 总被引:1,自引:0,他引:1
Melucci M Favaretto L Bettini C Gazzano M Camaioni N Maccagnani P Ostoja P Monari M Barbarella G 《Chemistry (Weinheim an der Bergstrasse, Germany)》2007,13(36):10046-10054
The design, synthesis and properties of liquid-crystalline semiconducting oligothiophenes containing dithienothiophene (DTT), benzothiadiazole (BTZ) and carbazole (CBZ) rigid cores are described. The effect of molecular structure (shape, size and substitution) on their thermal behaviour and electrical properties has been investigated. Polarised optical microscopy (POM) and differential scanning calorimetry (DSC) analyses have revealed highly ordered smectic mesophases for most of the newly synthesised compounds. X-ray diffraction (XRD) studies performed at various temperatures have shown that the smectic order is retained in the crystalline state upon cooling across the transition temperature, affording cast films with a more favourable morphology for FET applications. 相似文献
12.
Mateos E Cebolla VL Membrado L Piera E Caballero MA 《Journal of chromatographic science》2007,45(8):524-530
Gel permeation chromatography with differential refractometry is used to obtain molecular weight distributions (MWD) of poly-(epsilon-caprolactams). Elution is carried out using an m-cresolchlorobenzene mixture (50:50, v/v) at 50 degrees C. MW values are obtained by a Hamielec-based calibration method, using broad-MWD poly-(epsilon-caprolactam) standards with the same chemical nature and similar MWD to the samples. Relative errors for the number-average MW (Mn) using this calibration method range from 0.4% (in the low polyamide MW range) to 20% (in the high polyamide MW range). These values are much lower than those obtained from narrow-MWD polystyrene calibration, which range from 39% to 78%. Similar values have been obtained for the other usual average MW parameters. The ability to obtain repeatability parameters for a given confidence interval and the utilization of statistical criteria for chromatogram rejection allow this method to be used in quality control for MWD of poly-(epsilon-caprolactams). Thus, production variables are related to polyamide-6 behavior in its ulterior treatment. Typical relative standard deviation percentages (for n=6) of a polyamide sample range from 1.9% (for Mn) to 3.3% (for M(z+1)). 相似文献
13.
Ismaela Foltran Elisabetta Foresti Bruna Parma Piera Sabatino Norberto Roveri 《Macromolecular Symposia》2008,269(1):111-118
The possibility to prepare bioinspired collagen nanofibers by electrospinning from aqueous suspension of telopeptide-free collagen molecules avoiding both organic solvents and blends with any synthetic and natural polymers has been investigated. The results have highlighted the need for a basic atmosphere between the needle and the ground collector in order to increase the environmental pH during the collagen molecules self-assembly along the electrostatic force lines. Morphological, spectroscopic and calorimetric analyses carried out on the electrospun collagen nanofibers have opened the possibility to take advantage of this new approach in order to prepare an ideal biomimetic reinforcing component of new biomedical and surgical biomaterials. 相似文献
14.
Focusing on the Fourier fluids in the liquid state, which are characterized by linear thermal constitutive equation and low compressibility, this short note proposes a discrete approach based on the elementary scales, which allows removing the so-called Fourier paradox in classical continuum thermomechanics. As a corollary, the adopted line of reasoning allows highlighting some features on the elementary scales.
相似文献15.
Roberta Censi Valentina Martena Ela Hoti Ledjan Malaj Piera Di Martino 《Journal of Thermal Analysis and Calorimetry》2013,111(3):2009-2018
(R,S)-(±)-ibuprofen sodium salt (racemate) dihydrate (SID) was dehydrated and the physicochemical properties of SID and the anhydrous forms (SIA) were compared by different analytical techniques (scanning electron microscopy, helium pychnometry, differential scanning calorimetry, X-ray powder diffractometry). The dehydration of SID, followed by thermogravimetry in isothermal conditions, allowed to calculate the activation energy of the dehydration process and to predict the mechanism of dehydration. Dehydration occurred in one step and the activation energy was rather low, indicating the ease of water removal from the crystal. The mechanism of dehydration followed a three dimensional diffusion (Jander equation). Similarly to the dehydration, the hydration process was followed under isothermal conditions by exposing the anhydrous powder at 64% RH at different temperatures. The mechanism of hydration was governed by a two dimensional diffusion and the energy associated to the process was very low, indicating the ease of crystal hydration. The driving force for the hydration is higher than that for the dehydration. From a thermodynamic point of view this fact may explain why the hydrated form is more stable than the anhydrous one. Solubilities, determined at different temperatures in water and in phosphate buffer (pH 6.8), showed that SID is more soluble in water than SIA for temperatures higher than approximately 283 K. On the contrary, in phosphate buffer SIA is always more soluble than SID in the temperature range considered for the experiments. Drug release reflects the solubility in water and phosphate buffer previously reported. 相似文献
16.
Fustero S Catalan S Piera J Sanz-Cervera JF Fernandez B Aceña JL 《The Journal of organic chemistry》2006,71(10):4010-4013
Two families of bicyclic fluorinated uracils have been prepared starting from a gem-difluorinated unsaturated nitrile, by means of a ring-closing metathesis reaction to form the new ring, which is fused at the C-5/C-6 or N-1/C-6 positions of the uracil moiety. The selective formation of olefin regioisomers in the metathesis process can be controlled according to the reaction conditions (catalyst, solvent, and temperature). The acaricidal activities of the resulting compounds have also been investigated. 相似文献
17.
Fustero S García de la Torre M Sanz-Cervera JF Ramírez de Arellano C Piera J Simón A 《Organic letters》2002,4(21):3651-3654
[reaction: see text] A simple, asymmetric synthesis of tetramic acid derivatives is described in this paper. The key step is a carbonyl transfer from carbonyldiimidazole (CDI) to alpha-diimines (I) to form N-alkyl-4-alkylamino-5-methylenepyrrol-2-ones (II). In turn, these compounds can be easily transformed into tetramic acid derivatives (III) in two additional steps. 相似文献
18.
Antonio Palazzi Piera Sabatino Silvia Bordoni Carlo Castellari 《Journal of organometallic chemistry》2004,689(14):2324-2337
The reaction of sodium cyanopentacarbonylmetalates Na[M(CO)5(CN)] (M=Cr; Mo; W) with cationic Fe(II) complexes [Cp(CO)(L)Fe(thf)][O3SCF3], [L=PPh3 (1a), CN-Benzyl (1b), CN-2,6-Me2C6H3 (1c); CN-But (1d), P(OMe)3 (1e), P(Me)2Ph (1f)] in acetonitrile solution, yielded the metathesis products [Cp(CO)(L)Fe(NCCH3)][NCM(CO)5] [M=W, L=PPh3 (2a), CN-Benzyl (2b), CN-2,6-Me2C6H3 (2c); CN-But (2d), P(OMe)3 (2e), P(Me)2Ph (2f); M=Cr, L=(PPh3) (3a), CN-2,6-Me2C6H3 (3c); M=Mo, L=(PPh3) (4a), CN-2,6-Me2C6H3 (4c)]. The ionic nature of such complexes was suggested by conductivity measurements and their main structural features were determined by X-ray diffraction studies. Well-resolved signals relative to the [M(CO)5(CN)] moieties could be distinguished only when 13C NMR experiments were performed at low temperature (from −30 to −50 °C), as in the case of [Cp(CO)(PPh3)Fe(NCCH3)][NCW(CO)5] (2a) and [Cp(CO)(Benzyl-NC)Fe(NCCH3)][NCW(CO)5] (2b). When the same reaction was carried out in dichloromethane solution, neutral cyanide-bridged dinuclear complexes [Cp(CO)(L)FeNCM(CO)5] [M=W, L=PPh3 (5a), CN-Benzyl (5b); M=Cr, L=(PPh3) (6a), CN-2,6-Me2C6H3 (6c), CO (6g); M=Mo, L=CN-2,6-Me2C6H3 (7c), CO (7g)] were obtained and characterized by infrared and NMR spectroscopy. In all cases, the room temperature 13C NMR measurements showed no broadening of cyano pentacarbonyl signals and, relative to tungsten complexes [Cp(CO)(PPh3)FeNCW(CO)5] (5a) and [Cp(CO)(CN-Benzyl)FeNCW(CO)5] (5b), the presence of 183W satellites of the 13CN resonances (JCW ∼ 95 Hz) at room temperature confirmed the formation of stable neutral species. The main 13C NMR spectroscopic properties of the latter compounds were compared to those of the linkage isomers [Cp(CO)(PPh3)FeCNW(CO)5] (8a) and [Cp(CO)(CN-Benzyl)FeCNW(CO)5] (8b). The characterization of the isomeric couples 5a-8a and 5b-8b was completed by the analyses of their main IR spectroscopic properties. The crystal structures determined for 2a, 5a, 8a and 8b allowed to investigate the geometrical and electronic differences between such complexes. Finally, the study was completed by extended Hückel calculations of the charge distribution among the relevant atoms for complexes 2a, 5a and 8a. 相似文献
19.
Melucci M Gazzano M Barbarella G Cavallini M Biscarini F Maccagnani P Ostoja P 《Journal of the American Chemical Society》2003,125(34):10266-10274
We show that thin films grown by vacuum sublimation, or formed by melted powders, of semiconductor alpha-quinquethiophene (T5) exhibit a hierarchical self-affinity organization that spans scales from tens of nanometers to hundreds of micrometers. T5 organization was investigated by X-ray diffraction (XRD), atomic force microscopy (AFM), and optical microscopy. XRD showed that vacuum-evaporated T5 films were characterized by a preferred orientation of the h00 planes parallel to the glass substrate. Melting of the films followed by rapid quenching to room temperature led to the formation of micrometer-sized, single-crystal-like structures, characterized by uniaxially aligned stripes. XRD proved that the melting-quenching process enhanced molecular ordering and increased the size of domains with the molecule's long axes tilted by about 65 degrees with respect to the substrate plane and piled up side-by-side along parallel columns. AFM measurements on the melt-quenched structures showed that a hierarchical architecture was built by reiteration across multiple length scales of the same recurring motif. Because of the tendency of T5 to form highly crystalline vacuum-evaporated thin films, a field-effect hole mobility comparable to state-of-the-art FET mobility of alpha-sexithiophene films was reached, without any attempt to optimize deposition conditions. 相似文献
20.
Valentina Martena Roberta Censi Ela Hoti Ledjan Malaj Piera Di Martino 《Journal of Thermal Analysis and Calorimetry》2012,108(1):323-332
Formulation of poorly water-soluble crystalline drugs into their more soluble amorphous form is a common approach for improving
their bioavailability. In this study, the amorphous forms of nicergoline (NIC) and cabergoline (CAB) were obtained by different
methods (melting and precipitation under solvent evaporation). The physicochemical characteristics of the samples were determined
by HPLC, differential scanning calorimetry (DSC), thermogravimetry, and X-ray powder diffractometry. The physical stability
of the amorphous forms was investigated by DSC by considering how the onset temperature and the enthalpy content at the glass
transition vary with aging time and temperature. Using the Kohlrausch–Williams–Watts equation on the data obtained from the
experiments, the “mean molecular relaxation time constant” (τ) was estimated. This parameter was used to understand the stability of NIC and CAB in their glassy state at different temperatures,
and results showed that their stability is adequate to enable the formulation of these drugs into solid dosage forms. 相似文献