Polarizing Microscope Observations Research Articles

Morphology evolution induced by carbon nanotubes on thermal and mechanical characters of semi-crystalline aromatic polyimide

A series of nanocomposites based on a new semi-crystalline polyimide (PI) and multi-walled carbon nanotubes (MWCNTs) were prepared by in situ polymerization. The TEM measurement reveals the improved dispersion of carboxylic acid-functionalized MWCNTs (COOH-MWCNTs) in semi-crystalline PI compared with pristine MWCNTs. The TGA analysis show that the concentration of carboxylic acid groups on the surface of nanotubes is about 4.34 wt%. The FT-IR spectroscopy analysis indicate that the imide rings of the PI interact non-covalently with nanotubes. The Polarized optical microscopy observation reveals significant morphology evolution in semi-crystalline PI induced by MWCNTs. The SEM micrographs suggest the strong interfacial interaction between COOH-MWCNTs and PI main chains, and significant changes in the fracture surfaces morphology. The WAXRD measurements reveal that COOH-MWCNTs promote the semi-crystalline PI crystallinity and structure change. COOH-MWCNTs can more efficiently improve the mechanical and thermal properties of resulting nanocomposites than pristine MWCNTs. COOH-MWCNT/PI nanocomposites show increases of Young’s modulus and yield strength, as high as 20–30 %, without sacrificing the elongation at break at loadings of 0.5 wt% nanotubes. Furthermore, with increasing the loadings of COOH-MWCNTs to 1.0 wt%, Young’s modulus and yield strength decrease due to nanotube aggregation, but elongation at break increase about 46 %. An abrupt increase of elongation at break in pristine MWCNT/PI nanocomposites was also registered at nanotubes loadings increasing from 0.5 to 1 wt%. These results indicate that the properties of semi-crystalline PI nanocomposites reinforced with carbon nanotubes are not only determined by the dispersion of nanotubes in the PI matrix and their interfacial interactions, but also by the crystalline phase morphology evolution in the PI matrix.

Vibration-dependent morphology and crystal structure of isotactic polypropylene

A small homemade device was used to study the influence of mechanical vibration on the crystal structure and morphology of isotactic polypropylene (iPP) under different melting temperatures, vibration times, vibration frequencies, and cooling rates. The crystallite size, crystal structure, and crystallinity of iPP under or without vibration treatment were investigated by means of differential scanning calorimetry (DSC), wide angle X-ray diffraction (WAXD), and polarized microscopy observation (PLM). The crystallization of iPP varied with the length of vibration time, vibration frequency, cooling rate, and melt temperature. Compared with the data of conventional samples measured by DSC, vibration could increase the crystallinity of iPP, make melting peak of α-crystal move toward higher temperature and make that of β-crystal shift to lower temperature. Meanwhile, WAXD measurements showed that the vibration could reduce the content of β-crystal evidently, particularly at the lower vibration frequency, lower cooling rate, and higher melting temperature. Furthermore, PLM measurements showed that the vibration made the spherulite size smaller.

Photopyroelectric Calorimetry Study of the Smectic A-Hexatic B Transition in Single Homeotropic Domain 65OBC Liquid Crystal Samples

The work deals with the investigations of the smecticA-hexaticB phase transition in n-hexyl-4′-n-pentyloxybiphenyl-4-carboxylate liquid crystal compound in a single domain homeotropic sample and in a nonaligned sample. The specific heat, the thermal diffusivity, and the enthalpy exchange were monitored over the transition and, at the same time, polarization microscopy observations could be carried out. The transition during the first cooling run was found to be accompanied by a considerably larger defect annealing in the non aligned sample than in the homeotropic one.

Gemmological and mineralogical investigations and genesis of the kammererite from the Keşiş (Erzincan) and Kop (Erzurum) mountains

Even though there are many chromitite deposits in Turkey, the most productive chromitite deposits including chromian clinochlore and chromian are present in the eastern Anatolia region. Kammererite (chromian clinochlore), in essence, is one of the rarest clinochlore minerals as a sub-variety of large family of the chlorite minerals. Even though it is the monoclinic IIb-2 polytype, with symmetry C2/m, which is one of the most abundant regular-stacking one-layer chlorites occurring in nature, the crystallization of chromian clinochlore is less abundance. Hence, gem-quality magenta colored kammererite which may be formulized as [Mg5(Al,Cr,Fe)2Si3O10(OH)8] with reference to the abundance of the main oxides in the XRF bulk analyses, is only found in Turkey worldwide. Therefore, they are called Turkish kammererite. Beside of the mineral kammererite, the minerals uvarovite, magnesite, chromian spinel, chlorite and some garnets are also present in the paragenesis.Geological field observations and data in the region reveal that the kammererite specimens are crystallized as remobilized-origin on a chromitite matrix, deposited in the podiform-type chromitite ore deposits, and surrounded by the peridotitic and harzburgitic ultrabasic rocks. Thus, it can be stated that this rare mineral formation is derived from the secondary components of the hydrothermal alteration of the principle amphibole, pyroxene and biotite minerals in the surrounding peridotitic and harzburgitic (partially serpentinitic) rocks where they are embedded throughout the Northeastern Ophiolitic Belt comprising the Keşiş and Kop Mountains in the Eastern Anatolia region of Turkey.In this study, unique loose Turkish kammererite crystals were the first time investigated as both mineralogically and gemmologically. Accordingly, the well-known some further spectroscopic analytical methods were used to characterize and identify in detail for provenance and genesis.Firstly, as a structural characterization, in the light of the data obtained from X-ray fluorescence (XRF) and X-ray diffraction (XRD) as well as some essential gemmological measurements and polarizing microscope observations, dispersive confocal (green laser) micro-Raman spectroscopy (DCμRS) shows that the strong micro-Raman bands in the kammererite samples with C⊥ and C|| axes are peaked at 681, 541, 353, 197, and 112cm−1. These bands are a result vibrational and librational symmetric and asymmetric stretching and bending modes of (MgOH)−, (AlOH)2−, (CrOH)2−, (FeOH)2−, and (SiOH)1− molecules, which forms all kammererite structure.Secondly, as a provenance characterization, photoluminescence and cathodoluminescence spectra show that individual luminescence bands in the kammererite samples are due to mainly chemical defects caused by transition metal and rare earth elements in the lattice, which they are detected by the inductive coupled plasma-atomic emission spectroscopy (ICP-AES).Finally, these parameters provide positive identification regarding to geographic origin of the original Turkish kammererite. It can be seen that the obtained micro-Raman bands, specific gravity values, luminescence spectra, and trace element contents give a unique fingerprint for this kind of clinochlore gemstone.

Interaction and miscibility study of fumarate-based macromers with chitosan

This work is aimed to prepare Chitosan/Poly(ethylene glycol fumarate) (Ch/PEGF) blend films and to determine blend miscibility of the two polymers as a function of molecular interactions between Ch and PEGF. The blend films are prepared in various ratios (0/100 to 100/0) by the conventional solution-casting method. Interactions occurring in the blends are investigated and probed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and dynamic mechanical thermal analysis (DMTA). FTIR and XRD analyses reveal the existence of newly-formed hydrogen bond interactions between Ch and PEGF. The influence of Ch/PEGF blend ratio on thermal properties of the blend systems is discussed especially considering thermal stability. The results indicate that both melting point and crystallinity of PEGF component in the blends depend on the composition of the blends. The obtained results of FTIR, DSC, and XRD analyses suggest that the partially protonated amine groups of Ch interacts with the hydroxyl groups of PEGF and thus partial miscibility are occurred. The results are confirmed with polarized microscopy observations. It is shown that although weak hydrogen bonding exists between the polymers functional groups; the blends are partially miscible.

Spiral Configuration of Nitroxide Radicals Along the Polypeptide Helix and Their Magnetic Properties

Poly(l-glutamic acid) (PLGA) derivatives PTPALG and PTPOLG, which contain 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO) radicals linked to PLGA via amide and ester bonds, respectively, were synthesized by the dehydration-condensation reaction. The main chains of both PTPALG and PTPOLG were found to adopt the right-handed α-helical conformation, and accordingly, the terminal side-chain nitroxide radicals adopted the spiral configuration synchronized with the helical conformation of the main chain. Polarized microscopy observations reveal that PTPALG exhibited the lyotropic liquid crystalline (LC) phase at greater than 7.5 wt % concentration in chlorinated solvents, whereas PTPOLG kept the anisotropic liquid phase at up to 10 wt % concentration. From the analysis of superconducting quantum interference device (SQUID) magnetometer and electron spin resonance (ESR) data, the magnetic properties of PTPALG and PTPOLG appeared to result from interchain spin–spin interactions between nitroxide• radicals rather than intrachain interactions. Interestingly, observation of the double quantum |Δms| = 2 line in a half-field region (g = 4.015) in the case of PTPALG revealed the doublet (S = 1/2) to triplet (S = 1) state conversion at around 6 K, exhibiting to be shifted the critical temperature in the sample evaporated the solvents from the LC phase. In contrast, PTPOLG retained its paramagnetic properties in the temperature range 4–200 K.

Study of the smecticA–hexaticB phase transition in homeotropic single domain samples of 65OBC liquid crystal by photopyroelectric calorimetry

The smecticA-hexaticB phase transition was studied in a homeotropic single domain sample and in a non-aligned sample of n-hexyl-4'-n-pentyloxybiphenyl-4-carboxylate liquid crystal compound to probe the effect of different amount of defects on the phase transition. The specific heat, the thermal diffusivity and the enthalpy exchange were monitored over the transition and, at the same time, polarization microscopy observations could be carried out. The transition during the first cooling run was found to be accompanied by a considerably larger defect annealing in the non-aligned sample than in the homeotropic one, but the critical behaviour of the specific heat remained substantially the same.

Low temperature phase of the trigonal RbIn(MoO4)2 crystal

The present article is devoted to a new low-temperature phase transition found at about T pt = 84 K in the layered RbIn(MoO4)2 crystal. This phase transition is well proved by dynamical mechanical analysis through anomalies in the temperature behaviour of both real and imaginary parts of the Young's modulus. From the polarizing microscope observations it was found that below T pt the ferroelastic phase disappears. This transition has also been seen through strong changes in the shape of the electron paramagnetic resonance lines. EPR studies, performed in the liquid nitrogen temperature, yield evidence of strong rebuilding of the crystal unit cell in comparison with that of the high temperature paraelastic phase.

Large Pentacene and Fullerene Crystals Having a Well-Defined Polygon

We have been successful in growing well-defined polygon crystals of fullerene and pentacene in liquid and vapor phases, respectively. These crystals were grown directly or laminated on substrates, allowing us to carry out their detailed structural characterization. We estimated the crystal structure of fullerene crystals by comparing the results of microscope and X-ray diffraction (XRD) observations with the crystal structure of a solvate. We carried out spectroscopic and XRD measurements on the pentacene crystals. Combining density functional theory calculations with the polarizing microscope observation, we related the principal axes of refractive index to the crystal geometry of pentacene.

Temperature-dependent FTIR study on three kinds of hydrogen-bonded benzoic acid dimers in their melt states

In the present paper, three kinds of benzoic acid, 4-allyloxylbenzoic acid (ABA), 4-allyloxyl-2-fluorobenzoic acid (AFBA) and 4-allyloxyl-2, 6-difluorobenzoic acid (ADFBA) have been studied by polarizing microscope (POM), differential scanning calorimeter (DSC) and temperature-dependent FTIR. POM and DSC observations show no mesomorphic properties when heating ABA and ADFBA or cooling their melts. But distinct nematic properties are recorded when cooling AFBA's melt, though its slenderness ratio is smaller than of ABA's. Temperature-dependent FTIR results indicate that the introduction of lateral fluorine atoms lowers the thermal stability of hydrogen-bonded dimers of AFBA and ADFBA, which is unfavorable for the formation of mesophase. But DSC results indicate that the introduced lateral fluorine atoms can destroy the symmetry of AFBA and ADFBA molecules, which is considered to lower their crystallizing points and is favorable for the formation of mesophase. To ABA and ADFBA, at least part of their dimers disassemble to free acids which will act as “impurity” to prevent the formation of mesophase in ABA and ADFBA melts when temperature is higher than their crystallizing point. As to AFBA, there is a temperature range from its crystallizing point (115°C) to 120°C in which almost all the AFBA exist in dimers. This temperature range satisfies the necessary condition for the mesophase to form in AFBA's melt. So nematic properties can be observed in AFBA's melt.

Bilayer swelling of nonionic surfactant and sodium dodecylsulfate mixed system by refractive-index matching

Bilayer swelling behavior of nonionic and anionic surfactant mixed aqueous solution induced by adding glycerin was studied. The phenomenon were performed on a system, polyethylene glycol ether of tridecyl alcohol with the average number of ethylene oxide of 5 (CH3(CH2)12(OCH2CH2)5OH; abbreviation IT5) and SDS mixed aqueous solution, with white cream of the upper phase and micelles (L1) of the lower phase. White cream containing densely packed multilamellar vesicles was revealed by freeze-fracture transmission electron microscopy and polarized microscope observations. Phase transition from white cream/L1, two-phase, to clear unique vesicle phase can be induced by adding glycerin to replace water. The addition of glycerin lowers the turbidity of the dispersion and swells the interlamellar distance between bilayers, which could be explained by refractive-index matching between solvent and bilayers.

Electron‐transporting semi‐rigid polyester‐imides made up of a tetracarboxdiimide of p‐terphenyl analogue of 1,3,4‐oxadiazole: Preparation, and thermal, optical, and electrochemical properties

AbstractElectron‐transporting semi‐rigid polyester‐imides composed of a tetracarboxdiimide (2,5‐di(3,4‐dicarboxphthalimido)‐1,3,4‐oxadiazole; DDPOD) of p‐terphenyl analogue of 1,3,4‐oxadiazole were successfully prepared by the melt polycondensation of a monomer, a dialcohol derivative of DDPOD, with four diesters in the presence of zinc acetate as a catalyst, and their thermal, UV–vis absorption, photoluminescent (PL) and electrochemical properties were examined. The structures of the resulting polymers were characterized by Fourier transform infrared and 1H NMR spectroscopies and elemental analyses. Differential scanning calorimetry measurements, X‐ray diffraction analyses and polarizing microscope observations suggested that the polymers prepared from aliphatic diesters formed highly ordered thermotropic liquid crystalline smectic phases. The UV–vis and PL spectra in the solutions and in the films displayed that the obtained polymers showed absorption and bluish violet‐light emissions based on the DDPOD moiety. Cyclic voltammetry measurements revealed that these polymers had more stable HOMO levels and were more sensitive to oxidation than polymers comprising electron‐accepting 2,5‐diphenyl‐1,3,4‐oxadiazole in the backbones. The DDPOD unit brought the extension of differences between electron‐injection and hole‐injection barriers in the polymers. It was found that the polymers containing the DDPOD unit in the main chains in this study not only showed bluish violet light‐emitting properties but also behaved as electron‐transporting materials for organic electroluminescent devices. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Polymorphism and thermodynamic functions of liquid crystalline material 4-cyano-3-fluorophenyl 4-butylbenzoate

Heat capacity measurements were conducted between temperatures of 5K and 360K by adiabatic calorimetry for the liquid crystalline material 4-cyano-3-fluorophenyl 4-butylbenzoate to investigate the phase behavior and determine the thermodynamic functions. Five phases are identified: the metastable nematic phase, its glass phase (Tg=210K), stable crystal I (Tfus=288.43K), a new metastable crystal (crystal II), and the isotropic liquid. The enthalpy of fusion of crystal I is 22.22kJ·mol−1, and the entropy is 76.91J·K−1·mol−1. Polarizing microscopy observations were also conducted between T=100K and 300K to confirm the phase behavior. The melting point of crystal II (Tfus=286K) and the clearing temperature of the nematic phase (Tc=279.4K) were obtained using a microscope. On the other hand, the enthalpy of the clearing transition (526J·mol−1) and the entropy (1.88J·K−1·mol−1) were obtained from the thermodynamic functions. The Debye temperature of crystal II (55.3K) is significantly lower than that of crystal I (60.7K), indicating that the phonon density of states is considerably different between the two crystals. The existence of low-energy excitations in the nematic glass and a low-energy shift of the intramolecular modes in crystal II are also identified.

Growth of Isotropic Domains As a Mechanism of Dynamic Diffraction Grating Recording in Low Molecular Liquid-Crystalline Derivatives of Azobenzene

In this paper, we propose and explain the mechanism of dynamic molecular motions and isotropic domain formation during the diffraction grating recording in low molecular liquid-crystalline azobenzene derivatives. The photochromic molecules of 4-heptyl-4'-methoxyazobenzene, showing nematic liquid-crystalline properties close to the room temperature (from T = 34 °C), are used. A one-dimensional model of the grating formation is formulated based on in vivo polarized microscope observations. Formation and growth of the isotropic domains induced by the sinusoidally modulated Gaussian light intensity distribution is proposed as the mechanism and is used for experimental data fitting. The influence of the recording light intensity, grating period, and temperature on the domain growth rate factor is checked.

Dependence of alkyl-substituent length for bulk heterojunction solar cells utilizing 1,4,8,11,15,18,22,25-octaalkylphthalocyanine

Bulk heterojunction organic thin-film solar cells utilizing soluble phthalocyanine derivatives, 1,4,8,11,15,18,22,25-octaalkylphthalocyanine (CnPcH2, n = 6, 7, 9, 10), were investigated. Two broad peaks existing in the external quantum efficiency spectra almost correspond to the Q-band and B-band of CnPcH2. The solar cell utilizing C6PcH2 had the best photovoltaic properties as evidenced by open-circuit voltage, short-circuit current density, fill factor, and energy conversion efficiency. Almost the same photovoltaic properties were observed in the solar cells utilizing C9PcH2 and C10PcH2. We discuss the photovoltaic properties by taking into consideration the crystal structure and electronic state of CnPcH2 from the results of the absorbance spectra, X-ray diffraction measurement, and polarization microscope observation.

Physical Properties of SmAb Phase in an Achiral Bent–Core Smectic Liquid Crystal

Non-polar biaxial SmAb mesophase was observed in a 4-cyanoresorcinol bisbenzoate with two terephthalate–based wings bent-core (BC) compound (PAL 29) having 16 carbon atoms in the terminal alkyl chain. Electro-optic and dielectric properties of this phase have been studied in detail. The biaxial SmAb phase transforms to ferroelectric state by the application of higher voltage. The field dependent biaxiality is very small and the polarizing microscopic texture observations support the corresponding measurements. Dielectric study exhibits two relaxation processes in the polar phase temperature region and one in the apolar biaxial SmAb phase.

Thermally controlled optical shutter in an inter-molecular hydrogen bonded liquid crystal

Novel homologs series of supra-molecular liquid crystals have been isolated. Hydrogen bond is formed between mandelic acid (MD) and various homologs of p- n-alkyloxy benzoic acids (nOBA) and has been confirmed by FTIR studies. Optical polarizing microscopic observations show that all these materials exhibit rich liquid crystallinity with various mesophases. Phase transition temperatures and enthalpy values are experimentally evaluated by DSC studies and the phase diagram of homologous series has been constructed. An interesting feature is the observation of thermally controlled reversible optical shuttering action in one of the homolog, wherein with the increment of temperature the homeotropic texture changes to homogenous texture of smectic F. Thus, this optical shuttering phenomenon is reversible. Optical tilt angle data of two homologs have been fitted to power law equation and it is found that the mean field theory prediction is valid. The light intensity profile in homeotropic region of smectic F in one complex has been experimentally analyzed and a steep sudden decrement of the intensity of light manifesting the distortion of the molecular alignment is experimentally found.

Giant organic single-crystals of a thiophene/phenylene co-oligomer toward device applications

We present the preparation of giant organic thin single-crystals of 2,5-bis(4-biphenylyl)thiophene (BP1T), a thiophene/phenylene co-oligomer (TPCO). Large-size well-defined hexagon crystals of BP1T were obtained by recrystallization from 1,2,4-trichlorobenzene solution using the constant-volume decreasing-temperature method under various conditions. The largest crystal had a size of 7.6×4.4mm. We describe the detailed growth procedure and characterization of the resulting crystals. The polarizing microscope observation of the crystals confirms that they are present as single-crystals. In virtue of the large size of the crystal we were able to fabricate three field-effect transistor (FET) devices on one single crystal. The devices showed normal p-type FET characteristics. Furthermore, the emission features are examined. Major emission peaks were spectrally narrowed with increasing excitation energies. Several crystals exhibited the narrowed emission lines accompanied by many concentric fringes of various sizes. These observations strongly indicate that the emission is a coherent radiation.

Understanding of the Relaxor Behaviors : Comprehensive Investigations from Polarization, Raman Scattering and Transmission Electron Microscopy Observations(Current Topics)

Understanding of the Relaxor Behaviors : Comprehensive Investigations from Polarization, Raman Scattering and Transmission Electron Microscopy Observations(Current Topics)

Melt Molding of Uniaxially-Oriented Crystal Domains onto a Substrate

We have fabricated semiconducting oligomer films composed of uniaxially-oriented crystal domains by melt molding. It is highly important to generate a temperature gradient in the lateral direction parallel to the substrate on which the said oligomer films are fabricated. As a result, the melted oligomer layer starts to solidify from parts of lower temperatures to end up as a uniaxially aligned film. The uniaxial alignment is further promoted by slowly cooling that oligomer layer. In the present studies, the temperature gradient was set at ∼0.06–0.4 °C/mm. From the polarizing microscope observations, we confirm that within this range the temperature gradient efficiently produces the uniaxial orientation. This method has been applied to fabricating organic field-effect transistors. Those devices show an effective modulation of the drain current with varying gate voltage.