X-ray Birefringence Research Articles

X-ray Birefringence from a Model Anisotropic Crystal

Whereas the phenomenon of birefringence is well-established and widely applied in the case of linearly polarized visible light (for example, underpinning the use of the polarizing optical microscope), the study of birefringence using linearly polarized X-rays is an essentially unexplored field. To address this issue, we report a material that exhibits ideal birefringence behavior at X-ray energies near the Br K-edge. The designed material, the 1-bromoadamantane/thiourea inclusion compound, gives experimental behavior in excellent agreement with theoretical predictions for the dependence of transmitted X-ray intensity on both X-ray energy and crystal orientation. Our results vindicate the potential to exploit X-ray birefringence to establish a detailed understanding of molecular polarization, particularly as an experimental strategy to determine the orientational distributions of specific bonds in solids, for example, in the case of partially ordered materials or materials that undergo order–disorder phase transitions.

Synthesis, growth and optical properties of semi organic non linear optical single crystal: l-Arginine acetate

In the recent past, nonlinear optical materials are getting attention in the field fibre optic communication and optical signal processing. In the present study, the title compound was successfully synthesized by conventional chemical reaction and then the single crystal was grown by slow evaporation solution growth technique. l-Arginine acetate (LAA) is semi organic non linear optical single crystal and crystallizes in noncentrosymmetric space group. The grown good quality single crystals have been analyzed by different characterization analyses such as powder X-ray diffraction, high resolution X-ray diffraction (HRXRD), Raman spectroscopy, photoluminescence, SEM, micro-hardness, thermal and birefringence analyses.

Structural Investigations of a Non Calamitic Shaped Liquid Crystalline Compound Showing Unusual Phases

X-ray diffraction, birefringence, density and static dielectric permittivity measurements were performed on a calamitic hockey stick shaped mesogen. In addition to SmA phase, this compound exhibits two tilted mesophases – the SmC, synclinic and the SmCa, anticlinic phase. From x-ray diffraction and birefringence data, the orientational order parameters have been determined. The order parameters values drop at the SmC – SmCa phase boundary. Possible cause for the drop in the order parameter values has been discussed. Interestingly, it has been found that the dielectric anisotropy of this compound changes from positive to negative values in the SmCa phase.

Physical Properties of Three Liquid Crystals with Negative Dielectric Anisotropy from X-Ray Diffraction and Optical Birefringence Measurements

In this work, we report the results of x-ray diffraction, density and birefringence measurements on three fluorinated liquid crystalline compounds having negative dielectric anisotropy. Small angle x-ray diffraction data from aligned samples have been analyzed to determine the orientational order parameter as a function of temperature. The order parameter values were also determined from birefringence measurements and the results were compared with mean field theory. Structural parameters like intermolecular distance and layer thickness (in smectic B phase), apparent molecular length (in nematic phase) have been determined and the order of the phase transition in these compounds has been discussed.

Parallel Thermal Analysis Technology Using an Infrared Camera for High-Throughput Evaluation of Active Pharmaceutical Ingredients: A Case Study of Melting Point Determination

Various techniques for physical characterization of active pharmaceutical ingredients, including X-ray powder diffraction, birefringence observation, Raman spectroscopy, and high-performance liquid chromatography, can be conducted using 96-well plates. The only exception among the important characterization items is the thermal analysis, which can be a limiting step in many cases, notably when screening the crystal/salt form. In this study, infrared thermal camera technology was applied for thermal characterization of pharmaceutical compounds. The melting temperature of model compounds was determined typically within 5 min, and the obtained melting temperature values agreed well with those from differential scanning calorimetry measurements. Since many compounds can be investigated simultaneously in this infrared technology, it should be promising for high-throughput thermal analysis in the pharmaceutical developmental process.

Spontaneous molecular orientation of polyimides induced by thermal imidization (6). Mechanism of negative in-plane CTE generation in non-stretched polyimide films

The mechanism of negative coefficient of thermal expansion (CTE) generation for non-stretched polyimide (PI) films is proposed in this work. Negative CTE behavior was observed in some miscible binary blend films composed of a major fraction of a rod-like semi-crystalline PI derived from pyromellitic dianhydride (PMDA) with p-phenylenediamine (PDA) and flexible PIs based on 2,3,3′,4′-biphenyltetracarboxylic dianhydride (a-BPDA) whereas homo PMDA/PDA PI film shows a considerably low but a positive CTE value. The results suggest that the negative CTE generation is related to not only a considerably high extent of in-plane orientation of the PMDA/PDA chains but also to the crystallinity of the blends. The present work revealed that some other PIs, a poly(ester imide), and a polybenzoxazole system also display negative CTE and these systems also possess extremely high extents of in-plane chain orientation without exception. In addition to CTE, the morphologies were monitored as a function of imidization temperature for two PI systems, PMDA/2,2′-bis(trifluoromethyl)benzidine and PMDA/m-tolidine by wide-angle X-ray diffraction, FT-IR spectroscopy, birefringence, and film density measurements. The results suggested that the negative CTE phenomenon occurs when PI films possess very high extents of in-plane orientation and a less crystalline morphology simultaneously, thereby significant thermal expansion can be allowed to the thickness direction.

High crystalline quality single crystal chemical vapour deposition diamond

Homoepitaxial chemical vapour deposition (CVD) on high pressure, high temperature(HPHT) synthetic diamond substrates allows the production of diamond material withcontrolled point defect content. In order to minimize the extended defect content, however,it is necessary to minimize the number of substrate extended defects that reach the initialgrowth surface and the nucleation of dislocations at the interface between the CVD layerand its substrate. X-ray topography has indicated that when type IIa HPHT syntheticsubstrates are used, the density of dislocations nucleating at the interface can be less than 400 cm−2. X-ray topography, photoluminescence imaging and birefringence microscopy of HPHT grownsynthetic type IIa diamond clearly show that the extended defect content is growth sector dependent.⟨111⟩ sectors contain the highest concentration of both stacking faults and dislocations but⟨100⟩ sectors are relatively free of both. It has been shown that HPHT treatment of such materialcan significantly reduce the area of stacking faults and cause dislocations to move. Thisknowledge, coupled with an understanding of how growth sectors develop during HPHTsynthesis, has been used to guide selection and processing of substrates suitable for CVDsynthesis of material with high crystalline perfection and controlled point defectcontent.

Determination of the orientational order parameter of a binary mixture showing an induced smecticAd phase from magnetic susceptibility measurements

The diamagnetic susceptibility anisotropy(Δχ) measurement of a binary mixture comprising of a strongly polar mesogen(CPPCC) and a weakly polar mesogen (ME6O.5) showing an induced smecticAd phase is reported here. Assuming an axially symmetric molecule,the temperature dependence of the orientational order parameter⟨P2⟩ has been investigated from the anisotropy of the susceptibility at differenttemperatures throughout the entire composition range. The results are comparedwith x-ray and optical birefringence measurements along with the mean-fieldtheory of the smectic A phase. The maximum in the stability of the smecticAd phase(at xCPPCC = 0.33) corresponds to the minimum in the order parameter values. The order of the smectic tonematic phase transition has also been discussed.

Formation of physically stable amorphous phase of ibuprofen by solid state milling with kaolin

Ibuprofen was milled in the solid state with kaolin (hydrated aluminium silicate) in different ratio to examine the extent of transformation from crystalline to amorphous state. The physical stability of the resultant drug was also investigated. X-ray powder diffractometry (XRD) and birefringence by Scanning Electron Microscopy (SEM) studies indicated almost complete amorphization of the drug on ball milling with kaolin at 1:2 ratio. Fourier transform infrared spectroscopy (FTIR) data showed a reduction in the absorbance of the free and the hydrogen-bonded acid carbonyl peak of carboxylic acid group accompanied by a corresponding increase in the absorbance of the carboxylate peak, indicating an acid–base reaction between the carboxylic acid containing ibuprofen and kaolin on milling. The extent of amorphization and reduction in the carbonyl peak and increase in carboxylate peak was a function of kaolin concentration in the milled powder. On storage of milled powder (at 40 °C and 75% RH for 10 weeks), XRD and birefringence of SEM study showed the absence of reversion to the crystalline state and FTIR data revealed continued reduction of carbonyl peak, whereas, ibuprofen converted from its crystalline acid form to amorphous salt form on milling with kaolin. Kaolin-bound state of ibuprofen was physically stable during storage. In-vitro dissolution studies revealed that percent release of ibuprofen from the kaolin co-milled powder is in the order: 1:2 > 1:1 > 1:0.5 > 1:0.1> milled alone ibuprofen > crystalline ibuprofen.

Structure and dynamic mechanical properties of poly(ethylene terephthalate- co-4,4′-bibenzoate) fibers

Poly(ethylene terephthalate- co-4,4′-bibenzoate) (PETBB) fibers containing 5, 15, 35, 45, 55, and 65 mol% bibenzoate (BB) were melt spun. Fiber structure has been determined using wide angle X-ray diffraction, birefringence, and FTIR spectroscopy. When drawn to their respective maximum draw ratios, the structures and properties of high BB containing fibers (PETBB45, 55 and 65) are significantly different than those of PET and low BB containing fibers (PETBB5, 15, and 35). For example, 90% of the ethylene glycol units in high BB containing fibers are in the trans conformation, while only 80% of these units are in trans conformation in PET and low BB containing fibers. Overall orientation of the high BB containing fibers is higher (orientation factor f > 0.85) than those of PET and low BB containing fibers ( f < 0.6). Orientation of the crystalline regions is quite high ( f cr ∼ 0.95) for both groups of fibers, while orientation of the amorphous regions ( f am) of high BB containing fibers is higher (∼0.8) than those of the PET and low BB containing fibers (∼0.4). High BB containing fibers exhibit much higher storage modulus and modulus retention with temperature than low BB containing fibers. Glass transition temperature determined from the dynamic loss tangent peak decreased with increasing BB content, while this transition completely disappeared in the high BB containing fibers. The magnitude of the secondary transition, observed at about −50 °C, decreased with increasing BB content. Another secondary transition, not observed in PET, was observed at about 70 °C in high BB containing fibers. These dynamic mechanical results have been rationalized in terms of the observed structural parameters.

Molecular Orientation Distributions in Uniaxially Oriented Poly(l-lactic acid) Films Determined by Polarized Raman Spectroscopy

Molecular orientation distributions in the crystalline and amorphous regions were studied for uniaxially oriented poly(l-lactic acid) (PLLA) films using polarized Raman spectroscopy. By combining wide-angle X-ray diffraction and birefringence measurements, the tilt angle between the principal axis of the Raman tensor and the molecular chain axis was determined for Raman bands assigned to the crystalline regions only, and also to those being independent of morphology. The changes of the molecular orientation distribution functions during the drawing were analyzed in detail. The PLLA molecules in the crystalline regions were found to be highly oriented at a draw ratio of 4.5, probably as a result of crystal rotation and crystal slip. In contrast, the development of molecular orientation in the amorphous regions appeared to take place by pseudo-affine deformation. The results suggest that the film needs to be stretched to draw ratios above 4.5 to achieve successful molecular orientation in the amorphous regions.

External Calibration in PA12 Tube Extrusion

AbstractIn polyamide 12 (PA12) tube extrusion, calibration is crucial for the major final properties such as elongation at break or burst pressure. In external calibration, the extruded tube is pulled through a cylindrical calibrator located in a water tank under vacuum. A water flow rate is applied at the calibrator inner side, creating a lubricating water layer at the polymer outer surface. A combination of a quenching and a mechanical drawing was highlighted during calibration by on-line measurements. A subsequent high molecular orientation in the outer tube layers was also featured by X-Ray diffraction and birefringence evaluation in light microscopy. Besides, influence of lubrication level in the sizing-sleeve was investigated by an estimate of the lubricating water layer and a characterization of the tube final surface state in different calibration conditions. Firstly, we quantitatively showed that rising the water layer thickness leads to a diminution of the draw ratio in the calibration tank, DrCAL (ratio between line velocity and velocity at the calibrator entrance). Excellent correlation has been found between tube superficial orientation and DrCAL: a reduced elongation of the polymer in the calibrator leads to a lower level of superficial orientation. Secondly, two kinds of surface defects were detected on the tubes by light microscopy and microtopography. At last, several correlations were featured with mechanical properties. Elongation at break was found to strongly depend on the molecular orientation resulting from calibration. Moreover, origin of rupture was investigated during tensile testing in light microscopy. We emphasized that surface defects alignments perpendicular to the extrusion initiate the rupture by creating a significant crack via coalescence of initial defects. Thus, microstructure, surface state and tensile properties can be controlled by fitting the calibration parameters to improve lubrication and reduce the draw ratio in calibrator.

External Calibration in PA12 Tube Extrusion

In polyamide 12 (PA12) tube extrusion, calibration is crucial for the major final properties such as elongation at break or burst pressure. In external calibration, the extruded tube is pulled through a cylindrical calibrator located in a water tank under vacuum. A water flow rate is applied at the calibrator inner side, creating a lubricating water layer at the polymer outer surface. A combination of a quenching and a mechanical drawing was highlighted during calibration by on-line measurements. A subsequent high molecular orientation in the outer tube layers was also featured by X-Ray diffraction and birefringence evaluation in light microscopy. Besides, influence of lubrication level in the sizing-sleeve was investigated by an estimate of the lubricating water layer and a characterization of the tube final surface state in different calibration conditions. Firstly, we quantitatively showed that rising the water layer thickness leads to a diminution of the draw ratio in the calibration tank, DrCAL (rati...

Hydrophobic induced supramolecular self-organization of tetrahedral units based on van der Waals interactions

Nanostructured hybrid materials were prepared by sol–gel hydrolysis–polycondensation of tetrakis(4-trisisopropoxysilylphenyl)germane PGe and tetrakis(4-trisisopropoxysilylphenyl) tin PSn which present a tetrahedral germanium or tin central atom. Both precursors presented twelve directions for solid formation oriented regularly on the four directions of the tetrahedron. Their organization was evaluated by X-ray diffraction studies (nanometric scale) and birefringence measurements (micrometric scale). It has been shown that the organization of these solids was influenced by the experimental parameters. The intensities of birefringence lay in the same range (1.6 × 10−3 to 2.1 × 10−3) for all the gels XGe and XSn. Regular parallel rectangular chunks were observed in all cases. The orientation of the optical axis was found perpendicular to the edges of the chunks in all cases. The existence of such optical axes regularly oriented towards the edges of the chunks corresponded to an anisotropic organization at the micrometric scale. The results presented here strengthen the fact that the auto-organization observed in nanostructured organic–inorganic hybrid materials occurs during the formation of Si–O–Si bonds, which transforms intermolecular interactions into intramolecular ones corresponding to the weak van der Waals-type interactions existing between the organic units. The role of hydrophilic–hydrophobic interactions is discussed.

Structure development and properties of high-speed melt spun poly(butylene terephthalate)/poly(butylene adipate- co-terephthalate) bicomponent fibers

Ultra-high-speed bicomponent spinning of poly(butylene terephthalate) (PBT) as sheath and biodegradable poly(butylene adipate- co-terephthalate) (PBAT) as core was accomplished with the take-up velocity up to 10 km/min. The structure development of the individual component and the properties of PBT/PBAT fibers were investigated through the measurements on differential scanning calorimetry, wide-angle X-ray diffraction, birefringence and tensile test. Due to the mutual interaction between two polymer-melts along the spinline, the processability of both components in PBT/PBAT bicomponent spinning was improved compared with those of corresponding single component spinnings. Furthermore, in PBT/PBAT fibers, the structure development of PBT component was found to be greatly enhanced, which led to the improvement in its thermal and mechanical properties; whereas the structure development of PBAT component was significantly suppressed, in which nearly non-oriented structure was observed in both crystalline and amorphous phases.

Correlation between Structural Parameters and Property of PE Blown Films

Our objective in this study is to develop models which relate detailed structural parameters to performance, providing the means for predicting final film properties. In this work, we used different types of polyethylene (LLDPE, HDPE, and LDPE) at different process conditions in the film blowing process. The morphology of films was studied using X-ray diffraction, SEM, AFM, FTIR, and birefringence measurements. Herman's orientation factors of the films were determined via both WAXD pole figures and infrared dichroism. DSC, WAXD and SAXS were used to determine microstructural parameters including the degree of crystallinity, lamellar thickness, crystal size, length of crystal, and long spacing. By using the statistical design of experiments, a correlation between mechanical properties including tensile properties, Elmendorf tear, dart impact, and optical properties such as haze and clarity was obtained with the microstructural parameters.

External Calibration in PA12 Tube Extrusion

Abstract Elongation at break is one of the major end-use properties of polyamide 12 extruded tubes. It is strongly affected by the tube microstructure and the molecular orientation resulting from extrusion conditions. Molecular orientation was characterized by X-ray diffraction and birefringence evaluation in light microscopy. Measurements were carried out on (r, z) sections obtained by polishing and microtoming. On the other hand, polymer drawing was measured on line by tracer techniques. Calibration stage was determined as the key step of the process that generates orientation in tubes: as the tube is drawn through a cylindrical calibrator under vacuum and cooled from its outside surface, calibration leads to a highly oriented zone in the twenty external microns. Calibration conditions and elongation at break have been connected through orientation level in this region. Molecular orientation was found to strongly depend on the draw ratio in the calibration tank. Finally, birefringence of the tube external layers and elongation at break were successfully correlated. Elongation at break can be enhanced by reducing orientation resulting from calibration conditions.

Determination of Molecular Orientation of Uniaxially Stretched Polyamide Fibers by Polarized Infrared Spectroscopy: Comparison of X-Ray Diffraction and Birefringence Methods

Polarized infrared (IR) spectroscopy has been used to determine the crystalline and amorphous orientation of polyamide fibers. The transition moment angle of the band at 936 cm-1 of PA66 was determined to be 48 degrees using IR spectroscopy and birefringence measurement. The crystalline orientation of PA66 fibers was estimated from the band at 936 cm-1 while the amorphous orientation of PA66 fibers was obtained by an indirect method. The alpha crystalline orientation of PA6 has been obtained using the band at 930 cm-1 and the amorphous orientation of PA6 has been determined using the band at 1124 cm-1. Crystalline orientation increased rapidly at low draw ratios (DR<3) and increased slowly at higher draw ratios (DR>3) for both PA66 and PA6 fibers, while the amorphous orientation increased slowly throughout the whole extension range for PA66 fibers. A good correlation was found between the crystalline orientation values obtained by infrared spectroscopy and other methods such as X-ray diffraction for PA66 and PA6 fibers. On the basis of this observation, it has been concluded that polarized infrared spectroscopy can be used reliably to measure the orientation of polyamide fibers without combining with other techniques.

Biaxial orientation in HDPE films: comparison of infrared spectroscopy, X-ray pole figures and birefringence techniques

In this study, high-density polyethylene films (HDPE) were produced using different processes (film blowing and biaxial orientation) and processing conditions. The orientation of the films was characterized in terms of their biaxial crystalline, amorphous and global orientation factors using birefringence, Fourier transform infrared spectroscopy (FTIR) using a tilted incidence technique and X-ray pole figures. Evaluation of a simplified FTIR procedure without using the tilted method for the determination of crystalline orientation factors proposed in the literature is also evaluated and assessed. The results indicate that FTIR overestimate the crystalline orientation factors, particularly for the crystalline a-axis. Significant discrepancies are also observed for the b-axis orientation, which may be due to an overlap of the amorphous contribution and/or saturation of FTIR bands. Those differences are larger for films with low orientation, such as blown films. Amorphous phase orientation from FTIR depends on the band used and is not necessarily in agreement with that determined from combination of X-ray and birefringence.

Imparting disperse and cationic dyeability to polypropylene through melt blending

The present paper deals with improvement in disperse dyeability as well as imparting of cationic dyeablility to difficultly dyeable polypropylene by a melt blending technique. Isotactic polypropylene (PP) was blended with fibre grade polybutylene terephthalate (PBT), cationic dyeable polyethylene terephthalate (CDPET) and polystyrene (PS), individually. The resulting binary blends were spun and drawn into fibres at draw ratio 2, 2.5, and 3. The compatibility of blends, structural changes of fibres in terms of X-ray crystallinity, relative crystallinity, sonic modulus, birefringence and thermal stability were examined. The blended fibres were found to be disperse dyeable by the conventional method of high temperature and high pressure dyeing. And this dyeability increased with increase in the level of substitution. PP/CDPET blend also exhibited dyeablility with cationic dyes in addition to that with disperse dyes. The optimum level of blending was predicted keeping in view of tenacity and thermal stability of melt blend fibres. The wash fastness properties of the dyed fibres were found to be of high rate.