Birefringence Patterns Research Articles

An optical test to unveil twisting of birefringent crystals in spherulites.

Helical conformations and structures are frequently observed in materials. The presence of helices at points of the unit cell of a crystal, on a larger size scale in the crystalline lattice or even in the microscopic structure of crystals, affects the chemico-physical properties of a solid and, hence, also interactions with light. Here, attention has been drawn to the geometrical properties of helices produced by a hypothetical torque of a transparent crystal, and optical properties of twisted crystals easily observed by a polarizing microscope have been discussed. Radially grown spherulites are obtained by most substances crystallized from melt. The circular arrangement of elongated crystals reflects the optical behaviour of each crystal and, because of the larger dimensions of spherulites, allows investigations otherwise hardly feasible on separate crystals. According to the torsional analysis of elongated bodies and the birefringence theory, information on the existence of helically shaped crystals can be deduced, as hereinafter explained, from the microscopic appearance and birefringence pattern of spherulites. Indeed, twisting decreases the birefringence throughout an elongated crystal and, therefore, also the birefringence of spherulites formed by twisted radial crystals is reduced.

Laboratory Modeling of Coeval Brittle and Ductile Deformation During Magma Emplacement Into Viscoelastic Rocks

The mechanics of magma emplacement in the Earth's crust corresponds to the flow of a viscous fluid into a deforming solid. The Earth's crust through which magma is emplaced is visco-elasto-plastic, and field observations show that most intrusions are likely to be accommodated by combined brittle and ductile deformation of their host. However, mechanical models of magma emplacement account for either purely elastic, plastic or viscous end-member rheology of the host rock, therefore they cannot simulate the natural diversity of magma intrusion shapes and magma emplacement mechanisms. Thus they are of limited use to predict under which conditions intrusions of contrasting shapes form. Here we present a series of 2D experiments where a viscous fluid (oil) was injected into a host matrix (laponite gel), the visco-elasto-plastic rheology of which is varied from dominantly viscous to dominantly elastic. The oil intrusion in the elastic gel is a thin conduit with a sharp tip, like magmatic dykes, whereas the oil intrusion in the viscous gel is rounded, like diapirs. In addition, the oil intrusion exhibits complex, shapes. The experiments were run in a polariscope, which highlighted birefringence patterns related to deformation structures within the gel. Our experiments show a strong correlation between intrusion shapes and host matrix deformation modes: (1) thin intrusions dominantly propagate by tensile failure and elastic deformation of the host, (2) rounded diapiric intrusions dominantly propagate by viscous flow of the host, and (3) irregular hybrid intrusions propagate by coeval brittle (tensile and shear) and ductile deformation of the host. Our novel experiments are the first able to produce the natural diversity of intrusion shapes and host deformation mechanisms. In addition, our results show that the use of a polariscope in gel experiments is essential to unravel the mechanics of magma emplacement within a host of realistic visco-elasto-plastic rheology.

Anatomy into Interior Lamellar Assembly in Nuclei-Dependent Diversified Morphologies of Poly(l-lactic acid)

Sophisticated dissection into the interiors of the three different birefringent types of poly(l-lactic acid) (PLLA) spherulites via delicate fracturing across the thickness sections, coupled with proper etching techniques, was adopted to reveal the correlations between the diversified birefringence patterns and interior lamellae assembly. The three types of spherulites are circularly ringed spherulite (type 1), hexagon-shaped axialite (type 2), and circularly core–stripe dendrites (type 3). Such morphological diversification originates from different nuclei geometries. For all three different types (circularly ringed, hexagonal, and core–stripe) of PLLA aggregation into spherulites or dendrites/axialites, the dissected inner lamellar arrangement shares universal commonality of intersecting at a 60° angle in the intersection between different lamellar species, with distinct discontinuity in the grating structures being characteristic of all three types of aggregated PLLA spherulites. This kind of grating a...

Quantifying birefringence in the bovine model of early osteoarthritis using polarisation-sensitive optical coherence tomography and mechanical indentation

Recent studies have shown potential for using polarisation sensitive optical coherence tomography (PS-OCT) to study cartilage morphology, and to be potentially used as an in vivo, non-invasive tool for detecting osteoarthritic changes. However, there has been relatively limited ability of this method to quantify the subtle changes that occur in the early stages of cartilage degeneration. An established mechanical indenting technique that has previously been used to examine the microstructural response of articular cartilage was employed to fix the bovine samples in an indented state. The samples were subject to creep loading with a constant compressive stress of 4.5 MPa and, when imaged using PS-OCT, enabled birefringent banding patterns to be observed. The magnitude of the birefringence was quantified using the birefringence coefficient (BRC) and statistical analysis revealed that PS-OCT is able to detect and quantify significant changes between healthy and early osteoarthritic cartilage (p < 0.001). This presents a novel utilization of PS-OCT for future development as an in vivo assessment tool.

Optical Imaging and Molecular Sequencing of a Preserved Collection of Bivalve Larvae

From the 1980s through 1995, scientists at numerous marine, coastal, estuarine, and freshwater laboratories spawned bivalves to provide larvae for use in identifying species based on larval hinge structures and gross shell morphometry. These larvae were preserved in 95% ethanol and stored in sample vials, many of which dried out over the years. Advantage was taken of 50 of 56 species from this collection (and two additional species that were not in the collection for a total of 52 species) to explore the use of optical techniques (polarized light and a full-wave compensation plate) to highlight birefringence patterns of larval shells to discriminate individual species. Representative images of various developmental stages of 77% (40/52) of the larval bivalve species in the collection were successfully imaged. Similarities across birefringence patterns were observed at the taxonomic ordinal and familial level. Molecular polymerase chain reaction techniques were used in an effort to sequence many of the dried-out specimens and they successfully identified 19% (10/52) of the larval bivalve species with matches in GenBank. Here it has been demonstrated that optical techniques are efficient for imaging dried-out larval bivalve shells for classification purposes and we present successful sequences of 10 species of bivalve larvae from the preserved collection.

Scanning Electron Microscopic Aids for Identification of Larval and Post-Larval Bivalves

The identification of bivalve larvae and early postlarvae in plankton and benthic samples has long been a challenge, hampering both basic and applied research efforts in marine, estuarine, and freshwater environments. The usefulness of published optical micrographs of the early life-history stages of bivalves is limited because of the great morphological similarity of the imaged articulated shells, particularly at the early (straight-hinge) developmental stages. While a number of techniques have been refined in recent years and show promise for use in routine identifications of larval and post-larval bivalves (e.g., single-step nested multiplex polymerase chain reaction; in situ hybridization protocols through color coding with taxon-specific, dye-labeled DNA probes; coupled fluorescence in situ hybridization and cell sorting; and image analysis techniques using species-specific shell birefringence patterns under polarized light), no adequate comprehensive reference source exists that accurately depicts the morphology and morphometry of the shells of larval and post-larval stages of target bivalve species in a consistent format to assist in identification of such stages. To this end, scanning electron micrograph (SEM) sequences are presented of the disarticulated shell valves of laboratory-reared larval and post-larval stages of 56 species of bivalve molluscs from a wide spectrum of marine, estuarine, and freshwater habitats. Emphasis is placed on the usefulness of the morphology and morphometrics of consistently-oriented, disarticulated shell valves and associated hinge structures in discriminating the early life-history stages of these various bivalve species. Although the scanning electron micrograph sequences presented accurately depict the gross morphologies/ morphometrics and hinge structures of the disarticulated shell valves of the larvae and/or postlarvae of the 56 species of bivalves, it is important to emphasize that a scanning electron microscope is not necessary to observe even fine hinge structures associated with the early ontogenetic stages of these species. Such structures are readily visible using a wide range of optical compound microscopes equipped with high-intensity reflected light sources, although the disarticulated shell valves must be viewed in several planes of focus to discern the often subtle details seen clearly in the scanning electron micrographs. These morphological characters provide researchers with invaluable aids for the routine identification of the early life-history stages of these species isolated from plankton and benthic samples.

Biomimetically Structured Lamellae Assembly in Periodic Banding of Poly(ethylene adipate) Crystals

Nature tends to assemble hierarchical structures in similar ways to achieve compactness and functions. This work probes the interior lamellae assembly of crystalline spherulites of poly(ethylene adipate) (PEA) with striking birefringence patterns versus some known biological structures for optical color diffraction. Three-dimensional dissecting onto interior lamellar structures of spherulites in poly(ethylene adipate) (PEA) in bulk forms crystallized at 28 ± 3 °C were studied in correlation with thin-film forms. Interior morphology in bulk PEA samples revealed periodic hemisphere or arc-shaped layers resembling corrugate boards with liner-flute medium alteration. Interior spherulites clearly expose that the lamellae within the intralayer are kebabs (plates) in the radial direction while the interlayer region are thin sheaths (fibrils) composed of cilia-like lamellae in the tangential direction. The interior repetitive lamellar assembly of PEA banded spherulites in displaying periodic optical birefringence patterns is proven to highly resemble those in many biological structures for iridescence light interference.

Carbon fiber/epoxy matrix composite interphases modified with cellulose nanocrystals

Cellulose nanocrystals (CNCs) were used to modify the interphase between carbon fiber (CF) and an epoxy matrix to simultaneously strengthen and toughen the CF composite. CNCs were functionalized with 3-aminopropyltriethoxysilane (APTES) and surface modification was confirmed by Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS), which revealed the presence of the new chemical species. Functionalized CNCs (APTES-CNCs) were applied as part of a sizing to coat CFs and an optimum concentration was identified. Single fiber fragmentation tests (SFFT) showed that stronger adhesion between the CFs and the epoxy matrix was achieved for the fibers sized with APTES-CNCs, compared to unsized CFs and epoxy-only sized CFs. CFs sized with APTES-CNCs at a concentration of 1.0 wt% resulted in 81% increase in interfacial shear strength (IFSS) compared to unsized CFs, and the birefringent stress pattern seen during the SFFT supports the assumption that adding APTES-CNCs at the composite interphase promotes an improvement in the failure mode. These results demonstrate that sizing CFs with APTES-CNCs is an effective method to increase the interfacial properties in CF reinforced epoxy composites, and a potential approach for the development of ecofriendly and lightweight composite materials for aerospace and automotive applications.

Birefringence and incipient plastic deformation in elastically overdriven [100] CaF2 under shock compression

[100] CaF2 single crystals are shock-compressed via symmetric planar impact, and the flyer plate–target interface velocity histories are measured with a laser displacement interferometry. The shock loading is slightly above the Hugoniot elastic limit to investigate incipient plasticity and its kinetics, and its effects on optical properties and deformation inhomogeneity. Fringe patterns demonstrate different features in modulation of fringe amplitude, including birefringence and complicated modulations. The birefringence is attributed to local lattice rotation accompanying incipient plasticity. Spatially resolved measurements show inhomogeneity in deformation, birefringence, and fringe pattern evolutions, most likely caused by the inhomogeneity associated with lattice rotation and dislocation slip. Transiently overdriven elastic states are observed, and the incubation time for incipient plasticity decreases inversely with increasing overdrive by the elastic shock.

Photoinduced Birefringent Pattern and Photoinactivation of Liquid-Crystalline Copolymer Films with Benzoic Acid and Phenylaldehyde Side Groups.

In situ formation of N-benzylideneaniline (NBA) side groups achieved photoinduced cooperative reorientation of photoinactive copolymers with phenylaldehyde (PA) and benzoic acid (BA) side groups doped with 4-methoxyaniline (AN) molecules. Thermally stimulated molecular reorientation of the side groups was generated due to the axis-selective photoreaction of the NBA moieties. Selective coating with AN on the copolymer film formed NBA moieties in the desired region, resulting in a photoinduced birefringent pattern. Additionally, postannealing at an elevated temperature for a long time attained photoinactivation of the reoriented film, and recoating with AN to form NBA achieved the multiple birefringent patterns and repatterning of the reoriented structures. The slow thermal hydrolysis of NBA, which was 50 times slower than the thermally stimulated self-organization of the side groups due to the presence of BA side groups, contributed to the photodurability of the reoriented film and multiple birefringent patterns.

Polarized microscope assisted study of collagen fibres in Oral Submucous Fibrosis and their clinicopathologic correlation: An in-vitro study

BackgroundThe present study was aimed to evaluate and analyze orientation and birefringence pattern of collagen fibers histopathologically in different grades of OSMF using the special stain (Picrosirius red) under polarizing microscope and relate these factors with the severity of OSMF. Materials and Method45 confirmed cases of OSMF were taken from the archives. The selection of clinical cases was done according to classification by J.N Khanna and Andrade (1999). These cases were correlated histopathologically as per the criteria given by Pindborg J.J and Sirsat S.M (1966). The sections were stained with H & E and Picrosirius red stains and assessment was done accordingly. 10 cases of normal mucosa were taken as control. ResultsIn clinical grade I, 60% of the cases showed histopathological grade II, while 53.4% cases in clinical grade II correlated with histopathological grade III and 33.4% of clinical grade III cases showed histopathological grade IV. Upon application of Fisher’s exact test a significant P value <.01 was obtained suggesting no statistical significant correlation between these two parameters. However, the orientation pattern revealed a parallel orientation as OSMF advanced. Also as the severity of the disease increased, there was a gradual shift from green- greenish yellow colour of the fibres and a shift to orange red-red colour. ConclusionUpon correlation of clinical grades with histopathological grades, no statistically significant difference was found. Birefringence pattern of collagen revealed similar findings as other studies in case of clinical grades but histopathological grades showed a contrast finding.

Influence of cryogenic treatment on mechanical and interfacial properties of carbon nanotube fiber/bisphenol-F epoxy composite

Abstract The effects of cryogenic treatment (−196 °C) on properties of the carbon nanotube (CNT) fiber/epoxy composite are investigated using a temperature controlled cooling process with low cooling rate. The CNT fiber/epoxy single fiber composite fragmentation test is performed in conjunction with electrical resistance measurements to compare the interfacial properties at ambient and cryogenic temperatures. Weibull distribution for CNT fiber strengths shows a decreased variation (the shape parameter increases from 4.98 to 6.93) for cryo-treated fibers although their mechanical properties are not significantly influenced by the treatment. The electrical resistance measurement shows an increased electrical resistance changing rate with strain for the cryogenic treated sample, indicating better fiber/matrix interaction. In addition, the cryogenic treatment also improves interfacial bonding strength by 31% owing to the effect of differential thermal shrinkage for the CNT fiber and epoxy. An asymmetrical interfacial stress distribution is observed corresponding to the asymmetrical birefringence patterns of the fragmented fiber in the single fiber composite, which could be due to the twisted structure of the CNT fiber.

Experimental and Theoretical Investigations of Tetrakis (Thiourea) Palladium Chloride Semi-Organic Non-Linear Optical Crystal: An Approach to NLO Application

Semi-organic non-linear optical crystals of tetrakis (thiourea) palladium chloride (TTPC) were synthesized by a slow evaporation method. X-ray diffraction analysis performed on the title crystal established its orthorhombic structure and Pna2 1 space group. The crystalline perfection was investigated by means of high resolution X-ray diffraction (HRXRD) measurements. The values of transmittance, cutoff wavelength, refractive index and single oscillator parameters were computed through ultraviolet (UV) transmittance analysis. The second harmonic generation efficiency (SHG) of the TTPC crystals was verified by the Kurtz Perry technique. The potential of TTPC to act as a NLO material was further envisaged by the hyperpolarizability studies which resulted in higher values of dipoles and polarizability. To shed light on the pattern of charge distribution and donor-acceptor interactions prevailing in TTPC crystals, natural bond orbital (NBO) analysis was performed. Laser damage threshold (LDT) analysis on TTPC resulted in a LDT value of 5.1 GW/cm 2. The low birefringence value calculated from birefringence patterns attested the to suitability of the crystal to be used in harmonic generation devices. Using the HOMO-LUMO approach the values of significant global chemical molecular reactivity descriptors were determined.

Birefringent Pattern Formation in Photoinactive Liquid Crystalline Polymer Films Based on a Photoalignment Technique with Top-Coating of Cinnamic Acid Derivatives via H-Bonds.

The application of a top-coating of 4-methoxy cinnamic acid (MCA) onto a photoinactive liquid crystalline polymeric film containing benzoic acid (BA) side groups (P6BAM) is shown to enable thermally stimulated, photoinduced reorientation of the polymer structure. Annealing the MCA-coated P6BAM films leads to H-bond formation between BA and MCA, which also effectively smooths the film surface. Exposure to linearly polarized (LP) UV light initiates axis-selective photoreaction of the MCA groups; subsequent thermal treatment in the LC temperature range of P6BAM amplifies molecular reorientation of the BA side groups, while simultaneously eliminating the MCA molecules. Selective inkjet coating of MCA provides a facile route for the fabrication of patterned, oriented, and rewritable P6BAM films with multiple controlled alignment directions.

A no-moving-parts sensor for the detection of eye fixation using polarised light and retinal birefringence information

Polarised near-infra-red light is reflected from the foveal area in a detectable bow-tie pattern of polarisation states, offering the opportunity for eye tracking. A coaxial optical transducer was developed, consisting of a laser diode, a polariser, a filter, and a photodetector. Several such transducers may be used to interrogate different spots on the retina, thus eliminating the requirement for scanning systems with moving parts. To test the signal quality obtainable, using just one transducer, a test subject was asked to fixate successively on twelve targets located on a circle around the transducer, to simulate the retina’s being interrogated by twelve sensors placed on a 30 diameter circle surrounding the projection of the fovea. The resulting signal is close to the “ideal” sine wave that would have been recorded from a propeller-type birefringence pattern from a human fovea. The transducer can be used in the detection of fixation for medical and other purposes. It does not require calibration, strict restrictions on head position, or head-mounted appliances.

Structural Analysis of Enamel in Teeth from Head-and-Neck Cancer Patients Who Underwent Radiotherapy

Objective: To analyze macroscopic, microscopic, and ultrastructural aspects of enamel from head-and-neck cancer patients submitted to radiotherapy. Materials and Methods: Twenty sound extracted permanent molars were used and divided into 2 groups. The experimental group consisted of 10 molars from head-and-neck cancer patients submitted to radiotherapy with total doses that ranged from 50 to 70 Gy. Ten molars from patients who did not receive radiotherapy were matched with experimental-group samples by anatomic tooth group and comprised the control group. To perform a macroscopic analysis, standardized photos of different enamel faces were taken with a camera. Teeth were subjected to longitudinal cuts and hand polished to a final thickness of 0.1 mm. Enamel was analyzed under polarized light microscopy, and optical retardation values of birefringence were calculated in cervical, cusp, and occlusal pit areas. Subsequently, the same enamel areas were analyzed by scanning electron microscopy. Data from optical retardation values were statistically analyzed by 2-way ANOVA and Fisher's test (α < 0.05). Results: No macroscopic differences were observed between the irradiated and control groups. Polarized light microscopy analysis revealed that cervical enamel exhibited darker areas characterized by discrete birefringence patterns compared to the control enamel. Optical retardation values were only significantly different in the cervical enamel of the irradiated and control groups (p < 0.0001). Scanning electron microscopy analysis revealed more evident interprismatic spaces in the cervical and outer cusp enamel of irradiated samples. Conclusions: Head-and-neck radiotherapy reduced optical retardation values of birefringence in cervical enamel, and the interprismatic spaces became more evident.

Picrosirius Red and Polarization Microscopy - A Tool for Gender Differentiation.

Forensic dentistry is a branch of dentistry which in collaboration with legal profession serves an important role to maintain justice system of a country. Forensic dentists play a major role in identification of an individual. Within the literature various methods have been found to be useful in gender differentiation. An attempt was made for differentiation of gender using picrosirius red and polarization microscopy. To evaluate picrosirius red and polarization microscopy as a tool for gender differentiation by observing birefringence pattern and distribution of thick and thin collagen fibers in males and females. Labial mucosal tissue obtained from 30 deceased individuals (18 male and 12 female) during autopsy was fixed in 10% formalin at 12th hour. Tissue was processed, sectioned and stained using picrosirius red stain and the birefringence pattern of collagen fibers were studied with polarization microscope. The results were statistically analyzed using Z-test and one-way ANOVA to draw the significance. The proportion of thick and thin fibres among males and females were compared. It was found that there was statistically significant difference in proportion of thick and thin fibers between male and female. Thick fibres in males were (78.13%) more than females (65.74%) and thin fibres were more in females (34.24%) than males (21.32%). Picrosirius red and polarization microscopy may be used as a tool for gender differentiation. Yet the manner of death has to be considered during gender differentiation using this method, as in the present study out of 30 cases studied three cases of death due to debilitating diseases and poison consumption showed altered collagen distribution.

Differential diagnosis of periapical cyst using collagen birefringence pattern of the cyst wall.

ObjectivesPeriapical lesions, including periapical cyst (PC), periapical granuloma (PG), and periapical abscess (PA), are frequently affected by chemical/physical damage during root canal treatment or severe bacterial infection, and thus, the differential diagnosis of periapical lesions may be difficult due to the presence of severe inflammatory reaction. The aim of this study was to make differential diagnosis among PC, PG, and PA under polarizing microscope.Materials and MethodsThe collagen birefringence patterns of 319 cases of PC (n = 122), PG (n = 158), and PA (n = 39) obtained using a polarizing microscope were compared. In addition, 6 cases of periodontal fibroma (PF) were used as positive controls.ResultsCollagen birefringence was condensed with a thick, linear band-like pattern in PC, but was short and irregularly scattered in PG, and scarce or absent in PA. PF showed intense collagen birefringence with a short, palisading pattern but no continuous band-like pattern. The linear band-like birefringence in PC was ascribed to pre-existing expansile tensile stress of the cyst wall.ConclusionsIn this study all PCs (n = 122) were distinguishable from PGs and PAs by their characteristic birefringence, despite the absence of lining epithelium (n = 20). Therefore, the authors suggest that the presence of linear band-like collagen birefringence of the cyst wall aids the diagnostic differentiation of PC from PG and PA.

Effect of melt spinning conditions on the fiber structure development of polyethylene terephthalate

The effects of spinning conditions on fiber properties are not well explained by the fiber structures because the birefringence, crystallinity, and SAXS patterns are often similar. In this study, the effects on the fiber structure development of polyethylene terephthalate after necking was analyzed by simultaneous WAXD/SAXS measurements. An X-shaped SAXS pattern was observed for all fibers drawn at the minimum draw ratio. In contrast, by drawing under a drawing stress of 100 MPa, the strong diffraction of the smectic phase and an obviously larger long period less than 1 ms after necking were observed for fibers spun at 500–1500 m/min, while almost no smectic phase was observed for fibers spun at 2000 m/min. A higher crystallization rate and clear draw ratio dependence of crystallization rate were also observed for the fiber spun at 2000 m/min. The clear differences in structure development can explain their differences in tensile strength and thermal shrinkage.

Cracks in Polymer Spherulites: Phenomenological Mechanisms in Correlation with Ring Bands

This article reviews possible mechanisms of various crack forms and their likely correlations with interior crystal lamellae and discontinuous interfaces in spherulites. Complex yet periodically repetitive patterns of cracks in spherulites are beyond attributions via differences in thermal expansion coefficients, which would cause random and irregular cracks in the contract direction only. Cracks in brittle polymers such as poly(l-lactic acid) (PLLA), or poly(4-hydroxyl butyrate) (PHB), or more ductile polymers such as poly(trimethylene terephthalate) (PTT) are examined and illustrated, although for focus and demonstration, more discussions are spent on PLLA. The cracks can take many shapes that bear extremely striking similarity to the ring-band or lamellar patterns in the same spherulites. Crack patterns may differ significantly between the ring-banded and ringless spherulites, suggesting that the cracks may be partially shaped and governed by interfaces of lamellae and how the lamellar crystals assemble themselves in spherulites. Similarly, with some exceptions, most of the cracks patterns in PHB or PTT are also highly guided by the lamellar assembly in either ring-banded spherulites or ringless spherulites. Some exceptions of cracks in spherulites deviating from the apparent crystal birefringence patterns do exist; nevertheless, discontinuous interfaces in the initial lamellae neat the nuclei center might be hidden by top crystal over-layers of the spherulites, which might govern crack propagation.