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Ivan I Smalyukh - One of the best experts on this subject based on the ideXlab platform.
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fluorescence confocal Polarizing Microscopy of a fluorescent bent core liquid crystal exhibiting polarization splay modulated b7 structures and defects
ChemPhysChem, 2015Co-Authors: Matt Oneill, Rajdeep Deb, Nandiraju V S Rao, Noel A Clark, Ivan I SmalyukhAbstract:The B7 phases of bent-core molecules are polarization splay modulated fluid smectics that exhibit an unusually complex variety of exotic macroscopic structures, textures, and defects visible in polarized light Microscopy. Herein we describe optical studies of these structures using fluorescence confocal Polarizing Microscopy (FCPM) and depolarized transmission optical Microscopy to probe their organization in three dimensions. These experiments utilize recently reported fluorescent bent-core molecules designed to give strong polarized fluorescence. This new bent-core molecular family provides the means for probing a variety of bent-core phases and structures by using FCPM and multiphoton fluorescence nonlinear imaging techniques. Comparative textural analysis of the B7 structures obtained using different types of imaging and the corresponding structural models are discussed.
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multimodal nonlinear optical Polarizing Microscopy of long range molecular order in liquid crystals
Optics Letters, 2010Co-Authors: Taewoo Lee, Rahul P Trivedi, Ivan I SmalyukhAbstract:We demonstrate orientation-sensitive multimodal nonlinear optical Polarizing Microscopy capable of probing orientational, polar, and biaxial features of mesomorphic ordering in soft matter. This technique achieves simultaneous imaging in broadband coherent anti-Stokes Raman scattering, multiphoton excitation fluorescence, and multiharmonic generation Polarizing Microscopy modes and is based on the use of a single femtosecond laser and a photonic crystal fiber as sources of the probing light. We show the viability of this technique for mapping of three-dimensional patterns of molecular orientations and show that images obtained in different Microscopy modes are consistent with each other.
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defects surface anchoring and three dimensional director fields in the lamellar structure of cholesteric liquid crystals as studied by fluorescence confocal Polarizing Microscopy
Topology in Condensed Matter, 2006Co-Authors: Ivan I Smalyukh, Oleg D LavrentovichAbstract:We study three-dimensional director patterns and defects in cholesteric liquid crystals using fluorescence confocal Polarizing Microscopy for nondestructive three-dimensional imaging. We establish the detailed director fields of dislocations, their kinks, as well as the disclination nodes and oily streaks. Weak surface anchoring of the director at the bounding plates causes attraction, while strong anchoring causes repulsion between the edge dislocation and a boundary. We use a coarse-grained models of cholesteric elasticity and surface anchoring potential to explain the experimental results. We study dynamics of defects, and glide and climb of dislocations. We also consider the Peierls-Nabarro mechanisms hindering glide of dislocations across the cholesteric layers. The static and dynamic properties of defects in cholesteric lamellae can be used as a model for understanding similar phenomena in other lamellar systems, such as diblock copolymers and SmA liquid crystals.
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optical trapping of colloidal particles and measurement of the defect line tension and colloidal forces in a thermotropic nematic liquid crystal
Applied Physics Letters, 2005Co-Authors: Ivan I Smalyukh, A N Kuzmin, Aliaksandr V Kachynski, Paras N Prasad, Oleg D LavrentovichAbstract:We demonstrate optical trapping and manipulation of transparent microparticles suspended in a thermotropic nematic liquid crystal with low birefringence. We employ the particle manipulation to measure line tension of a topologically stable disclination line and to determine colloidal interaction of particles with perpendicular surface anchoring of the director. The three-dimensional director fields and positions of the particles manipulated by laser tweezers are visualized by fluorescence confocal Polarizing Microscopy.
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free standing films of twist grain boundary tgba and utgbc liquid crystals studied by fluorescence confocal Polarizing Microscopy
Liquid Crystals, 2003Co-Authors: Ivan I Smalyukh, Oleg D Lavrentovich, R Pratibha, N V MadhusudanaAbstract:The director structures, meniscus profile, and defects in free-standing films of the twist grain boundary TGBA and UTGBC* liquid crystals were studied. The films were characterized by a combination of Polarizing Microscopy and fluorescence confocal Polarizing Microscopy. Five principal regions of meniscus were distinguished. When film thickness in the meniscus is much smaller then the TGB pitch, there is no difference between the free-standing films of TGB and ordinary smectic A liquid crystals. When the film thickness is larger than the TGB pitch, filamentary texture is observed. The 3D director pattern of the filaments are similar to the ground state director fields of TGBA and UTGBC* liquid crystals. In the intermediate thickness region of the meniscus, when the film thickness and TGB pitch are commensurate, a unique radial pattern is observed. Based on the fluorescence confocal Polarizing Microscopy studies of the director field, we propose a model for the 3D director structure in this part of the men...
Oleg D Lavrentovich - One of the best experts on this subject based on the ideXlab platform.
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defects surface anchoring and three dimensional director fields in the lamellar structure of cholesteric liquid crystals as studied by fluorescence confocal Polarizing Microscopy
Topology in Condensed Matter, 2006Co-Authors: Ivan I Smalyukh, Oleg D LavrentovichAbstract:We study three-dimensional director patterns and defects in cholesteric liquid crystals using fluorescence confocal Polarizing Microscopy for nondestructive three-dimensional imaging. We establish the detailed director fields of dislocations, their kinks, as well as the disclination nodes and oily streaks. Weak surface anchoring of the director at the bounding plates causes attraction, while strong anchoring causes repulsion between the edge dislocation and a boundary. We use a coarse-grained models of cholesteric elasticity and surface anchoring potential to explain the experimental results. We study dynamics of defects, and glide and climb of dislocations. We also consider the Peierls-Nabarro mechanisms hindering glide of dislocations across the cholesteric layers. The static and dynamic properties of defects in cholesteric lamellae can be used as a model for understanding similar phenomena in other lamellar systems, such as diblock copolymers and SmA liquid crystals.
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optical trapping of colloidal particles and measurement of the defect line tension and colloidal forces in a thermotropic nematic liquid crystal
Applied Physics Letters, 2005Co-Authors: Ivan I Smalyukh, A N Kuzmin, Aliaksandr V Kachynski, Paras N Prasad, Oleg D LavrentovichAbstract:We demonstrate optical trapping and manipulation of transparent microparticles suspended in a thermotropic nematic liquid crystal with low birefringence. We employ the particle manipulation to measure line tension of a topologically stable disclination line and to determine colloidal interaction of particles with perpendicular surface anchoring of the director. The three-dimensional director fields and positions of the particles manipulated by laser tweezers are visualized by fluorescence confocal Polarizing Microscopy.
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fluorescence confocal Polarizing Microscopy three dimensional imaging of the director
Pramana, 2003Co-Authors: Oleg D LavrentovichAbstract:Much of the modern understanding of orientational order in liquid crystals (LCs) is based on Polarizing Microscopy (PM). A PM image bears only two-dimensional (2D) information, integrating the 3D pattern of optical birefringence over the path of light. Recently, we proposed a technique to image 3D director patterns by fluorescence confocal Polarizing Microscopy (FCPM). The technique employs the property of LC to orient the fluorescent dye molecules of anisometric shape, added in small quantities to the LC. In LC, smooth director deformations do not alter mass density of the material. Thus the density of dye is also uniform across the sample, except, perhaps, near the surfaces or at the cores of topological defects. In polarized light, the measured fluorescence signal is determined by the spatial orientation of the molecules rather than by dye concentration (as in regular biological samples stained with tissue-specific dyes). The contrast is enhanced when both excitation and detection of fluorescence light are performed in polarized light. This short review describes the essence of FCPM technique and illustrates some of its applications, including imaging of Frederiks electric-field induced effect in a nematic LC and defects such as dislocations in cholesteric LCs.
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free standing films of twist grain boundary tgba and utgbc liquid crystals studied by fluorescence confocal Polarizing Microscopy
Liquid Crystals, 2003Co-Authors: Ivan I Smalyukh, Oleg D Lavrentovich, R Pratibha, N V MadhusudanaAbstract:The director structures, meniscus profile, and defects in free-standing films of the twist grain boundary TGBA and UTGBC* liquid crystals were studied. The films were characterized by a combination of Polarizing Microscopy and fluorescence confocal Polarizing Microscopy. Five principal regions of meniscus were distinguished. When film thickness in the meniscus is much smaller then the TGB pitch, there is no difference between the free-standing films of TGB and ordinary smectic A liquid crystals. When the film thickness is larger than the TGB pitch, filamentary texture is observed. The 3D director pattern of the filaments are similar to the ground state director fields of TGBA and UTGBC* liquid crystals. In the intermediate thickness region of the meniscus, when the film thickness and TGB pitch are commensurate, a unique radial pattern is observed. Based on the fluorescence confocal Polarizing Microscopy studies of the director field, we propose a model for the 3D director structure in this part of the men...
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three dimensional director structures of defects in grandjean cano wedges of cholesteric liquid crystals studied by fluorescence confocal Polarizing Microscopy
Physical Review E, 2002Co-Authors: Ivan I Smalyukh, Oleg D LavrentovichAbstract:We use a nondestructive technique of fluorescence confocal Polarizing Microscopy to visualize three-dimensional director patterns of defects in Grandjean-Cano wedges filled with a cholesteric liquid crystal of pitch p=5 microm. Strong surface anchoring of the director causes a stable lattice of dislocations in the bulk. Optical slicing in the vertical cross sections of the wedges allows us to establish the detailed structure of dislocations and their kinks. Dislocations of Burgers vector b=p/2 are located in the thin part of the sample, very close to the bisector plane. Their cores are split into a pair of tau(-1/2) and lambda(+1/2) disclinations. Pairs of lambda(-1/2) and tau(+1/2) disclinations are observed when the b=p/2 dislocation forms a kink. The kinks along the b=p/2 dislocations change the level of dislocations by +/-p/4 and +/-p/2; these kinks are confined to the glide plane and are very long, (5-10) p. Above some critical thickness h(c) of the wedge sample, the dislocations are of Burgers vector b=p. They are often found away from the bisector plane. The core of b=p dislocations is split into a pair of nonsingular lambda(-1/2) and lambda(+1/2) disclinations. The kinks along the b=p dislocation are of a typical size p and form cusps in the direction perpendicular to the glide plane. At the cusp, lambda(-1/2) and lambda(+1/2) disclinations interchange ends. Other defect structures inlude "Lehmann clusters," i.e., dislocations of zero Burgers vector formed by two lambda(-1/2) and two lambda(+1/2) disclinations and dislocations of nonzero Burgers vector with a core split into more than two disclinations. We employ the coarse-grained Lubensky-de Gennes model of the cholesteric phase to describe some of the observed features. We calculate the elastic energy of a dislocation away from the core, estimate the energy of the core split into disclinations of different types, study the effect of finite sample thickness on the dislocations energy, and calculate the Peach-Koehler elastic forces that occur when a dislocation is shifted from its equilibrium position. Balance of the dilation/compression energy in the wedge and the energy of dislocations defines the value of h(c) and allows to estimate the core energy of the dislocations. Finally, we consider the Peierls-Nabarro mechanisms hindering glide of dislocations across the cholesteric layers. Because of the split disclination character of the core, glide is difficult as compared to climb, especially for b=p dislocations.
Simarjeev Singh - One of the best experts on this subject based on the ideXlab platform.
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evaluation of collagen in leukoplakia oral submucous fibrosis and oral squamous cell carcinomas using Polarizing Microscopy and immunohistochemistry
Asian Pacific Journal of Cancer Prevention, 2018Co-Authors: Krishna Singh Arora, Amit Nayyar, Prabhpreet Kaur, Karandeep Singh Arora, Ankur Goel, Simarjeev SinghAbstract:Objectives: Picrosirius red and MMP are capable of degrading extracellular matrix proteins, expressed in lesions such as squamous cell carcinomas. The present study was undertaken with an aim to analyze and compare changes in collagen using Picrosirius red staining under Polarizing Microscopy and immunohistochemical staining using anti MMP-13 in samples of oral leukoplakia, oral submucous fibrosis and oral squamous cell carcinoma. Materials and Methods: A total of 70 slides were prepared and divided into 3 groups. Group I comprised 10 slides of normal gingival tissue, Group II 40 slides of potentially malignant disorders and Group III 20 slides of well differentiated oral squamous cell carcinoma. Half the slides for each group were stained with Picrosirius red stain and the remainder with antibodies to MMP-13. Rerults: In Group II, MMP-13 connective tissue expression was greater in OSMF as compared to leukoplakia. Group III showed elevated expression among 70% of cases. Picrosirius red staining in Group II cases, showed higher staining Yellow-Orange andGreen-Yellow mature fibers in OSMF than leukoplakia cases while in Group III, 50% OSCC cases showed Green-yellow stained immature thin fibers. Conclusion: In future, therapeutic measures targeted against MMP-13 may inhibit collagenolysis to some extent and delay spread of tumors. An easy and reliable method to determine the state of the stroma in such cases may be Picrosirius red staining with Polarizing Microscopy.
Dan Dayan - One of the best experts on this subject based on the ideXlab platform.
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collagen fibres in the wall of odontogenic keratocysts a study with picrosirius red and Polarizing Microscopy
Journal of Oral Pathology & Medicine, 2008Co-Authors: A Hirshberg, Amos Buchner, Sima Sherman, Dan DayanAbstract:The collagen in the walls of 15 keratocysts was studied histochemically by staining sections with picrosirius red and examining them with Polarizing Microscopy. This was compared to 15 cases of dentigerous cyst and 15 cases of radicular cyst. Polarization colours of the collagen fibres were recorded according to their width. No differences were found between the polarization colours of thin fibres (<0.8 microm) in all three lesions; the polarization colours of thick fibres (1.6-2.4 microm) in keratocysts were significantly more greenish-yellow when compared with those of dentigerous cysts and radicular cysts. The staining of the collagen fibres in the keratocysts is similar to that reported in odontogenic neoplasms, which suggests that the stroma of keratocysts could be regarded not just as a structural support of the cyst wall, but as playing a part in the neoplastic behaviour of the cyst.
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stromal differences in salivary gland tumors of a common histopathogenesis but with different biological behavior a study with picrosirius red and Polarizing Microscopy
Acta Histochemica, 2006Co-Authors: Irit Allon, Amos Buchner, Marilena Vered, Dan DayanAbstract:Summary Salivary gland neoplasms – pleomorphic adenoma, polymorphous low-grade adenocarcinoma, and adenoid cystic carcinoma – share a common histogenetic trait, but differ markedly in their biological properties. The objective of the study was to assess the polarization colors of picrosirius red-stained stromal collagen fibers in these salivary gland neoplasms to evaluate their possible role in the histopathogenesis of the tumors and to evaluate the potential usefulness of this approach as a diagnostic tool. Ten cases of each tumor type and 10 cases of mucous extravasation phenomenon (control) were examined using picrosirius red staining and Polarizing Microscopy. In each case, at least 50 thin (∼0.8 μm) and 50 thick (1.6–2.4 μm) collagen fibers were counted and classified as green-yellow or yellow-orange, the mean percentage was calculated and statistical differences analyzed by one-way ANOVA. Results showed a similar thin fiber distribution in all tumor types and controls (82–88% green-yellow, 12–18% yellow-orange, p >0.05). Thick fibers showed a different distribution in polymorphous low-grade adenocarcinoma and adenoid cystic carcinoma (approximately 50% green-yellow) compared to pleomorphic adenoma and mucous extravasation phenomenon (approximately 13% green-yellow) ( p =0.001). Thick fiber distribution was similar in polymorphous low-grade adenocarcinoma and adenoid cystic carcinoma ( p >0.05). We conclude that with picrosirius red staining and Polarizing Microscopy, stromal collagen fibers differ significantly in pleomorphic adenoma from those in polymorphous low-grade adenocarcinoma and adenoid cystic carcinoma, but not from mucous extravasation phenomenon. Similarity between polymorphous low-grade adenocarcinoma and adenoid cystic carcinoma may indicate that these tumor types represent a single entity with a broad spectrum of biological behavior.
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the central odontogenic fibroma and the hyperplastic dental follicle study with picrosirius red and Polarizing Microscopy
Journal of Oral Pathology & Medicine, 1996Co-Authors: A Hirshberg, Amos Buchner, Dan DayanAbstract:The central odontogenic fibroma (COF) is an uncommon odontogenic tumor in which the microscopic appearance is similar to that of the hyperplastic dental follicle (HDF). Distinction between these lesions is based mainly on their clinical and radiologic features. The collagen of 5 cases of COF and 13 cases of HDF was studied histochemically by staining sections with Picrosirius red and examining them by Polarizing Microscopy. Polarization colors of the collagen fibers of the lesions were recorded according to their width. While no differences were seen between the polarization colors of thin fibers (< 0.8 mm) in both lesions, the polarization colors of thick fibers (1.6–2 mm) of COF were significantly more green and greenish-yellow as compared with those of HDF. These findings suggest that the Picrosirius red polarization method can be used as a diagnostic tool to differentiate between COF and HDF.
Ingo Dierking - One of the best experts on this subject based on the ideXlab platform.
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textures of liquid crystals
2003Co-Authors: Ingo DierkingAbstract:Preface.Foreword. 1. Introduction.2. Surface Anchoring and Elasticity.3. Polarizing Microscopy.4. The Blue Phases.5. The Nematic and Cholesteric Phases.6. Twist Grain Boundary Phases.7. The Fluid Smectic Phases.8. The SmC Subphases.9. The Hexatic Phases.10. Soft Crystal Phases and Crystallization.11. Other Liquid Crystal Phases.Appendix A.Appendix B.Color Plates.Index.
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fluorescence confocal Polarizing Microscopy imaging liquid crystal director fields in three dimensions
ChemPhysChem, 2001Co-Authors: Ingo DierkingAbstract:Conventional Polarizing Microscopy allows only information from two dimensions, on account of optical integration along the path of light propagation. Real three-dimensional imaging of orientational order has now become possible with fluorescence confocal Polarizing Microscopy. This technique provides a useful tool in the visualization of director fields in liquid crystal cells, as schematically shown in the picture, and will be of great potential in the study of director distributions in defect structures of anisotropic fluids.
