Measurements of the splay and bend elastic constants of octyl-cyano biphenyl near the nematic-sme... more Measurements of the splay and bend elastic constants of octyl-cyano biphenyl near the nematic-smectic A transition are presented. The pretransitional increase of obeys the relation iSK^ ^ (T-T v , with V = 1. АННОТАЦИЯ Были измерены константы упругости деформации поперечного и продольного изгиба на октил-циано-бифениле. Вблизи нематико-смектического перехода уве личивается по закону <5К^ (Т-Т^) , где v-1. KIVONAT Oktil-ciano bifenil feszitési és hajlitási rugalmas állandóját mér tük a nematikus-szmektikusA átmenet közelében. K, növekedése a fázisátmenet közelében a SK^ ^ (т-Tg^) , \ > = 1 összefüggésnek tesz eleget.
Instabilities are discussed which take place when a nematic liquid crystal (LC) layer, enclosed b... more Instabilities are discussed which take place when a nematic liquid crystal (LC) layer, enclosed between a planar reference plate and a photosensitive substrate, is illuminated with polarized light from the reference side (reverse geometry). The dependence of the observed effects on the wavelength, polarization direction of the light, and on the thickness of the LC layer is explained by a model based on photoinduced surface torque. The application possibilities of the phenomena are also explored.
In this communication, we summarise our results related to light-induced orientational phenomena ... more In this communication, we summarise our results related to light-induced orientational phenomena at liquid crystal–polymer interfaces. We investigated photoalignment for various nematics at the interface with the photosensitive polymer layer polymethyl methacrilate functionalised with azo dye Disperse Red 1. It was found that the efficiency of photoalignment exhibits marked differences depending on the structure of the rigid core of the liquid crystal molecules. It was demonstrated that the photo-orientation process is also significantly affected by the type of mesophase in which irradiation is carried out. The observations highlight the importance of the mutual influence of the polymer and the liquid crystal in light-induced processes.
AbstractInvestigating the symmetry properties of compensated chiral liquid crystals we point out ... more AbstractInvestigating the symmetry properties of compensated chiral liquid crystals we point out that the macroscopic description suggested recently by Pleiner and Brand1 can not be applied for these materials. We also discuss the hysteresis of the homeotropic to fingerprint texture transition in compensated cholesterics and its consequence on the measurement of the temperature dependence of the pitch.
We provide experimental evidence for the influence of the molecular structure of the nematic liqu... more We provide experimental evidence for the influence of the molecular structure of the nematic liquid crystal (NLC) on the photoalignment process in three dimensions at the interface with a polymer layer. In particular, the experimental findings are explained through the presence (or absence) of the π−π aromatic interactions between the NLC and the polymer. The influence of the nematic-to-smectic A phase transition on the photocontrol is also addressed. Furthermore, we demonstrate that the photo-induced reorientation scenarios can be eventually connected to conformational changes in the photosensitive polymer.
We provide experimental evidence that photoalignment at the nematic liquid crystal (NLC)-polymer ... more We provide experimental evidence that photoalignment at the nematic liquid crystal (NLC)-polymer interface can not be simply considered as a twodimensional process. Moreover, our experiments clearly indicate that the photoaligning process does not depend on the individual properties of the NLC material and those of the interfacing polymer exclusively. According to our measurements, the polymer and the NLC layer "sense-each-other", i.e., the polymer-liquid crystal interface should be regarded as a coupled system, where the two components mutually influence each other. Furthermore, we show that the temperature induced anchoring transition also has to be taken into account for the complete description of the photoalignment mechanism.
In-plane periodic modulation of the director field of an initially homeotropic liquid crystal lay... more In-plane periodic modulation of the director field of an initially homeotropic liquid crystal layer with negative dielectric anisotropy is studied in external electric field with time varying amplitude envelope. Periodically turning a low frequency electric field on and off the cell, an in-plane periodic modulation of the director develops with a length scale that is orders of magnitude larger than the cell gap and can be as large as couple of centimetres. Doping the liquid crystal layer with low concentration of dichroic dye allows easy mapping of the director. We show that the periodic pattern is a periodic arrangement of +1 and −1 point defects, so called 'umbilics'. We argue that the in-plane direction of the director is governed by the local flow that accompanies the turn on and off of the electric field. The finite size and the shape of the cell, incompressibility constraint and the nature of the surface alignment material, all together with the flow, are ultimately responsible for the development of the observed periodic director modulation.
The threshold intensity for the laser induced deformation of nematic liquid crystals is calculate... more The threshold intensity for the laser induced deformation of nematic liquid crystals is calculated as a function of the spot size ot the il luminating beam. It is shown, that due to the small size of the light spot, the optical threshold is higher than that expected from the Fredericks threshold formula for static electric fields of infinite large dimension in the cell plane. Experimental data measured on a homeotrop OCB /octyl-cyano-byphenyl/ sample fit well the theoretical curve. Results obtained on the temperature and wavelength dependence of the threshold can be interpreted on the basis of the given theory.
In a planar liquid crystal sample sandwiched between a photosensitive and a reference plate insta... more In a planar liquid crystal sample sandwiched between a photosensitive and a reference plate instabilities occurred, when the cell was illuminated from the reference side. The instabilities were induced both by polarized white light source and monochromatic laser beams. Static and dynamic regimes were found; for laser irradiation dynamic instability was found only in a range of polarization directions. A model, developed for monochromatic excitation, predicts that at certain thicknesses dynamic instability is forbidden. Experiments on a wedge-like cell confirmed this conclusion.
The optical reorientation process in nematic guest-host mixtures is investigated. It is found tha... more The optical reorientation process in nematic guest-host mixtures is investigated. It is found that for certain dyes the optical Freedericksz threshold is two orders of magnitude lower as in the pure host. The observations can be interpreted in terms of an enhanced optical torque which increases with the dye concentration.
We explore periodic structures of smectic-C (SmC) liquid crystals, induced optically by a polariz... more We explore periodic structures of smectic-C (SmC) liquid crystals, induced optically by a polarization grating. The studied cells contain a passive surface of rubbed polyimide and an active photosensitive substrate of azo-dye doped polyimide. In a nematic phase the director field can be periodic independent of the angle between the grating vector and the rubbing direction. In the SmA phase periodic structure can be induced only by layer undulations. The SmC behaves similarly to the nematic phase, but the director can rotate only on a cone, which results in a more complex geometry. The periodic pattern is superimposed with four different director and layer structures. In spite of the coexistence of the nonuniform structures the diffraction efficiency is better in the SmC, than in the nematic phase.
Liquid Crystals: Physics, Technology, and Applications, 1998
In this paper some electrooptic properties such as the spontaneous polarization Ps, and tilt angl... more In this paper some electrooptic properties such as the spontaneous polarization Ps, and tilt angle and dielectric measurements are described for a novel ternary ferroelectric liquid crystal mixture based alkoxyphenyl esters and alkoxy- benzoic acids. A theory of dielectric response is presented and the suggested model is in good accordance with the values of elastic constant and switching time respectively.
The electric field of a CW laser beam can reorient a nematic liquid crystal. Experiments on the i... more The electric field of a CW laser beam can reorient a nematic liquid crystal. Experiments on the influence of a superposed quasistatic electric field are reported showing that this can reinforce or weaken the laser induced reorientation depending on the substance and geometry.
Condensed Matter Physics is certainly one of the scientific disciplines presently characterized b... more Condensed Matter Physics is certainly one of the scientific disciplines presently characterized by a high rate of growth, both qualitatively and quantitatively. As a matter of fact, being updated on several topics is getting harder and harder, especially for junior scientists. Thus, the requirement of providing the readers with a reliable guide into the forest of printed matter, while recovering in the original form some fundamental papers suggested us to edit critical selections on appealing subjects. In particular, the present Series is conceived to fill a cultural and professional gap between University graduate studies and current research frontiers. To this end each volume provides the reader with a critical selection of reprinted papers on a specific topic, preceded by an introduction setting the historical view and the state of art. The choice of reprints and the perspective given in the introduction is left to the expert who edits the volume, under the full responsibility of the Editorial Board of the Series. Thus, even though an organic approach to each subject is pursued, some important papers may be omitted just because they lie outside the editor's goal.
Zárójelentés a "Folyadékkristályok és polimerek kölcsönhatása" c. OTKA pályázathoz A pályázat sor... more Zárójelentés a "Folyadékkristályok és polimerek kölcsönhatása" c. OTKA pályázathoz A pályázat során elvégzett munkák elsősorban az előre megadott témakörhöz kapcsolódtak. Emellett néhány olyan vizsgálatot is végeztünk, amelyek nem szerepeltek az előzetes tervben, ezekre nemtzetközi együttműködés keretében került sor. Módszer az azimutális kötési energia mérésére [1] Polimer felületeken a folyadékkristály beáll valamilyen, a polimer szerkezete által meghatárotott irányba. Mágneses analógia alapján ezt az irányt "könnyű tengely"-nek (easy axis) nevezik. Amennyiben a folyadékkristályt tér hatásának tesszük ki, a direktortér a minta belsejében erősen deformálódik. Számos esetben feltételezik, hogy folyadékkristály felületi orientációja eközben nem változik. Ez a feltevés azonban csak közelitőleg igaz, valójában a felületen is elfordul a direktor a könnyű tengelytől. Ennek az elfordulásnak a mérésére dolgoztunk ki igen érzékeny módszert.
A comprehensive study of laser induced optical anisotropy in amorphous GeSe2 films is presented. ... more A comprehensive study of laser induced optical anisotropy in amorphous GeSe2 films is presented. This anisotropic structure of the amorphous network can be reoriented reversibly by changing the incident beam polarisation. A model is constructed which accounts for experimental findings, in particular for the logarithmic time development of the laser induced anisotropy. АННОТАЦИЯ В статье подробно рассматривается оптическая анизотропия, вызыванная под действием лазерной обработки в аморфных пленках с составом GeSe2. Анизо тропная структура аморфного материала может быть обратимо переориентирована при помощи изменения поляризации возбжденного лазера. Была создана модель, с помощью которой хорошо объясняются полученные экспериментальные данные, особенно логарифмическая зависимость двойного преломления от времени. KIVONAT A cikkben az amorf GeSe2 vékonyrétegekben lézerrel indukált optikai anizotrópiát vizsgáljuk meg részletesen. Ez az anizotrop szerkezet reverzibi lisen átorientálható a bemenő lézerfény polarizációjának változtatásával. Meg adunk egy modellt, amely megmagyarázza a kísérleti eredményeket, többek között az indukált kettőstörés logaritmikus időfüggését.
Reorientation cycles of photo-induced anisotropy in an amorphous chalcogenide film have been inve... more Reorientation cycles of photo-induced anisotropy in an amorphous chalcogenide film have been investigated. The kinetics of the reorientation process show a simple power-law time dependence on short time scale. A model based on bistable defect centres with widely distributed relaxation times is proposed. It is speculated that excitations from or to the band tails might be involved in the reorientation
We use a molecular-motor model previously proposed for a nematic cell with an azo-dye monolayer t... more We use a molecular-motor model previously proposed for a nematic cell with an azo-dye monolayer to calculate the director orientation when light is normally impinged on the cell. We consider an initial planar configuration for which one of the surrounding plates, which we call the reference plate, is submitted to a hard-anchoring boundary condition. The other confining plate has a coating monolayer of azo-dye molecules such that the change of the orientation of azo-dye isomers, due to light, causes changes in the nematic director. The boundary conditions on both plates along with the optical field determine the director configuration in the bulk. The existence of periodic solutions for the density of isomers in trans and cis states, corresponding to weak optical fields, has been discussed in the literature. Using a similar approach, we find an approximate expression for the density of isomers, written in terms of the director angle, which allows us to close the equation for the director configuration on the boundary having a photosensitive plate. We decouple the director's angle and the isomer densities by assuming extremely different temporal time scales between them. We show for a given sample that switching times inversely depend on the trans-cis transition rate of photoexcitation whereas relaxation times do not depend on it. On the other hand, switching and relaxation times linearly depend on effective surface viscosity values. Our model allows us to estimate surface viscosity values.
Magnetic field induced reorientation of nematic liquid crystals on polymer layers is studied near... more Magnetic field induced reorientation of nematic liquid crystals on polymer layers is studied near the glass transition temperature of the polymer. Kinetic curves for different field strengths and temperatures are presented. A model is developed, which takes into account the structural rearrangements in the polymer induced by its interaction with the anisotropic potential of the liquid crystal. Simulations based on the model are in good quantitative agreement with the experimental data.
Liquid crystal layers sandwiched between a reference plate and a photosensitive substrate were in... more Liquid crystal layers sandwiched between a reference plate and a photosensitive substrate were investigated. We focused on the reverse geometry, where the cell was illuminated by a laser beam from the reference side. In planar cells instabilities occurred, static and dynamic ones, depending on the angle between the laser polarization and the director orientation on the reference plate. In cells where the molecules were aligned along the normal of the reference plate, dynamic pattern was observed at all angles of polarization. A simple model based on a photo-induced surface torque gives account of the findings. Light scattering studies revealed some basic properties of the instabilities.
Measurements of the splay and bend elastic constants of octyl-cyano biphenyl near the nematic-sme... more Measurements of the splay and bend elastic constants of octyl-cyano biphenyl near the nematic-smectic A transition are presented. The pretransitional increase of obeys the relation iSK^ ^ (T-T v , with V = 1. АННОТАЦИЯ Были измерены константы упругости деформации поперечного и продольного изгиба на октил-циано-бифениле. Вблизи нематико-смектического перехода уве личивается по закону <5К^ (Т-Т^) , где v-1. KIVONAT Oktil-ciano bifenil feszitési és hajlitási rugalmas állandóját mér tük a nematikus-szmektikusA átmenet közelében. K, növekedése a fázisátmenet közelében a SK^ ^ (т-Tg^) , \ > = 1 összefüggésnek tesz eleget.
Instabilities are discussed which take place when a nematic liquid crystal (LC) layer, enclosed b... more Instabilities are discussed which take place when a nematic liquid crystal (LC) layer, enclosed between a planar reference plate and a photosensitive substrate, is illuminated with polarized light from the reference side (reverse geometry). The dependence of the observed effects on the wavelength, polarization direction of the light, and on the thickness of the LC layer is explained by a model based on photoinduced surface torque. The application possibilities of the phenomena are also explored.
In this communication, we summarise our results related to light-induced orientational phenomena ... more In this communication, we summarise our results related to light-induced orientational phenomena at liquid crystal–polymer interfaces. We investigated photoalignment for various nematics at the interface with the photosensitive polymer layer polymethyl methacrilate functionalised with azo dye Disperse Red 1. It was found that the efficiency of photoalignment exhibits marked differences depending on the structure of the rigid core of the liquid crystal molecules. It was demonstrated that the photo-orientation process is also significantly affected by the type of mesophase in which irradiation is carried out. The observations highlight the importance of the mutual influence of the polymer and the liquid crystal in light-induced processes.
AbstractInvestigating the symmetry properties of compensated chiral liquid crystals we point out ... more AbstractInvestigating the symmetry properties of compensated chiral liquid crystals we point out that the macroscopic description suggested recently by Pleiner and Brand1 can not be applied for these materials. We also discuss the hysteresis of the homeotropic to fingerprint texture transition in compensated cholesterics and its consequence on the measurement of the temperature dependence of the pitch.
We provide experimental evidence for the influence of the molecular structure of the nematic liqu... more We provide experimental evidence for the influence of the molecular structure of the nematic liquid crystal (NLC) on the photoalignment process in three dimensions at the interface with a polymer layer. In particular, the experimental findings are explained through the presence (or absence) of the π−π aromatic interactions between the NLC and the polymer. The influence of the nematic-to-smectic A phase transition on the photocontrol is also addressed. Furthermore, we demonstrate that the photo-induced reorientation scenarios can be eventually connected to conformational changes in the photosensitive polymer.
We provide experimental evidence that photoalignment at the nematic liquid crystal (NLC)-polymer ... more We provide experimental evidence that photoalignment at the nematic liquid crystal (NLC)-polymer interface can not be simply considered as a twodimensional process. Moreover, our experiments clearly indicate that the photoaligning process does not depend on the individual properties of the NLC material and those of the interfacing polymer exclusively. According to our measurements, the polymer and the NLC layer "sense-each-other", i.e., the polymer-liquid crystal interface should be regarded as a coupled system, where the two components mutually influence each other. Furthermore, we show that the temperature induced anchoring transition also has to be taken into account for the complete description of the photoalignment mechanism.
In-plane periodic modulation of the director field of an initially homeotropic liquid crystal lay... more In-plane periodic modulation of the director field of an initially homeotropic liquid crystal layer with negative dielectric anisotropy is studied in external electric field with time varying amplitude envelope. Periodically turning a low frequency electric field on and off the cell, an in-plane periodic modulation of the director develops with a length scale that is orders of magnitude larger than the cell gap and can be as large as couple of centimetres. Doping the liquid crystal layer with low concentration of dichroic dye allows easy mapping of the director. We show that the periodic pattern is a periodic arrangement of +1 and −1 point defects, so called 'umbilics'. We argue that the in-plane direction of the director is governed by the local flow that accompanies the turn on and off of the electric field. The finite size and the shape of the cell, incompressibility constraint and the nature of the surface alignment material, all together with the flow, are ultimately responsible for the development of the observed periodic director modulation.
The threshold intensity for the laser induced deformation of nematic liquid crystals is calculate... more The threshold intensity for the laser induced deformation of nematic liquid crystals is calculated as a function of the spot size ot the il luminating beam. It is shown, that due to the small size of the light spot, the optical threshold is higher than that expected from the Fredericks threshold formula for static electric fields of infinite large dimension in the cell plane. Experimental data measured on a homeotrop OCB /octyl-cyano-byphenyl/ sample fit well the theoretical curve. Results obtained on the temperature and wavelength dependence of the threshold can be interpreted on the basis of the given theory.
In a planar liquid crystal sample sandwiched between a photosensitive and a reference plate insta... more In a planar liquid crystal sample sandwiched between a photosensitive and a reference plate instabilities occurred, when the cell was illuminated from the reference side. The instabilities were induced both by polarized white light source and monochromatic laser beams. Static and dynamic regimes were found; for laser irradiation dynamic instability was found only in a range of polarization directions. A model, developed for monochromatic excitation, predicts that at certain thicknesses dynamic instability is forbidden. Experiments on a wedge-like cell confirmed this conclusion.
The optical reorientation process in nematic guest-host mixtures is investigated. It is found tha... more The optical reorientation process in nematic guest-host mixtures is investigated. It is found that for certain dyes the optical Freedericksz threshold is two orders of magnitude lower as in the pure host. The observations can be interpreted in terms of an enhanced optical torque which increases with the dye concentration.
We explore periodic structures of smectic-C (SmC) liquid crystals, induced optically by a polariz... more We explore periodic structures of smectic-C (SmC) liquid crystals, induced optically by a polarization grating. The studied cells contain a passive surface of rubbed polyimide and an active photosensitive substrate of azo-dye doped polyimide. In a nematic phase the director field can be periodic independent of the angle between the grating vector and the rubbing direction. In the SmA phase periodic structure can be induced only by layer undulations. The SmC behaves similarly to the nematic phase, but the director can rotate only on a cone, which results in a more complex geometry. The periodic pattern is superimposed with four different director and layer structures. In spite of the coexistence of the nonuniform structures the diffraction efficiency is better in the SmC, than in the nematic phase.
Liquid Crystals: Physics, Technology, and Applications, 1998
In this paper some electrooptic properties such as the spontaneous polarization Ps, and tilt angl... more In this paper some electrooptic properties such as the spontaneous polarization Ps, and tilt angle and dielectric measurements are described for a novel ternary ferroelectric liquid crystal mixture based alkoxyphenyl esters and alkoxy- benzoic acids. A theory of dielectric response is presented and the suggested model is in good accordance with the values of elastic constant and switching time respectively.
The electric field of a CW laser beam can reorient a nematic liquid crystal. Experiments on the i... more The electric field of a CW laser beam can reorient a nematic liquid crystal. Experiments on the influence of a superposed quasistatic electric field are reported showing that this can reinforce or weaken the laser induced reorientation depending on the substance and geometry.
Condensed Matter Physics is certainly one of the scientific disciplines presently characterized b... more Condensed Matter Physics is certainly one of the scientific disciplines presently characterized by a high rate of growth, both qualitatively and quantitatively. As a matter of fact, being updated on several topics is getting harder and harder, especially for junior scientists. Thus, the requirement of providing the readers with a reliable guide into the forest of printed matter, while recovering in the original form some fundamental papers suggested us to edit critical selections on appealing subjects. In particular, the present Series is conceived to fill a cultural and professional gap between University graduate studies and current research frontiers. To this end each volume provides the reader with a critical selection of reprinted papers on a specific topic, preceded by an introduction setting the historical view and the state of art. The choice of reprints and the perspective given in the introduction is left to the expert who edits the volume, under the full responsibility of the Editorial Board of the Series. Thus, even though an organic approach to each subject is pursued, some important papers may be omitted just because they lie outside the editor's goal.
Zárójelentés a "Folyadékkristályok és polimerek kölcsönhatása" c. OTKA pályázathoz A pályázat sor... more Zárójelentés a "Folyadékkristályok és polimerek kölcsönhatása" c. OTKA pályázathoz A pályázat során elvégzett munkák elsősorban az előre megadott témakörhöz kapcsolódtak. Emellett néhány olyan vizsgálatot is végeztünk, amelyek nem szerepeltek az előzetes tervben, ezekre nemtzetközi együttműködés keretében került sor. Módszer az azimutális kötési energia mérésére [1] Polimer felületeken a folyadékkristály beáll valamilyen, a polimer szerkezete által meghatárotott irányba. Mágneses analógia alapján ezt az irányt "könnyű tengely"-nek (easy axis) nevezik. Amennyiben a folyadékkristályt tér hatásának tesszük ki, a direktortér a minta belsejében erősen deformálódik. Számos esetben feltételezik, hogy folyadékkristály felületi orientációja eközben nem változik. Ez a feltevés azonban csak közelitőleg igaz, valójában a felületen is elfordul a direktor a könnyű tengelytől. Ennek az elfordulásnak a mérésére dolgoztunk ki igen érzékeny módszert.
A comprehensive study of laser induced optical anisotropy in amorphous GeSe2 films is presented. ... more A comprehensive study of laser induced optical anisotropy in amorphous GeSe2 films is presented. This anisotropic structure of the amorphous network can be reoriented reversibly by changing the incident beam polarisation. A model is constructed which accounts for experimental findings, in particular for the logarithmic time development of the laser induced anisotropy. АННОТАЦИЯ В статье подробно рассматривается оптическая анизотропия, вызыванная под действием лазерной обработки в аморфных пленках с составом GeSe2. Анизо тропная структура аморфного материала может быть обратимо переориентирована при помощи изменения поляризации возбжденного лазера. Была создана модель, с помощью которой хорошо объясняются полученные экспериментальные данные, особенно логарифмическая зависимость двойного преломления от времени. KIVONAT A cikkben az amorf GeSe2 vékonyrétegekben lézerrel indukált optikai anizotrópiát vizsgáljuk meg részletesen. Ez az anizotrop szerkezet reverzibi lisen átorientálható a bemenő lézerfény polarizációjának változtatásával. Meg adunk egy modellt, amely megmagyarázza a kísérleti eredményeket, többek között az indukált kettőstörés logaritmikus időfüggését.
Reorientation cycles of photo-induced anisotropy in an amorphous chalcogenide film have been inve... more Reorientation cycles of photo-induced anisotropy in an amorphous chalcogenide film have been investigated. The kinetics of the reorientation process show a simple power-law time dependence on short time scale. A model based on bistable defect centres with widely distributed relaxation times is proposed. It is speculated that excitations from or to the band tails might be involved in the reorientation
We use a molecular-motor model previously proposed for a nematic cell with an azo-dye monolayer t... more We use a molecular-motor model previously proposed for a nematic cell with an azo-dye monolayer to calculate the director orientation when light is normally impinged on the cell. We consider an initial planar configuration for which one of the surrounding plates, which we call the reference plate, is submitted to a hard-anchoring boundary condition. The other confining plate has a coating monolayer of azo-dye molecules such that the change of the orientation of azo-dye isomers, due to light, causes changes in the nematic director. The boundary conditions on both plates along with the optical field determine the director configuration in the bulk. The existence of periodic solutions for the density of isomers in trans and cis states, corresponding to weak optical fields, has been discussed in the literature. Using a similar approach, we find an approximate expression for the density of isomers, written in terms of the director angle, which allows us to close the equation for the director configuration on the boundary having a photosensitive plate. We decouple the director's angle and the isomer densities by assuming extremely different temporal time scales between them. We show for a given sample that switching times inversely depend on the trans-cis transition rate of photoexcitation whereas relaxation times do not depend on it. On the other hand, switching and relaxation times linearly depend on effective surface viscosity values. Our model allows us to estimate surface viscosity values.
Magnetic field induced reorientation of nematic liquid crystals on polymer layers is studied near... more Magnetic field induced reorientation of nematic liquid crystals on polymer layers is studied near the glass transition temperature of the polymer. Kinetic curves for different field strengths and temperatures are presented. A model is developed, which takes into account the structural rearrangements in the polymer induced by its interaction with the anisotropic potential of the liquid crystal. Simulations based on the model are in good quantitative agreement with the experimental data.
Liquid crystal layers sandwiched between a reference plate and a photosensitive substrate were in... more Liquid crystal layers sandwiched between a reference plate and a photosensitive substrate were investigated. We focused on the reverse geometry, where the cell was illuminated by a laser beam from the reference side. In planar cells instabilities occurred, static and dynamic ones, depending on the angle between the laser polarization and the director orientation on the reference plate. In cells where the molecules were aligned along the normal of the reference plate, dynamic pattern was observed at all angles of polarization. A simple model based on a photo-induced surface torque gives account of the findings. Light scattering studies revealed some basic properties of the instabilities.
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