Pub Date : 2015-01-02DOI: 10.1080/21680396.2015.1025305
P. Collings, Joshua N. Goldstein, Elizabeth J. Hamilton, Benjamin R. Mercado, K. Nieser, Margaret H. Regan
Chromonic liquid crystals form when certain molecules are dissolved in a solvent, usually water, and the molecules spontaneously assemble into anisotropic structures. If the density of these structures is high enough and the temperature is low enough, they organize into a liquid crystal phase with orientational and sometimes with positional order also. Chromonic liquid crystals have been studied for more than half a century, yet theoretical, computational, and experimental investigations in the last decade have revealed many more details about them. The molecular structures that form chromonic liquid crystals are quite varied, and as a result the assemblies that these molecules form vary significantly also. Recent research has begun to shed light on these assembly processes, revealing that these too can be quite different from one system to another.
{"title":"The nature of the assembly process in chromonic liquid crystals","authors":"P. Collings, Joshua N. Goldstein, Elizabeth J. Hamilton, Benjamin R. Mercado, K. Nieser, Margaret H. Regan","doi":"10.1080/21680396.2015.1025305","DOIUrl":"https://doi.org/10.1080/21680396.2015.1025305","url":null,"abstract":"Chromonic liquid crystals form when certain molecules are dissolved in a solvent, usually water, and the molecules spontaneously assemble into anisotropic structures. If the density of these structures is high enough and the temperature is low enough, they organize into a liquid crystal phase with orientational and sometimes with positional order also. Chromonic liquid crystals have been studied for more than half a century, yet theoretical, computational, and experimental investigations in the last decade have revealed many more details about them. The molecular structures that form chromonic liquid crystals are quite varied, and as a result the assemblies that these molecules form vary significantly also. Recent research has begun to shed light on these assembly processes, revealing that these too can be quite different from one system to another.","PeriodicalId":18087,"journal":{"name":"Liquid Crystals Reviews","volume":"3 1","pages":"1 - 27"},"PeriodicalIF":5.1,"publicationDate":"2015-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/21680396.2015.1025305","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"60430940","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2015-01-02DOI: 10.1080/21680396.2015.1030462
Cheng-Cher Huang, Shun Wang, Lidong Pan, Z. Q. Liu, B. McCoy, Y. Sasaki, K. Ema, P. Barois, R. Pindak
For more than one decade, were the only three confirmed commensurate SmC* variant phases with periodicities less than or equal four layers. In 2006, employing ellipsometry and resonant X-ray diffraction (RXRD), our research team first discovered a new liquid crystal mesophase having a six-layer periodicity in one ternary mixture which includes one sulfur-containing compound. From our ellipsometric results, this phase showed antiferroelectric-like optical response. This novel discovery inspired renewed interest to search for liquid crystal mesophases with commensurate periodicities greater than four layers. Soon after, another mesophase having a six-layer structure and showing a ferrielectric-like dielectric response, instead, was uncovered by RXRD measurements on a different binary mixture which has one bromine-containing compound. Meanwhile mesophases having a 5-, 8-, 12- or 15-layer periodicity were reported. However, numerous questions remain to be addressed associated with these unusual reported phases. Theoretical models giving rise to mesophases with periodicities greater than four layers have been developed; but, to date, none of them have provided satisfactory explanations of all the physical phenomena related to the mesophases exhibiting a six-layer structure. Moreover, the question “what is the source of long-range interactions between liquid-like smectic layers, which are responsible for establishing mesophases with long periodicities and mean-field behavior of the smectic-A–smectic-C transition?” remains unanswered for more than three decades.
在十多年的时间里，只有三个被证实的周期小于或等于四层的相应的SmC*变相。2006年，我们的研究团队利用椭偏仪和共振x射线衍射(RXRD)首次在含一种含硫化合物的三元混合物中发现了一种具有六层周期性的新型液晶中间相。从我们的椭偏结果来看，这一相表现出反铁电的光学响应。这一新发现激发了人们对寻找周期性大于四层的液晶中间相的兴趣。不久之后，另一种中间相具有六层结构，并表现出类似铁电的介电响应，相反，通过RXRD测量发现了另一种二元混合物，其中含有一种含溴化合物。同时，还报道了具有5层、8层、12层或15层周期性的中间相。然而，与这些不寻常的报告阶段相关的许多问题仍有待解决。提出了周期大于四层的中间相的理论模型;但是，到目前为止，他们都没有提供令人满意的解释所有的物理现象有关的中间相显示六层结构。此外，问题是“液体类近晶层之间的远程相互作用的来源是什么?这些相互作用负责建立具有长周期的中间相和近晶- a -近晶- c跃迁的平均场行为?”这个问题三十多年来一直没有答案。
{"title":"Liquid crystal mesophases beyond commensurate four-layer periodicity","authors":"Cheng-Cher Huang, Shun Wang, Lidong Pan, Z. Q. Liu, B. McCoy, Y. Sasaki, K. Ema, P. Barois, R. Pindak","doi":"10.1080/21680396.2015.1030462","DOIUrl":"https://doi.org/10.1080/21680396.2015.1030462","url":null,"abstract":"For more than one decade, were the only three confirmed commensurate SmC* variant phases with periodicities less than or equal four layers. In 2006, employing ellipsometry and resonant X-ray diffraction (RXRD), our research team first discovered a new liquid crystal mesophase having a six-layer periodicity in one ternary mixture which includes one sulfur-containing compound. From our ellipsometric results, this phase showed antiferroelectric-like optical response. This novel discovery inspired renewed interest to search for liquid crystal mesophases with commensurate periodicities greater than four layers. Soon after, another mesophase having a six-layer structure and showing a ferrielectric-like dielectric response, instead, was uncovered by RXRD measurements on a different binary mixture which has one bromine-containing compound. Meanwhile mesophases having a 5-, 8-, 12- or 15-layer periodicity were reported. However, numerous questions remain to be addressed associated with these unusual reported phases. Theoretical models giving rise to mesophases with periodicities greater than four layers have been developed; but, to date, none of them have provided satisfactory explanations of all the physical phenomena related to the mesophases exhibiting a six-layer structure. Moreover, the question “what is the source of long-range interactions between liquid-like smectic layers, which are responsible for establishing mesophases with long periodicities and mean-field behavior of the smectic-A–smectic-C transition?” remains unanswered for more than three decades.","PeriodicalId":18087,"journal":{"name":"Liquid Crystals Reviews","volume":"3 1","pages":"58 - 78"},"PeriodicalIF":5.1,"publicationDate":"2015-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/21680396.2015.1030462","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"60430623","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Lukishova, A. Liapis, L. Bissell, G. Gehring, R. Boyd
We present here our results on using liquid crystals (LCs) in experiments with nonclassical light sources: (1) single-photon sources exhibiting antibunching (separation of all photons in time), which are key components for secure quantum communication systems and (2) entangled photon source with photons exhibiting quantum interference in a Hong–Ou–Mandel interferometer. In the first part, both nematic and cholesteric liquid crystal (CLC) hosts were used to create definite linear or circular polarization of antibunched photons emitted by different types of single emitters (dye molecules, nanocrystal quantum dots (NQDs), nanodiamonds with color centers, etc.). If the photon has unknown polarization, filtering it through a polarizer to produce the desired polarization for quantum key distribution with bits based on polarization states of photons will reduce by half the efficiency of a quantum cryptography system. In the first part, we also provide our results on observation of a circular polarized microcavity resonance in NQD fluorescence in a 1-D chiral photonic bandgap CLC microcavity. In the second part of this paper with indistinguishable, time-entangled photons, we demonstrate our experimental results on simulating quantum mechanical barrier tunneling phenomena. A Hong–Ou–Mandel dip (quantum interference effect) is shifted when a phase change was introduced on the way of one of entangled photons in pair (one arm of the interferometer) by inserting in this arm an electrically controlled planar-aligned nematic LC layer between two prisms in the conditions close to a frustrated total internal reflection. By applying different AC-voltages to the planar-aligned nematic layer and changing its refractive index, we can obtain various conditions for incident photon propagation – from total reflection to total transmission. Measuring changes of tunneling times of photon through this structure with femtosecond resolution permitted us to answer some unresolved questions in quantum mechanical barrier tunneling phenomena.
本文介绍了我们在非经典光源实验中使用液晶(lc)的结果:(1)单光子源表现出反聚束(所有光子在时间上的分离)，这是安全量子通信系统的关键组件;(2)在Hong-Ou-Mandel干涉仪中表现出量子干涉的光子纠缠光子源。在第一部分中，向列相和胆甾相液晶(CLC)宿主被用于创建由不同类型的单发射器(染料分子、纳米晶体量子点(NQDs)、具有色心的纳米钻石等)发射的反束光子的明确的线性或圆偏振。如果光子具有未知的偏振，则将其通过偏振器过滤以产生基于光子偏振态的量子密钥分配所需的偏振，这将使量子密码系统的效率降低一半。在第一部分中，我们还提供了我们在一维手性光子带隙CLC微腔中观察NQD荧光的圆偏振微腔共振的结果。在本文的第二部分，我们用不可区分的时间纠缠光子，展示了我们模拟量子力学势垒隧穿现象的实验结果。在接近失谐全内反射的条件下，在一对纠缠光子(干涉仪的一条臂)的其中一条臂中插入一个可控制的平面向列LC层，在这条臂中引入相位变化，从而改变了hong - u - mandel dip(量子干涉效应)。通过对平面向列层施加不同的交流电压并改变其折射率，我们可以得到入射光子从全反射到全透射的各种传输条件。用飞秒分辨率测量光子通过该结构的隧穿时间的变化，使我们能够回答量子力学势垒隧穿现象中一些尚未解决的问题。
{"title":"Single-photon experiments with liquid crystals for quantum science and quantum engineering applications","authors":"S. Lukishova, A. Liapis, L. Bissell, G. Gehring, R. Boyd","doi":"10.1117/12.2184372","DOIUrl":"https://doi.org/10.1117/12.2184372","url":null,"abstract":"We present here our results on using liquid crystals (LCs) in experiments with nonclassical light sources: (1) single-photon sources exhibiting antibunching (separation of all photons in time), which are key components for secure quantum communication systems and (2) entangled photon source with photons exhibiting quantum interference in a Hong–Ou–Mandel interferometer. In the first part, both nematic and cholesteric liquid crystal (CLC) hosts were used to create definite linear or circular polarization of antibunched photons emitted by different types of single emitters (dye molecules, nanocrystal quantum dots (NQDs), nanodiamonds with color centers, etc.). If the photon has unknown polarization, filtering it through a polarizer to produce the desired polarization for quantum key distribution with bits based on polarization states of photons will reduce by half the efficiency of a quantum cryptography system. In the first part, we also provide our results on observation of a circular polarized microcavity resonance in NQD fluorescence in a 1-D chiral photonic bandgap CLC microcavity. In the second part of this paper with indistinguishable, time-entangled photons, we demonstrate our experimental results on simulating quantum mechanical barrier tunneling phenomena. A Hong–Ou–Mandel dip (quantum interference effect) is shifted when a phase change was introduced on the way of one of entangled photons in pair (one arm of the interferometer) by inserting in this arm an electrically controlled planar-aligned nematic LC layer between two prisms in the conditions close to a frustrated total internal reflection. By applying different AC-voltages to the planar-aligned nematic layer and changing its refractive index, we can obtain various conditions for incident photon propagation – from total reflection to total transmission. Measuring changes of tunneling times of photon through this structure with femtosecond resolution permitted us to answer some unresolved questions in quantum mechanical barrier tunneling phenomena.","PeriodicalId":18087,"journal":{"name":"Liquid Crystals Reviews","volume":"2 1","pages":"111 - 129"},"PeriodicalIF":5.1,"publicationDate":"2014-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1117/12.2184372","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"63600822","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2014-07-03DOI: 10.1080/21680396.2014.963716
A. Sengupta, S. Herminghaus, C. Bahr
The hydrodynamic properties of nematic liquid crystals are characterized by a complex mutual coupling between flow, viscosity, and nematic order. While the flow behaviour of nematic bulk samples is well known, corresponding studies in microfluidic settings are still at an early stage. The presence of the four confining channel walls – and in particular the nature of the surface anchoring of the nematic order on the walls – adds new phenomena to the already rich and multifaceted flow behaviour. We present an overview of recent studies focusing on the microfluidics of nematic liquid crystals. Particular topics are the functionalization of the channel walls for defined surface anchoring conditions and the resulting structures of the nematic director field, the controlling and tuning of the flow velocity profile and director field configuration and resulting opto-fluidic applications, and the behaviour of topological defects in the flowing nematic and their application for a guided colloidal transport.
{"title":"Liquid crystal microfluidics: surface, elastic and viscous interactions at microscales","authors":"A. Sengupta, S. Herminghaus, C. Bahr","doi":"10.1080/21680396.2014.963716","DOIUrl":"https://doi.org/10.1080/21680396.2014.963716","url":null,"abstract":"The hydrodynamic properties of nematic liquid crystals are characterized by a complex mutual coupling between flow, viscosity, and nematic order. While the flow behaviour of nematic bulk samples is well known, corresponding studies in microfluidic settings are still at an early stage. The presence of the four confining channel walls – and in particular the nature of the surface anchoring of the nematic order on the walls – adds new phenomena to the already rich and multifaceted flow behaviour. We present an overview of recent studies focusing on the microfluidics of nematic liquid crystals. Particular topics are the functionalization of the channel walls for defined surface anchoring conditions and the resulting structures of the nematic director field, the controlling and tuning of the flow velocity profile and director field configuration and resulting opto-fluidic applications, and the behaviour of topological defects in the flowing nematic and their application for a guided colloidal transport.","PeriodicalId":18087,"journal":{"name":"Liquid Crystals Reviews","volume":"2 1","pages":"110 - 73"},"PeriodicalIF":5.1,"publicationDate":"2014-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/21680396.2014.963716","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"60430717","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2014-07-03DOI: 10.1080/21680396.2014.974697
Liwei Li, D. Bryant, P. Bos
In this review, we provide an overview of recent efforts in designing high-quality tunable liquid crystal (LC) lenses with concentric electrodes. The design concepts are introduced, and details about fabrication and evaluation methods are given. Computational and experimental approaches are used to gain understanding of the fundamental limiting factors affecting the performance of LC lenses. In addition, directions for improvement of image quality, speed, optical power, and off-axis performance are proposed.
{"title":"Liquid crystal lens with concentric electrodes and inter-electrode resistors","authors":"Liwei Li, D. Bryant, P. Bos","doi":"10.1080/21680396.2014.974697","DOIUrl":"https://doi.org/10.1080/21680396.2014.974697","url":null,"abstract":"In this review, we provide an overview of recent efforts in designing high-quality tunable liquid crystal (LC) lenses with concentric electrodes. The design concepts are introduced, and details about fabrication and evaluation methods are given. Computational and experimental approaches are used to gain understanding of the fundamental limiting factors affecting the performance of LC lenses. In addition, directions for improvement of image quality, speed, optical power, and off-axis performance are proposed.","PeriodicalId":18087,"journal":{"name":"Liquid Crystals Reviews","volume":"2 1","pages":"130 - 154"},"PeriodicalIF":5.1,"publicationDate":"2014-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/21680396.2014.974697","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"60430831","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2014-01-02DOI: 10.1080/21680396.2013.878672
G. Foffano, J. Lintuvuori, A. Tiribocchi, D. Marenduzzo
Dispersing colloidal particles into liquid crystals provides a promising avenue to build a novel class of materials, with potential applications, among others, as photonic crystals, biosensors, metamaterials and new generation liquid crystal devices. Understanding the physics and dynamical properties of such composite materials is then of high-technological relevance; it also provides a remarkable challenge from a fundamental science point of view due to the intricacies of the hydrodynamic equations governing their dynamical evolution. Here, we provide an overview of our current theoretical understanding of the dynamical and hydrodynamic properties of colloid–liquid crystal composites, focussing on the results obtained from computer simulations; no or very limited previous knowledge of the field of liquid crystals is assumed. While our main emphasis is on the dynamics, we also review a selection of equilibrium results and simulations to provide the necessary background. We start by describing what we know about the simplest possible problem: that of a single particle in a nematic, or cholesteric, liquid crystal. We then consider two particles, and review the conditions which lead to the formation of a dimer; we then again focus on dynamical problems. Finally, we turn to the more complicated case of a dispersion, reviewing here simulations motivated by optical tweezer and rheological experiments. We close by making a list of some of the many open problems in this rapidly developing research field.
{"title":"The dynamics of colloidal intrusions in liquid crystals: a simulation perspective","authors":"G. Foffano, J. Lintuvuori, A. Tiribocchi, D. Marenduzzo","doi":"10.1080/21680396.2013.878672","DOIUrl":"https://doi.org/10.1080/21680396.2013.878672","url":null,"abstract":"Dispersing colloidal particles into liquid crystals provides a promising avenue to build a novel class of materials, with potential applications, among others, as photonic crystals, biosensors, metamaterials and new generation liquid crystal devices. Understanding the physics and dynamical properties of such composite materials is then of high-technological relevance; it also provides a remarkable challenge from a fundamental science point of view due to the intricacies of the hydrodynamic equations governing their dynamical evolution. Here, we provide an overview of our current theoretical understanding of the dynamical and hydrodynamic properties of colloid–liquid crystal composites, focussing on the results obtained from computer simulations; no or very limited previous knowledge of the field of liquid crystals is assumed. While our main emphasis is on the dynamics, we also review a selection of equilibrium results and simulations to provide the necessary background. We start by describing what we know about the simplest possible problem: that of a single particle in a nematic, or cholesteric, liquid crystal. We then consider two particles, and review the conditions which lead to the formation of a dimer; we then again focus on dynamical problems. Finally, we turn to the more complicated case of a dispersion, reviewing here simulations motivated by optical tweezer and rheological experiments. We close by making a list of some of the many open problems in this rapidly developing research field.","PeriodicalId":18087,"journal":{"name":"Liquid Crystals Reviews","volume":"2 1","pages":"1 - 27"},"PeriodicalIF":5.1,"publicationDate":"2014-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/21680396.2013.878672","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"60430029","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2014-01-02DOI: 10.1080/21680396.2014.929984
J. R. Wolf
Hydrogen bonding has been extensively used to create the mesogenic core of calamitic liquid crystals. While the field of polymeric hydrogen-bonded liquid crystals has been extensively studied, most of the research has been devoted to side chain hydrogen-bonded polymeric liquid crystals with far less effort devoted to the study of main chain hydrogen-bonded liquid crystals despite the variety of liquid crystalline (LC) phases they possess. In this review, centrosymmetric and noncentrosymmetric main chain hydrogen-bonded polymers are discussed with an emphasis on the structure/property relationships and the variety of LC phases observed in the resulting polymers.
{"title":"Review: main chain hydrogen-bonded liquid crystalline polymers","authors":"J. R. Wolf","doi":"10.1080/21680396.2014.929984","DOIUrl":"https://doi.org/10.1080/21680396.2014.929984","url":null,"abstract":"Hydrogen bonding has been extensively used to create the mesogenic core of calamitic liquid crystals. While the field of polymeric hydrogen-bonded liquid crystals has been extensively studied, most of the research has been devoted to side chain hydrogen-bonded polymeric liquid crystals with far less effort devoted to the study of main chain hydrogen-bonded liquid crystals despite the variety of liquid crystalline (LC) phases they possess. In this review, centrosymmetric and noncentrosymmetric main chain hydrogen-bonded polymers are discussed with an emphasis on the structure/property relationships and the variety of LC phases observed in the resulting polymers.","PeriodicalId":18087,"journal":{"name":"Liquid Crystals Reviews","volume":"34 1","pages":"28 - 46"},"PeriodicalIF":5.1,"publicationDate":"2014-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/21680396.2014.929984","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"60430153","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2014-01-02DOI: 10.1080/21680396.2014.938783
A. M. Figueiredo Neto
The physico-chemical properties of cholesteric liquid crystals still provide new insights for researchers investigating the structure, local ordering, and phase transitions in condensed matter physics in spite of the fact that they have been known for more than a century. Among cholesterics, the micellar lyotropic cholesteric liquid crystals present outstanding properties which place them in a special category of complex-fluids. One of these key properties is the possibility for changing the micelle shape and shape anisotropy as a function of temperature and/or relative composition of the mixture. Moreover, the existence of polar and nonpolar regions in the lyotropic cholesteric medium, i.e. the loci of the polar heads and hydrocarbon chains of the amphiphilic molecules, respectively, permits a large number of different types of chiral dopants to induce helical structure in the mesophases. Besides this point, the existence of three types of cholesteric phases, originating from the cholesterization of the two uniaxial and one biaxial nematic phases, opens an interesting field of research into fundamental aspects of phase transition and statistical mechanics. In this review, we put together different aspects of the physics of these liquid crystals, from texture observations in a polarized light microscope, to the structure, local ordering, and phase transitions. Some perspectives of new studies are suggested in the concluding remarks.
{"title":"Micellar cholesteric lyotropic liquid crystals","authors":"A. M. Figueiredo Neto","doi":"10.1080/21680396.2014.938783","DOIUrl":"https://doi.org/10.1080/21680396.2014.938783","url":null,"abstract":"The physico-chemical properties of cholesteric liquid crystals still provide new insights for researchers investigating the structure, local ordering, and phase transitions in condensed matter physics in spite of the fact that they have been known for more than a century. Among cholesterics, the micellar lyotropic cholesteric liquid crystals present outstanding properties which place them in a special category of complex-fluids. One of these key properties is the possibility for changing the micelle shape and shape anisotropy as a function of temperature and/or relative composition of the mixture. Moreover, the existence of polar and nonpolar regions in the lyotropic cholesteric medium, i.e. the loci of the polar heads and hydrocarbon chains of the amphiphilic molecules, respectively, permits a large number of different types of chiral dopants to induce helical structure in the mesophases. Besides this point, the existence of three types of cholesteric phases, originating from the cholesterization of the two uniaxial and one biaxial nematic phases, opens an interesting field of research into fundamental aspects of phase transition and statistical mechanics. In this review, we put together different aspects of the physics of these liquid crystals, from texture observations in a polarized light microscope, to the structure, local ordering, and phase transitions. Some perspectives of new studies are suggested in the concluding remarks.","PeriodicalId":18087,"journal":{"name":"Liquid Crystals Reviews","volume":"2 1","pages":"47 - 59"},"PeriodicalIF":5.1,"publicationDate":"2014-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/21680396.2014.938783","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"60430559","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2014-01-02DOI: 10.1080/21680396.2014.947528
A. Minasyan, T. Galstian
Polymer-liquid crystal (LC) composite materials provide cost-effective ways to achieve enhanced electro-optic functionalities. Corresponding bulk-dispersed and phase-separated (of various degrees) morphologies were intensively studied in the past and are shortly described in this work. In addition, we consider the specific case when the polymer-LC structures are formed near to the cell substrates. To achieve this, partially cured and oriented polymer coatings are used as alignment layers for dual frequency chiral LC. The partial curing is intended to allow a partial interpenetration between the LC and the polymer molecules to form surface-stabilized polymer networks. After a short interpenetration period (between the polymer coatings and the bulk LC), a positive dielectric torque is applied and UV exposition is used to definitely cure the material system. Our electro-optical, spectroscopic and microscopic studies show that the pre-curing duration plays a crucial role in the behavior of the cell. It is shown that the molecular interdiffusion generates defects of LC alignment around polymer aggregates on the cell's internal surfaces. The obtained out-of-plane alignment and small polymer aggregates are at the origin of formation of controllable light scattering. Among others, some linear defects are formed by the positive torque, which are, however, eliminated when a negative dielectric torque is applied.
{"title":"Surface polymer-stabilized dual frequency chiral liquid crystals","authors":"A. Minasyan, T. Galstian","doi":"10.1080/21680396.2014.947528","DOIUrl":"https://doi.org/10.1080/21680396.2014.947528","url":null,"abstract":"Polymer-liquid crystal (LC) composite materials provide cost-effective ways to achieve enhanced electro-optic functionalities. Corresponding bulk-dispersed and phase-separated (of various degrees) morphologies were intensively studied in the past and are shortly described in this work. In addition, we consider the specific case when the polymer-LC structures are formed near to the cell substrates. To achieve this, partially cured and oriented polymer coatings are used as alignment layers for dual frequency chiral LC. The partial curing is intended to allow a partial interpenetration between the LC and the polymer molecules to form surface-stabilized polymer networks. After a short interpenetration period (between the polymer coatings and the bulk LC), a positive dielectric torque is applied and UV exposition is used to definitely cure the material system. Our electro-optical, spectroscopic and microscopic studies show that the pre-curing duration plays a crucial role in the behavior of the cell. It is shown that the molecular interdiffusion generates defects of LC alignment around polymer aggregates on the cell's internal surfaces. The obtained out-of-plane alignment and small polymer aggregates are at the origin of formation of controllable light scattering. Among others, some linear defects are formed by the positive torque, which are, however, eliminated when a negative dielectric torque is applied.","PeriodicalId":18087,"journal":{"name":"Liquid Crystals Reviews","volume":"2 1","pages":"60 - 71"},"PeriodicalIF":5.1,"publicationDate":"2014-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/21680396.2014.947528","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"60430617","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2013-12-01DOI: 10.1080/21680396.2013.869667
P. Dolganov, E. Kats
In this paper we review various amazing features of polar smectic structures and phase transitions between them. In a series of experimental and theoretical studies over the last decades, a lot of new and unexpected structures have been observed and described theoretically in the realm of polar smectic liquid crystals. Not all of these structures were correctly identified experimentally and/or correctly interpreted theoretically. At least in part, the problem is in the uncertainty about which theoretical model can provide an adequate minimal description of all available experimental data. The approach we are advocating in this work is to rely on a systematic, well elaborated, and perfectly suitable to describe mean field behavior in the vicinity of phase transition lines, theoretical frame – Landau phase transitions theory. Structural and symmetry properties of the polar smectic liquid crystals require utilization of the Landau theory with the discretized over the smectic layers two-component order parameter. Furthermore, both components of the order parameter (its modulus, related to interlayer distance, and phase, related to azimuthal orientation of molecules) can be space non-uniform, describing various smectic structures. We show that this theory describes the experimentally discovered polar smectic phases and predicts a number of new structures.
{"title":"Landau theory description of polar smectic structures","authors":"P. Dolganov, E. Kats","doi":"10.1080/21680396.2013.869667","DOIUrl":"https://doi.org/10.1080/21680396.2013.869667","url":null,"abstract":"In this paper we review various amazing features of polar smectic structures and phase transitions between them. In a series of experimental and theoretical studies over the last decades, a lot of new and unexpected structures have been observed and described theoretically in the realm of polar smectic liquid crystals. Not all of these structures were correctly identified experimentally and/or correctly interpreted theoretically. At least in part, the problem is in the uncertainty about which theoretical model can provide an adequate minimal description of all available experimental data. The approach we are advocating in this work is to rely on a systematic, well elaborated, and perfectly suitable to describe mean field behavior in the vicinity of phase transition lines, theoretical frame – Landau phase transitions theory. Structural and symmetry properties of the polar smectic liquid crystals require utilization of the Landau theory with the discretized over the smectic layers two-component order parameter. Furthermore, both components of the order parameter (its modulus, related to interlayer distance, and phase, related to azimuthal orientation of molecules) can be space non-uniform, describing various smectic structures. We show that this theory describes the experimentally discovered polar smectic phases and predicts a number of new structures.","PeriodicalId":18087,"journal":{"name":"Liquid Crystals Reviews","volume":"1 1","pages":"127 - 149"},"PeriodicalIF":5.1,"publicationDate":"2013-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/21680396.2013.869667","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"60430476","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":3,"RegionCategory":"材料科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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