Pub Date : 2020-01-02DOI: 10.1080/1358314X.2020.1771847
A. Draude
Active matter, in which local energy is converted into directed motion, is an area of strong interest in current soft matter research for potential applications in soft robotics. Living nematics are a category of active matter where nematic phases have active particles dispersed in them. In this paper, Turiv et al. study high and low concentrations of swimming bacteria in the nematic phase of the lyotropic chromonic liquid crystal DSCG via microscopy. Photo-alignment is used to create patterned director fields. Patterns including splay and bend are used to focus the trajectory of the bacteria and rectilinear jets undulate at high concentrations of bacteria. These jets are shown to be stabilised by the background director field and the experimental results are supported by simulations. In flows of either concentration of bacteria micro-spheres are shown to be transported along the pre-patterned flows.
{"title":"Research news","authors":"A. Draude","doi":"10.1080/1358314X.2020.1771847","DOIUrl":"https://doi.org/10.1080/1358314X.2020.1771847","url":null,"abstract":"Active matter, in which local energy is converted into directed motion, is an area of strong interest in current soft matter research for potential applications in soft robotics. Living nematics are a category of active matter where nematic phases have active particles dispersed in them. In this paper, Turiv et al. study high and low concentrations of swimming bacteria in the nematic phase of the lyotropic chromonic liquid crystal DSCG via microscopy. Photo-alignment is used to create patterned director fields. Patterns including splay and bend are used to focus the trajectory of the bacteria and rectilinear jets undulate at high concentrations of bacteria. These jets are shown to be stabilised by the background director field and the experimental results are supported by simulations. In flows of either concentration of bacteria micro-spheres are shown to be transported along the pre-patterned flows.","PeriodicalId":18110,"journal":{"name":"Liquid Crystals Today","volume":"29 1","pages":"18 - 19"},"PeriodicalIF":3.1,"publicationDate":"2020-01-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/1358314X.2020.1771847","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46673640","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2020-01-02DOI: 10.1080/1358314X.2020.1771841
R. Walker
ABSTRACT This article will review some of our recent work concerning the relationships between molecular structure and the observation of the fascinating twist-bend nematic, NTB, phase. From a chemist’s perspective, understanding the molecular features influencing the formation and stabilisation of the NTB phase is of paramount importance, and allows for the design of new materials that have targeted properties. As such, recent work in Aberdeen has had the primary aim of enhancing our current understanding of these relationships in dimeric liquid crystals, through the synthesis and characterisation of a diverse range of materials, including a selection of supramolecular liquid crystals. A second aim has been to explore the intriguing question as to how the NTB phase, having spontaneous structural chirality, would respond at a microscopic level to the presence of intrinsic molecular chirality – the inclusion of chiral fragments in the dimers – and to obtain examples of the ‘chiral’ twist-bend nematic phase (N*TB) for comparative study alongside the conventional NTB phase. We also show that bent achiral molecules form heliconical smectic phases, as predicted by Dozov in his seminal 2001 work.
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Pub Date : 2019-10-02DOI: 10.1080/1358314X.2020.1726065
J. Lydon
ABSTRACT There is a strategic difference between the process of cell division by mitosis in animal cells and that in cells of higher plants. One particularly puzzling feature is the absence of centrioles in plant cells, when they appear to be of central importance in the control of the process in animal cells. It is argued that in both cases the dividing cell uses the versatility of the liquid crystalline state of the mitotic cytoplasm created by the wide-scale assembly of microtubules prior to mitosis. It is not the centrioles per se which are vital – it is the director field of the mesophase which is crucial – and alternative procedures have been developed by plants and animals to create this. In both cases, they can be related to known spontaneous alignment states of liquid crystalline systems.
{"title":"A liquid crystal model for mitotic cell division - and the enigma of centriole involvement in mitosis in animals but not plants","authors":"J. Lydon","doi":"10.1080/1358314X.2020.1726065","DOIUrl":"https://doi.org/10.1080/1358314X.2020.1726065","url":null,"abstract":"ABSTRACT There is a strategic difference between the process of cell division by mitosis in animal cells and that in cells of higher plants. One particularly puzzling feature is the absence of centrioles in plant cells, when they appear to be of central importance in the control of the process in animal cells. It is argued that in both cases the dividing cell uses the versatility of the liquid crystalline state of the mitotic cytoplasm created by the wide-scale assembly of microtubules prior to mitosis. It is not the centrioles per se which are vital – it is the director field of the mesophase which is crucial – and alternative procedures have been developed by plants and animals to create this. In both cases, they can be related to known spontaneous alignment states of liquid crystalline systems.","PeriodicalId":18110,"journal":{"name":"Liquid Crystals Today","volume":"28 1","pages":"86 - 95"},"PeriodicalIF":3.1,"publicationDate":"2019-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/1358314X.2020.1726065","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42948757","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-10-02DOI: 10.1080/1358314X.2020.1726068
A. Draude
Nematic liquid crystals have complex rheological properties compared to isotropic liquids, and achieving precise flows can be difficult experimentally. In this paper, Čopar et al. demonstrate transitions a discontinuous transition from homeotropic to planar director orientation in a microfluidic channel with homeotropic boundaries as the flow rate is increased. Furthermore, they demonstrate the existence of a topologically protected intermediate state, which is chiral despite the chosen system (5CB) being achiral. The authors go on to show that small amounts of chiral dopant can break the symmetry of the system and only one handedness is observed in the intermediate state. Laser tweezers which give rise to localised heating are also employed to manipulate the flow states. It is proposed that such phenomena could be exploited technology in optical shutters, in which the state is carefully tuned by the flow rate and/or laser heating.
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Pub Date : 2019-07-03DOI: 10.1080/1358314X.2019.1681113
Thomas Machon
ABSTRACT We review some our results concerning the topology of knotted and linked defects in nematic liquid crystals. We discuss the global topological classification of nematic textures with defects, showing how knotted and linked defect lines have a finite number of ‘internal states’, counted by the Alexander polynomial of the knot or link. We then give interpretations of these states in terms of umbilic lines, which we also introduce, as well as planar textures. We show how Milnor polynomials can be used to give explicit constructions of these textures. Finally, we discuss some open problems raised by this work.
{"title":"The topology of knots and links in nematics","authors":"Thomas Machon","doi":"10.1080/1358314X.2019.1681113","DOIUrl":"https://doi.org/10.1080/1358314X.2019.1681113","url":null,"abstract":"ABSTRACT We review some our results concerning the topology of knotted and linked defects in nematic liquid crystals. We discuss the global topological classification of nematic textures with defects, showing how knotted and linked defect lines have a finite number of ‘internal states’, counted by the Alexander polynomial of the knot or link. We then give interpretations of these states in terms of umbilic lines, which we also introduce, as well as planar textures. We show how Milnor polynomials can be used to give explicit constructions of these textures. Finally, we discuss some open problems raised by this work.","PeriodicalId":18110,"journal":{"name":"Liquid Crystals Today","volume":"28 1","pages":"58 - 67"},"PeriodicalIF":3.1,"publicationDate":"2019-07-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1080/1358314X.2019.1681113","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"43211407","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-07-03DOI: 10.1080/1358314X.2019.1693104
M. Nagaraj
Pattern formation in out-of-equilibrium systems is diverse. Examining the nature of hydrodynamic patterns in active nematics has been a topic of interest for the past couple of years. Sokolov et al. investigate the dynamics of circularly aligned swimming bacteria. They show that in an active matter system the interplay of activity, elasticity and geometry leads to a wellcontrolled pattern formation and finer control of dynamic structures and transport phenomena. They report the emergence of bend stripes, an activityinduced undulations of the liquid crystal director field, in areas of high local curvature. Parameters such as velocity, relaxation rate and vorticity are compared for two experimental geometries; a pendant drop attached to a glass slide and in a thin free-standing film suspended between filaments. Hydrodynamic simulations are used to explain the origin of bend stripes. The effect of adding an extensile active stress on the hydrodynamic flows and its implications on the time evolution of the director field and the local curvature are compared. The instability patterns are seen to introduce a strong anisotropy to the angular distribution of emerging topological defects.
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Pub Date : 2019-07-03DOI: 10.1080/1358314x.2019.1693097
A. Mertelj
Conference report FLC 2019: frontiers of chirality and polarity in soft matter The 17 International Conference on Ferroelectric Liquid Crystal, after 28 years, again took place in picturesque Boulder from August 4–7, 2019. It was held under the auspices of the Soft Materials Research Center, the NSF Materials Research Science and Engineering Center at the University of Colorado Boulder. The local organisers Noel Clark (Honorary Chair), Dave Walba (Conference Chair), Matt Glaser, Eva Korblova, Joe Maclennan, Christine Morrow, and Dakota Nanton provided a pleasant and inspiring ambient for the 83 attendees from 13 countries (Figure 1). The FLC 2019 focused on frontiers of polarity and chirality in soft matter. In six plenary lectures, 12 invited talks and 19 oral presentations, as well as 21 posters the main themes: (i) design and synthesis of novel ferroelectric/polar liquid crystal materials; (ii) the twist-bend phases; (iii) spontaneous achiral symmetry breaking (chiral self-assembly of achiral molecules); (iv) fluid ferroelectrics and ferromagnetics; (v) blue phases; (vi) liquid crystals and biology; (vii) simulation, modelling and theory; (viii) advances in resonant X-ray scattering; and (ix) industrial applications, were covered. In his plenary lecture, Corrie Imrie presented a range of new liquid crystal dimers and other types of materials which exhibit the twist-bend nematic and, the recently observed twist-bend smectic phases and discussed structure–property relationships. Oleg Lavrentovich demonstrated electrically driven three-dimensional particle-like dissipative solitons representing self-trapped waves of oscillating director, called director bullets, which propagate with a very high speed perpendicularly to the electric field. Ewa Gorecka showed that a molecular system built of achiral mesogenic dimeric molecules exhibits a complexity with four levels of structural chirality, which were studied using resonant X-ray scattering. Alenka Mertelj presented a new modulated nematic phase, called the splay nematic phase, which results from polar ordering of the molecules and consequent instability towards splay deformation. Frank Giesselmann reviewed some new aspects of chirality in lyotropics, among them chiral structures that appear due to anomalously small twist elastic constants in chromonic and standard micellar lyotropic nematics confined to, e.g. cylindrical capillaries. Carsten Tschierske discussed the development of polarity and chirality in systems made of molecules with a shape at the cross-over from linear to bent which provides a series of interesting phenomena related to layer coupling, emergent polar order and concerning chirality issues. In the concluding session, chaired by Joe Maclennan, the prizes were awarded and future prospects for ferroelectric liquid crystals and chiral/ polar soft matter were discussed. The Luckhurst-Samulski prize, which is handed out for the best paper published each year in Liquid Crystals, was awa
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