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Image: Micrograph of blue pigment suspended in a liquid crystal, courtesy of Dr Susanne Klein
Theo Murphy international scientific meeting organised by Dr Susanne Klein, Professor Peter Raynes FRS and Professor Roy Sambles FRS
This conference will bring together world leaders plus young researchers in two areas: isotropic particles in anisotropic liquid crystals and colloidal liquid crystals (clay platelets or carbon nanotubes in isotropic fluids for example). These two areas of modern materials research are rich in complex science and have substantial applications potential ranging from e-inks through to biofluidics.
Biographies of the organisers and speakers are available below. Audio recordings of the presentations are freely available and the programme can be downloaded here. Papers will be published in a future issue of Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences
Dr Susanne Klein, Hewlett-Packard, UKOrganiser
After gaining a diploma in theoretical physics and a PhD in medical physics at the University of Saarland in Germany Susanne Klein spent a year at the University of Frankfurt as a German Telecom research fellow looking into the effects of geometric phases in optics and telecommunication. In 1995 she moved to the University of Bristol to work with Sir Michael Berry FRS on problems in polarization optics. She stayed there for three years as a Royal Society Research Assistant. Since then she has been working in HP Labs, first on the optical characterization of liquid crystal director fields, then on colloidal liquid crystals and colloids in liquid crystals and recently she has moved into the field of material research for 3D and 2.5D printing. For the last 10 years she has been a visiting research fellow in the School of Chemistry at the University of Bristol and has had the privilege to supervise a number of bright PhD students.
Professor Peter Raynes FRS, University of York, UKOrganiser
Following degrees in Physics at Cambridge, Peter Raynes joined the Royal Signals and Radar Establishment (now part of QinetiQ) at Malvern in 1971 to work on liquid crystals materials and devices. In 1992 he moved to the Sharp Laboratories of Europe Ltd at Oxford, where he was Director of Research until he took up to the Chair of Optoelectronics in the Department of Engineering Science at Oxford University in 1998. In 2010 he retired from Oxford and moved to York, where he is now a Leverhulme Emeritus Research Fellow in the Department of Chemistry. Throughout his research career he has worked on liquid crystal materials and displays. He has been responsible for many device inventions; some are still in widespread use and have enabled mobile phones and laptop PCs. He has also worked with chemists at Hull University and BDH (now part of Merck) helping develop several highly successful ranges of liquid crystal materials; these gained two Queen’s Awards for Technological Achievement.
Professor Roy Sambles FRS, University of Exeter, UKOrganiser
Professor Roy Sambles has been Professor of Experimental Physics at The University of Exeter since 1991. His present research concerns primarily the electromagnetic properties of structured metals and the viscodynamics of liquid crystals. He was awarded the George Gray medal of the British Liquid Crystal Society in 1998, and the Young Medal and Prize by the Institute of Physics in 2003, and elected a Fellow of the Royal Society in 2002. He is a Fellow of the Institute of Physics. In addition to his research activities he is presently a Council member of the EPSRC, a DSAC Independent and a member of: the Scientific Advisory Committee for IoP publishing; the editorial board of ‘Thin Solid Films’; and the Counter Terrorism Science and Technology Centre Oversight Board.
Professor Oleg Lavrentovich, Kent State University, USAElectrically controlled dynamics of colloidal particles in liquid crystals
Oleg D Lavrentovich is a Trustees Research Professor at the Liquid Crystal Institute, Kent State University, Kent, Ohio. His research interests include optical, electro-optical, electrokinetic phenomena in liquid crystals and 3D imaging of soft matter.
We explore electrically-induced dynamics of colloidal inclusions in a liquid crystal. In the uniform electric field, the dynamics is caused through two prime mechanisms, dielectric reorientation of the director (backflow effect) and through electrophoresis. In addition to the classic Smoluchowski linear term in the velocity vs. field dependency, there is also a nonlinear contribution to the velocity that is quadratic in the field; its direction is generally different from the direction of the electric field. In a non-uniform electric field, the particles can be moved by the dielectrophoretic effect; as an example, we demonstrate a formation of a liquid crystal from elongated gold nanorods dispersed in an isotropic fluid. The work was supported by NSF DMR-1104850 and DOE grant DE-FG02-06ER 463031
Dr Torsten Hegmann, Kent State University, USAGold nanoparticles as additives for liquid crystals
Torsten Hegmann obtained his PhD at the Martin Luther University in Halle (Germany) in 2001, and carried out postdoctoral work as a DAAD/NATO fellow at Queen’s University in Kingston, ON (Canada). After eight years at the University of Manitoba in Winnipeg, MB (Canada) as Assistant and Associate Professor, he is now an Associate Professor and Ohio Research Scholar in Science and Technology of Advanced Nanomaterials at Kent State University's Liquid Crystal Institute. Dr Hegmann’s research interests span from the synthesis and characterization of liquid crystals and nanomaterials over structure–property relationships and self-assembly processes in LCs and LC nanocomposites to the design of magnetic nanoparticle drug carriers for brain drug delivery.
Gold nanoparticles (Au NPs) have emerged as a promising class of materials with an enormous potential for modulating and improving the characteristics of liquid crystals (LCs) used in device applications. Recent, global research activities including research performed in our lab show that Au NPs induce distinct effects in LCs that may point to new directions for the use of these LC colloids in optical and sensing applications.[1,2] This talk will summarize recent fundamental research performed in my lab on nematic liquid crystals doped with functionalized Au NPs and position these results within the field. We have demonstrated the use of chiral dopant, (S)-naproxen, decorated Au NPs that effectively induce chiral nematic LC phases not only with a stronger CD response (tighter helical pitch) but also with the opposite helical sense in comparison to pure (S)- naproxen doped into the same nematic host. We have established that parameters such as the nature of the interface as well as the concentration and surface modification of the NPs doped into a nematic host can be tuned to either result in the formation of unique defect patterns (i.e. the formation of birefringent stripes surrounded by larger domains with homeotropic alignment) or produce a temperature-dependent alignment change from planar to vertical that could be exploited for sensor applications. We also showed an unprecedented dual alignment/switching mode with drastically reduced values of the threshold voltage (Vth) by doping LCs with gold NPs, and the formation of convection rolls (Williams Kapustin domains). This research is currently expanded to Au nanorods, gold nanostars, and magic-sized quantum dots.
 (a) O Stamatoiu, M Mirzaei, X Feng, T Hegmann, Top Curr Chem 2012, in press (b) U Shivakumar, J Mirzaei, X Feng, A Sharma, P Moreira, T Hegmann, Liq Cryst 2011, 38, 1495-1514.
 (a) H Qi, T Hegmann, J Mater Chem 2008, 18, 3288-3294; (b) T Hegmann, H Qi, V M Marx, J Inorg Organomet Polym Mater 2007, 17, 483-508.
 (a) H Qi, J O’Neil, T Hegmann, J Mater Chem 2008, 18, 374-380; (b) H Qi, T Hegmann, JACS 2008, 130, 14201-14206.
 (a) H Qi, T Hegmann, J Mater Chem 2006, 16, 4197-4205; (b) M Urbanski, B Kinkead, H Qi, T Hegmann, H -S Kitzerow, Nanoscale 2010, 2, 1118-1121; (c) B Kinkead, M Urbanski, H Qi, H -S Kitzerow, T Hegmann, Proc SPIE 2010, 7775, 777511
 H Qi, T Hegmann, ACS Appl Mater Interfaces 2009, 1, 1731-1738.
 H Qi, B Kinkead, T Hegmann, Adv Funct Mater 2008, 18, 212-221.
 M Urbanski, B Kinkead, T Hegmann, H -S Kitzerow, Liq Cryst 2010, 37, 1151-1156.
 S Umadevi, X Feng, T Hegmann, Ferroelectrics 2012, in press
 M Mirzaei, M Urbanski, K Yu, H -S Kitzerow, T Hegmann, J Mater Chem 2011, 21, 12710-12716.
Professor Yuriy Reznikov, Institute of Physics of National Academy of Sciences of Ukraine, Ukraine Strong coupling between ferromagnetic particles and rod-like particles in aqueous suspensions
Yuriy Reznikov, PhD, Professor in Physics, head of the Department of Crystals at the Institute of Physics (Kyiv, Ukraine). His primary interests are photo-induced and surface phenomena in liquid crystals as well as novel LCD technologies and nanophysics of liquid crystals. Yuriy Reznikov is a co-inventor of effect of photoalignment of liquid crystals. He has been focusing on the study and application of liquid crystal nano-colloids, electro-optics, photorefraction and photonics effects in liquid crystals. Yuriy Reznikov is a co-author of 19 USA patents including basic patents on photoalignment technology, more than 170 papers.
A two-component dispersion of hard rods, one of which is magnetically sensitive, is studied theoretically and experimentally. It is shown that control of the ordering of the magneto-sensitive component by H-field provides effective way to order the non-magnetic component. We found that magnetically-induced ordering of low concentrated ferromagnetic nanoparticles in isotropic phase of the suspension of V2O5 rods in water results in a strong birefringence of the suspension despite V2O5 rods themselves not being sensitive to magnetic field. Furthermore, ferromagnetic nanoparticles also cause extremely high sensitivity of the suspension in the nematic phase; if the native suspension requires magnetic field, H> 7kGs to be reoriented, the doped suspension effectively responds to the magnetic field, H< 30Gs.
Professor Robert Richardson, University of Bristol, UKX-ray studies of particles in liquid crystals
Professor Richardson’s main research interest is the area of Soft Condensed Matter including Liquid Crystals, Molecular Crystals, Surfaces and Interfaces, Thin Organic Films, Colloids and Polymers. The theme that runs through the work is developing or using new structural techniques (particularly X-ray and neutron scattering) for partially disordered materials. The information obtained is used to understand and develop their properties. In recent years, he has been focusing on the following themes.
Nematic liquid crystal comprising small elongated molecules have been the basis for the highly successful display technology. However, they do have some limitations. Displays based on director rotation in transparent materials (e.g. twisted nematic) require polarization and colour filters which absorb a significant fraction of the light. Reflective displays based on the absorption light by guest dye molecules could improve on this. However, they tend to have poor contrast because the orientational order parameter of the dye molecules within the nematic host is low. Suspensions of pigment particles have therefore been investigated as materials for future display applications. In principle, rod shaped particles with the transition dipoles of an absorption in the visible spectrum lying along their axes would be an ideal system. Different combinations of plate and rod like particles with different stabilizers in isotropic and nematic solvents have been used. The principle aim of this work is to characterise the electro-optic properties and understand their origins at the nanoscale level. This can then inform the development of better materials. Several experimental methods have been used to elucidate the properties of the pigment suspensions but absorption spectroscopy and X-ray scattering have predominated.
Professor Jan Lagerwall, Seoul National University, Graduate School of Convergence Science & Technology, KoreaExploring and applying liquid crystals in new geometries prepared by microfluidics and electrospinning
Jan Lagerwall got his MSc in Physics and PhD in Materials Science at Chalmers University of Technology, Gothenburg, Sweden, working primarily with chiral smectic liquid crystals. During post-docs in the USA and Germany he started working also with nanoparticles and lyotropic liquid crystals, and he developed the new field of liquid crystal electrospinning. After three years as a group leader at Martin-Luther University Halle-Wittenberg, Germany, setting up an additional activity in liquid crystal microfluidics, he took on a professorship at Seoul National University, Korea, in September 2010. In April 2007 he obtained the Swedish Docent title in Physics at Chalmers University of Technology and in December 2010 additionally the German Habilitation in Physical Chemistry at Martin-Luther-Universität Halle-Wittenberg. The current research interests are broad, reflecting his activity at an institute of convergence science, ranging from liquid crystal phase transitions in spherical shells to wearable technology and smart textiles, via nanoparticle dispersion and polymer physical chemistry.
We use coaxial electrospinning to prepare composite fibers with a core of LC (nematics or smectics, chiral or non-chiral) inside a polymer sheath, the LC providing functionality and responsiveness [1-3]. With chiral nematics in the core we can produce non-woven textiles with iridescent color that can be tuned (or removed) by heating or cooling . The fibers have wide application possibilities, e.g. as sensors. Using a nested capillary microfluidics set-up we also produce and investigate thin shells of LC, suspended in aqueous host phases [4-6]. The various arrangements of topological defects and other geometrical features developing by self-asesmbly in these shells, and the possibility of tuning the result by modifying boundary conditions, LC phase and thickness and diameter of the shell, make this new LC configuration very attractive.
 J P F Lagerwall, J T McCann, E Formo, G Scalia, Y Xia, Chem.Commun, 42, 5420 (2008)
 E Enz, U Baumeister, J Lagerwall, Beilstein J Org Chem, 5 (2009)
 E Enz, J Lagerwall, J Mater Chem, 20, 6866 (2010)
|4] H-L Liang, S Schymura, P Rudquist, J Lagerwall, Phys Rev Lett 106, 24, 247801 (2011)
 H-L Liang, R Zentel, P Rudquist, J Lagerwall, Soft Matter, DOI:10.1039/C2SM07415J, in press (2012)
 H-L Liang, E Enz, G Scalia, J Lagerwall, Mol Cryst Liq Cryst, 549, 69 (2011)
Professor Matthias Schmidt, University of Bayreuth, GermanyDensity functional theory for colloidal platelet mixtures
Matthias Schmidt received a Diploma in physics at the Friedrich-Alexander-Universitaet Erlangen-Nuernberg in 1994 and a PhD at the Heinrich-Heine-Universität Duesseldorf in 1996. He worked as a software developer with Siemens AG and as a postdoc in Fargo and in the Soft Condensed Matter group of Utrecht University. Schmidt obtained the Habilitation in Theoretical Physics 2005 in Düsseldorf and was appointed Lecturer at Bristol University in 2005, and promoted to Senior Lecturer in 2007 and Professor in 2008. In the same year Schmidt accepted a Chair of Theoretical Physics at the University of Bayreuth in Germany, supported by the Krupp foundation. His scientific interests include equilibrium and out-of-equilibrium Statistical Mechanics of liquids, colloidal dispersions, and their interfaces. Primary methods for investigations are (Monte Carlo) computer simulations and (dynamical) density functional theory.
Density functional theory for inhomogeneous classical liquids is a powerful tool to formulate the Statistical Mechanics of bulk and inhomogeneous classical many-body systems. The central variational principle can be elegantly formulated using Levy's method, and robust approximations for the free energy functional can be constructed using Rosenfeld's fundamental measure theory. After a brief introduction to these general topics, the presentation describes applications of DFT to mixtures of anisometric hard particles, including platelet-platelet and platelet-sphere mixtures. Rich bulk phase diagrams and interfacial effects at substrates and in sedimentation equilibrium are reported. The relevance for describing collective phenomena in corresponding colloidal mixtures is pointed out.
Professor Philippe Poulin, Centre de Recherche Paul Pascal de Bordeaux, FranceLiquid processing of carbon nanotubes
Philippe Poulin is CNRS researcher at the Centre de Recherche Paul Pascal in Bordeaux - France. His fields of interest include soft condensed matter, nanostructured and functional materials. He obtained a PhD degree in Physical Chemistry from the University of Bordeaux in 1995. Then he undertook postdoctoral research at the University of Pennsylvania, USA before taking up his current CNRS position in 1998. P Poulin is currently working on the physical chemistry of nanotube dispersions and of their phase behavior in complex fluids including liquid crystals and nanotube self assemblies with surfactants or polymers. P Poulin is author or co-author of 100 publications and co-inventor of 12 patent applications.
Processing carbon nanotubes in liquid states offers opportunities to control their spatial organization in films, composites, fibers, etc. The use of molecular or macromolecular dispersants allows the interactions between the nanotubes to be finely tuned. As a consequence different states can be obtained from disordered dispersions with low percolation thresholds to ordered liquid crystalline phases in which the nanotubes exhibit long range orientational ordering. We show in this presentation the effect of attractive interactions on the phase behavior of carbon nanotubes. We discuss the possibility to control the morphology of carbon nanotube networks and their resultant electro-optical properties. In particular it is expected that weak attractive interactions should improve electrical contacts between nanotubes and be of interest to develop efficient conductive inks. At high concentration carbon nanotubes form liquid crystals which are of interest to develop anisotropic conductors. We show the influence of processing conditions on the order parameter of nanotube based liquid crystals. When dried they can be used to form highly conductive films. The conductivity anisotropy as a function of the order parameter reveals much greater variations than that of conventional dielectric liquid crystals in which the conductivity anisotropy arises from the anisotropic mobility of charge carriers.
Professor Giusy Scalia, Seoul National University, KoreaCarbon nanotubes in liquid crystals
Guisy Scalia received her undergraduate degree in Physics at the University of Naples and PhD, also in Physics, at Chalmers University of Technology, Göteborg, Sweden. The early interest during the doctoral studies was on electro-optic effects of ferroelectric liquid crystals in waveguiding geometries as well as using guided modes for the structural analysis of films of orthoconic antiferroelectric liquid crystals, during a stay at the University of Exeter. Directly after PhD in 2002, she became permanent researcher at the national research institute ENEA in Italy, starting to work on composites of carbon nanotubes and liquid crystals. She worked on this topic also during a stay as Marie Curie EIF fellow at the Max Planck Institute for Solid State Research in Stuttgart, Germany, 2006-2008. In 2010 she joined Seoul National University as Assistant Professor. Her current research interests span a broad range from semiconducting liquid crystals to liquid crystal nanocomposites formed with different types of nanoparticles, especially carbon based ones. The work in her group targets several different issues, from the challenges in nanoparticle dispersion to the measurement of composite properties.
Carbon nanotubes are notoriously difficult to handle, making their efficient dispersion and alignment challenging. Liquid crystals are very effective per se in imposing organization on carbon nanotubes, and orientational alignment can be successfully transferred by both families of liquid crystals, thermotropics as well as lyotropics, onto embedded nanotubes. The two groups are advantageous for different aspects: while thermotropics are very easy to align macroscopically, profiting from the very well developed aligning techniques, and to reorient with external fields, lyotropics are more compatible with common dispersion methods for carbon nanotubes. These aspects and the achieved results using both classes of liquid crystal, and single- as well as multiwall carbon nanotubes with varying characteristics, will be discussed together with the important, general issue of the dispersion of nanotubes. There will be a particular focus on how the details of the LC matrix can strongly affect the result, lyotropics and thermotropics each having their pros and cons and results from nematic and isotropic hosts being quite different. While the molecular structure of the host seems not to play a critical role for the nanotube ordering this aspect becomes crucial for the capacity of the LC to efficiently disperse the CNTs.
Dr Jeroen S van Duijneveldt, University of Bristol, UKLiquid crystals in natural clay suspensions
Jeroen van Duijneveldt was appointed to a lectureship at the University of Bristol in 1997 and currently is Reader in Physical Chemistry. He obtained his Ph.D. in 1994 at the Van 't Hoff Laboratory in Utrecht under supervision of Professor Lekkerkerker and Dr Dhont. Subsequently, he joined the group of Prof. Allen at the Physics Department at the University of Bristol as a Dutch Ramsay Memorial Fellow. He has published over 50 papers.
He is a member of the Royal Dutch Chemical Society, the Royal Society of Chemistry (RSC), the Society of Chemical Industry and the Institute of Physics. He is treasurer of the RSC Colloid and Interface Science Group and member of the Faraday Council of RSC.
His research focuses on soft condensed matter: colloidal suspensions, emulsions, liquid crystals, and polymers. Such systems find many applications, for instance as inks, paints, home and personal care products and foods. Real systems tend to be complex, consisting of many components that are often difficult to characterise in detail. Well-defined model systems are therefore studied instead. A central theme is the use of polymers to control particle interactions, structure and phase behaviour in colloidal suspensions.
Onsager was the first to propose a theory of the isotropic / nematic transition for suspensions of hard rod-like particles, which occurs due to the fact that the gain in translational entropy overweighs the loss in orientational entropy on increase of concentration. The same phenomenon was also predicted and observed in hard platelet suspensions.
The scope for observing liquid crystals in suspensions of natural clay particles will be addressed. Sepiolite consists of rod-like particles and indeed displays a nematic phase; the spread in particle lengths however modifies and enriches the phase behaviour compared to the theory for monodisperse rods. Furthermore the mineral is porous which allows incorporation of guest molecules such as dyes.
One might expect plate-like smectite clay particles (especially montmorillonite) to be perfect candidates to form colloidal liquid crystals, due to their high aspect ratio (400 nm diameter and 1 nm sheet thickness). However, a nematic phase in montmorillonite suspensions remains elusive, and only recently has a nematic phase been observed in aqueous suspensions of related clays, nontronite and beidellite. Often a sol / gel transition pre-empts the formation of a nematic phase. The effect of adsorbing surfactant on the clay surface will be discussed.
Professor Henk Lekkerkerker, Utrecht University, The NetherlandsLiquid crystal phase transitions in suspensions of mineral colloids: new life from old roots
Henk N W Lekkerkerker(1946) studied chemistry at Utrecht University (MSc 1968) and obtained his doctorate at the University of Calgary (Canada) in 1971. He then moved to Brussels initially as a postdoctoral fellow at the Université Libre de Bruxelles (Belgium) and subsequently became a Professor of Theoretical Physical Chemistry at the Vrije Universiteit Brussel. From 1985 til present he is a Professor of Physical Chemistry at the Van ‘t Hoff laboratory, Utrecht University, and since 2006 he is also Academy Professor of the Royal Netherlands Academy of Arts and Sciences.For his work on phase behaviour of colloidal dispersions he received the Onsager Medal(1999), the Bakhuys Roozeboom Gold Medal of the Royal Netherlands Academy of Arts Sciences (2003),and the Liquid Matter Prize of the European Physical Society(2008) In September 2011 the Royal Society of Chemistry awarded him the Lennard-Jones prize for outstanding contributions to statistical mechanics and thermodynamics.
One of the most remarkable phenomena exhibited by concentrated suspensions of colloidal particles is the spontaneous transition from fluid-like structures to those exhibiting long-range spatial and/or orientational order (colloidal crystals and colloidal liquid crystals). The fact that such ordering can occur in suspensions in which interparticle forces are purely repulsive provides a dramatic realization of the predictions made by Lars Onsager in the 1940’s and later substantiated by computer simulations. From these studies it is clear, that the ordering is driven by entropy.
Liquid crystalline phases in suspensions of mineral colloidal particles have been known for a long time. Zocher reported in 1925 on the observation of a nematic phase in suspensions of V2O5 and a smectic phase in suspensions of -FeOOH.
In recent years the number of mineral colloidal liquid crystals has steadily increased. These systems are interesting due to the fact that size and shape of the particles can be tuned by dedicated chemical synthesis methods leading to novel and interesting phase behavior A very important development is the discovery of a number of natural clays(nontronite,beidellite) that show nematic liquid crystal phases at concentrations as low as 2 wt% This opens the way to produce lyotropic liquid crystals with cheap and abundantly available materials. Modern optical microscopy and Synchrotron X-ray scattering techniques allow these systems to be studied in detail. Furthermore the electric magnetic and optical properties can be varied over a wide range leading to interesting phenomena. In this talk I will review the phases formed and their structural characteristics and compare the results with computer simulations and theoretical predictions.
Professor Helen Gleeson, University of Manchester, UKPushing, pulling and twisting liquid crystal systems; exploring new directions with laser manipulation
Helen gained her PhD in physics from Manchester University in 1986. Following a period as a postdoctoral researcher, she joined the academic staff in Physics and Astronomy at Manchester in 1989. She has held a number of posts in the University, including Associate Dean for Research in the Faculty of Engineering and Physical Sciences (2002-2007) and Head of the School of Physics and Astronomy (2008-2010).
Her research involves experimental studies of liquid crystals, in particular systems with reduced symmetry. Key interests include the structures and properties of liquid crystals, laser interactions with liquid crystal droplets and most recently biaxial nematic phases. She also has an interest in using liquid crystals as sensors.
Helen has held visiting positions at the Universities of Sydney, Case Western Reserve and Griffith (Brisbane). She is a past Chairman of the British Liquid Crystal Society and Vice Chairman of the International Liquid Crystal Society. She has published more than 120 papers and given well over 200 presentations at conferences. Helen takes an active interest in outreach and has given many lectures to schools and the general public. She was awarded an OBE for Services to Science in 2009.
Optical tweezers are exciting tools with which to explore liquid crystal systems; the motion of particles held in laser traps through liquid crystals is perhaps the only approach that allows a low Erickson number regime to be accessed. This offers a new method of studying the microrheology associated with micron-sized particles suspended in liquid crystal media – and such hybrid systems are of increasing importance as novel soft-matter systems. This talk describes the microrheology experiments that are possible in nematic materials and discusses the sometimes unexpected results that ensue. It also touches on the inverse system; micron-sized droplets of liquid crystal suspended in an isotropic medium and shows some remarkable light-induced changes in chirality that result in a micron-sized opto-mechanical transducer. Opportunities for the future are discussed.
Co-authors:M R Dickinson, J E Sanders and Y Yang, The University of Manchester, UK
Professor Igor Muševič, J Stefan Institute and University of Ljubljana, SloveniaTopology and nematic colloids
Igor Muševič received his PhD degree in Physics from the Faculty of Mathematics and Physics, University of Ljubljana, Slovenia, in 1993. He is a full Professor of Physics at the University of Ljubljana and the Head of the Solid State Department at J Stefan Institute in Ljubljana, Slovenia. His research interests are physics and application of liquid crystals, surfaces of soft matter, low temperature scanning microscopy and single atom manipulation. He is co-author of more than 150 scientific papers and articles, more than 30 domestic and international patents and co-author of a monograph "The Physics of Ferroelectric and Antiferroelectric Liquid Crystrals", World Scientific, 2000. He has received several national and international prizes and awards.
Topology has long been considered as an abstract mathematical discipline with little connection to materials science. However, the emergence of a new class of topological materials that includes topological insulators, topological memories and knotted colloidal soft matter, provides strong evidence that topology might play an important role in the design of novel materials with counter-intuitive properties. Here, we discuss the importance of topology in the design and assembly of nematic colloids, where the structural forces between the colloidal particles are much more complex than the forces between the electric charges. This is because the topology of the electromagnetic field has little importance in water-based colloids, but is a novel paradigm in liquid-crystal colloids. In this case the topology of the ordering field is responsible for the striking observations of topological-defect-mediated interactions in 2D colloids, such as the assembly of 2D nematic colloidal crystals and colloidal interactions mediated by entanglement, where knotted topological defect loops form knots and links of arbitrary complexity. In all cases, the colloidal binding energy is of the order of several 1000 kBT. This is several orders of magnitude higher than for water-based colloids and could provide new strategies for topological soft materials and applications in photonics.
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