Videos and presentation materials from other INI events are also available.
Event  When  Speaker  Title  Presentation Material 

MLCW02 
18th March 2013 09:00 to 09:50 
J Ball 
Satisfaction of the eigenvalue constraints on the $Q$tensor
We discuss how Onsager theory with the MaierSaupe interaction leads naturally to a bulk free energy depending on the $Q$tensor that blows up as the minimum eigenvalue $\lambda_{\rm min}(Q)\rightarrow 1/3$, using methods closely related to those of Katriel, Kventsel, Luckhurst and Sluckin (1986). With this bulk energy, and in the one constant approximation for the elastic energy, it is shown that for suitable boundary conditions, minimizers $Q$ of the total free energy for a nematic liquid crystal filling a region $\Omega$ satisfy the physical requirement that $\inf_{x\in\Omega}\lambda_{\rm min}(Q(x))>1/3$.


MLCW02 
18th March 2013 09:50 to 10:40 
The physics of unphysical simulations
Simulations are patient. In particular, they can be used to model systems that are interesting but `unrealistic'. In fact, from the time of Onsager onwards, unphysical limits have played a key role in our understanding of lyotropic liquid crystals. Interestingly, simulations allow us to probe interesting limits that are inaccessible to experiments.


MLCW02 
18th March 2013 11:00 to 11:50 
Density Functional Theory for HardBody Models of Liquid Crystals
Hardbody models for lyotropic liquid crystalline phases date back to Onsager (1949) who showed that a fluid of hard rods can exhibit a transition from an isotropic to a nematic phase that is driven purely by entropy. Onsager’s treatment is based on a secondvirial description of the free energy that is accurate in the (Onsager) limit of very long thin rods (spherocylinders). For shorter spherocylinders and for smectic and crystalline phases, as well as for treating inhomogeneous fluids, e.g. situations arising at interfaces between phases and in anchoring and wetting at substrates, it is necessary to develop theories in which the ensemble averaged onebody particle density depends on both the orientation and the position of the particles. Density Functional Theory (DFT), developed first for simple fluids with spherical particles, is one such theory and it has emerged as powerful means of tackling phase transitions and the structure and thermodynamics of inhomogeneous fl uids. This lecture will provide an overview of the basics of DFT before focusing on the successful geometrybased Fundamental Measure Theory (FMT) approach introduced originally by Rosenfeld (1989) for hardsphere mixtures. FMT for spheres has as its starting point the incorporation of the exact second virial contribution into the free energy functional. Attempts to extend the ideas of FMT to hard bodies of arbitrary shape were made by Rosenfeld (1994, 1995). These failed to yield a stable nematic phase for spherocylinders, partly because they did not include the correct Onsager limit. In recent years there has been renewed effort to develop improved FMT that go towards capturing this limit. I shall describe progress for a variety of model colloidal liquid crystalline fluids including hard spherocylinders, mixtures of hard spheres and rods, and hard thin platelets. If time permits I shall mention some recent applications of Dynamical DFT to nonequilibrium properties.


MLCW02 
18th March 2013 11:50 to 12:40 
Coarsegrained modelling and computer simulations of liquid crystals
Coarsegrained models for liquid crystals are typically based on pair potentials where an entire mesogenic molecule is represented by one (or a few) anisotropic geometrical object (e.g. a spherocylinder, or an ellipsoid) with either purely repulsive or attractiverepulsive interactions. Computer simulations relying on these simple offlattice models are able to reproduce the experimental phase sequences and order parameters of thermotropic mesogens and are useful for studying the relationship between specific molecular properties (e.g. shape or interaction anisotropies) and macroscopic liquid crystalline behaviour.
We will review the principal coarsegrained level models currently used in computer simulations of liquid crystals and discuss their advantages and shortcomings using the results for selected cases. 

MLCW02 
18th March 2013 14:00 to 14:50 
Active liquid crystals and the origins of cellular locomotion
I will report theory and simulations of the continuum equations for a droplet of active polar liquid crystal. These equations offers a simple representation of a ``cell extract", such a droplet of actomyosin solution, in which myosin motors moving on actin filaments create internal stresses as a result of biological activity. (This system can in turn be viewed as a strippeddown representation of the cytoskeleton which causes locomotion of eukarotic cells.) Actomyosin is an active liquid crystal whose polarity describes the mean sense of alignment of actin fibres. In the absence of polymerization and depolymerization processes (`treadmilling') which arise respectively at the plus and minus ends of the filaments, the active dynamics should be unchanged when polarity is reversed. Our results suggest that, contrary to most literature opinion, locomotion can arise in the absence of treadmilling, by spontaneous symmetry breaking (SSB) of polarity inversion symmetry.


MLCW02 
18th March 2013 14:50 to 15:40 
A Vanakaras 
Biaxial Nematics: Symmetry and Hierarchical Domain Structure
We present theoretical and computer simulation studies on the structure of nematic liquid crystals formed by bentcore mesogens (BCM) and by boardlike colloids (BLC). The presence of local orientational and/or positional ordering is a key feature for the interpretation of the biaxial nematic ordering observed in these systems.
In the first part we present the full phase diagram, calculated from MC molecular simulations, of sterically interacting BLC, for a range of experimentally accessible molecular dimensions/anisometries of colloids of this shape. New classes of phase transition sequences such as nematicnematic and, for the first time, a direct transition from a discotic and a biaxial nematic to an orthogonal smecticA phase have been identified. We demonstrate rigorously the formation of supramolecular entities and explain the observed phase transitions in terms of the "shape anisotropy" of these entropy driven supramolecular assemblies. In the second part the structure of nematic liquid crystals formed by bentcore mesogens is studied in the context of MC simulations of a simple molecular model that captures the symmetry, shape, and flexibility of achiral BCMs. Our results indicate the formation of (i) clusters exhibiting local smectic order, orthogonal or tilted, with strong inlayer polar correlations and antiferroelectric juxtaposition of successive layers and (ii) large homochiral domains through the helical arrangement of the tilted smectic clusters, while the orthogonal clusters produce achiral (untwisted) nematic states. The results of our work offers a deeper understanding of the nematicnematic transitions and, ultimately, of the nematic phase and can serve as a comprehensive guide to experiment, towards the design of anisotropic liquids with the desired functionality, as well as to theory for testing and improving analytical molecular models using simple intermolecular potentials. 

MLCW02 
18th March 2013 16:00 to 16:50 
S Belli 
Brickbybrick stabilizing the Biaxial Nematic Phase
A fascinating way to improve the presentday liquid crystal technology consists of imagining to use new liquid crystal phases with "exotic" properties, like the biaxial nematic phase. However, as an essential step in this direction one has to establish the conditions under which such a phase is thermodynamically stable. Inspired by a recent experiment on a colloidal suspension of mineral goethite particles [1], we use a mean field theory to investigate the phase behavior of boardlike particles. By modelling these “nanoscopic bricks” as cuboids with a hardbody interaction, we analyze the conditions of stability of the longsearched biaxialnematic phase. We show that under specific conditions sizepolydispersity, a common property in most colloids, can increase appreciably the stability of this liquid crystal phase [2]. Moreover, we deduce that this effect can be interpreted in terms of an effective attraction, and therefore that a similar stability could be induced by a nonadsorbing depletant, like a polymeric solution [3].
[1] E. van den Pol et al., Phys. Rev. Lett. 103, 055901 (2009) [2] S. Belli, A. Patti, M. Dijkstra and R. van Roij, Phys. Rev. Lett. 107, 148303 (2011) [3] S. Belli, M. Dijkstra and R. van Roij, J. Phys.: Condens. Matter 24, 284128 (2012)


MLCW02 
19th March 2013 09:00 to 09:50 
Liquid Crystal Director Models with Coupled Electric Fields
Historically, many liquidcrystal devices and experiments have involved lowmolecularweight nematic liquid crystals, in supramicronsize confinements, with coupled electric fields. In such settings, equilibrium orientational properties can be modeled most effectively using the OseenFrank elastic theory coupled with the equations of electrostatics. In this (mostly) expository talk, we will discuss some of the issues that arise in the mathematical and numerical treatment of such classical models. These issues include the intrinsic minimax nature of such models, which arises from the negativedefinite way in which the electrostatic potential enters the free energy functional and which can also arise when Lagrange multipliers are used to enforce the pointwise unitvector constraints on the liquidcrystal director field, as well as the complications this indefiniteness adds to the assessment of local stability of equilibria. We will also discuss the anomalous behavior that can be exhibited at the thresholds of certain electricfieldinduced instabilities because of the nature of the coupling between the director field and the electric field. In addition, we will contrast the macroscopic OseenFrank model with the mesoscopic Landaude Gennes model in such contexts.


MLCW02 
19th March 2013 09:50 to 10:40 
Modelling a planar bistable device on different scales
This talk focuses on the development, analysis and numerical implementation of mathematical models for a planar bistable nematic device reported in a paper by Tsakonas, Davidson, Brown and Mottram. We model this device within a continuum Landaude Gennes framework and investigate the cases of strong and weak anchoring separately. In both cases, we find six distinct states and compute bifurcation diagrams as a function of the anchoring strength. We introduce the concept of an optimal boundary condition that prescribes the optimal interpolation between defects at the vertices. We develop a parallel latticebased Landaude Gennes interaction potential, by analogy with the LebwohlLasher latticebased model and study multistability within this discrete framework too by means of Monte Carlo methods. We also use the offlattice based Gay Berne model to study the structure of the stable states. The different numerical approaches are compared and we discuss their relative strengths a nd shortcomings. We conclude by a brief discussion on a multiscale modelling approach wherein we can couple a latticebased interaction potential to a conventional continuum model. This is joint work with Chong Luo and Radek Erban.


MLCW02 
19th March 2013 11:00 to 11:50 
N Mottram 
Modelling planar bistable devices: from Qtensor to director models
In this talk we continue the theme of bistable devices from the previous presentation. Here we compare the Qtensor model to a director based model, i.e. moving from a mesoscopic approach to a macroscopic approach, in a number of practical examples. We consider the polygonal confinement considered in the previous talk and extend to more general cases of bistability and multistability arising from the morphology of bounding substrates. Bifurcation diagrams of stable states, as parameters such as anchoring strength are varied, are computed. We review some of the advantages and disadvantages of the two modelling approaches and compare results to experimental measurements. Although a director based model is inherently restricted in its inability to model effects such as surface melting and disclination lines, we find that all stable states are in fact reproduced. Additionally we find that, rather surprisingly, the dynamics of switching in the bistable devices can be modelled accu rately using a director theory.


MLCW02 
19th March 2013 11:50 to 12:40 
SAFT force fields for coarsegrained MD simulations
A dangerous overconfidence now prevails in the assumption that detailed allatom or unitedatom models which are used to represent the properties of fluid molecules (e.g. the OPLStype potentials) are sufficient to describe molecular systems with a precision that supplements experiments. More than 1% of all recent articles published in the open science and engineering community deal with molecular simulations at this level and in some cases the accuracy of the results is taken for granted. The fitting of parameter of the force fields is, however, still rather unsophisticated as compared to other aspects of computer modelling. Common practice is to hand fit a few parameters to a few experimental data points (e.g., a radial distribution function, solubility data and/or enthalpies at a given temperature or phase state). In this contribution we propose a new way of obtaining the required force field parameters. In our methodology one requires access to a physicalbased equation of state that describes the complete Helmholtz free energy in closed algebraic form, i.e., an equation of state (EoS) that is based on a defined intermolecular potential. Such an equation can then be used to explore a very large parameter space to estimate the locally optimal parameter set that provides an optimal description of the available macroscopical experimental data. This parameter set represents not just a unique fit to a single temperature or density, but rather an overarching average. If the equation of state is expressed in terms of the free energy of the system for a well defined intermolecular potential, it can be used to develop a “topdown averaged” intermolecular potential. Here we follow this line of thought and present a proofofconcept of such methodology, employing a recently developed EoS of the Statistical Associating Fluid Theory (SAFT) family using the socalled Mie intermolecular potential.


MLCW02 
20th March 2013 09:00 to 09:50 
Glassy dynamics, spinodal fluctuations, and nucleation in suspensions of colloidal hard rods and plates
Using computer simulations we study nucleation in a colloidal supension of hard rods. We study the kinetic pathways for the isotropictonematic transition in a fluid of long hard rods, and find spinodal decomposition as well as nucleation and growth depending on the supersaturation [1]. In supersaturated isotropic fluid states of short hard rods, we observe nucleation of multilayered crystalline clusters. At sufficiently high supersaturations, we find that the nucleation is hampered by glassy dynamics. For intermediat rods, we find that the formation of the (stable) smectic phase out of a supersaturated isotropic state is strongly suppressed by an isotropicnematic spinodal instability that causes huge spinodallike orientation fluctuations with nematic clusters diverging in size [2]. In suspensions of colloidal platelets, we find that the cubatic phase is metastable, and that perpendicularly oriented particle stacks in the isotropic fluid phase inhibits the formation of the columnar phase [3].
[1] A. Cuetos and M. Dijkstra, Physical Review Letters 98, 095701 (2007). [2] R. Ni, S. Belli, R. van Roij, and M. Dijkstra, Physical Review Letters 105, 088302 (2010). [3] M. Marechal, A. Patti, M. Dennison, and M. Dijkstra, Physical Review Letters 108, 206101 (2012). 

MLCW02 
20th March 2013 09:50 to 10:40 
Simulations of model biaxial particles
The behaviour of axially symmetric particles has been wellinvestigated by both theory and computer simulation. Colloidal particles with such shapes have also been studied experimentally. For one component systems, nematic and smectic phases have been observed for rodlike particles, while discotic nematic and columnar phases have been noted for discs. If, however, one considers less symmetrical particles, then other phases become possible. Freiser (1970) showed theoretically that such a system might form a biaxial nematic phase, in which all particle axes are partially aligned, as opposed to a normal, uniaxial nematic where only one axis is ordered. Experimentally, a biaxial nematic phase has been reported for lyotropic systems (Yu & Saupe, 1980) and for suspensions of boardlike goethite particles (van den Pol et al., 2009). There also exist reports of thermotropic biaxial nematic phases, though debate still continues as to whether these really exist for these systems. I would like to present simulation results (and hopefully some simple theory) on two types of model particle which might show biaxial behaviour. The first model is of Vshaped particles (also called boomerangs, bananas and bentcores), while the second is closely related to the boardlike shapes of goethite mentioned above. In both cases the particles interact via repulsive interactions only. Both models have received previous theoretical and simulation attention, but hopefully a little extra investigation will not come amiss.
In both cases we used constant pressure, and sometimes constant stress, molecular dynamics simulations, compressing the system from an initial isotropic phase. For relatively straight Vshped particles, the simulations are straightforward and result in uniaxial nematic and biaxial smectic phases. For a bond angle of less than ca. 130 degrees, however, the system tends to jam on compression and equilibration becomes problematic. We therefore investigated mixtures of Vshapes to see whether mixing suppressed the smectic phases, giving room for a biaxial nematic phase to form. While, at least to date, this hope was not fulfilled, we still observed some effects that we believe are of interest.
The other system studied is of fused hexagons – a model related to hard boards. The phase behaviour observed here was rather rich. Depending on geometry we found rodlike, discotic and biaxial nematic phases. Rodlike particles formed both uniaxial and biaxial smectic A and C phases. Disclike particles formed not only columnar phases but also lamellar phases. Hopefully we will be able to rationalise the presence of at least some of these structures using simpleminded stability analysis.


MLCW02 
20th March 2013 11:00 to 11:50 
Phase behaviour in mixtures of unixial hard particles: biaxiality and confinement
The nematic biaxial phase has remained a key challenge in the science of liquid crystals since it was first proposed. Recently the first experimental evidence of stable biaxial nematic phases has been obtained in thermotropic liquid crystals of single component biaxial mesogens by Madsen et al., and others. Still elusive however is the possibility of stabilizing biaxial nematic phases in mixtures of uniaxial particles. This avenue has been explored in some detail using theory and computer simulation, but leads one to the conclusion that, at least in the case of mixtures of hard particles, the nematic biaxial phase is thermodynamically unstable with respect to demixing into two uniaxial phases. Theoretical calculations have, however, pointed out that with an appropriate attractive unlike interaction, a homogeneous biaxial nematic phase could be stabilized. Experimental work on mixtures of rod and disclike molecules has tended to confirm the view that such a system would favou r phase separation, until the recent studies of Apreutesei and Mehl. In this contribution, we use canonical Monte Carlo molecular simulations to study model mixtures of rodlike and disklike molecules interacting through two intermolecular potential models: one incorporating spherically symmetric (isotropic) attractive interactions; another with anisotropic attractive interactions. These models exhibit nematic and smectic biaxial phases. In the final part of the talk, if time allows, I will briefly discuss the changes in the phase behavior that occur when uniaxial disclike particles are placed in confinement between parallel walls and consider the surface ordering and capillary phenomena in this system.


MLCW02 
20th March 2013 11:50 to 12:40 
E Virga 
Different flavours of the meanfield theory
Since the proposal for a remarkably simple theory of ferromagnetism made by Weiss in 1906, under the assumption that each molecule suffered an effective magnetic field (le champ intérieur, in Weiss' words) mimicking the average action of all other molecules, the notion of mean field has grown and acquired a life of its own. The most striking application to liquid crystal science of the meanfield formalism is perhaps the MaierSaupe theory for the nematic phase. Many other models and approximations are comprised under the general heading of meanfield theory, though often one may hardly find any trace of an average, collective field there, its place being taken instead by a generalized order field. Some theories in this ample catalogue are variational, while others are not. All feature a key selfconsistency condition, which may involve a probability distribution density as well as an order field. The lecture will attempt to justify the key selfconsistency equatio n in a rigorous way for the different flavours that theory has taken.


MLCW02 
20th March 2013 14:00 to 14:50 
L Longa 
LebwohlLasher models of liquid crystals: from quadrupolar to spontaneously induced chiral order
In 1972 P. A. Lebwohl and Q. Lasher (LL) (PRA 6, 426 (1972)) have carried out standard Monte Carlo simulations on the lattice version of the MaierSaupe (MS) model to test predictions of the MS meanfield calculations. Preserving uniaxial symmetry ($D_{\infty h}$)for nematics they assumed liquid crystalline molecules to occupy the sites of a three dimensional cubic lattice subjected to periodic boundary conditions. Pair interaction potential, limited to nearestneighbor molecules, was given by the second Legendre polynomial of the relative angle between the molecular long axes. The simulations showed that the LL lattice model undergoes a weak firstorder phase transition between isotropic and uniaxial nematic order, in qualitative agreement with MS predictions. Since the model has proved to correctly account for the essential symmetry of liquid crystalline orientational order a large amount of work has been and is currently devoted to generalizations of the LL model to more complex situations. They involve, without trying to be exhaustive, (a) investigation of the nematic ordering in confined geometries, subject to different surface anchoring fields, (b) effect of an external field on the isotropic  nematic phase transition(s), (c) simulations of electrooptical devices, (d) simulation of chiral liquid crystal phases, (e) orientational properties of elastomers and (f) physics of twodimensional systems.
In this talk, after a brief review of properties and generalizations of the LL model, I will concentrate on simple versions of this model that can be useful in investigating spontaneous formation of macroscopic chiral domains of opposite handednesses observed in bentcore, dimer and ferrocene mesogens. More specifically, I will discuss properties of the LL model with quadrupolar and octupolar pairinteractions. The model will be shown to generate longrange biaxial order along with ambidextrous twist deformations. A possibility of generating nonzero splay and bent configurations will also be discussed. The class of LL models is generic in the sense that only symmetry allowed terms are retained in the interaction potential. Hence, orientational structures identified not only characterize nematiclike states but can also coexist with a longrange positional order, characteristic of smectic, columnar or crystalline phases. 

MLCW02 
20th March 2013 14:50 to 15:40 
Atomistic molecular dynamics simulations of cyanobiphenyls: A test bench for liquid crystal theories
The recent increase in computer speed has determined unprecedented possibilities of modelling physical and chemical processes “in silico”. This is most true for liquid crystals, as the large system sizes and long time scales necessary for reliable predictions of their selfassembly are now becoming affordable, and where atomistic molecular dynamics simulations have proved that an accurate but classical description of intermolecular forces is adequate for obtaining a quantitative agreement with experiments for nematics and discotics. In this context, in Bologna we developed a force field for nalkyl cyanobiphenyls (nCBs)able to reproduce their experimental phase transition temperatures within a few degrees. The choice of nCBs as prototypical liquid crystal systems opens the way to an informative cross comparison between experiments, simulations, and theory. In fact, the abundance of experimental studies provides a rich database of almost any possible physical property, which serves as a stringent test for simulation predictions, and is able to reveal weaknesses and strengths of the microscopic model. Once the model has been validated, simulations can be considered superior to theoretical predictions, because they rely on a much lower number of assumptions. It becomes then possible to “revisit” and validate existing and maybe even very successful theories, not only on the basis of their predictions (comparison with the experiment) but also on their physical foundations (comparison with simulation s). This presentation will cover all the stages of this “virtuous” exercise, including: the derivation of the force field; II) the calculation of macroscopic observables III) the comparison with mean field descriptions for the nematic and smectic phases; IV) new attempts of addressing continuum theories for liquid crystal alignment. To conclude, a personal perspective of where theory could help the simulation and of future applications will be given.


MLCW02 
20th March 2013 16:00 to 16:50 
Microphase separation driven transitions in macromolecular liquid crystals by computer simulations
We present the results of some recent simulations of macromolecular liquid crystal systems that undergo orderdisorder transitions driven by a microphase separation. Molecular dynamics simulations are performed to study a liquid crystal elastomer of a sidechain architecture crosslinked in the SmA phase. Several effects have been observed: (i) the increase of the SmAI transition temperature as the result of crosslinking; (ii) memory effects in liquid crystallinity and shape when the elastomer is driven through the SmI transition; (iii) both cases of homogeneous director reorientation and stripe formation when the load is applied along the nematic director [1]. In another set of results we consider bulk selfassembly of liquid crystal dendrimers studied by means of coarsegrained molecular dynamics simulations. We discuss the details of the modelling and its application to polymermodified gold nanoparticles. The particular model dendrimer being studied demonstrates conforma tional bistability, with both rodlike and disclike conformations stable at lower temperatures. Each conformation can be induced by the external field of appropriate symmetry, promoting further selfassembly of macromolecules into a bulk monodomain SmA or a columnar phase, respectively [2]. The domains of both phases are found to coexist and influence the system properties in a broad temperature interval including transition to the macroscopically isotropic phase. We also discuss the effect of surface anchoring on the selfassembly of these macromolecules [3].
[1] J.M.Ilnytskyi, M.Saphiannikova, D.Neher, M.P.Allen, Soft Matter (2012), DOI: 10.1039/c2sm26499d [2] J.M.Ilnytskyi, J.S.Lintuvuori, M.R.Wilson, Condens. Matter Phys. 13, 33001 (2010). [3] J.M.Ilnytskyi, M.Schoen, M.R.Wilson, in preparation.


MLCW02 
21st March 2013 09:00 to 09:50 
Design of liquid crystal superstructures: geometry, topology, flow, and mesophase
Structuring of liquid crystalline fluids allows for various exciting material mechanisms such as selfassembly [1], memory effects [2], entanglement [3], nonlinear electrophoresis [4], nonlinear rotary dynamics [5], and nanoscopic surface shape changing [6]. Here, we present strategies for creating colloidal and bulk liquid crystal superstructures, in 2D and 3D, using nematic, twisted nematic, and cholesteric blue phases. Our work is based on the numerical minimization of the phenomenological Landaude Gennes free energy and solving hybrid Lattice Boltzmann algorithm for BerisEdwards nematodynamics model, with full link to experiments. We show that 3D colloidal crystals can be assembled from elastic dipoles of spherical beads in nematic liquid crystals or via inherently inhomogeneous order profiles in cholesteric blue phases [7]. By using colloidal platelets, we show that crystalline [8] and quasicrystalline symmetry can be imprinted into the structures. Topological defects are manipulated into structures of knots and links using various colloidal arrays [9]. Finally, passive and active material flow is used to produce distinct backflow generated complex nematic profiles in microfluidic channels.
[1] P. Poulin, H. Stark, T. C. Lubensky, D. A. Weitz, Science 275, 1770 (1997). [2] T. Araki, M. Buscaglia, T. Bellini, and H. Tanaka, Nature Materials 10, 303 (2011). [3] M. Ravnik, et al, Phys. Rev. Lett. 99, 247801 (2007). [4] O. D. Lavrentovich, I. Lazo and O. P. Pishnyak, Nature 467, 947 (2010). [5] J. S. Lintuvuori, K. Stratford, M. E. Cates, D. Marenduzzo, Phys. Rev. Lett. 107, 267802 (2012). [6] D. Vanzo, M. Ricci, R. Berardi and C. Zannoni, Soft Matter 8, 11790 (2012). [7] M. Ravnik, G. P. Alexander, J. M. Yeomans, and S. Zumer, Proc. Natl. Acad. Sci. USA 108, 5188 (2011). [8] J. Dontabhaktuni, M. Ravnik and S. Zumer, Soft Matter 8, 1657 (2012). [9] U. Tkalec, M. Ravnik, S. Copar, S. Zumer and I. Musevic, Science 333, 62 (2011).


MLCW02 
21st March 2013 09:50 to 10:40 
Isotropicpolar phase transition in an amphiphilic fluid
We present Monte Carlo simulations of the isotropicpolar (IP) phase transition in an amphiphilic fluid carried out in the isothermalisobaric ensemble. Our model consists of LennardJones spheres where the attractive part of the potential is modified by an orientationdependent function. This function gives rise to an angle dependence of the intermolecular attractions corresponding to that characteristic of point dipoles. Our data show a substantial systemsize dependence of the dipolar order parameter. We analyze the systemsize dependence in terms of the orderparameter distribution and a cumulant involving its first and second moments. The order parameter, its distribution, and susceptibility observe the scaling behavior characteristic of the classical 3DHeisenberg universality class. Because of this scaling behavior and because all cumulants have a common intersection irrespective of system size we conclude that the IP phase transition is continuous. Considering pre ssures 1.3≤ P≤3.0 we demonstrate that a line of continuous phase transition exists which is analogous to the Curie line in systems exhibiting a ferroelectric transition. Our results are can be explained semiquantitatively by a simple meanfield theory adapted from the theory of IP phase transitions in fluids in which molecules carry an electromagnetic point dipole.


MLCW02 
21st March 2013 11:00 to 11:50 
Modeling Multicomponent Liquid Crystal Systems
Multicomponent thermotropic liquid crystal mixtures are widely used in the display industry to obtain desired material properties. Usually, the behavior of such mixtures differs little from that of pure materials. In other systems, such as lyotropic, chromonic, colloidal and elastomeric liquid crystals, the behavior can be dramatically different. Standard mean field theories assume a single component, and do not provide an adequate description for such systems. I will discuss strategies to incorporate both attractive and repulsive interactions of multicomponent systems into mean field models, and present some results.


MLCW02 
21st March 2013 11:50 to 12:40 
J de Pablo 
Directed assembly in liquid crystals. Nanoparticles and nanodroplets
Liquid crystals are remarkably sensitive to interfacial interactions. Small perturbations at a liquid crystal interface can in fact be amplified over relative long distances, thereby providing the basis for a wide range of applications. Our recent research efforts have focused on the reverse phenomenon; that is, we have sought to manipulate the interfacial assembly of nanoparticles or the organization of surface active molecules by controlling the structure of a liquid crystal. This presentation will consist of a review of the basic principles that are responsible for liquid crystalmediated interactions, followed by demonstrations of those principles in the context of two types of systems. In the first, a liquid crystal is used to direct the assembly of nanoparticles; through a combination of molecular and continuum models, it is found that minute changes in interfacial energy and particle size lead to liquidcrystal induced attractions that can span multiple orders of magni tude. Theoretical predictions are confirmed by experimental observations, which also suggest that LCmediated assembly provides an effective means for fabrication of plasmonic devices. In the second application, the structure of a liquid crystal is controlled by confinement. It is shown that when confined to submicron droplets, the morphology of the liquid crystal depends on a delicate balance between bulk and interfacial contributions to the free energy; that balance can be easily perturbed by adsorption of analytes at the interface, thereby providing the basis for development of chemical or biological sensors. Theoretical predictions also indicate that the threedimensional order of a liquid crystal can be projected onto a twodimensional interface, and give rise to novel nanostructures that are not found in simple isotropic fluids.


MLCW02 
21st March 2013 14:00 to 14:50 
Molecular modeling of liquid crystal elastomers
Liquid crystal elastomers (LCE) are functional materials consisting of weakly crosslinked polymer networks with embedded liquid crystalline (mesogenic) molecules. Consequently, LCE are characterized by a pronounced coupling between macroscopic strain and orientational mesogenic order. As the latter can be controlled by external stimuli such as temperature, electric field, or ultraviolet light, LCE have great potential for application as sensors and actuators.
Here largescale molecular simulations of swollen mainchain LCE will be presented. The simulated experiments include temperature scans, stressstrain runs, and the application of an external electric field. Our isostress Monte Carlo simulations are capable of reproducing isotropic, nematic and smectic phases, as well as a stressinduced isotropictonematic transition. Moreover, a transversal electric field is seen to induce nematic director rotation resulting in orientational stripe domains. The role of sample swelling has been explored as well.
The simulation output has also been used to connect to typical experimental observables, such as sample dimensions, specific heat, deuterium magnetic resonance spectra, and scattered Xray patterns.


MLCW02 
21st March 2013 14:50 to 15:40 
The Round Table Discussion  
MLCW02 
22nd March 2013 09:00 to 09:50 
Structure and Dynamics of Anisotropic Soft Matter
This paper presents theory and modeling of structure and dynamics of three representative anisotropic soft matter materials :(i) confined nematics ; (ii) membranes and surfactantladen interfaces, and (iii) fiberfilled soft membranes, highlighting the interactions between geometry, order parameters, and material anisotropy. (i)Confined nematics are described using nematodynamics in the bulk, at surfaces and contact lines and used to analyze cholesteric collagen solutions under shear and in film casting processes and demonstrate how liquid crystalline polymer models are able to resolve experimentally observed flowalignment, banded textures, and free surface undulations. (ii) Membranes are described using membranodynamics, which extends the HelfrichBoussinesqScriven model by accounting for bending and torsion dissipation, and is used to establish direct connections between membrane shape and rheology. Lastly we describe (iii) fiberfilled membranes using the integration of nematodynamics and membranodynamics and apply the theory to plant cell walls, where the paranematic order of the cellulose semiflexible fibrils is coupled to the soft pectinbased membrane curvature, as reported experimentally.


MLCW02 
22nd March 2013 09:50 to 10:40 
Liquid crystals out of equilibrium: connecting molecular dynamics, kinetic and hydrodynamic equations
I will start from the microscopic Hamiltonian dynamics and use projectionoperator formalism to derive a generalized Langevin equation for liquid crystalline systems. Using Markovian approximation this equation then may be tuned into a bona fide stochastic differential equation which may be used for molecular dynamics simulations. Further on, using ideas of propagation of chaos, we can derive kinetic DoiSmoluchwski type equation, and finally, the hydrodynamic equations as equations for the moments.
