A5074553785- Liquid Crystal Research Advancements
- Advanced Materials and Mechanics
- Micro and Nano Robotics
- Nonlinear Dynamics and Pattern Formation
- Photonic Crystals and Applications
- Microfluidic and Bio-sensing Technologies
- Advanced Thermodynamics and Statistical Mechanics
- Pickering emulsions and particle stabilization
- Characterization and Applications of Magnetic Nanoparticles
- Geometric and Algebraic Topology
- Modular Robots and Swarm Intelligence
- Plant Reproductive Biology
- Mathematics and Applications
- Theoretical and Computational Physics
- Lipid Membrane Structure and Behavior
- Molecular spectroscopy and chirality
- Homotopy and Cohomology in Algebraic Topology
- Material Dynamics and Properties
- Surfactants and Colloidal Systems
- Force Microscopy Techniques and Applications
- Plant and animal studies
- Cellular Mechanics and Interactions
- NMR spectroscopy and applications
- Sports Dynamics and Biomechanics
- Logic, programming, and type systems
University of Warwick
2015-2024
Belfast City Council
2018
University of Bristol
2018
Google (United States)
2016
Coventry (United Kingdom)
2014
University of Oxford
2006-2012
University of Pennsylvania
2009-2012
California University of Pennsylvania
2010
The homotopy theory of topological defects is a powerful tool for organizing and unifying many ideas across broad range physical systems. Recently, experimental progress was made in controlling measuring colloidal inclusions liquid crystalline phases. structure these systems quite rich but, at the same time, subtle. Motivated by experiment power reasoning, classification uniaxial nematic crystals reviewed expounded upon. Particular attention paid to ambiguities that arise systems, which have...
The last years have witnessed remarkable advances in our understanding of the emergence and consequences topological constraints biological soft matter. Examples are abundant relation to (bio)polymeric systems range from characterization knots single polymers proteins that whole chromosomes polymer melts. At same time, considerable been made description interplay between physical properties complex fluids, with development techniques now allow researchers control formation interaction...
Applications for photonic crystals and metamaterials put stringent requirements on the characteristics of advanced optical materials, demanding tunability, high Q factors, applicability in visible range, large-scale self-assembly. Exploiting interplay between structural properties, colloidal lattices embedded liquid (LCs) are promising candidates such materials. Recently, stable two-dimensional configurations were demonstrated nematic LCs. However, question as to whether 3D structures can...
We investigate the hydrodynamic interactions between micro-organisms swimming at low Reynolds number. By considering simple model swimmers, and combining analytic numerical approaches, we time-averaged flow field around a swimmer. At short distances swimmer behaves like pump. large velocity depends on whether stroke is invariant under combined time-reversal parity transformation. then consider two swimmers find that interaction them consists of parts: passive term, independent motion second...
The Hopf fibration is an example of a texture: topologically stable, smooth, global configuration field. Here we demonstrate the controlled sculpting in nematic liquid crystals through control point defects. We how these are related to torons by use topological visualization technique derived from Pontryagin-Thom construction.
We present numerical modelling of colloidal particles in chiral nematics with cubic symmetry (blue phases) within the framework Landau-de Gennes free energy. The interaction potential a single, nano-sized particle -1/2 disclination line is calculated as generic trapping mechanism for cholesteric blue phases. shown to be highly anisotropic and have threefold rotational symmetry. discuss equilibration texture respect positions unit cell size phase. also describe how preservation liquid crystal...
Knots and knotted fields enrich physical phenomena ranging from DNA molecular chemistry to the vortices of fluid flows textures ordered media. Liquid crystals provide an ideal setting for exploring such topological through control their characteristic defects. The use colloids in generating defects configurations liquid has been demonstrated spherical toroidal particles shows promise development novel photonic devices. Extending this existing work, we describe full implications representing...
We provide exact solutions of the Stokes equations for a squirming sphere close to no-slip surface, both planar and spherical, interactions between two squirmers, in three dimensions. These allow hydrodynamic swimming microscopic organisms with confining boundaries, or each other, be determined arbitrary separation and, particular, proximity regime where approximate methods based on point singularity descriptions cease valid. give detailed description circular motion an squirmer moving...
Abstract Active nematics are driven, non-equilibrium systems relevant to biological processes including tissue mechanics and morphogenesis, active metamaterials in general. We study the three-dimensional spontaneous flow transition of an nematic infinite slab geometry using a combination numerics analytics. show that it is determined by interplay two eigenmodes – called S- D-mode unstable at same activity threshold spontaneously breaks both rotational symmetry chiral symmetry. The onset...
We present an investigation of the phase diagram cholesteric liquid crystals within framework Landau-de Gennes theory. The free energy is modified to incorporate all three Frank elastic constants and allow for a temperature dependent pitch in phase. It found that region stability cubic blue phases depends significantly on value constants, being reduced when bend constant larger than splay twist smaller other two. Most dramatically we find large increase I, qualitative change diagram, system...
We perform large scale three-dimensional molecular dynamics simulations of unlinked and unknotted ring polymers diffusing through a background gel, here cubic lattice. Taking advantage this architecture, we propose new method to unambiguously identify quantify inter-ring threadings (penetrations) relate these the polymers. find that both number persistence time increase with length chains, ultimately leading percolating network penetrations. discuss implications findings for possible...
We show that the number of distinct topological states associated with a given knotted defect, L, in nematic liquid crystal is equal to determinant link L. give an interpretation these states, demonstrate how they may be identified experiments, and describe consequences for material behavior interactions between multiple knots. stable knots can created bulk cholesteric illustrate topology by classifying simulated Hopf link. In addition, we heuristic resolution strand crossings defect...
We describe the flows and morphological dynamics of topological defect lines loops in three-dimensional active nematics show, using theory numerical modeling, that they are governed by local profile orientational order surrounding defects. Analyzing a continuous span loop profiles, ranging from radial tangential twist to wedge ±1/2 we show distinct geometries can drive material flow perpendicular or along segment, whose variation around closed lead net motion, elongation, compression shape,...
Umbilic defects of strength s=±1 were induced in a nematic liquid crystal with negative dielectric anisotropy, confined to Hele-Shaw cells homeotropic boundary conditions, and their annihilation dynamics followed experimentally. The speeds individual annihilating defect pairs strengths equal magnitude opposite sign determined as function several externally applied parameters, such cell gap, electric field amplitude, frequency, temperature. It was shown that do not approach each other at...
We present a hydrodynamic model for thin spherical shell of active nematic liquid crystal with an arbitrary configuration defects. The flows generated by defects in the director lead to formation stable vortices, analogous those seen confined systems flat geometries, which generate effective dynamics four +1/2 that reproduces tetrahedral planar oscillations observed experiments. As activity is increased and two counterrotating vortices dominate flow, are drawn more tightly into pairs,...
The homotopy theory of topological defects in ordered media fails to completely characterize systems with broken translational symmetry. We argue that the problem can be understood terms lack rotational Goldstone modes such and provide an alternate approach correctly accounts for interaction between translations rotations. Dislocations are associated, as usual, branch points a phase field, whereas disclinations arise critical singularities field. introduce three-dimensional model...
We describe in detail the hydrodynamics of a simple model linked sphere swimmers. calculate asymptotic form both time averaged flow field generated by single swimmer and interactions between swimmers dilute suspension, showing how each depends on parameters describing its swimming stroke. emphasize importance reversal symmetry determining far around show that are highly dependent relative phase their strokes.
We study the dynamics of ring polymers confined to diffuse in a background gel at low concentrations.
In equilibrium liquid crystals, chirality leads to a variety of spectacular three-dimensional structures, but chiral and achiral phases with the same broken continuous symmetries have identical long-time, large-scale dynamics. this Letter, starting from active model H*, general hydrodynamics pseudoscalar in momentum-conserving fluid, we demonstrate that qualitatively modifies dynamics layered crystals systems both two three dimensions due an "odder" elasticity. dimensions, cholesterics...
We investigate the way in which oscillating dumb-bells, a simple microscopic model of apolar swimmers, move at low Reynold's number. In accordance with Purcell's Scallop Theorem single dumb-bell cannot swim because its stroke is reciprocal time. However motion two or more mutual phase differences, not time reversal invariant, and hence swimming possible. use analytical numerical solutions Stokes equations to calculate hydrodynamic interaction between swimmers discuss their relative motion....
We describe the consequences of time-reversal invariance Stokes equations for hydrodynamic scattering two low-Reynolds-number swimmers. For swimmers that are related to each other by a transformation, this leads striking result angle between is preserved scattering. The illustrated particular case linked-sphere model swimmer. more general pairs swimmers, not time reversal, we find can alter their trajectories several tens degrees. identical contractile lead formation bound state.
We review recent numerical work investigating the equilibrium phase diagram, and dynamics of cholesteric blue phases. In results confirm predictions classic analytical theories, extend them to incorporate different values elastic constants, or effects an applied electric field. There is a striking increase in stability I systems where undergoes helical sense inversion, anomalous electrostriction observed this reproduced. Solving equations motion allows us present for transition kinetics...
Drops of active liquid crystal have recently shown the ability to self-propel, which was associated with topological defects in orientation filaments [Sanchez {\em et al.}, Nature {\bf 491}, 431 (2013)]. Here, we study onset and different aspects motility a three-dimensional drop fluid on planar surface. We analyse theoretically how is affected by profiles various types locations, shape drop, surface friction at substrate. In scope thin approximation, derive exact expressions for flow that...
We propose a construction of cholesteric pitch axis for an arbitrary nematic director field as eigenvalue problem. Our definition leads to Frenet-Serret description orthonormal triad determined by this axis, the director, and mutually perpendicular direction. With tool we are able compare defect structures in cholesterics, biaxial nematics, smectics. Though they all have similar ground state manifolds, different cannot be, general, translated from one phase other.