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Research

    

Research Program Overview

Research Directions We study organizing principles of mesoscale self-assembly phenomena that lead to creation of artificial materials and structures with emergent physical behavior and properties arising from the patterning of molecular order combined with the organization of nano- and micro-sized particles into precisely controlled configurations. These phenomena may enable technological breakthroughs in the development of flexible information displays, efficient conversion of solar energy to electricity, novel optically controlled materials capable, in turn, of controlling light, etc. The emergent scientific frontiers in these fields show an exceptional promise of significant new discovery becoming possible only now, after recent breakthroughs in different branches of science and technology. They require dealing with a hierarchy of length and time scales as well as inspiration and creation of entirely new concepts, laws, and generalizations. We pursue this study in a broad range of nano-structured soft matter systems, with the focus on fundamental aspects, such as the role that topology and geometry play in pre-determining self-assembly. The common theme that unites our research interests is the emergence of various degrees of (liquid crystalline) order as a result of the self-assembly. Examples of current research projects are described below.

Optical Contact-Free Control & Generation of Topological Defects

Torons Defects are responsible for many well-known processes: plastic deformations and fracture in metals are governed by dislocations, vortices in the atmosphere show up as tornadoes, disclinations in condensed matter can mediate phase transitions, cosmic strings have played an important role in the early Universe cosmology, etc. Defects in liquid crystals can be obtained in phases with varying degrees of orientational and positional order and have been routinely used as model systems, for example, in many “cosmology in laboratory” experiments. We have developed methods for non-contact optical generation of defects in liquid crystals described in our 2010 Nature Materials article by use of optical phase singularities in tightly focused laser beams. This new unique experimental capability already allowed us to obtain crystalline and quasi-crystalline patterns of defects and will contribute to the fundamental understanding of defects & their properties.

Topologically Nontrivial Active Colloids and Non-Equilibrium Self-Assembly

We combine topology and active matter paradigms in an effort to achieve topology-dictated nonequilibrium self-assembly of topologically distinct active particles. Active colloids are a distinct category of nonequilibrium matter in which energy uptake, dissipation and movement take place at the level of discrete microscopic constituents. They are known to provide types of self-assembly not accessible in traditional condensed matter systems, such as “living crystals” recently studied by Chaikin, Pine and colleagues. However, only topologically trivial types of active colloids have been realized in the past (in other words, the used constituent active particles were spherical or topologically isomorphic to spheres). Our preliminary observations show that the interplay of topologies of surfaces and flow fields generated by the self-propulsion of active particles can result in highly unusual yet controlled and practically useful forms of self-assembly. To pursue this research direction, our group recently succeeded with practical realization of such active topological colloids. The research on this system transcends the traditional disciplines, ranging from mathematics (topological theories), to physics (active particle behavior, self-assembly), and to chemistry and chemical engineering (material synthesis, photopolymerization, and surface functionalization). The future project outcomes may potentially impinge on our ability of designing new nano- and meso-scale materials with properties not encountered in naturally occurring systems.

Sculpturing Nano-Structured Matter by Controlled Self-Assembly

Colloids Shape Particles embedded in a liquid crystal can interact with each other via elasticity-mediated forces. We study how the host medium’s intrinsic order translates into the self-organization of immersed inclusions depending on shapes/sizes of particles, molecular alignment, and used host anisotropic fluids. Controlled molecular alignment and inter-particle interaction forces are explored for nanocrystals and colloids of complex shapes. The interactions are strongly anisotropic and structures "mimic" molecular alignment fields. The self-assembly properties can be controlled by designing surface boundary conditions and particle shapes. We seek to establish general understanding of this emergent self-assembly behavior, as well as approaches to control structural self-assembly of nano-sized particles, which are much needed for the development of novel methods of manufacturing tunable optical materials.

Biofilms and Cell-Matrix Interactions in Contexts of Cyanobacteria & Biofuels

Bacteria often live in multicellular communities known as biofilms. Unlike their planktonic counterparts, bacteria in biofilms are encapsulated in an extracellular matrix, a complex mixture of macromolecules (including DNA). We use biophotonics and soft matter approaches to quantitatively explore interactions of cells with the extracellular polymeric matrix in the biofilms. Our group utilizes holographic laser trapping to manipulate positions and orientations of hundreds of cells in 3D, measure cell-matrix interaction forces, the strength of binding of bacteria to surfaces, and many-body interactions between bacteria during the so-called "quorum sensing" and at later stages of the biofilm formation. This study will advance quantitative understanding of structural organization in bacterial biofilms and is of both biomedical and technological importance.

Laser-guided Self-Assembly of Dynamically-Controlled Photonic Structures

Toron Arrays Our study shows that the self-assembly of photonic liquid crystal structures can be guided by laser beams. In a topologically frustrated chiral nematic liquid crystal, a focused beam can locally switch between a uniform state and a long-term-stable localized structure with a distorted solitonic molecular alignment field. The structures are stable over long time at no external fields, but can also be “erased” by applying a voltage pulse or “reshaped” by a laser beam. Our research group explores the fundamental physics of these phenomena in contexts of applications such as tunable photonic crystals, singular optics, data storage devices, light/voltage-controlled diffraction gratings, & all-optical information displays.

Particle-like Excitations of Continuous Fields

Toron Hopf A wide variety of quantum field and condensed phase phenomena arise as a result of the existence of particle-like excitations of continuous fields. In a liquid crystal model system, we have observed distinctive particle-like excitations in molecular orientation patterns that enable a continuous localized twist in 3D, which we call “toron”. The basic configuration is a double twist cylinder closed on itself in the form of a torus and coupled to a surrounding uniform field by a pair of point singularities, so that the topological charge is conserved. Remarkably, such structure enables significant localized molecular twist in all directions and can be incorporated into a uniform field. Numerical calculations show that this structure can be a ground state for confined chiral nematics. We also recently demonstrated that the torons are topologically equivalent to the much-storied Hopf fibration and that each toron can be transformed to it by annihilating topological point defects with each other. We continue to explore the stability, structural diversity, and possible new condensed matter phases formed by these and other “building blocks” with topological singularities.

Self-Assembly of Organic Liquid Crystalline Semiconductors

Organic photovoltaic devices are poised to fill the low-cost niche in the solar cell market and have a potential option of being produced in the form of flexible films. However, power conversion efficiencies for organic materials remain low (~8%). In collaboration with NREL, we employ self-organization of organic molecules into ordered columnar discotic and lamellar phases in the effort to improve charge carrier mobility and efficiency of the organic PVs. This becomes possible only now, after recent advances in understanding of fundamental phenomena in organic photovoltaic materials and those associated with self-assembled structures of molecular alignment in nano-confined liquid crystals.

 

Knotted Fields

Knots knotted fields Since the origins of the mathematical knot theory, development of which was prompted by early attempts of understanding structure of atoms, knotted fields and vortices arise in superstring and quantum field theories, quantum chromodynamics, plasmas, cosmology, elementary particles, and other systems. Their complex structures can be predicted from solutions of nonlinear field equations, but are rarely accessible to direct experimental visualization. On the other hand, colloids and liquid crystals offer complexity in degrees of freedom and symmetries that allow for probing analogous phenomena on completely different scales, such as kinetics of atoms in glasses and cosmic strings in the early Universe. To extend these possibilities, our group developes nematic colloids with mutually tangled physical knots of particles and molecular orientation fields. The interplay of topologies of surfaces, fields, and defects guides the molecular orientation field to comply with the knotted particle shape, generating knotted, linked, and other three-dimensional configurations that match theoretical predictions and may allow for insights into many topologically analogous phenomena in other branches of physics. Ranging from scales of elementary particles to cosmology, there are few theoretical predictions of knotted field configurations that can be tested by experiments, which is due to the lack of experimentally accessible systems and techniques. Our model system of knotted nematic colloids for probing of a potentially scale-invariant interplay of topologies of knotted surfaces, fields, and defects. Similar to probing the cosmological Kibble mechanism using LC phase transitions and melting of atomic crystals with colloids, this model system may enable new cosmology- and particle-physics-relevant experiments in laboratory as well as topological soft matter arising from the directed mesoscale self-organization of knotted colloidal “atoms” driven by topological relations.

Topological Colloids and Liquid Crystals under Topological Surface Confinement

Handlebody Boojums Being abundant in nature, colloids find increasingly important applications in science and technology, ranging from direct probing of kinetics in crystals and glasses to fabrication of third-generation quantum-dot solar cells. Since naturally occurring colloidal particles have shapes that are typically determined by minimization of interfacial tension (e.g. during phase separation) or facetted crystal growth, their surfaces tend to have minimum-area spherical or topologically equivalent shapes such as prisms and irregular grains (all continuously deformable – homeomorphic – to spheres). Our research group fabricates and studies colloidal particles with different numbers of handles and genus g. When introduced into a nematic liquid crystal, these particles induce three-dimensional director fields and topological defects dictated by colloidal topology. While electric fields, photothermal melting, and laser tweezing cause transformations among configurations of particle-induced structures, three-dimensional nonlinear optical imaging reveals that topological charge is conserved and that the total hedgehog charge of particle-induced defects obeys predictions of the Gauss-Bonnet and Poincaré-Hopf index theorems. This allowed us to establish and experimentally test the procedure for assignment and summation of topological charges in three-dimensional director fields. These direction may lay the groundwork for new applications of colloids and liquid crystals that range from topological memory devices, to new types of self-assembly, to the experimental study of low-dimensional topology.

Nanostructured Self-Assembly and Controlled Alignment of
Anisotropic Nanoparticles in Complex Fluids

Nanorods Self-assembly of nano-sized functional units is an exceptionally promising way of designing inexpensive artificial composite materials with new macroscopic physical behavior and properties. The main objective of this project (funded by the DOE) is to explore self-organization of anisotropic nanoparticles into colloidal composites with tunable ordered structures. The research is focusing on understanding and control of self-assembly of metal and semiconductor nanoparticles, as well as on material behavior arising from their ordered self-organization and alignment. Fundamental studies of shape-dependent colloidal interactions and ordering of quantum dots and plasmonic metal nanoparticles will reveal underpinning physical mechanisms that guide mesoscale morphology and ultimately determine material properties of the self-assembled composites. These properties are characterized and correlated with hierarchical structures and composition. Control of the particle and molecular structural organization, along with the ensuing composite properties, is achieved by using intrinsic assembly and re-alignment into various mesomorphic phases, applying electric, magnetic, mechanical, and optical fields, as well as changing surface treatment at the nanostructured solid and liquid crystal interfaces. Analytical and numerical modeling of colloidal interactions and material properties will provide important insights at different stages of this project. This research may enable new, cheaper, and more efficient renewable energy technologies, a new breed of energy-efficient information displays and consumer devices, as well as a fertile ground for new basic science.

Soft Condensed Matter Research

Soft Matter Research

Liquid crystals and colloids

Our research is focused on finding new liquid crystal phases and structures and new types of colloidal and molecular interactions with the goal of developing novel materials for technological applications of importaance for the society (such as information displays).

Optics & Photonics Research

Optics & Photonics research

Adaptive light & matter

We are interested in novel physics phenomena and technical approaches that allow for optical control of properties and structural organization in ordered soft materials as well as in the use of soft materials such as liquid crystals to control light.

Nanoscience & Nanotechnology Research

Nanoscience & nanotechnology research

Nano-structured materials & nano-scale phenomena for metamaterials assembly

Our focused effort is to understand organization of nano-structured materials & nano-scale phenomena (such as interactions between nanoparticles) with the goal of finding novel approaches for optical metamaterials self-assembly

Biophysics and Biomolecular Materials Research

Biophysics & Biomaterials Research

Physics of biomolecular assembly & biological cells

We study the physics phenomena behind biomolecular assembly & interactions between cells. For example, the image to the right shows a nematic-like ordering of rod-shaped bacteria in the extracellular polymeric matrix of DNA.

Renewable Energy Research

Renewable Energy Research

Soft Condensed Matter Physics & Nanoscience for Renewable Energy

We develop novel organic photovoltaic solar cells and light-harvesting approaches utilizing nanostructured soft materials such as smectic and columnar discotic liquid crystals that are doped with nanoparticles or infiltrated into nanostructured materials.

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© 2012 Ivan I. Smalyukh. All Rights Reserved

Last update - August, 2013