Ivan I. Smalyukh, Asst. Professor of Physics, Univ. of Colorado at Boulder
The PI will conduct interdisciplinary research at the interfaces of liquid crystal (LC) physics, nanoscience, and photonics, focusing on fundamental and applied aspects of self-assembly in LC composite materials. He seeks to identify the organizing principles behind self-organization of nano- and micro-sized particles dispersed in LC mesophases ranging from the classical thermotropic nematic to the novel phases composed of bent-core molecules, and to those formed by DNA and live bacteria. PI will establish how director structures around nano- and micro-sized particles immersed in LCs depend on particle?s shape, size, surface treatment, type of the LC mesophase, and applied external fields. He will use topological defects, nano-scale periodic defect arrays in LC blue phases, and strongly-distorted director structures for spatial patterning of particles. LC?s sensitivity to external fields, surface treatment, temperature, and light will enable unprecedented degrees of control over formed self-assembled structures of molecules and inclusions of various shapes and chemical composition. In order to engage this class of problems, the PI will utilize fluorescence-detectable nano- and micro-sized particles ranging from nanocrystals to live bacteria, so that their spatial localization and alignment in the LC samples can be revealed using fluorescence confocal imaging. To get insights into the physics phenomena behind the self-assembly, optical imaging and laser manipulation will be combined synergistically with freeze fracture transmission electron microscopy and synchrotron x-ray micro-beam diffraction, so that the hierarchical self-assembly structures from nanometer to tens of microns length scales can be known. The fundamental phenomena will be examined in the broader contexts ranging from development of self-assembly-based tunable optical metamaterials to understanding bacteria-extracellular matrix interactions in biofilms. This work will advance knowledge of self-assembly in complex fluids and will impinge on fields as diverse as nano-scale interactions and ensuing collective behavior, novel display technologies, efficient conversion of solar energy to electricity using inexpensive organic solar cells, metamaterial fabrication, and bacterial biofilms. PI is will integrate the proposed research projects into a broad range of education and outreach activities.
NON-TECHNICAL SUMMARY: PI is researching organizing principles of nanoparticle and molecular self-assembly into precisely controlled structures in liquid crystals. Fundamental understanding of this ?smart? assembly will shed light on biological organization at the cellular and molecular levels and will enable development of new electrically- and optically-controlled materials with unique properties needed for wide-angle beam steering, efficient conversion of solar energy into electricity, and for practical devices of importance to society, such as flexible displays and data storage devices. PI will integrate this research into educational and outreach programs, including ?Light, Color, & Matter? Wizard Shows in elementary and secondary schools, Science Tours for high school students, advising student chapters of professional societies, providing research experiences for students and faculty from minority-serving institutions and helping them to define their educational and research goals, teaching ?Liquid Crystals: From Fundamentals to Applications? conference short courses for liquid crystal industry, participating in the SPIE visiting lecturer program by giving public lectures worldwide, and organizing international conferences and inter-continental advanced materials and photonics (I-CAMP) summer schools. Lectures of the I-CAMP summer schools will be webcast in real time and then transformed into web-based video archives and interactive tutorials. Moreover, these summer schools will be integrated with outreach forums and career development programs for students and postdoctoral fellows and will attract underrepresented minority participants.
Intelectual Merits Topological defects are ubiquitous in superfluids, liquid crystals, Langmuir monolayers, and Bose-Einstein condensates. They determine supercurrents in superfluids, impinge on electro-optic switching in polymer dispersed liquid crystals, and mediate chemical response at nematic-isotropic fluid interfaces, but the role of surface topology in appearance, stability, and core structure of these defects remains poorly understood. In our research, we demonstrated robust generation of topological defects by controlling surface topology of colloidal particles that impose tangential boundary conditions for the alignment of liquid crystal molecules. To do this, we designed handlebody-shaped polymer particles with different genus g. When introduced into a nematic liquid crystal, these particles distort the nematic molecular alignment field while obeying topological constraints and induce boojums that allow for topological charge conservation. We have characterized three-dimensional textures of boojums using polarized nonlinear optical imaging of molecular alignment and explained our findings by invoking symmetry considerations and numerical modeling of experiment-matching director fields, order parameter variations, and nontrivial handle-shaped core structure of defects. Finally, we have proposed that this interplay between the topologies of colloidal surfaces and boojums may lead to controlled self-assembly of colloidal particles in nematic and paranematic hosts that, in turn, may enable reconfigurable topological composites, which can be controlled by light and electric fields. These studies were described in our 2013 Nature and PNAS articles. In another effort, we have studied translational and rotational diffusion of anisotropic gold nanoparticles dispersed in the bulk of a nematic liquid crystal fluid host. Experimental data reveal strong anisotropy of translational diffusion with respect to the uniform far-field director, which is dependent on shape and surface functionalization of colloids as well as on their ground-state alignment. For example, elongated NPs aligned parallel to the far-field director translationally diffuse more rapidly along the director whereas diffusion of NPs oriented normal to the director is faster in the direction perpendicular to it while they are also undergoing elasticity-constrained rotational diffusion. To understand physical origins of these rich diffusion properties of anisotropic nanocolloids in uniaxially anisotropic nematic fluid media, we compared them to diffusion of prolate and oblate ellipsoidal particles in isotropic fluids as well as to diffusion of shape-isotropic particles in nematic fluids. We also showed that surface functionalization of NPs with photosensitive azobenzene groups allows for in situ control of their diffusivity through trans-cis isomerization that changes surface anchoring. (Phys Rev E 2013). We also developed active elastomeric liquid crystal particles. Gold nanocrystals infiltrated into these particles mediate energy transfer from laser light to heat, so that the inherent coupling between the temperature-dependent order and shape allows for dynamic morphing of these particles and well-controlled stable shapes. Continuous changes of particle shapes are followed by their spontaneous realignment and transformations of director structures in the surrounding cholesteric host, as well as locomotion in the case of a nonreciprocal shape morphing. These findings bridge the fields of liquid crystal solids and active colloids, may enable shape-controlled self-assembly of adaptive composites and light-driven micromachines, and can be understood by employing simple symmetry considerations along with electrostatic analogies. (Phys Rev Lett 2013). Other scientific and technological breakthroughs include development of new 3D imaging techniques, development of metal and semiconductor nanoparticle dispersions in thermotropic liquid crystals, development of structured composites based on graphene and graphene oxide, etc. Broader Impacts The research efforts involved 14 undergraduate students (co-supported by CU Undergraduate Research Opportunities Program and Discovery Learning Apprenticeship Program). Two of PI's graduate students (Rahul Trivedi and Julian Evans) successfully defended their PhDs; Rahul is now a research team leader at Intel and Julian is a postdoctoral fellow. The PI organized I-CAMP'13 summer school on Liquid Crystals in Cambridge, UK (http://i-camp.colorado.edu/i-camp2013/ ) and started organizing the I-CAMP'14 summer school on topology in materials systems and light in South Africa (http://i-camp.colorado.edu/i-camp2014/ ). These schools are part of the highly successful annual summer school series organized by the PI and supported by the International Institute for Complex Adaptive Matter ( http://i-camp.colorado.edu ). As part of his industrial outreach, the PI was teaching conference short courses and in-company courses, such as the SC790 course on Fundamentals and Applications of Liquid Crystals at the Photonics West 2013 conference. The PI was also supervising CU SPIE and MRS student chapters, giving Saturday Physics lectures, as well as conducting outreach at both high school and middle school levels. The new topological and other colloidal dispersion soft matter systems developed by the PI and his team may lead to technological devices and practical applications of importance for the society.
