Ivan I. Smalyukh

Self-Alignment of Plasmonic Gold Nanorods in Reconfigurable Anisotropic Fluids for Tunable Bulk Metamaterial Applications

We demonstrate the bulk self-alignment of dispersed gold nanorods imposed by the intrinsic cylindrical micelle self-assembly in nematic and hexagonal liquid crystalline phases of anisotropic fluids. External magnetic field and shearing allow for alignment and realignment of the liquid crystal matrix with the ensuing long-range orientational order of well-dispersed plasmonic nanorods. This results in a switchable polarization-sensitive plasmon resonance exhibiting stark differences from that of the same nanorods in isotropic fluids. The device-scale bulk nanoparticle alignment may enable optical metamaterial mass production and control of properties arising from combining the switchable nanoscale structure of anisotropic fluids with the surface plasmon resonance properties of the plasmonic nanorods.

Preparation and in vitro characterization of a eutectic based semisolid self-nanoemulsified drug delivery system (SNEDDS) of ubiquinone: mechanism and progress of emulsion formation

The objectives of the present work were, first, to develop a self-nanoemulsified drug delivery system (SNEDDS) based on the eutectic properties of ubiquinone (CoQ10); and second, to study the progress of emulsion formation and drug release mechanisms by turbidimetry and droplet size analysis. Binary phase diagrams of CoQ10 with menthol and essential oils were constructed and used to develop the self-nanoemulsified formulation. Pseudo ternary phase diagram was constructed to identify the efficient self-emulsification region. Release mechanisms of the resultant formulas were quantified using turbidimetry in combination with dissolution studies. Turbidity time profiles revealed three distinctive regions: lag phase, plateau, and the pseudolinear phase. Lag phase was attributed to the liquid crystalline properties of the formula. Plateau turbidity was correlated with droplet size. Laser diffraction analysis revealed an average droplet diameter of 100 nm. Emulsification rate was obtained from the corrected slope of the pseudolinear phase of the profile. Stability of the formula was further evaluated using Fourier transform-infrared (FT-IR) attached to an attenuated total reflectance (ATR) accessory. The present study revealed a eutectic based semisolid self-emulsified delivery system that can overcome the drawbacks of the traditional emulsified systems such as low solubility and irreversible precipitation of the active drug in the vehicle with time.

Shape-Controlled Colloidal Interactions in Nematic Liquid Crystals

Hairy Polygon Solution The packing of rods on the surface of a sphere leads to packing defects at the opposite poles. It is, however, possible to flat-pack rods onto a torus. This topological problem is well known as the hairy ball theorem, and arises when you place spherical particles inside a nematic liquid crystal. Lapointe et al. (p. 1083) considered the packing of liquid crystal molecules onto lithographically fabricated polygons and found that the number of dipoles that formed depended upon whether the polygon had an odd or even number of sides. The defect structures were attracted to each other, such that the liquid crystal could pull together the particles in a form of controlled self-assembly. Polygons dispersed in a liquid crystal solvent form either dipolar or quadrupolar interactions, thus driving self-assembly. Robust control over the positions, orientations, and assembly of nonspherical colloids may aid in the creation of new types of structured composite materials that are important from both technological and fundamental standpoints. With the use of lithographically fabricated equilateral polygonal platelets, we demonstrate that colloidal interactions and self-assembly in anisotropic nematic fluids can be effectively tailored via control over the particles’ shapes. The particles disturb the uniform alignment of the surrounding nematic host, resulting in both a distinct equilibrium alignment and highly directional pair interactions. Interparticle forces between polygonal platelets exhibit either dipolar or quadrupolar symmetries, depending on whether their number of sides is odd or even, and drive the assembly of a number of ensuing self-assembled colloidal structures.

Three-dimensional imaging of orientational order by fluorescence confocal polarizing microscopy

We develop the technique of fluorescence confocal polarizing microscopy to image three-dimensional patterns of orientational order. The method employs the property of anisometric fluorescent dye molecules to orient in an anisotropic medium. When the confocal observation is performed in polarized light, the detected fluorescence signal is determined by the orientation of the molecules. The technique literally adds a new dimension to the studies of the ordered media such as liquid crystals by revealing how the orientation of molecules changes not only in the plane of observations, but also along the direction of observation.

Elasticity-Mediated Self-Organization and Colloidal Interactions of Solid Spheres with Tangential Anchoring in a Nematic Liquid Crystal

Using laser tweezers, we study colloidal interactions of solid microspheres in the nematic bulk caused by elastic distortions around the particles with tangential surface anchoring. The interactions overcome the Brownian motion when the interparticle separation r-->p is less than 3 particle diameters. The particles attract when the angle theta between r-->p and the uniform far-field director n0 is between 0 degrees and approximately 70 degrees and repel when 75 degrees <or approximately theta<or=90 degrees. The particles aggregate in chains directed at approximately 30 degrees to n0 and, at higher concentrations, form complex kinetically trapped structures.

Plasmon-Enhanced Energy Transfer for Improved Upconversion of Infrared Radiation in Doped-Lanthanide Nanocrystals

Upconversion of infrared radiation into visible light has been investigated for applications in photovoltaics and biological imaging. However, low conversion efficiency due to small absorption cross-section for infrared light (Yb(3+)), and slow rate of energy transfer (to Er(3+) states) has prevented application of upconversion photoluminescence (UPL) for diffuse sunlight or imaging tissue samples. Here, we utilize resonant surface plasmon polaritons (SPP) waves to enhance UPL in doped-lanthanide nanocrystals. Our analysis indicates that SPP waves not only enhance the electromagnetic field, and hence weak Purcell effect, but also increase the rate of resonant energy transfer from Yb(3+) to Er(3+) ions by 6 fold. While we do observe strong metal mediated quenching (14-fold) of green fluorescence on flat metal surfaces, the nanostructured metal is resonant in the infrared and hence enhances the nanocrystal UPL. This strong Coulombic effect on energy transfer can have important implications for other fluorescent and excitonic systems too.

Liquid crystals of aqueous, giant graphene oxide flakes

We report the observation of liquid crystals formed by giant graphene oxide flakes (aspect ratio above 10000) suspended in water. As their concentration increases, the flakes undergo transitions from an isotropic dispersion to a biphasic system and then to a discotic nematic liquid crystal. The gel-like liquid crystal displays an unusual defect-free uniform director alignment over hundreds of micrometres. We characterize the nematic order parameter, optical birefringence and elastic properties of this novel mesomorphic system.

Ordered Droplet Structures at the Liquid Crystal Surface and Elastic-Capillary Colloidal Interactions

We demonstrate a variety of ordered patterns, including hexagonal structures and chains, formed by colloidal particles (droplets) at the free surface of a nematic liquid crystal (LC). The surface placement introduces a new type of particle interaction as compared to particles entirely in the LC bulk. Namely, director deformations caused by the particles lead to distortions of the interface and thus to capillary attraction. The elastic-capillary coupling is strong enough to remain relevant even at the micron-scale when its buoyancy-capillary counterpart becomes irrelevant.

Topography from Topology: Photoinduced Surface Features Generated in Liquid Crystal Polymer Networks

Films subsumed with topological defects are transformed into complex, topographical surface features with light irradiation of azobenzene-functionalized liquid crystal polymer networks (azo-LCNs). Using a specially designed optical setup and photoalignment materials, azo-LCN films containing either singular or multiple defects with strengths ranging from |½| to as much as |10| are examined. The local order of an azo-LCN material for a given defect strength dictates a complex, mechanical response observed as topographical surface features.

Tunable optical metamaterial based on liquid crystal-gold nanosphere composite

Effect of the surrounding anisotropic liquid crystal medium on the surface plasmon resonance (SPR) exhibited by concentrated suspensions of gold nanospheres has been investigated experimentally and compared with the Mie scattering theory. The observed polarization-sensitive SPR and the red-shift in the SPR wavelength with increasing concentration of the gold nanospheres in the liquid crystal matrix have been explained using calculations based on the Maxwell Garnet effective medium theory. Agglomeration of the gold nanospheres that could also lead to such a red-shift has been ruled out using Atomic force microscopy study of thin nanoparticle-doped smectic films obtained on solid substrates. Our study demonstrates feasibility of obtaining tunable optical bulk metamaterials based on smectic liquid crystal - nanoparticle composites.