Liquid Crystal & Nanocomposite Laboratory - Hegmann Group

 
 
The goal of our research is the fabrication of liquid crystal (LC) - nanoparticle composites using functionalized nanoparticles (primarily metal and semiconductor) and thermotropic amphiphilic and non-amphiphilic (conventional) LCs. Of particular interest is the design of LC nanocomposite materials, chiral and non-chiral, that will respond to external stimuli such as temperature and applied electric fields. LCs are extremely useful in a variety of applications (flat panel displays, light shutters, spatial light modulators, and others) because external perturbations via applied electric as well as modified surfaces (e.g., alignment layers) can cause significant changes in the macroscopic properties.  Over the past two decades there has been considerable interest in LC dispersions such as filled nematics (i.e. nematic LCs containing small amounts of dispersed silicon dioxide or titanium dioxide NPs) or nanoparticles dispersed in smectic phases, in part, with unique electro-optical behavior.  Our research strives to improve on these systems by designing specifically functionalized nanoparticles for applications (mixtures, dispersions) or self-assembly in LCs. LC displays have found widespread use in mobile phones, PDAs, electronic games, notebooks, PC screens, super flat TVs, and many industrial control units. LCDs more or less replaced bulky, high-energy cost cathode ray tubes (CRTs) because of their characteristics such as light weight, energy efficiency, and no radiation. New materials, designs, and switching modes enable the production of ultra-sharp large screen TVs, now well over 100", with wide viewing angles and high contrast ratios.  In order to compete with other emerging information display technologies (OLED, luminescent conducting polymers, laser, digital light processing and combinations thereof) in the future, new LC mixtures, new switching modes as well as novel materials combinations resulting in lower operating voltages, faster switching, higher contrast, or self-illumination in the final display are required. A promising class of materials with an enormous potential for improving LCD characteristics are nanoscale particles. Recent, global research activities already demonstrated that different types of NPs can have a profound effect on the performance of LCDs and may point to new directions for significant improvements in efficiency and performance. To achieve this and to gain a fundamental understanding of the unique interactions between nanomaterials and LCs, our lab is developing a systematic approach of functionalizing NPs and LCs to fine-tune mutually beneficial interactions. This approach will open up a new area of nanomaterials for developing novel or improved electro-optic applications of LCs. Research in our lab shows that conventional LCs used in twisted nematic (TN) or in-plane switching (IPS) mode LCDs (i.e. rod-like nematic LCs with positive dielectric anisotropy) and functionalized metal NPs interact in a unique manner with one another as a result of: (1) orientational ordering of the LC phase, (2) topological defects, (3) induced chirality, and (4) long range forces between the colloidal clusters.  In addition, interactions between these components with different substrates such as glass or alignment layers used in LCDs affect their properties (altered dielectric properties, lower threshold voltages, and commonly lower elastic constants) and the overall organization (e.g., alignment). Our group is also developing approaches to use LCs as matrices for the assembly of semiconductor nanorods. This multi-investigator project with researchers at the University of Manitoba and the California Institute of Technology focuses on the design of an artificial photosynthesis system converting sunlight into chemical fuels (i.e. hydrogen). Another research area, in collaboration with researchers from Physics (Johan van Lierop, University of Manitoba), Medicine (David F. Moore, Tulane University), and Pharmacology (Don Miller, University of Manitoba), focuses on the development of magnetic core/shell NPs for magnetically directed drug convection to the brain. We are using a variety of techniques to analyze and characterize the materials we make: NMR, MS, FT-IR, UV-vis-NIR, luminescence, circular dichroism, SEM, TEM, AFM, dynamic light scattering, DSC, polarized optical microscopy, fluorescence confocal polarizing microscopy (FCPM), electro-optic measurements, and XRD (powder and SAXS-WAXS), etc.../Site_3/FCPM.html../Site_2/SAXS_WAXS.htmlshapeimage_1_link_0shapeimage_1_link_1

Welcome to the Hegmann Group website @ KSU

See our Covers in:

Nanoscale, Adv. Funct. Mater., J. Mater. Chem.

PCCP, Liq. Cryst.

Internal Links:

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LCI

Faculty & Staff

© (T. Hegmann), 26/04/12

Read about our research in:

U of M Bulletin and in

ACCN News (issue: June 2008)