Welcome to the Hegmann Group website @ KSU

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 LCs and point to new directions for significant improvements in efficiency and performance.
Another unique approach for the design of metamaterials is based on organized arrays of nanomaterials in a reconfigurable anisotropic medium such as a liquid crystal phase.
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 to interact with LCs and fine-tune these 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). We have also shown quite unique dual alignment and electro-optic switching modes in nanomaterial-coped nematic LCs.

Our group is also developing approaches to use LCs as matrices for the assembly of semiconductor nanorods. This multi-investigator project initially with researchers at the University of Manitoba and the California Institute of Technology focuses on the design of nanorod arrays mimicking an artificial photosynthesis system that converts sunlight into chemical fuels such as hydrogen.

Another research area, in collaboration with researchers from Medicine (D.F. Moore, Tulane University), and Pharmacology (D.M. Miller, University of Manitoba), focuses on the development of magnetic core/shell NPs for magnetically directed drug convection to the brain. Here we are also leading efforts to establish a regenerative medicine initiative at Kent State University (ReMedIKS).
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.

Welcome to the Hegmann Group website @ KSU

See our Covers in:

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

PCCP, Liq. Cryst.

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© (T. Hegmann), 17/04/13