Liquid Crystals and Other Mesophases
Liquid crystals form a fourth state of matter that combines properties of liquids (e.g. fluidity) with those of crystalline solids (e.g. anisotropy). This combination provides unique opportunities for controlling molecular interactions, packing, and orientations over macroscopic length scales and also induces self-healing properties. Synthetic liquid crystalline materials are best known for their applications in liquid crystal displays (LCDs). However, they are used for many other technologies and have also been widely applied by nature (e.g. cell membranes).
We are most proficient in the preparation and investigation of new mesomorphic dyes (also see organic dyes and pigments) and generally aspire to develop new molecular design criteria for liquid crystals. Our recent efforts have focused on mesophases with p-p stacking intermolecular interactions for applications in organic electronic devices as sensing, charge transport, and light emitting materials. A new direction is the development of side-chain free calamitic and discotic liquid crystals that promise better properties as organic semiconductors.
Columnar Mesomorphism of Board-Shaped Perylene, Diketopyrrolopyrrole, Isoindigo, Indigo, and Quinoxalino-Phenanthrophenazine Dyes. Eichhorn et al., 2021 ChemPlusChem, 86. Mesomorphic rotaxanes: Sheltering ionic cores with interlocking components. Suhan, et al., 2013, J. Am. Chem. Soc. 135 (1), 400. Quasi temperature independent electron mobility in hexagonal columnar mesophases of an H-bonded benzotristhiophene derivative. Demenev, et al., 2010, Chem. Mater. (22,4) 1420-28.
Mono-layer protected metal(oxide) nanoparticles are promising building blocks for the next generation of sensors, drug delivery systems, catalysts, optical, and electronic materials. These nanoparticles and nanocrystals are inherently unstable and must be protected by a coating that usually consists of self-assembled organic ligands, organic polymers, or inorganic polymers.
Our focus has been on the development of new self-assembled organic ligands because they are structurally defined and versatile, they do not significantly increase the size of nanoparticles, and they can leave the metal(oxide) surface accessible for other molecules. We presently work on ligands that form thermally and chemically more stable monolayers and reactive ligands that can be cross-linked at the surface of the nanoparticles without cross-linking NPs. The latter approach may leave sufficient surface area available for other molecules to bind to the metal surface in between the cross-linked ligands. Thermally and chemically stable nanoparticles protected by a porous monolayer are promising materials for catalysis, sensing, and the delivery of pharmaceuticals.
Self-Organization of Metal Nanoparticles in 2 and 3 Dimensions by Yu, et al., in “Anisotropic Nanomaterials: Preparation, Properties, and Applications”, Quan Li, Ed., Springer, Heidelberg, 2015, 289-336.
Organic Dyes & Pigments
Organic dyes are ubiquitous in nature and manufactured products. Their technological development has seen many academic and commercial success stories and is as important and vibrant today as it has been over the last 150 years. Almost every new technology requires the development of new, tailor-made dyes that may function as colourants, light emitters, stabilizers, semiconductors, initiators, recognition sites, etc. Both, molecular and supramolecular structures affect the properties of dyes and must be optimized for every desired application. Thus dye-design at just the molecular level is inadequate to control the resultant properties and a central objective of our research program is the development of new design criteria for self-assembling dyes, in its broadest sense of meaning, i.e. to control properties not only at the molecular but also at the supramolecular level of complexity.
Current projects focus on the development of side-chain free dyes that self-assemble into π-stacking nematic and columnar mesophases (also see liquid crystals) and of cross-linkable amphiphilic dyes that self-assemble at interfaces with defined orientations of the dye core.
Topochemical Polymerization of a Nematic Tetraazaporphyrin Derivative to Generate Soluble Polydiacetylene Nanowires. Tahir, et al., 2019, Langmuir, 35(47) 15158.
Self-organization of Porphyrins and Phthalocyanines in two and three dimensions by Eichhorn, et al., in “Handbook of Porphyrin Science: Towards Tuned Properties of Porphyrinoids”, Vol. 42, Karl M. Kadish, Kevin M. Smith, Roger Guilard, Eds., World Scientific, Singapore, 2016, 173-232.
Cross-linking of discotic tetraazaporphyrin dyes in 2 and 3 dimensions by “click” chemistry. Kayal, et al., 2013, J. Mater. Chem. C, 1(42), 7064.
Polymer Composites & Fibers
Our work on polymer composites and fibers is mostly conducted in collaboration with industrial and academic partners. We typically contribute our expertise in the synthesis and characterization of these materials.
Reduced weld strength due to secondary cell formation in vibration weld region of microcellular glass fiber reinforced nylon-6 shells. Guo, et al., 2019, Welding in the World, 63 (4), 1115-1120.
Carbon-embedded mesoporous Nb-doped TiO2 nanofibers as catalyst support for the oxygen reduction reaction in PEM fuel cells. Navaei Alvar, et al., 2016, J. Mater. Chem. A 4 (17), 6540.
Thermal conductivity of polyurethane composites containing nanometer and micrometer sized silver particles. Iqbal, et al., 2012, J. Therm. Anal. Calorim. (108,3) 933.
HPLC and GPC
UV-vis (polarized), IR (polarized), Raman, Photoluminescence (all variable temperature)
Variable temperature polarized optical microscopy
Transmission XRD Bruker D8 Discover with VÅNTEC-500 detector. Instec variable temperature stage (-20 to 380 ºC) and Oxford cryostream (-100 to 150 ºC)
Reflection XRD Proto AXRD with variable temperature stage (20 to 300 ºC)
TGA-5500, DSC-2500, and DMA-850 by TA Instruments.