A5011478027- Liquid Crystal Research Advancements
- Synthesis and properties of polymers
- Conducting polymers and applications
- Epoxy Resin Curing Processes
- Molecular spectroscopy and chirality
- Organic Electronics and Photovoltaics
- Membrane Separation and Gas Transport
- Synthesis and Properties of Aromatic Compounds
- Polymer Nanocomposites and Properties
- Polymer composites and self-healing
- Surfactants and Colloidal Systems
- Advanced Materials and Mechanics
- Metal-Organic Frameworks: Synthesis and Applications
- Advanced Battery Materials and Technologies
- X-ray Diffraction in Crystallography
- Tribology and Wear Analysis
- Crystallization and Solubility Studies
- Silicone and Siloxane Chemistry
- Perovskite Materials and Applications
- Plant Reproductive Biology
- Hydrogen Storage and Materials
- Synthetic Organic Chemistry Methods
- Advanced Polymer Synthesis and Characterization
- Molecular Junctions and Nanostructures
- Photochromic and Fluorescence Chemistry
University of North Carolina at Chapel Hill
2008-2025
Applied Physical Sciences (United States)
2017-2025
Delft University of Technology
2012-2021
Communities In Schools of Orange County
2020
Faculty (United Kingdom)
2014-2017
European Space Agency
2013
Université du Québec à Trois-Rivières
2010
European Space Research and Technology Centre
2010
Radboud University Nijmegen
2010
Langley Research Center
2003-2008
We have synthesized liquid crystal (LC) mesogens based on a nonlinear oxadiazole unit that exhibit nematic phases near $200\text{ }\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. Polarized microscopy and conoscopy indicate these LCs are biaxial nematics. Unambiguous quantitative evidence for biaxiality is achieved using $^{2}\mathrm{H}$ NMR spectroscopy. ``2D powder'' spectra, obtained by rotating $^{2}\mathrm{H}$-labeled samples about an axis perpendicular to the magnetic field at...
EDOT-OMeTPA was prepared in a simple condensation reaction. When applied to perovskite solar cells, the new hole transporter shows comparable performance state-of-the-art Spiro-OMeTAD; however estimated cost contribution is two orders of magnitude lower.
Water stable methyl modified MOF-5s have been synthesized via a solvothermal route. Methyl- and 2,5-dimethyl-modified show the same topology hydrogen uptake capability as that of MOF-5. The H2 capacity MOF-5, however, drops rapidly when exposed to ambient air, whereas capacities remain for 4 days.
Abstract State‐of‐the‐art perovskite‐based solar cells employ expensive, organic hole transporting materials (HTMs) such as Spiro‐OMeTAD that, in turn, limits the commercialization of this promising technology. Herein an HTM (EDOT‐Amide‐TPA) is reported which a functional amide‐based backbone introduced, allows material to be synthesized simple condensation reaction with estimated cost <$5 g −1 . When employed perovskite cells, EDOT‐Amide‐TPA demonstrates stabilized power conversion...
The ramifications of changing molecular geometry in a series all-aromatic liquid crystals derived from p-quinquephenyl are reported. Substituting heterocyclic rings such as thiophene, oxadiazole, oxazole, or 1,3-phenylene into the p-quinquephenylene core affects shape changes via substituent's exocyclic bond angle. In general, we found that introducing nonlinearity molecules depresses melting transition temperature. symmetric (boomerang-shaped) molecules,...
Abstract Boomerang-shaped liquid crystals based on 2,5-bis(p-hydroxyphenyl)-1,3,4-oxadiazole (ODBP) having a ~ 134° bend in the mesogenic cores were synthesized and their properties investigated by optical microscopy differential scanning calorimetry. Substituting nonlinear ODBP core with p-dodecyloxyphenyl tails resulted non-linear mesogen that exhibited five distinct mesophases clearing temperature of 204°C. The highest phase appears to be nematic followed smectic C phase. latter freely...
We have explored the opto-electronic properties of a new series hole-transport materials based on main-chain triphenylamine-based poly(azomethine)s. 4,4′-Diaminotriphenylamine (TPA) was polymerized under benign conditions with either terephthalaldehyde (TPA-14Ta), 2,5-thiophenedicarboxaldehyde (TPA-25Th) or 1,3-isophthalaldehyde (TPA-13Iso) to yield polymers an Mn 5700–16 000 g mol−1. Despite non-linear, ‘kinked’, backbone geometry, all form lyotropic solutions in chloroform and this liquid...
New temperature dependent X-ray diffraction (XRD) data on the bent-core mesogens based nonlinear 2,5-bis(p-hydroxyphenyl)-1,3,4-oxadiazole (ODBP) unit enable a consistent interpretation of supramolecular structure in this class liquid crystals. Strong evidence for cybotaxis high phase explains small-angle four-spot pattern and calls into question prior XRD interpretations. We find that can be satisfactorily explained by skewed cybotaxis, stratified arrangement tilted, (BCMs). also observe...
Small-molecule donor materials can be prepared in one step using simple condensation chemistry.
A new liquid-crystalline ion gel exhibits unprecedented properties: conductivity up to 8 mS cm(-1) , thermal stability 300 °C, and electrochemical window 6.1 V, as well adjustable transport anisotropy (up 3.5×) elastic modulus (0.03-3 GPa). The combination of ionic liquid magnetically oriented rigid-rod polyanion provides widely tunable properties for use in diverse devices.
The ubiquitous biomacromolecule DNA has an axial rigidity persistence length of ~50 nm, driven by its elegant double helical structure. While and multiple helix structures appear widely in nature, only rarely are these found synthetic non-chiral macromolecules. Here we describe a conformation the densely charged aromatic polyamide poly(2,2'-disulfonyl-4,4'-benzidine terephthalamide) or PBDT. This macromolecule represents one most rigid simple molecular known, exhibiting extremely high (~1...
The development of perovskite solar cells (PSCs) has ushered in a new era technology, characterized by its exceptional efficiency and cost-effective production. However, the soft fragile nature perovskites makes module encapsulation challenging. Polyolefin elastomers (POEs) have been reported to be promising encapsulants for modules. little research exists on identifying criteria among different types POEs as encapsulants. Here, two with morphologies were compared first POE crystallizes...
The chemistry and physics of high-performance fibre spinning based on main-chain liquid crystal polymer (MCLCP) solutions melts is discussed, which the largest industrial application technology. high modulus strength polymer-based fibres due to exceptionally orientational order that can be achieved, reaching values 0.95 higher. Together with ensures strong intermolecular interactions, often hydrogen bonding, it possible make unusual mechanical thermal properties. such reach at about 50–75%...
Polarising optical microscopy (POM) shows evidence for a reversible uniaxial nematic (NU) to biaxial (NB) phase transition in quiescent melt of bent-core mesogens (BCM). A second superimposed Schlieren texture, attributed director field, grows into the NU on lowering temperature and disappears again heating, indicating fully NB transition. This POM result together with recent X-ray data provides new signature this class BCMs, offers method assessment phases.
A series of azomethine-based HTMs is synthesized using simple condensation chemistry. Their photovoltaic performance and moisture barrier properties are presented.
A symmetric, low-molecular-mass liquid crystal based on the oxadiazole ring was synthesized and characterized. The symmetric position of heterocyclic group in centre crystal, bis(4-hexyloxyphenyl)4,4-(1,3,4-oxadiazole-2,5-diyl)dicarboxylate, yields a very rigid non-linear mesogenic core. Despite this structure, broad crystalline range with smectic C phase found. Conoscopic experiments freely suspended films revealed existence two optical axes phase, indicating symmetry anticipated for either...
We have synthesized homologous series of para-, meta-, and ortho-substituted aryl ether diamine monomers, with either 2, 3, or 4 linkages per monomer unit, prepared their corresponding poly(ether imide)s 3,3′,4,4′-biphenyl dianhydride (BPDA) 3,3′,4,4′-oxydiphthalic (ODPA). All polymers were obtained in high molecular weights gave good quality films expected mechanical thermal properties. The ortho- meta-substituted diamines fully amorphous polymers, whereas the para-based resulted...
Practical methods for hydrogen storage are still a major bottleneck in the realization of an energy economy based on as carrier.(1) Surface adsorption within crystalline, nanoporous, metal−organic frameworks (MOFs) provides promising method that relies sufficiently strong interactions large fraction capacity. Only few MOF structures were studied up to date using neutron diffraction resolve sites.(2-5) Here we use situ characterize (deuterium) sites Cr MIL-53. The strongest present at three...
New stereoregular homo- and copolymers with an ester group at every backbone carbon atom were prepared from ethyl, benzyl tert-butyl diazoacetate (Mw of homopolymers up to 690 kDa 430 kDa). With polarizing optical microscopy we found that the poly(ethyl 2-ylideneacetate) poly(benzyl are able form stable accessible thermotropic lyotropic nematic phases. Both two polymers show relatively high storage moduli glass transition temperature (Tg), as evidenced by dynamic mechanical thermal analysis....