Torsten Hegmann

Bio: Torsten Hegmann is an academic researcher from Liquid Crystal Institute. The author has contributed to research in topics: Liquid crystal & Nanoparticle. The author has an hindex of 34, co-authored 122 publications receiving 3745 citations. Previous affiliations of Torsten Hegmann include Kent State University & University of Manitoba.

Nanoparticles in Liquid Crystals: Synthesis, Self-Assembly, Defect Formation and Potential Applications

Abstract: Revolutionary developments in the fabrication of nanosized particles have created enormous expectations in the last few years for the use of such materials in areas such as medical diagnostics and drug-delivery, and in high-tech devices. By its very nature, nanotechnology is of immense academic and industrial interest as it involves the creation and exploitation of materials with structural features in between those of atoms and bulk materials, with at least one dimension limited to between 1 and 100 nm. Most importantly, the properties of materials with nanometric dimensions are, in most instances, significantly different from those of atoms or bulk materials. Research efforts geared towards new synthetic procedures for shape and size-uniform nanoscale building blocks as well as efficient self-assembly protocols for manipulation of these building blocks into functional materials has created enormous excitement in the field of liquid crystal research. Liquid crystals (LCs) by their very nature are suitable candidates for matrix-guided synthesis and self-assembly of nanoscale materials, since the liquid crystalline state combines order and mobility at the molecular (nanoscale) level. Based on selected relevant examples, this review attempts to give a short overview of current research efforts in LC-nanoscience. The areas addressed in this review include the synthesis of nanomaterials using LCs as templates, the design of LC nanomaterials, self-assembly of nanomaterials using LC phases, defect formation in LC-nanoparticle suspensions, and potential applications. Despite the seeming diversity of these research topics, this review will make an effort to establish logical links between these different research areas.

Impact of nanoscale particles and carbon nanotubes on current and future generations of liquid crystal displays

Abstract: In this Highlight article we will describe the current impact of nanoscale materials (nanoparticles and carbon nanotubes) in liquid crystal nanocomposites on the improvement of LC display (LCD) applications, an industry currently worth more than $60 billion per year. First tendencies clearly demonstrate the potential of nanomaterials to improve upon current LCD technologies with the discovery of new or modified switching modes, lower operating voltages, faster switching speeds, and higher contrast ratios—enormous advantages in a world with more LCDs than people (see ref. : D. W. Bruce, J. W. Goodby, J. R. Sambles and H. J. Coles, Introduction: New directions in liquid crystal science, Philos. Trans. R. Soc. London, Ser. A, 2006, 364, 2567–2571).

Nanoparticles in liquid crystals and liquid crystalline nanoparticles.

Abstract: Combinations of liquid crystals and materials with unique features as well as properties at the nanoscale are reviewed. Particular attention is paid to recent developments, i.e., since 2007, in areas ranging from liquid crystal-nanoparticle dispersions to nanomaterials forming liquid crystalline phases after surface modification with mesogenic or promesogenic moieties. Experimental and synthetic approaches are summarized, design strategies compared, and potential as well as existing applications discussed. Finally, a critical outlook into the future of this fascinating field of liquid crystal research is provided.

Formation of periodic stripe patterns in nematic liquid crystals doped with functionalized gold nanoparticles

Abstract: Mixtures of nematic liquid crystals (LCs) were produced by doping small quantities of gold nanoparticles coated with non-chiral hexane- (Au1), dodecane- (Au2) or chiral Naproxen-functionalized dodecane thiolates (Au3, Au4). Circular dichroism (CD) spectroscopy confirmed the optical activity for both Naproxen-functionalized gold nanoclusters. The small CD measured for Au1 and Au2 as well as the weak CD above 400 nm measured for Au3 and Au4 is attributed to scattering artifacts of dense particles aggregating in solution. For all mixtures, characterization of the nanoparticle doped nematic phase by polarized optical microscopy revealed the formation of uniform stripe textures or patterns separated by areas of homeotropic alignment due to a spatial separation of particle-rich and particle-poor domains. Similar characteristic textures were also observed for mixtures of the chiral nematic phase produced by doping either only the Naproxen-functionalized thiol 3b or Naproxen and additionally dodecane thiolate-protected gold nanoparticles Au2. On the basis of these findings, observed for the first time for alkane thiolate-capped gold nanoclusters doped into nematic LCs, two different scenarios are suggested. In the first scenario, the optically active gold nanoparticles Au3 and Au4 transfer chirality to the non-chiral nematic LC host. In the second scenario, all functionalized gold nanoclusters Au1–Au4 form topological defects resulting in chain-like particle aggregates, separated by areas of homeotropic alignment due to particles residing at the LC–glass interface.

Quantum dots as liquid crystal dopants

Abstract: Liquid crystal nanoscience, a field exploring the mutually beneficial combination of the unique properties of nanoscale materials and fluid, yet ordered liquid crystalline phases, is increasingly focusing on semiconductor quantum dots. In one major research thrust, the anisotropic properties of the liquid crystal host are sought to facilitate the assembly of quantum dots into arrays, in another, both size- and shape-dependent optical and electronic properties of quantum dots are used to manipulate optical, electro-optical and alignment properties of liquid crystalline materials. This feature article reviews recent accomplishments and new insights in this fascinating area of soft matter nanocomposites including work from our laboratory on a series of CdSe and CdTe quantum dots as additives in nematic liquid crystal hosts.

Mn3O4-Graphene Hybrid as a High Capacity Anode Material for Lithium Ion Batteries

Abstract: We developed two-step solution-phase reactions to form hybrid materials of Mn3O4 nanoparticles on reduced graphene oxide (RGO) sheets for lithium ion battery applications. Mn3O4 nanoparticles grown selectively on RGO sheets over free particle growth in solution allowed for the electrically insulating Mn3O4 nanoparticles wired up to a current collector through the underlying conducting graphene network. The Mn3O4 nanoparticles formed on RGO show a high specific capacity up to ~900mAh/g near its theoretical capacity with good rate capability and cycling stability, owing to the intimate interactions between the graphene substrates and the Mn3O4 nanoparticles grown atop. The Mn3O4/RGO hybrid could be a promising candidate material for high-capacity, low-cost, and environmentally friendly anode for lithium ion batteries. Our growth-on-graphene approach should offer a new technique for design and synthesis of battery electrodes based on highly insulating materials.

The gold–sulfur interface at the nanoscale

Abstract: Thiolate-protected gold surfaces and interfaces, relevant for self-assembled monolayers of organic molecules on gold, for passivated gold nanoclusters and for molecule-gold junctions, are archetypal systems in various fields of current nanoscience research, materials science, inorganic chemistry and surface science. Understanding this interface at the nanometre scale is essential for a wide range of potential applications for site-specific bioconjugate labelling and sensing, drug delivery and medical therapy, functionalization of gold surfaces for sensing, molecular recognition and molecular electronics, and gold nanoparticle catalysis. During the past five years, considerable experimental and theoretical advances have furthered our understanding of the molecular structure of the gold-sulfur interface in these systems. This Review discusses the recent progress from the viewpoint of theory and computations, with connections to relevant experiments.