Hao Qi

Bio: Hao Qi is an academic researcher from University of Manitoba. The author has contributed to research in topics: Liquid crystal & Homeotropic alignment. The author has an hindex of 14, co-authored 19 publications receiving 1257 citations. Previous affiliations of Hao Qi include University of Winnipeg.

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).

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.

Unprecedented Dual Alignment Mode and Freedericksz Transition in Planar Nematic Liquid Crystal Cells Doped with Gold Nanoclusters

Abstract: We demonstrate that alkylthiol-capped gold nanoclusters doped into nematic liquid crystals (N-LCs) with positive dielectric anisotropy give rise to an unprecedented dual alignment mode and electro-optical response, which has a potential impact on current liquid crystal (LC) display technologies and N-LC optical-biosensor design. By fine-tuning experimental conditions (temperature, electric field, and alignment), N-LCs doped with gold nanoclusters can be aligned and electrically reoriented either like N-LCs with a positive dielectric anisotropy in a planar cell or, alternatively, as N-LCs with a negative dielectric anisotropy in a homeotropic cell, both at lower threshold voltages than the pure N-LC.

Multiple alignment modes for nematic liquid crystals doped with alkylthiol-capped gold nanoparticles.

Abstract: The ability of alkylthiol capped gold nanoparticles (Au NPs) to tune, alter, and reverse the alignment of nematic liquid crystals (LCs) has been investigated in detail. Adjusting the concentration of the suspended Au NPs in the nematic LC host, optimizing the sample preparation protocol, or providing different sample substrates (untreated glass slides, rubbed polyimide-coated LC test cell, or ITO-coated glass slides) results in several LC alignment scenarios (modes) including vertical alignment, planar alignment, and a thermally controlled alignment switch between these two alignment modes. The latter thermal switch between planar and homeotropic alignment was observed particularly for lower concentrations (i.e., around 1 to 2 wt %) of suspended NPs in the size regime of 1.5−2 nm and was found to be concentration-dependent and thermally reversible. Different scenarios are discussed that could explain these induced alignment modes. In one scenario, the NP-induced alignment is related to the temperature-dep...

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.

Chiral Inorganic Nanostructures

Abstract: The field of chiral inorganic nanostructures is rapidly expanding. It started from the observation of strong circular dichroism during the synthesis of individual nanoparticles (NPs) and their assemblies and expanded to sophisticated synthetic protocols involving nanostructures from metals, semiconductors, ceramics, and nanocarbons. Besides the well-established chirality transfer from bioorganic molecules, other methods to impart handedness to nanoscale matter specific to inorganic materials were discovered, including three-dimentional lithography, multiphoton chirality transfer, polarization effects in nanoscale assemblies, and others. Multiple chiral geometries were observed with characteristic scales from angstroms to microns. Uniquely high values of chiral anisotropy factors that spurred the development of the field and differentiate it from chiral structures studied before, are now well understood; they originate from strong resonances of incident electromagnetic waves with plasmonic and excitonic st...

Development of structural complexity by liquid-crystal self-assembly.

Abstract: Since the discovery of the liquid-crystalline state of matter 125 years ago, this field has developed into a scientific area with many facets. This Review presents recent developments in the molecular design and self-assembly of liquid crystals. The focus is on new exciting soft-matter structures distinct from the usually observed nematic, smectic, and columnar phases. These new structures have enhanced complexity, including multicompartment and cellular structures, periodic and quasiperiodic arrays of spheres, and new emergent properties, such as ferroelctricity and spontaneous achiral symmetry-breaking. Comparisons are made with developments in related fields, such as self-assembled monolayers, multiblock copolymers, and nanoparticle arrays. Measures of structural complexity used herein are the size of the lattice, the number of distinct compartments, the dimensionality, and the logic depth of the resulting supramolecular structures.