Liquid‐Crystal Composites Composed of Photopolymerized Self‐Assembled Fibers and Aligned Smectic Molecules

A new liquid‐crystal composite, composed of photopolymerizable self‐assembled fibers and a smectic liquid crystal, and its photopolymerized composite have been prepared. The fibers oriented along the smectic layers are obtained by self‐assembly of an amino acid derivative with terminal methacryloyl groups in the smectic liquid crystal. The oriented fibrous structures are fixed by photopolymerization, resulting in the formation of microgrooves on the substrate surfaces. The aligned direction of the liquid‐crystalline molecules is changed to the direction along the fibers after thermal annealing. The patterning of liquid‐crystal alignment is achieved for these liquid‐crystal composites by patterned photopolymerization.     

Control and Suppression of Surface Relief Gratings in Liquid‐Crystalline Perfluoroalkyl–Azobenzene Polymers

Semifluorinated azobenzene liquid‐crystalline side‐chain polymers with different perfluoroalkyl lengths are used to develop surface relief gratings (SRGs). With sufficient fluorinated side‐chain lengths, surface relief gratings could be completely suppressed due to the self‐assembled liquid‐crystalline order at the surface. This indicates that there is a surface‐dependent nature to SRG formation. The SRG formation from the semifluorinated azobenzene liquid‐crystalline side‐chain polymers is compared to methoxy‐terminated azobenzene side‐chain polymers, and results show that the perfluoroalkyl–azobenzene polymers require a longer formation time than the methoxy‐terminated polymers.     

Template‐Assisted Self‐Assembly of Spherical Colloids into Complex and Controllable Structures

Colloidal aggregates with well‐controlled sizes, shapes, and structures have been fabricated by dewetting aqueous dispersions of monodispersed spherical colloids across surfaces patterned with two‐dimensional arrays of relief structures (or templates). The capability and feasibility of this approach have been demonstrated with the organization of polymer latex or silica beads into homo‐aggregates, including circular rings; polygonal and polyhedral clusters; and linear, zigzag, and spiral chains. It was also possible to generate hetero‐aggregates in the configuration of HF and H₂O molecules that contained spherical colloids of different sizes, compositions, densities, functions, or a combination of these features. These uniform, well‐defined aggregates of spherical colloids are ideal model systems to investigate the aerodynamic, hydrodynamic, and optical properties of colloidal particles characterized by non‐spherical shapes and/or complex topologies. They can also serve as a new class of building blocks to generate hierarchically self‐assembled structures that are expected to exhibit interesting features valuable to areas ranging from condensed matter physics to photonics.     

Self‐Assembled Shape‐Memory Fibers of Triblock Liquid‐Crystal Polymers

New thermoplastic liquid‐crystalline elastomers have been synthesized using the telechelic principle of microphase separation in triblock copolymers. The large central block is made of a main‐chain nematic polymer renowned for its large spontaneous elongation along the nematic director. The effective crosslinking is established by small terminal blocks formed of terphenyl moieties, which phase separate into semicrystalline micelles acting as multifunctional junction points of the network. The resulting transient network retains the director alignment and shows a significant shape‐memory effect, characteristic and exceeding that of covalently bonded nematic elastomers. Its plasticity at temperatures above the nematic–isotropic transition allows drawing thin well‐aligned fibers from the melt. The fibers have been characterized and their thermal actuator behavior—reversible contraction of heating and elongation on cooling—has been investigated.     

Fast and High‐Contrast Electro‐optical Switching of Liquid‐Crystalline Physical Gels: Formation of Oriented Microphase‐Separated Structures

Fast and high‐contrast responses with low driving voltages in twisted nematic (TN) cells are achieved for anisotropically oriented structures of liquid‐crystalline physical gels. They are prepared by hydrogen‐bonded aggregation of an L ‐lysine‐based gelator in nematic liquid crystals. When the mixtures of the nematic liquid crystals and the gelator are prepared in TN cells, fibrous aggregates of the gelator align along the twisted‐nematic orientation of the liquid crystal, forming oriented phase‐separated structures.     

Recent Advances in the Design of Polymerizable Lyotropic Liquid‐Crystal Assemblies for Heterogeneous Catalysis and Selective Separations

Organic lyotropic liquid‐crystal (LLC) assemblies mimic molecular sieves in their nanoporous structures and their ability to incorporate catalytic functional groups. This article focuses on recent advances made by our research group in incorporating new catalytic properties into polymerizable LLC assemblies and studying the molecular‐transport properties of the crosslinked networks.     

Orientational Switching of Mesogens and Microdomains in Hydrogen‐Bonded Side‐Chain Liquid‐Crystalline Block Copolymers Using AC Electric Fields

In this report, we show that the microstructures of hydrogen‐bonded side‐chain liquid‐crystalline block copolymers can be rapidly aligned in an alternating current (AC) electric field at temperatures below the order–disorder transition but above the glass transition. The structures and their orientation were measured in real time with synchrotron X‐ray scattering. Incorporation of mesogenic groups with marked dipolar properties is a key element in this process. A mechanism related to the dissociation of hydrogen bonds is proposed to account for the fast orientation switching of the hydrogen‐bonded blends.     

Large Area Self‐Assembly of Nematic Liquid‐Crystal‐Functionalized Gold Nanorods

Fascinating nematic‐ and smectic‐like self‐assembled arrays are observed for gold nanorods partially capped with either laterally or terminally attached nematic liquid crystals upon slow evaporation of an organic solvent on TEM grids. These arrays can be manipulated and reoriented by applying an external magnetic field from quasi‐planar to vertical similar to a Fréedericksz transition of common organic nematic liquid crystals. Birefringence and thin film textures of these self‐assembled gold nanorod arrays observed by polarized optical microscopy are strongly reminiscent of common organic nematic liquid crystal textures between crossed polarizers and, additionally, support the formation of ordered liquid crystal‐like anisotropic superstructures. The ordering within these arrays is also confirmed in bulk samples using small angle X‐ray scattering (SAXS).     

Anisotropic Change of Liquid‐Crystal Domains by Polarized Infrared Pulse Laser Irradiation for a Columnar Mesophase

The infrared photoinduced alignment change of liquid‐crystal domains was investigated for a hexagonal columnar mesophase of a liquid‐crystalline triphenylene derivative. A uniform and anisotropic alignment change of domains was observed when a polarized infrared (IR) light corresponding to the wavelength of the aromatic C–C stretching absorption band of the triphenylene core was used to irradiate the sample. The relationship between the aligned azimuthal angle of the columnar axis and the polarization of the IR incident irradiation was investigated. IR absorption dichroism is induced as a result of the reorientation of triphenylene core. Texture observation and polarizing microscope FTIR spectra show that a change of the molecular alignment occurred and that the direction of columns depends on the polarization angle of the IR light used for irradiation. The mechanism of the alignment change in a columnar liquid crystal film by IR irradiation is also discussed. The technique could provide a novel technology to control the columnar alignment of highly viscous liquid crystals.     

Synthesis,Properties, and Photopolymerization of Liquid‐Crystalline Oxetanes: Application in Transflective Liquid‐Crystal Displays

Mixtures of liquid‐crystalline di‐oxetanes and mono‐oxetanes are made for the purpose of making birefringent films by photopolymerization. The composition of a di‐oxetane mixture that forms spin‐coated films of planarly aligned nematic monomers is reported. These films are photopolymerized in air. The molecular order of the monomers can be changed on the microscale to form thin films with alternating birefringent and isotropic parts by using a combination of photopolymerization and heating. The interface observed between the birefringent and isotropic 10 μm × 10 μm domains is very sharp and the films show hardly any surface corrugation. In addition, the polymerized films are thermally stable, making them very suitable for use as patterned thin‐film retarders in high‐performance transflective liquid‐crystal displays (LCDs) which satisfy customer demand for displays that are brighter and thinner and that deliver better optical performance than conventional LCDs with an external non‐patterned retarder.     

Electropolymerization of a Bifunctional Ionic Liquid Monomer Yields an Electroactive Liquid‐Crystalline Polymer

The preparation and polymerization of a bifunctional imidazolium‐based ionic liquid (IL) monomer that incorporates both a vinyl group and a thiophene moiety is reported. Potentiodynamic electropolymerization of the monomer produces an optically birefringent polymer film that strongly adheres to the electrode surface. Fourier transform IR spectroscopy shows that polymerization occurs through both the vinyl and thienyl groups. Cylic voltammetry (CV) is used to determine the polymer oxidation potential (1.66 V) and electrochemical bandgap, E_g, of 2.45 eV. The polymer exhibits electrochromism, converting from yellow in the neutral form (λ_max = 380 nm) to blue in the polaronic state at 0.6 V (λ_max = 672 nm) and to blue‐grey in the bipolaronic state at 1.2 V (λ_max > 800 nm). Topographic atomic force microscopy (AFM) images reveal isolated (separated) fibrils. Grazing‐incidence small‐angle X‐ray scattering (GISAXS) studies indicate a lamellar structure with a lattice spacing of 3.2 nm. Wide‐angle X‐ray diffraction (WAXD) studies further suggest that the polymerized thiophene sheets are oriented perpendicular to the polymerized vinylimidazolium. The electrical conductivity, as determined by four‐probe dc conductivity measurements was found to be 0.53 S cm^?1 in the neutral form and 2.36 S cm^?1 in the iodine‐doped state, values higher than typically observed for polyalkylthiophenes. The structural ordering is believed to contribute to the observed enhancement of the electrical conductivity.     

Rapid Fabrication of Two‐ and Three‐Dimensional Colloidal Crystal Films via Confined Convective Assembly

We have developed a self‐assembly method for fabricating well‐ordered two‐dimensional (2D) and three‐dimensional (3D) colloidal crystal films. With a minute amount of a polystyrene colloidal suspension and without any special equipment, the proposed method can be used to rapidly deposit high‐quality colloidal crystal films over a large surface area. By controlling the lift‐up rate of the substrate, we modulate the meniscus thinning rate, which determines whether the colloidal particles are assembled into two or three dimensions. The proposed method can be used to fabricate not only monolayered colloidal crystals with colloidal particles of various sizes, but also multilayered colloidal crystals. In addition, the method enables us to fabricate binary colloidal crystals by consecutively depositing large and small particles.     

Hierarchical Self‐Assembly of Peptide‐Coated Carbon Nanotubes

Numerous applications, from molecular electronics to super‐strong composites, have been suggested for carbon nanotubes. Despite this promise, difficulty in assembling raw carbon nanotubes into functional structures is a deterrent for applications. In contrast, biological materials have evolved to self‐assemble, and the lessons of their self‐assembly can be applied to synthetic materials such as carbon nanotubes. Here we show that single‐walled carbon nanotubes, coated with a designed amphiphilic peptide, can be assembled into ordered hierarchical structures. This novel methodology offers a new route for controlling the physical properties of nanotube systems at all length scales from the nano‐ to the macroscale. Moreover, this technique is not limited to assembling carbon nanotubes, and could be modified to serve as a general procedure for controllably assembling other nanostructures into functional materials.     

Supramolecular Self‐Assembly of Nanoconfined Ionic Liquids for Fast Anisotropic Ion Transport

Materials involving nanoconfinement of ionic liquids (ILs) have been pursued for functionalities and ionic devices. However, their complex synthesis, challenges to achieve long‐range order, and laborious tunability limit their practical implementation. Herein, these challenges are addressed by complexing surfactants to ILs, yielding a facile, modular, and scalable approach. Based on structural screening, ionic complexation of di‐n‐nonylamine to the terminal sulfonic acid of 1‐(4‐sulfobutyl)‐3‐methylimidazolium hydrogen sulfate IL is selected as a proof of concept. Spontaneous homeotropic smectic order over micrometers is observed, with alternating ionic and alkyl layers. The 1 nm thick ionic layers involve 2D crystalline internal order up to 150 °C, strongly promoting anisotropic ion transport (σ_||/σ_⊥ > 6500), and curiously, still allowing fluidity. High ionic conductivity of 35 mS cm^?1 and mesoscopic diffusion coefficient of ≈10^?5 cm² s^?1 at 150 °C along the ionic layers are observed. Fast anisotropic ion transport by simply complexing two components open doors to functional materials and applications.     

1,3,6,8‐Tetraphenylpyrene Derivatives: Towards Fluorescent Liquid‐Crystalline Columns?

Tetraphenylpyrene has been selected as a discotic core to promote liquid‐crystalline fluorescent columns in view of its high fluorescence quantum yield in solution and ease of substitution by flexible lateral side chains. The synthesis and characterization of ten new derivatives of pyrene have been carried out; the pyrene core has been substituted at the 1,3,6,8‐positions by phenylene rings bearing alkoxy, ester, thioether, or tris(alkoxy)benzoate groups on the para position; the compounds have been characterized by mass spectrometry and ¹H NMR and UV‐vis spectroscopies. In order to generate liquid‐crystalline phases, the nature, number, and size of the side chains as well as the degree of polarity around the tetraphenylpyrene core have been varied. However, the desired liquid‐crystalline behavior has not been observed. The supramolecular order together with the absorption and emission properties in solution and the solid state are discussed and compared to theoretical predictions. Quantum‐chemical calculations rationalize the high solid‐state fluorescence of a tetraphenylpyrene derivative for which the crystal structure has been determined.     

Self‐Assembly in Hopper‐Shaped Crystals

Hopper shape is a special type of crystal morphology. Hopper‐shaped crystals possess unique properties and show promise in many different applications. The understanding of how the building blocks (atoms, ions, and molecules) assemble into hopper‐shaped crystals and how the environmental factors influence the assembly process is critical to the properties and applications of hopper‐shaped crystals. In this review, the important interfacial instability theories that outline the underlying mechanisms for the formation of hopper‐shaped crystals are discussed. Next, the relevant experimental developments based on three categories of synthetic approaches are discussed: the growth through the control of the solute concentration, the temperature gradient, and the capping agent. At the end of the review, the applications, opportunities, and potential challenges of the hopper‐shaped crystals are discussed.     

Fabrication of Multicomponent Microsystems by Directed Three‐Dimensional Self‐Assembly

We have developed a directed self‐assembly process for the fabrication of three‐dimensional (3D) microsystems that contain non‐identical parts and a statistical model that relates the process yield to the process parameters. The self‐assembly process uses geometric‐shape recognition to identify different components, and surface tension between liquid solder and metal‐coated areas to form mechanical and electrical connections. The concept is used to realize self‐packaging microsystems that contain non‐identical subunits. To enable the realization of microsystems that contain more than two non‐identical subunits, sequential self‐assembly is introduced, a process that is similar to the formation of heterodimers, heterotrimers, and higher aggregates found in nature, chemistry, and chemical biology. The self‐assembly of three‐component assemblies is demonstrated by sequentially adding device segments to the assembly solution including two hundred micrometer‐sized light‐emitting diodes (LEDs) and complementary metal oxide semiconductor (CMOS) integrated circuits. Six hundred AlGaInP/GaAs LED segments self‐assembled onto device carriers in two minutes, without defects, and encapsulation units self‐assembled onto the LED‐carrier assemblies to form a 3D circuit path to operate the final device. The self‐assembly process is a well‐defined statistical process. The process follows a first‐order, non‐linear differential equation. The presented model relates the progression of the self‐assembly and yield with the process parameters—component population and capture probability—that are defined by the agitation and the component design.     

Binary and Ternary Polymer‐Mediated “Bricks and Mortar” Self‐Assembly of Gold and Silica Nanoparticles

An amine‐functionalized polymer has been used to simultaneously assemble carboxylic acid functionalized gold and silica nanoparticles into extended aggregates. This three component assembly process is highly versatile, with aggregate morphology controlled through stoichiometry, and nanoparticle segregation within the aggregate regulated through order of component addition.     

Thermoplastic Elastomer Hydrogels via Self‐Assembly of an Elastin‐Mimetic Triblock Polypeptide

Protein‐based analogues of conventional thermoplastic elastomers can be designed with enhanced properties as a consequence of the precise control of primary structure. Protein 1 undergoes a reversible sol–gel transition, which results in the formation of a well‐defined elastomeric network above a lower critical solution temperature. The morphology of the network is consistent with selective microscopic phase separation of the endblock domains. This genetic engineering approach provides a method for specification of the critical architectural parameters, such as block length and sequence, which define macromolecular properties that are important for downstream applications.     

Electrotunable Non‐reciprocal Laser Emission from a Liquid‐Crystal Photonic Device

A liquid crystal (LC) photonic device with an anisotropic optical heterojunction structure has been fabricated. The device has a phase‐retarding nematic LC (NLC) layer sandwiched between two polymer cholesteric LC films with right‐handed helices of different pitches. Electrotunable non‐reciprocal light transmittance and unidirectional circularly polarized (CP) lasing emission have been successfully demonstrated for this device structure. Two left CP (LCP) lasing emission peaks are observed at the edges of the overlapping region between the two photonic bands in the structure and are shifted upon the application of a voltage. In contrast, a non‐reciprocal right CP (RCP) lasing emission peak emerges at one of the band edges and diminishes upon the application of a voltage. These phenomena are interpreted based on the selective reflection of RCP light and the reorientation of the NLC molecules by the application of a voltage.