Miscibility and Alignment Effects of Mixed Monolayer Cyanobiphenyl Liquid‐Crystal‐Capped Gold Nanoparticles in Nematic Cyanobiphenyl Liquid Crystal Hosts

Against the rule: Liquid crystal hosts ( 5CB and 8CB ) are doped with different thiol decorated gold nanoparticles (see figure). The “simple” hexanethiol and dodecanethiol capped nanoparticles ( Au1 and Au2 ) are more compatible to the nematic cyanobiphenyl liquid crystals than nanoparticles capped simultaneously with alkylthiols and a nematic cyanobiphenyl thiol ( Au3 and Au4 ).

     

Light‐Driven Reversible Alignment Switching of Liquid Crystals Enabled by Azo Thiol Grafted Gold Nanoparticles

Stimuli‐directed alignment control of liquid crystals (LCs) with desired molecular orientation is currently in the limelight for the development of smart functional materials and devices. Here, photoresponsive azo thiol (AzoSH) was grafted onto gold nanoparticles (GNPs). The resulting hybrid GNPs were able to homogeneously mix with a commercially available nematic LC host, as evidenced by Cryo‐TEM. Interestingly, the LC nanocomposites were found to undergo reversible alignment transition upon light irradiation as a consequence of the trans–cis photoisomerization of the azo groups on the GNP surface. LC molecules in either planar or bare glass cells were able to change their alignment to vertical upon UV irradiation, while the vertically aligned LC molecules returned to the planar or random orientation under visible irradiation. Neither the azo thiol molecules nor the unfunctionalized GNPs alone promoted the alignment of the LC molecules in the system upon light irradiation. The photoinduced vertical alignment without applied electric or magnetic field was very stable over time and with respect to temperature. Furthermore, an optically switchable device based on the photostimulated reversible alignment control of LCs was demonstrated.     

Magnetic Field‐Induced Shape Transitions in Multiphase Polymer‐Liquid Crystal Blends

Summary: This paper presents a computational study of phase separation‐phase ordering‐texturing in blends of polymer coils and rod‐like nematic liquid crystals under the presence of magnetic fields, using an extended version of the Matsuyama‐Evans‐Cates model (Phys. Rev. E 2000 , 61, 2977). This work demonstrates that demixing in these blends leads to droplet morphologies with tunable droplet shapes and director textures. In contrast to filled nematics, where solids are suspended in a nematic liquid crystal matrix, demixing in coil‐mesogenic rods blends leads to nematic emulsions, in which the deformable viscoelastic polymer drops are suspended in a nematic matrix. Under strong anchoring conditions, the imposition of a magnetic field leads to a director re‐orientation that due to strong anchoring produces a droplet shape change. Magnetic field‐induced shape transitions in these blends are shown to be second order with a finite critical field threshold that diverges as anchoring strength vanishes. A morphological‐texture diagram summarizes the magnetic field‐anchoring conditions that promote anisotropic shapes. This work presents additional material processing routes to design and control bi‐phasic morphologies in polymer‐liquid crystal blend.

Computed morphology phase diagram in terms of magnetic field strength Λ_M and anchoring strength. Λ_ϕQ.     

Electrorheological Effect and Electro‐Optical Properties of Side‐on Liquid Crystalline Polysiloxane in a Nematic Solvent

The electrorheological (ER) effect and the electro‐optical properties of a ′′side‐on′′ liquid crystalline polysiloxane (PS) are investigated. A large ER effect is observed and the response to the shear stress of neat PS in the nematic phase is shown to be affected by the shear rate. PS is also mixed with a low‐molar nematic liquid crystal (5CB) in order to improve the response behavior to the applied electric field. The rheological properties of such mixtures are highly dependent on the concentration of 5CB. The composites respond faster to the applied electric field and have improved electro‐optical properties. This study offers a new perspective on the development of liquid crystal materials for the ER effect.     

笼形倍半硅氧烷修饰的金纳米粒子对4-正戊基4'-氰基联苯液晶性能的影响

为有效降低液晶器件的开启电压,获得具有低功耗特性的液晶显示器件。本文采用巯基功能化的笼形倍半硅氧烷(POSS)作为修饰配体,硼氢化钠为还原剂,采用一步法还原氯金酸制备出粒径约为5 nm的金纳米粒子。将该金纳米粒子以不同质量分数掺杂到向列相液晶4-正戊基4'-氰基联苯(5CB)中,研究了其对液晶黏度、阈值电压、相变温度的影响。结果表明,POSS修饰的金纳米粒子可以使液晶材料5CB的黏度降低、阈值电压减小。该金纳米粒子的掺入,拓宽了液晶材料的相变温度范围。     

Liquid‐Crystalline Phases Made of Gold Nanoparticles

Spontaneous formation of smectic and columnar structures was observed when spherical gold nanoparticles were functionalized with mesogenic thiols (see layered structure and X‐ray pattern of a sample in smectic phase). The particle ordering is stimulated by softening of the interparticle potential and flexibility for deformation of the grafting layer.

     

A Nanohelicoidal Nematic Liquid Crystal Formed by a Non‐Linear Duplexed Hexamer

The twist‐bend modulated nematic liquid‐crystal phase exhibits formation of a nanometre‐scale helical pitch in a fluid and spontaneous breaking of mirror symmetry, leading to a quasi‐fluid state composed of chiral domains despite being composed of achiral materials. This phase was only observed for materials with two or more mesogenic units, the manner of attachment between which is always linear. Non‐linear oligomers with a H‐shaped hexamesogen are now found to exhibit both nematic and twist‐bend modulated nematic phases. This shatters the assumption that a linear sequence of mesogenic units is a prerequisite for this phase, and points to this state of matter being exhibited by a wider range of self‐assembling structures than was previously envisaged. These results support the double helix model of the TB phase as opposed to the simple heliconical model. This new class of materials could act as low‐molecular‐weight surrogates for cross‐linked liquid‐crystalline elastomers.     

Controlling the Spatial Organization of Liquid Crystalline Nanoparticles by Composition of the Organic Grafting Layer

Understanding how the spatial ordering of liquid crystalline nanoparticles can be controlled by different factors is of great importance in the further development of their photonic applications. In this paper, we report a new key parameter to control the mesogenic behavior of gold nanoparticles modified by rodlike thiols. An efficient method to control the spatial arrangement of hybrid nanoparticles in a condensed state is developed by changing the composition of the mesogenic grafting layer on the surface of the nanoparticles. The composition can be tuned by different conditions of the ligand exchange reaction. The thermal and optical behavior of the mesogenic and promesogenic ligands were investigated by using differential scanning calorimetry (DSC) and hot‐stage polarized optical microscopy. The chemical structure of the synthesized hybrid nanoparticles was characterized by ¹H NMR spectroscopy, thermogravimetric analysis (TGA), XPS, and elemental analysis, whereas the superstructures were examined by small‐angle X‐ray diffraction (SAXSRD) analysis. Structural studies showed that the organic sublayer made of mesogenic ligands is denser with an increasing the average ligand number, thereby separating the nanoparticles in the liquid crystalline phases, which changes the parameters of these phases.     

Redox‐Active Hybrid Polyoxometalate‐Stabilised Gold Nanoparticles

We report the design and preparation of multifunctional hybrid nanomaterials through the stabilization of gold nanoparticles with thiol‐functionalised hybrid organic–inorganic polyoxometalates (POMs). The covalent attachment of the hybrid POM forms new nanocomposites that are stable at temperatures and pH values which destroy analogous electrostatically functionalised nanocomposites. Photoelectrochemical analysis revealed the unique photochemical and redox properties of these systems.     

Amine‐Functionalized Polyglycidyl Methacrylate Microsphere as a Unified Template for the Synthesis of Gold Nanoparticles and Single‐Crystal Gold Plates

Polyglycidyl methacrylate (PGMA) microspheres, crosslinked and surface‐functionalized by amine, can be used as a solid‐state template for the synthesis of gold (Au) crystals in the forms of either nanoparticles (NPs) or plates. It is discovered that the polymer microsphere acts as an internal template to cultivate Au NPs inside the microsphere or an external template to generate the single‐crystal plates depending on the critical concentration (C_cr) of gold ions. The ion–dipole interaction and the structure‐dependent solubility of gold induce two distinct gold nanostructures in the presence of the functionalized polymer microspheres. The catalytic activity and long‐term storage of the developed gold nanostructures that can be easily scaled‐up for mass production through the developed novel methodology is demonstrated.     

Light‐Induced Reversible Self‐Assembly of Gold Nanoparticles Surface‐Immobilized with Coumarin Ligands

A novel light‐induced reversible self‐assembly (LIRSA) system is based on the reversible photodimerization and photocleavage of coumarin groups on the surface of gold nanoparticles (AuNPs) in THF solution. Facilitated by coumarin groups, light irradiation at 365 nm triggers the stable assembly of monodisperse AuNPs; the resulting self‐assembly system can be disassembled back to the disassembled state by a relatively short exposure to benign UV light. The reversible self‐assembly cycle can be repeated 4 times. A specific concentration range of coumarin ligand and the THF solvent were identified to be the two predominant factors that contribute to the LIRSA of AuNPs. This is the first successful application of reversible photodimerization based on a coumarin derivative in the field of AuNP LIRSA. This LIRSA system may provide unique opportunities for the photoregulated synthesis of many adjustable nanostructures and devices.     

DNA Dangling‐End‐Induced Colloidal Stabilization of Gold Nanoparticles for Colorimetric Single‐Nucleotide Polymorphism Genotyping

A single‐nucleotide polymorphism (SNP) detection method was developed by combining single‐base primer extension and salt‐induced aggregation of gold nanoparticles densely functionalized with double‐stranded DNA (dsDNA‐AuNP). The dsDNA‐AuNPs undergo rapid aggregation in a medium of high ionic strength, whereas particles having a single‐base protrusion at the outermost surface disperse stably, allowing detection of a single‐base difference in length by color changes. When SNP typing primers are used as analytes to hybridize to the single‐stranded DNA on the AuNP surface, the resulting dsDNA‐AuNP works as a visual indicator of single‐base extension. A set of four extension reaction mixtures is prepared using each of ddNTPs and subsequently subjected to the aggregation assay. Three mixtures involving ddNTP that is not complementary to the SNP site in the target produce the aggregates that exhibit a purple color. In contrast, one mixture with the complementary ddNTP generates the single‐base protrusion and appears red. This method could potentially be used in clinical diagnostics for personalized medicine.     

In Situ Formation of Dual‐Phase Thermosensitive Ultrasmall Gold Nanoparticles

A novel method for the in situ synthesis of dual‐phase thermosensitive ultrasmall gold nanoparticles (USGNPs) with diameters in the range of 1–3 nm was developed by using poly(N‐isopropylacrylamide)‐block‐poly(N‐phenylethylenediamine methacrylamide) (PNIPAM‐b‐PNPEDMA) amphiphilic diblock copolymers as ligands. The PNPEDMA block promotes the in situ reduction of gold precursors to zero‐valent gold and subsequently binds to the surface of gold nanoparticles, while PNIPAM acts as a stabilizing and thermosensitive block. The as‐synthesized USGNPs stabilized by a thermosensitive PNIPAM layer exhibit a sharp, reversible, clear–opaque transition in aqueous solution between 30 and 38 °C. An unprecedented finding is that these USGNPs also show a reversible soluble–precipitate transition in nonpolar organic solvents such as chloroform at around 0 °C under acidic conditions.     

Fluorescent Gold Nanoparticles: Synthesis of Composite Materials of Two‐Component Disulfide Gels and Gold Nanoparticles

Pseudoenantiomeric ethynylhelicene oligomers containing a disulfide group formed two‐component gels, which showed different solvent properties from gels without the disulfide group. The disulfide gels reacted with gold nanoparticles, and the resulting organic–inorganic composite materials exhibited fluorescence emission between 600–800 nm, along with emission from the oligomers at 450 nm. The disulfide gels and isolated gold nanoparticles loaded with the oligomers did not show the former emission. The 600–800 nm emission reversibly disappeared upon sol formation with heating, which was accompanied by an enhancement of the emission at 450 nm. The novel emission was also observed in the solid state.