Liquid Crystalline Inorganic Nanosheet Colloids Derived From Layered Materials

Time evolution of the inner structure of antimony phosphate nanosheet suspension developing structural colouration

Structural colouration observed in antimony phosphate nanosheet suspensions has been known for two decades, but the stability of their inner structures has not been a topic in colloidal nanosheet systems. In this study, we investigate the time evolution of structures in suspension using UV-visible spectrometry and small-angle X-ray scattering. Here, we report that antimony phosphate nanosheet systems re-organise their inner structures, especially at lower concentrations (isotropic or biphasic region), and that the basal spacing decreases with time after sample preparation, although the evolution speed depends on the sample concentration. The stability of the inner structure of the suspension is essential for their application as structural colour materials in sensors and colourants.

Colloidal phase behavior of high aspect ratio clay nanotubes in symmetric and asymmetric electrolytes

HYPOTHESIS

Imogolite nanotubes (INTs) are unique anisometric particles with monodisperse nanometric diameters. Aluminogermanate double-walled INTs (Ge-DWINTs) are obtained with variable aspect ratios by controlling the synthesis conditions. It thus appears as an interesting model system to investigate how aspect ratio and ionic valence influence the colloidal behavior of highly anisometric rods.

EXPERIMENTS

The nanotubes were synthesized by hydrothermal treatment for 5 or 20 days to modify the aspect ratio while the electrostatic interactions were investigated by comparing the colloidal stability in symmetric and asymmetric electrolytes. The phase behavior and their related microstructure were determined by optical observations and small-angle X-ray scattering measurements, coupled with interparticle distance modelling.

FINDINGS

We revealed that colloidal suspensions of Ge-DWINTs prepared in NaCl are guided by repulsive double layer forces, undergoing different liquid crystal phase transitions before stiffen into a glass-like state. We found that the microstructure can be rationalized by taking into account the anisometric nature of the particles. By contrast, dispersions prepared with asymmetric electrolytes are governed by strong attractive forces and thus form space-filling gels containing large nanotubes aggregates.

Deposition of silver nanoparticles on nanoscroll-supported inorganic solid using incompletely rolled-up kaolinite

Nanoscroll-supported platy particles were prepared by incomplete rolling-up of kaolinite layers; when the rolling-up of the kaolinite layer followed by its exfoliation incompletely proceeds, kaolinite nanoscrolls were found at the edge of kaolinite platy particles. To assess the support property of these nanoscroll-supported platy particles, when the deposition of Ag nanoparticles was conducted, these nanoparticles were present on the surface of platy particles and in the tubular interior of nanoscrolls at the edge of platy particles but absent on the surface of ordinal kaolinites, as revealed by X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy. These results indicated the successful formation and support property of nanoscroll-supported platy particles.

Fabricating defogging metasurfaces via a water-based colloidal route

Metamaterials possess exotic properties that do not occur in nature and have attracted significant attention in research and engineering. Two decades ago, the field of metamaterials emerged from linear electromagnetism, and today it encompasses a wide range of aspects related to solid matter, including electromagnetic and optical, mechanical and acoustic, as well as unusual thermal or mass transport phenomena. Combining different material properties can lead to emergent synergistic functions applicable in everyday life. Nevertheless, making such metamaterials in a robust, facile, and scalable manner is still challenging. This paper presents an effective protocol allowing for metasurfaces offering a synergy between optical and thermal properties. It utilizes liquid crystalline suspensions of nanosheets comprising two transparent silicate monolayers in a double stack, where gold nanoparticles are sandwiched between the two silicate monolayers. The colloidally stable suspension of nanosheets was applied in nanometre-thick coatings onto various substrates. The transparent coatings serve as absorbers in the infrared spectrum allowing for the efficient conversion of sunlight into heat. The peculiar metasurface couples plasmon-enhanced adsorption with anisotropic heat conduction in the plane of the coating, both at the nanoscale. Processing of the coating is based on scalable and affordable wet colloidal processing instead of having to apply physical deposition in high vacuum or lithographic techniques. Upon solar irradiation, the colloidal metasurface is quickly (60% of the time taken for the non-coated glass) heated to the level where complete defogging is assured without sacrificing transparency in the visible range. The protocol is generally applicable allowing for intercalation of any nanoparticles covering a range of physical properties that are then inherited to colloidal nanosheets. Because of their large aspect ratio, the nanosheets will inevitably orient parallel to any surface. This will allow for a toolbox capable of mimicking metamaterial properties while assuring facile processing via dip coating or spray coating.

Nacre-inspired layered composite gels with broad tunable mechanical strength and structural color for stress visualization

The brick-and-mortar architecture of nacre shells brings radiant structural colors, high toughness, and strength, inspiring numerous designs for structural and optical materials. However, constructing structural color is not always easy, especially among soft materials where aligning components against random and dynamically active environments is generally difficult. Here, we propose a composite organohydrogel capable of visualizing multiple levels of stress, featuring broad tunable mechanical properties, dynamic mechanochromism, deep low working temperatures, and anti-drying attributes. In the composite gels, the intercalation between α-zirconium phosphate (α-ZrP) nanoplates and poly-(diacetone acrylamide-co-acrylamide) is induced by shear-orientation-assisted self-assembly followed by solvent replacement. The highly tailorable (from ∼780 nm to ∼445 nm) range of colors was achieved by regulating the concentration of α-ZrP and glycerol inside the matrix. With the help from glycerol, the composite gels exhibited long-term stability (7 d) in the arid condition and remarkable low-temperature tolerance (-80 °C). The extraordinary mechanical property (compressive strength up to 119 MPa) of composite gels is achieved by the assembled α-ZrP plates with a small aspect ratio, high negative charge repulsion, and abundant hydrogen bonding sites. As a result, the mechanochromic sensor based on the composite gel enjoys a wide range of stress detection (0-1862 KPa). This study provides a new strategy for constructing high strength structural-colored gels, opening up opportunities for sensitive yet strong mechanochromic sensors in extreme environments.

Effect of Vanadium Oxide on the Crystallization of CaO-Al2O3-SiO2 Glass

This study investigated the effect of vanadium oxide on the crystallization of CaO-Al₂O₃-SiO₂ (CAS) glass. Specifically, this study subjected CAS glass-ceramics (GCs) with precipitated hexagonal platy particles of metastable CaAl₂Si₂O₈ (CAS GC-H), a layered crystal, that was prepared using metallic molybdenum (Mo) particles as nucleation agents. When the parent glass of CAS GC-H was crystallized with the addition of vanadium oxide in the 0.052-0.21 wt % range, the obtained platy particles of metastable CaAl₂Si₂O₈ displayed an increase in the aspect ratio from 20 to 15 compared with conventional CAS GC-Hs. In addition, no crystallization occurred in the CAS glass with vanadium oxide in the 0.052-0.21 wt % range in the absence of metallic Mo particles. Meanwhile, a CAS glass containing 1.0 wt % vanadium oxide without the addition of metallic Mo particles showed the precipitation of metastable CaAl₂Si₂O₈. Therefore, these results indicated that the aspect ratio of layered crystals in glass was controlled by the addition of a relatively small content of vanadium oxide, and a new nucleation agent for the precipitation of metastable CaAl₂Si₂O₈ in CAS glass using a relatively high content of vanadium oxide was developed.

Deep ultraviolet hydrogel based on 2D cobalt-doped titanate

Birefringent optical elements that work in deep ultraviolet (DUV) region become increasingly important these years. However, most of the DUV optical elements have fixed birefringence which is hard to be tuned. Here, we invent a birefringence-tunable optical hydrogel with mechano-birefringence effect in the DUV region, based on two-dimensional (2D) low-cobalt-doped titanate. This 2D oxide material has an optical anisotropy factor of 1.5 × 10^-11 C² J^-1 m^-1, larger than maximum value obtained previously, leading to an extremely large specific magneto-optical Cotton-Mouton coefficient of 3.9 × 10⁶ T^-2 m^-1. The extremely large coefficient enables the fabrication of birefringent hydrogel in a small magnetic field with an ultra-low concentration of 2D oxide material. The hydrogel can stably and continuously modulate 303 nm DUV light with large phase tunability by varying the strain (compression or stretching) from 0 to 50%. Our work opens the door to design and fabricate new proof-of-concept DUV birefringence-tunable element, as demonstrated by optical hydrogels capable of DUV modulation by mechanical stimuli.

Effect of carbon on the co-presence of metallic tungsten as a nucleation agent and Eu2+ in glass: crystallization of CaO-Al2O3-SiO2 glass probed with Eu2+ luminescence

This study demonstrated simple redox control in glasses by improving the method used to added glass raw materials. Specifically, the effect of carbon on the co-presence of metallic tungsten (W) particles as nucleation agents and Eu2+ ions in CaO-Al2O3-SiO2 (CAS) glass was investigated via their crystallization to form CAS glass-ceramics (GCs). In this study, the glass specimens were prepared by mixing glass cullet containing metallic W particles and Eu2+ ions, respectively, with a glass batch containing carbon. Whereas the glass specimen was yellowish because of the presence of Eu2+ when carbon was not added during the remelting process, the glass specimen prepared with carbon was black because of the presence of metallic W particles. In addition, this specimen displayed the 470 nm emission band in its fluorescence spectrum recorded under 393 nm excitation, which was attributed to the presence of Eu2+. According to the fluorescence and transmission spectra, the glass specimen showed a darker coloration and more intense 470 nm emission band compared with the specimen prepared by the conventional melting method that included a remelting process. These results indicated that metallic W and Eu2+ were reduced with greater efficiency by the melting method that involved mixing the glass cullet and batch. In addition, the heat-treated glass specimen prepared by the aforementioned mixing method contained a greater amount of metastable CaAl2Si2O8 with increasing heat treatment time as revealed by X-ray diffraction analysis and scanning electron microscopy observation. The intensity of the 470 nm emission band decreased with increasing intensity of the band at 420 nm because of the incorporation of Eu2+ into the crystalline phase, and the increase in intensity of the 420 nm band was lineally proportional to the volume fraction of the crystallized glass specimens. The results therefore indicated that the co-presence of metallic W particles as nucleation agents and Eu2+ as a probe for tracking the crystallization process was achieved by the addition of carbon during the remelting process of mixed cullet containing W and Eu2+ through crystallization of the CAS glass. The results thus demonstrate the importance of improving the method used to added glass raw materials.

Microstructural Control of CaO-Al2O3-SiO2 Glass Ceramics by Oxidation and Mixing with Nucleation Agents

Microstructural control of CaO-Al₂O₃-SiO₂ (CAS) glass ceramics (GCs) was achieved by oxidation and mixing with nucleation agents. CAS GCs were precipitated with hexagonal platy particles of metastable CaAl₂Si₂O₈ layered crystals (CAS GC-H), which are typically prepared under a reductive atmosphere that forms metallic Mo or W particles as nucleation agents. The average particle size of crystals decreased significantly from 50 to 11 μm when the CAS GC-H containing metallic W particles was prepared under an oxidative atmosphere. Compared to this CAS-GC-H, the crystal particle size increased from 8-20 to 10-30 μm when the CAS GC-H was prepared by mixing glass cullet containing metallic Mo and that containing metallic W particles. These results indicate that one microstructure of CAS GC-H is controlled on the micrometer scale from a parent glass with one composition by varying the experimental conditions related to the glass melting state.

Assessment of the Crystallization Process of CaO-Al2O3-SiO2 Glass Probed with Tb3+ Luminescence

The ratio of the intensity of Tb³⁺ fluorescence at 543 nm because of an electric dipole transition (⁵D₄–⁷F₅) relative to that at 437 nm due to a magnetic dipole transition (⁵D₃–⁷F₄) was determined to be proportional to the amount of metastable CaAl₂Si₂O₈ crystals precipitated in CaO–Al₂O₃–SiO₂ glass. The present results indicate that Tb³⁺ luminescence can be used as a probe to evaluate the crystallization of glass.

The ratio of the intensity of Tb³⁺ fluorescence at 543 nm due to an electric dipole transition (⁵D₄−⁷F₅) to that at 437 nm because of magnetic dipole transition (⁵D₃−⁷F₄) was used to probe the precipitation of metastable CaAl₂Si₂O₈ crystals in CaO−Al₂O₃−SiO₂ glass.

Biomineral-Inspired Colloidal Liquid Crystals: From Assembly of Hybrids Comprising Inorganic Nanocrystals and Organic Polymer Components to Their Functionalization

Bioinspired organic/inorganic synthetic composites have been studied as high-performance and functional materials. In nature, biominerals such as pearls, teeth, and bones are self-organized organic/inorganic composites. The inorganic components are composed of calcium carbonate (CaCO₃) and hydroxyapatite (HAp), while the organic components consist of peptides and polysaccharides. These composites are used as structural materials in hard biological tissues. Biominerals do not show significantly higher performances than synthetic composites such as glass-fiber- or carbon-fiber-reinforced plastics. However, biominerals consist of environmentally friendly and biocompatible components that are prepared under mild conditions. Moreover, they form elaborate nanostructures and self-organized hierarchical structures. Much can be learned about material design from these biomineral-based hierarchical and nanostructured composites to assist in the preparation of functional materials.

Inspired by these biological hard tissues, we developed nanostructured thin films and bulk hybrid crystals through the self-organization of organic polymers and inorganic crystals of CaCO₃ or HAp. In biomineralization, the combination of insoluble components and soluble acidic macromolecules controls the crystallization process. We have shown that poly(acrylic acid) (PAA) or acidic peptides called polymer additives induce the formation of thin film crystals of CaCO₃ or HAp by cooperation with insoluble organic templates such as chitin and synthetic polymers bearing the OH group. Moreover, we recently developed CaCO₃- and HAp-based nanostructured particles with rod and disk shapes. These were obtained in aqueous media using a macromolecular acidic additive, PAA, without using insoluble polymer templates. At appropriate concentrations, the anisotropic particles self-assembled and formed colloidal liquid-crystalline (LC) phases.

LC materials are generally composed of organic molecules. They show ordered and mobile states. The addition of stimuli-responsive properties to organic rod-like LC molecules led to the successful development of informational displays, which are now widely used. On the other hand, colloidal liquid crystals are colloidal self-assembled dispersions of anisotropic organic and inorganic nano- and micro-objects. For example, polysaccharide whiskers, clay nanosheets, gibbsite plate-shaped particles, and silica rod-shaped particles exhibit colloidal LC states.

In this Account, we focused on the material design and hierarchical aspects of biomineral-based colloidal LC polymer/inorganic composites. We describe the design and preparation, nanostructures, and self-assembled behavior of these new bioinspired and biocompatible self-organized materials. The characterization results for these self-assembled nanostructured colloidal liquid crystals found using high-resolution transmission electron microscopy, small-angle X-ray scattering, and neutron scattering and rheological measurements are also reported. The functions of these biomineral-inspired liquid crystals are presented. Because these biomineral-based LC colloidal liquid crystals can be prepared under mild and aqueous conditions and they consist of environmentally friendly and biocompatible components, new functions are expected for these materials.

Fine tuning the structural colours of photonic nanosheet suspensions by polymer doping

Aqueous suspensions of nanosheets are readily obtained by exfoliating low-dimensional mineral compounds like H₃Sb₃P₂O₁₄. The nanosheets self-organize, at low concentration, into a periodic stack of membranes, i.e. a lamellar liquid-crystalline phase. Due to the dilution, this stack has a large period of a few hundred nanometres, it behaves as a 1-dimensional photonic material and displays structural colours. We experimentally investigated the dependence of the period on the nanosheet concentration. We theoretically showed that it cannot be explained by the usual DLVO interaction between uniform lamellae but that the particulate nature of nanosheet-laden membranes must be considered. Moreover, we observed that adding small amounts of 100 kDa poly(ethylene oxide) (PEO) decreases the period and allows tuning the colour throughout the visible range. PEO adsorbs on the nanosheets, inducing a strong reduction of the nanosheet charge. This is probably due to the Lewis-base character of the EO units of PEO that become protonated at the low pH of the system, an interpretation supported by theoretical modeling. Oddly enough, adding small amounts of 1 MDa PEO has the opposite effect of increasing the period, suggesting the presence of an additional intermembrane repulsion not yet identified. From an applied perspective, our work shows how the colours of these 1-dimensional photonic materials can easily be tuned not only by varying the nanosheet concentration (which might entail a phase transition) but also by adding PEO. From a theoretical perspective, our approach represents a necessary step towards establishing the phase diagram of aqueous suspensions of charged nanosheets.

Gold-clay nanocomposite colloids with liquid-crystalline and plasmonic properties

Imparting liquid-crystal (LC) materials with the plasmonic properties of metal nanoparticles is actively pursued for applications. We achieved this goal by synthetizing gold nanoparticles onto clay nanosheets, leading to nematic nanocomposite suspensions. Optical observations and structural analysis show the growth of the gold nanoparticles without altering the LC properties of the nanosheets. These colloids display plasmonic structural colours and they can be aligned by an electric field, which is relevant for fundamental and materials chemistry of colloidal LC.

Expansion of orderly stacked metakaolinite layers and order destruction using a kaolinite-tetraphenylphosphonium chloride intercalation compound

The expansion of metakaolinite layers with stacking order and the order destruction were examined by the heat treatment of a kaolinite-tetraphenylphosphonium chloride intercalation compound (Kaol-TPhPCl) at 540 °C under a nitrogen atmosphere followed by the manual grinding of the product using a mortar and a pestle. Fourier-transform infrared spectroscopy and solid-state ²⁷Al nuclear magnetic resonance spectroscopy with magic angle spinning revealed the kaolinite dehydroxylation. Moreover, the absence of kaolinite diffraction lines and the appearance of the 1.85 nm diffraction line in the X-ray diffraction pattern, together with the observation of the hexagonal plate-like morphology in the field-emission scanning electron microscopy, indicated the kaolinite amorphization with the orderly-stacked layers. These results, along with the disappearance of the 1.85 nm diffraction line upon the manual grinding of heat-treated Kaol-TPhPCl, clearly indicated the formation of expanded metakaolinite layers with stacking order and the subsequent order destruction by manual grinding.

Metakaolinite layers were expanded via the heat treatment of a kaolinite-tetraphenylphosphonium chloride intercalation compound and the obtained metakaolinite stacking order was destroyed upon manual grinding.

Precise control of cyclodextrin-based pseudo-polyrotaxane lamellar structure via axis polymer composition

Self-assembly of cyclodextrin (CD) with guest polymers has attracted much attention owing to its biocompatibility and accessibility. In this study, we investigate the composition effect of poly(ethylene oxide)m-b-poly(propylene oxide)n-b-poly(ethylene oxide)m (EOmPOnEOm) triblock copolymers on lamellar or plate structures formed by complexation with β-CD. EO5PO29EO5, EO14PO29EO14, and EO75PO29EO75 show periodic lamellar morphology consisting of single-crystalline pseudo-polyrotaxane (PPR) nanosheets with a thickness equal to the central PO length. This is because β-CDs selectively cover the PO component and cause the microphase separation between β-CD and EO layers. The thickness of the EO layers increases linearly with increasing number of EO units, which suggests that the EO chains are constrained into virtual cylinders with the diameter of the β-CD. This means that we can precisely control the thickness of both the crystal (β-CD and PO) and the amorphous (EO) layers in the lamellar structure. In contrast, EO2PO29EO2 forms a thin plate structure, where not only PO but also EO chains are covered with β-CD. Furthermore, the length of the central PO component is necessary to form the lamellar structure with the phase separation between the β-CD and EO layers. These findings provide a more fundamental understanding to enhance the variety and applicability of CD-based self-assembled materials.

Nacre Is a Liquid-Crystal Thermometer of the Oceans

Nacre, or mother of pearl, is a biomaterial with a layered structure. In a recent geological study, researchers found that the width of the nacre layers depends on the formation temperature, which is determined by the ocean water temperature. A linear dependence of layer width with respect to temperature is understandable within the transient liquid-crystalline nature of incipient nacre. Thus, developing nacre is a liquid-crystal thermometer recording its formation temperature. A more complete understanding of nacre formation is of interest not only for biology and geology, in terms of biomineralization and paleoclimatology, but also for materials science: for reproducing nacre or fabricating synthetic analogues and also potentially for developing new classes of layered materials with layer spacings tunable by pH and temperature.

Bottom-up synthesis of titanophosphate nanosheets by the aqueous solution process

The synthesis of titanophosphate nanosheets in aqueous sols was examined by the bottom-up process. The nanosheets were formed by mixing titanium iso-propoxide, phosphoric acid, and tetraalkylammonium hydroxide (NR₄OH) aqueous solutions, followed by diluting with water and heating at 80 °C, forming translucent aqueous sols of titanophosphate nanosheets with the same crystal structure as layered titanium phosphate Ti₂O₃(H₂PO₄)₂·2H₂O. Whether the nanosheets were crystallized depended on the reactions during the mixing of reagents before the water dilution. By controlling the acid-base reactions between the Ti species, phosphoric acid, and the hydroxides of bulky cations in the aqueous sols, the one-pot process yielded highly water-dispersible, flake-like titanophosphate nanosheets. Under some synthetic conditions, nanosheets formed even in weakly basic aqueous sols. These nanosheets can be coated on a substrate with low alkali-resistance, or used for the removal of metal ions from neutral aqueous solutions.

Bioinspired selective synthesis of liquid-crystalline nanocomposites: formation of calcium carbonate-based composite nanodisks and nanorods

Here we report new organic/inorganic hybrid colloidal liquid crystals that consist of colloidal calcium carbonate (CaCO₃)/poly(acrylic acid) (PAA) hybrid nanodisks. We selectively synthesized anisotropic liquid-crystalline CaCO₃-based nanodisk and nanorod composites in water/methanol mixtures, which formed discotic and calamitic nematic liquid crystals in their colloidal dispersions, respectively. The vaterite nanodisks and calcite nanorods were selectively synthesized in methanol-rich and water-rich solutions, respectively. The observation of these materials with transmission electron microscopy clarified the atomic-scale structures of these nanodisks and nanorods, revealing the self-organized CaCO₃/PAA hybrid structures with the ability to form colloidal liquid crystals. The liquid crystals were prepared under mild and aqueous conditions by methods using acidic polymers inspired by the biomineralization process. The present approach provides new insights into the design of organic/inorganic hybrid colloidal liquid crystals and development of environmentally friendly functional hybrid materials.

Preparation and Comparative Stability of a Kaolinite-Tetrabutylphosphonium Bromide Intercalation Compound for Heat and Solvent Treatments

A kaolinite-tetrabutylphosphonium bromide (TBPBr) intercalation compound (Kaol-TBPBr) was prepared from kaolinite providing inorganic aluminosilicate layers and TBPBr as intercalated salts between the layers through the use of an intermediate, a kaolinite-dimethylsulfoxide (DMSO) intercalation compound (Kaol-DMSO). The experimental data through complementary techniques, including X-ray diffraction, Fourier transform infrared spectroscopy, solid-state ¹³C and ²⁹Si nuclear magnetic resonance (NMR) spectroscopy with cross polarization and magic angle spinning, inductively coupled plasma emission spectrometry, and ion chromatography, indicate complete removal of DMSO and intercalation of TBPBr with an increase in the basal spacing from 1.12 nm (Kaol-DMSO) to 1.53 nm (Kaol-TBPBr). In contrast to a similar intercalation compound, a kaolinite-tetrabutylammonium bromide (TBABr) intercalation compound (Kaol-TBABr) with a basal spacing of 1.51 nm, Kaol-TBPBr displayed interesting features such as enhanced thermal stabilities as well as bold resistance against several solvents. Kaol-TBPBr withstood thermal decomposition of the organic species over 100 °C much better than Kaol-TBABr. When Kaol-TBPBr and Kaol-TBABr were refluxed in methanol, ethanol, acetone, or toluene for 1 day, Kaol-TBPBr preserved the expanded kaolinite layers, while the Kaol-TBABr structure completely collapsed due to the release of TBABr. Thus, with these particular and unique features of Kaol-TBPBr, organophosphonium salts appear to be promising guest species for intercalation chemistry of kaolinite.

Electric-Alignment Immobilization of Liquid Crystalline Colloidal Nanosheets with the Aid of a Natural Organic Polymer

Inorganic nanosheets obtained by exfoliation of a layered crystal in water form colloidal liquid crystals, and their alignment can be controlled by an electric field. In order to realize the immobilization of the electrically aligned niobate nanosheets without external forces, an aqueous gelator, agar, is introduced to the niobate nanosheet system to utilize the thermosensitive sol-gel transition property of agar. Alignment of nanosheets in a niobate-agar system is performed by applying an electric field above the sol-gel transition temperature, and then, the sample is cooled down, followed by cooling below the transition temperature with the electric field turned off. The aligned structure is kept for more than 24 h after the removal of the electric field. The concentration of agar is a key parameter for both the orientation of nanosheets and the retention of the orientation.

Autonomously isolated pseudo-polyrotaxane nanosheets fabricated via hierarchically ordered supramolecular self-assembly

Autonomously isolated PPR nanosheets are fabricated via complexation between β-CD and a carboxyl-terminated poloxamer and the structural coloration was exhibited.

Liquid Crystalline Colloidal Mixture of Nanosheets and Rods with Dynamically Variable Length

Here, we demonstrate the novel double-component liquid crystalline colloids composed of mesogenic inorganic nanosheets and the rods with dynamically variable length controlled by temperature. As the length-controllable rod, stiff biopolymer microtubule is used, which was successfully polymerized/depolymerized from tubulin proteins through a biochemical process even in the presence of the nanosheets. The mesoscopic structure of the liquid crystal phase was reversibly modifiable as caused by the change of the rod length.

Materials Nanoarchitectonics Using 2D Layered Materials: Recent Developments in the Intercalation Process

Layered inorganic solids as an attractive classification of 2D materials offer material diversity and a wide range of interesting properties. Layered inorganic solids provide an expandable 2D nanospace between each individual layer, the so called interlayer space, to accommodate/arrange guest species such as molecules, nanoparticles, and polymer chains and design unique nanoarchitectures, resulting in the production of intercalation compounds showing different properties in comparison to those of virgin layered materials and guest species. Layered inorganic solids can also be exfoliated to result in nanosheet production. Further ordering of exfoliated nanosheets is also possible via different methods and normally leads to creating soft materials presenting properties and applications different from that of relatively rigid intercalation compounds. Here, the latest studies and up-to-date developments on the possible techniques of designing novel types of materials using layered inorganic solids are specifically highlighted.

Soft chemistry of ion-exchangeable layered metal oxides

Disassembly and re-assembly of layered metal oxides by soft chemical approaches can be used to tailor functionalities in artificial photosynthesis, energy storage, optics, and piezoelectrics.

New composite thixotropic hydrogel composed of a polymer hydrogelator and a nanosheet

A composite gel composed of a water-soluble aromatic polyamide hydrogelator and the nanosheet Laponite®, a synthetic layered silicate, was produced and found to exhibit thixotropic behaviour. Whereas the composite gel contains the gelator at the same concentration as the molecular gel made by the gelator only, the composite gel becomes a softer thixotropic gel compared to the molecular gel made by the gelator only. The reason for this could be that bundles of polymer gelator may be loosened and the density of the polymer network increased in the presence of Laponite.

Photonic water dynamically responsive to external stimuli

Fluids that contain ordered nanostructures with periodic distances in the visible-wavelength range, anomalously exhibit structural colours that can be rapidly modulated by external stimuli. Indeed, some fish can dynamically change colour by modulating the periodic distance of crystalline guanine sheets cofacially oriented in their fluid cytoplasm. Here we report that a dilute aqueous colloidal dispersion of negatively charged titanate nanosheets exhibits structural colours. In this 'photonic water', the nanosheets spontaneously adopt a cofacial geometry with an ultralong periodic distance of up to 675 nm due to a strong electrostatic repulsion. Consequently, the photonic water can even reflect near-infrared light up to 1,750 nm. The structural colour becomes more vivid in a magnetic flux that induces monodomain structural ordering of the colloidal dispersion. The reflective colour of the photonic water can be modulated over the entire visible region in response to appropriate physical or chemical stimuli.

Sandwich organization of non-ionic surfactant liquid crystalline phases as induced by large inorganic K4Nb6O17 nanosheets

While retaining its lamellar liquid crystal phase, K4Nb6O17 nanosheets were used as a template to sandwich and stabilize an alkylpoly(ethylene oxide) nonionic surfactant-water system showing monodomain (lamella) formation within the inorganic niobate sheets that appears to be not dependent on the surfactant liquid crystalline state in solution but more its concentration.

Controllable doping of nitrogen and tetravalent niobium affords yellow and black calcium niobate nanosheets for enhanced photocatalytic hydrogen evolution

Yellow (N-doped) and black (N-/Nb⁴⁺-codoped) [Ca₂Nb₃O₁₀]⁻ nanosheets with molecular thickness were fabricated by liquid exfoliation of selectively doped KCa₂Nb₃O₁₀ perovskite.

Liquid-crystalline calcium carbonate: biomimetic synthesis and alignment of nanorod calcite

Liquid-crystalline CaCO₃ crystals were obtained by bio-inspired crystallization through amorphous CaCO₃. These calcite nanorods were macroscopically aligned by applying mechanical force to the liquid-crystalline phase.

Liquid-crystalline CaCO₃ has been prepared for the first time. The nanorods of CaCO₃ calcite are obtained by bio-inspired crystallization through aqueous colloidal precursors of amorphous CaCO₃ stabilized by poly(acrylic acid). The synthesized calcite nanocrystals have well-tuned morphologies that are preferable for formation of liquid-crystalline phases in concentrated aqueous colloidal solution. The one-dimensional alignment of calcite crystals is achieved by mechanical shearing of the aqueous colloidal solution showing liquid-crystalline phases. These CaCO₃-based liquid crystals formed by a self-organization process in mild conditions may have great potential for use as environmentally friendly materials.

Synthesis of curtain-like crumpled boehmite and γ-alumina nanosheets

Boehmite and γ-alumina nanosheets with a curtain-like crumpled morphology have been synthesized via a template-free hydrothermal process.

Photo-Induced Anomalous Deformation of Poly(N-Isopropylacrylamide) Gel Hybridized with an Inorganic Nanosheet Liquid Crystal Aligned by Electric Field

Poly-(N-isopropylacrylamide) (PNIPA) hydrogel films doped with uniaxially aligned liquid crystalline (LC) nanosheets adsorbed with a dye are synthesized and its anomalous photothermal deformation is demonstrated. The alignment of the nanosheet LC at the cm-scale is easily achieved by the application of an in-plane or out-of-plane AC electric field during photo-polymerization. A photoresponsive pattern is printable onto the gel with μm-scale resolution by adsorption of the dye through a pattern-holed silicone rubber. When the gel is irradiated with light, only the colored part is photothermally deformed. Interestingly, the photo-irradiated gel shows temporal expansion along one direction followed by anisotropic shrinkage, which is an anomalous behavior for a conventional PNIPA gel.