Assembly Of Nanocrystals Research Articles

Modelling-assisted geometrical optimization of colloidal quantum color convertor based pixels fabricated by dielectrophoretic directed assembly

Hypothesis: Building competitive color conversion pixels for microdisplays made of semiconductor nanocrystals requires reaching a deposition thickness high enough to absorb all the blue light from the backlight unit. In the case of dielectrophoretic directed assembly of such nanocrystals, modeling and simulations may help understand what the intrinsic limitations of the process are, and may be used to propose new assembly routes.Experiments: A theoretical model of dielectrophoretic interactions between polarizable nano-spheres and an electrostatically patterned substrate has been developed. Monte Carlo simulations have been run using this model to rationalize the effects of parameters driving the dielectrophoretic directed assembly and to find optimal deposition conditions for reaching a maximal thickness of nanocrystal pixels. Experiments with CdSe quantum plates and with alumina spheres embedding quantum plates (micro-pearls) have been carried out and compared to the model.Findings: Modeling and simulations reveal that the directed assembly of semiconductor nanocrystals is limited essentially by the small object size, which sets the maximum dielectrophoretic force they can undergo. They indicate that using larger objects should allow reaching unprecedented assembly heights, but will induce lateral extension of the assembly. This trade-off has been illustrated with diagrams in the parameter space and confirmed experimentally with micro-pearls.

Enhanced rheology and firefighting performance of fluorine-free soft foams through the assembly of cellulose nanofibres and cellulose nanocrystals at the air–liquid interface

In this work, we developed soft and highly stable perfluorocarbon-free foams based on cellulose nanofibres (CNFs), cellulose nanocrystals (CNCs) and alkyl polyglycoside (APG). Neither the CNCs nor the CNFs can effectively stabilise the APG foam, which is reflected in the spontaneous degradation of the foam. Interestingly, blending these two nanocelluloses and foaming resulted in an ultrastable foam. The reflective optical interference technique was used to visualise liquid flow in the liquid film, and the results showed that the foam film with a thickness of only a few tens of nanometres gained excellent mechanical stability by tuning the assembly of CNCs and CNFs at the air–liquid interface. Moreover, the interfibril interactions at the Plateau borders reduce the bubble coarsening rate and drainage rate. In pool fire extinguishing tests, increasing the total concentration of CNCs and CNFs improved the foam stability, but increasing the viscosity led to a decrease in the foam spreading rate. Thus, a formulation with 0.4 % nanocellulose has poorer firefighting performance than a formulation with 0.15 % nanocellulose. When the ratios of CNCs and CNFs are properly controlled, the burnback performance of perfluorocarbon-free foam is better than that of state-of-the-art fluorinated AFFFs for n-heptane pool fires. The sustainability of the firefighting process is considerably improved by switching to the nonperfluorinated liquid foam developed in this work.

Broadband Circularly Polarized Luminescent Films Based on the Heterogeneous Assembly of Cellulose Nanocrystals.

Broadband circularly polarized films display promising applications for multiwavelength lasers and "smart" windows in buildings. Herein, broadband films are fabricated through the heterogeneous assembly of cellulose nanocrystals (CNCs) and thermoplastic polyurethane (TPU) particles in mixed solvents of water and DMF. During the heterogeneous assembly process, a portion of the small TPU particles coassembled with CNCs to form chiral nematic structures and another portion of the TPU particles fused together to form large aggregates. These large aggregates are located around the helical structures of CNCs and induce a twisting effect on the helical axis of the chiral nematic phase. Helical axis twisting continuously occurs in various directions, leading to broad-band reflections of the films. Additionally, multicolor and white right-handed circularly polarized luminescent (CPL) films have been attained by integrating three organic dyes into the chiral structures of CNCs. A high dissymmetry factor value of -0.47 was achieved for the white CPL film.

Polyphenol assisted assembly of prussian blue analogs nanocrystals decorated 3D GO functional microspheres for polymer fiber bifunctional membrane with high oil-water emulsion permeability and powerful photocatalytic self-cleaning ability

Due to the intricate components of wastewater and physical stacking of graphene oxide (GO), the current GO membranes exhibit the fatal defects of low porosity and poor anti-fouling ability. Herein, a three dimensional (3D) FeCo-PBA@GO functional microsphere was constructed via anchoring GO nanosheets onto hard template of 3D polymethyl methacrylate (PMMA) microsphere driven by hydrogen bond and van der Waals force. On this basis, the Prussian blue analogs nanocrystals (FeCo-PBA) grew in situ on such functional microsphere and further assembled onto porous polyacrylonitrile (PAN) fiber mat through the tannic acid assisted spraying technique, resulting in highly permeable and photocatalytic self-cleaning FeCo-PBA@GO/PAN fibrous composite membrane. Interestingly, the unique 3D nanostructure of FeCo-PBA@GO microsphere arranging on membrane surface effectively prevented the dense physical stacking of GO nanosheets and increased the oil repellence property, thereby regulating the water channel and breaking through permeability limitation of membrane. As a result, the composite membrane exhibited superior separation fluxes (˃3029 L m−2 h−1) for different oil/water (O/W) emulsions, with rejection rate above 99.0 %. Owing to rich active sites and enhanced electron/mass transport property of FeCo-PBA functional layer, the composite membrane could effectively degrade various dyes by peroxymonosulfate (PMS) activation, with the degradation efficiency of 93.1–96.9 % within 40 min and demonstrated favorable antifouling and photocatalytic self-cleaning ability after cycling separation of O/W emulsion. In addition, the generated multiple reactive oxygen species and photocatalytic mechanism were proposed. This work provides a versatile pathway to prepare multifunctional GO advanced membranes for large-scale treatment of complex emulsified oily wastewater.

Preparation of Oriented Nanoporous Magnetite Films by a Template-Free Solution Process from Iron Oxyhydroxide Films

Nanoporous oxide films composed of nanocrystal assemblies with an aligned crystallographic orientation are key nanostructures for efficient interfacial reactions. However, a simple, template-free method for their formation remains a challenge. Layered metal hydroxide (LMH) films are a promising precursor for spontaneous formation of nanoporous oxide films.[1-4] LMHs have a layered structure comprising 2D sheets of edge-shared octahedral hydroxide, i.e., brucite structure, with or without interlayer anions and water molecules. Calcination of LMH results in dehydration, anion elimination, and volume shrinkage, leading to the spontaneous formation of nanoporous oxides.In this study, we have prepared nanoporous and ferrimagnetic magnetite (Fe3O4) films by using layered iron hydroxides, namely, green rust (GR), as a precursor. Generally, GR has a brucite-type structure containing Fe2+ and Fe3+ ions, and is highly susceptible to oxidation by oxygen in water and air, leading to the formation of iron oxyhydroxides (FeOOH). Here, GR films were electrochemically deposited on FTO substrates in an aqueous solution containing Fe2+ and NO3 − ions at room temperature. Drying the GR films in air resulted in the formation of two-type FeOOH films, depending on the electrodeposition condition. Characterization using X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, and FT-IR spectroscopy revealed that one is [010]-oriented γ-FeOOH films, and the other is [001]-oriented δ-FeOOH films. The obtained FeOOH films had a mille-feuille like morphology with 500–700 nm thickness. Heat treatment of these two-type FeOOH films under vacuum at 500 °C resulted in the formation of [110]- and [111]-oriented nanoporous Fe3O4 films. The obtained Fe3O4 films showed a ferrimagnetic behavior in VSM measurements and had a nanoporous structure comprising nanoparticles with 50–100 nm diameter.Finally, a possilble interpretation for the observed orientation relationships between the FeOOH and Fe3O4 was also discussed on the basis of pyrolysis intermediates of FeOOH and similarity in their atomic arrangements. References T. Shinagawa, M. Watanabe, T. Mori, J.-i. Tani, M. Chigane and M. Izaki, Inorg. Chem., 57, 13137 (2018).T. Shinagawa, M. Chigane and M. Izaki, ACS Omega, 6, 2312 (2021).T. Shinagawa, M. Chigane and M. Takahashi, Cryst. Growth Des., 22, 4122 (2022).T. Shinagawa, N. Kotobuki and A. Ohtaka, Nanoscale Adv., 5, 96 (2023). Figure 1

Assembly of ITO Nanocrystals into Nanotubes Using Polycarbonate Membranes for Dual-Band Electrochromic Modulation

Assembly of ITO Nanocrystals into Nanotubes Using Polycarbonate Membranes for Dual-Band Electrochromic Modulation

CTAB-induced synthesis of two-dimensional copper oxalate particles: using l-ascorbic acid as the source of oxalate ligand.

Copper oxalate is typically synthesized through a precipitation reaction involving copper salts mixed with oxalic acid or oxalate solutions. However, in this study, we were successful in synthesizing well-formed square-like copper oxalate particles under liquid-phase conditions at ambient temperature and pressure using ascorbic acid as the source of the oxalic acid ligand. The addition of cationic surfactant cetyltrimethylammonium bromide (CTAB) caused the morphology of copper oxalate particles to undergo a transition from three-dimensional to two-dimensional. And the inhibition of the assembly of primary copper oxalate nanocrystals along the [001] direction became stronger with the increase of CTAB concentration. The impact of CTAB on the crystallization, growth, and self-assembly processes of primary copper oxalate nanocrystals was analysed using various testing methods. Based on these analyses, the possible mechanism of CTAB-induced synthesis of two-dimensional copper oxalate particles was finally proposed.

Chiral Effect on the Electrochemistry of Magnetic Ferrite Colloidal Nanocrystal Assembly Modified by Amino Acids.

Chirality on the molecular or nanometer scale is particularly significant in chemistry, materials science, and biomedicine. Chiral electrochemical reactions on solid surfaces are currently a hot research topic. Herein, a chiral solid surface is constructed in aqueous solutions by mixing chiral molecules, d- and l-glutamic, with γ-Fe2O3 and Fe3O4 nanoparticles (NPs) and MnFe2O4 colloidal nanocrystal assembly (CNA). Cyclic voltammetry and differential pulse voltammetry measurements are conducted in a phosphate buffer solution (PBS) containing ascorbic acid (AA) or isoascorbic acid (IAA), and a chiral effect appears on the electroreduction of ferric ions of amino acid-modified magnetic samples. A negative or positive potential shift is observed, respectively, for magnetic structures modified by l- and d-glutamic acid in aqueous AA electrolyte, while the opposite is observed for these samples in IAA electrolyte. The reduction peak current increases by 0.8-1.2 times for the electrodes modified with l- and d-glutamate molecules, improving the electron transport efficiency. The chiral effect is absent when the electrolytes contain achiral uric acid or dopamine, or even chiral l-/d-/ld-tartaric acid. The chiral recognition between d-/l-glutamic acid and AA/IAA at the electrochemical interface is suggested to be related to their spinal configurations. These observations will be helpful for the rational design of inorganic functional chiral micro/nanostructures.

Cholesteric Liquid Crystal‐Mediated Chiral Plasmonic Films with Strong Chiroptical Response, Dynamic Tunability, and Reversible Thermal Reconfigurability

AbstractChiral assemblies of plasmonic nanocrystals (NCs) are of immense interest due to their distinctive physicochemical characteristics and promising potential in future optoelectronic applications. Despite recent advances in the construction of chiral NC assemblies, most approaches have led to the formation of static irreversible structures with modest optical responses and limited configurational tunability. Herein, a way to prepare a thermally reconfigurable helical assembly of Au nanorods (AuNRs) with a strong chiroptical response is introduced by employing cholesteric liquid crystals (CLCs) as a chiral template. Circular dichroism (CD) spectroscopy and polarized optical microscopy are used to verify the strong chiroptical activity and dynamic optical tunability of chiral plasmonic film of AuNR–CLC composites and to unveil the interactions between constituents. For the system, chiral dopants are employed to induce strong helical procession along the hierarchical structure of the CLC template, resulting in a strong CD response, which can further be enhanced by increasing the amount of AuNRs. Furthermore, the thermotropic nature of the CLC template leads to the reversible on/off switching of the chiroptical responses of the system at a moderate temperature window with almost complete recovery of the original response, suggesting its feasibility as a promising material for chiral optoelectronic devices.

Nanocrystal Assemblies: Current Advances and Open Problems.

We explore the potential of nanocrystals (a term used equivalently to nanoparticles) as building blocks for nanomaterials, and the current advances and open challenges for fundamental science developments and applications. Nanocrystal assemblies are inherently multiscale, and the generation of revolutionary material properties requires a precise understanding of the relationship between structure and function, the former being determined by classical effects and the latter often by quantum effects. With an emphasis on theory and computation, we discuss challenges that hamper current assembly strategies and to what extent nanocrystal assemblies represent thermodynamic equilibrium or kinetically trapped metastable states. We also examine dynamic effects and optimization of assembly protocols. Finally, we discuss promising material functions and examples of their realization with nanocrystal assemblies.

Nanoparticle Surfactants at Complex Emulsion Interfaces.

Using nanoparticle surfactants to stabilize the liquid-liquid interface has attracted significant attention for developing all-liquid constructs including emulsions and liquid devices. Here, an efficient strategy is demonstrated to stabilize complex emulsions that consist of multiphase droplets by using the co-assembly between the cellulose nanocrystal and amine-functionalized polystyrene. Cellulose nanocrystal surfactants (CNCSs) form and assembly in situ at the specified area of emulsion interface, showing a unique pH responsiveness due to their dynamic nature and allowing the reconfiguration of complex emulsion from encapsulated to Janus structures. Such complex emulsions can be further used as the templates to fabricate polymeric particles with hollow, semi-spherical, and spherical shapes on large scale. These findings establish a promising platform for designing intelligent soft matter that can be used in microreactors, sensors, and anisotropic materials.

Oriented Linear Self-Assembly of Colloidal Nanocrystals through Regioselective Formation of Hydrogen-Bonded Supramolecular Bridges.

The linear assembly of nanocrystals (NCs) with orientational order presents a significant challenge in the field of colloidal assembly. This study presents an efficient strategy for assembling oleic acid (OAH)-capped, faceted rare earth NCs─such as nanorods, nanoplates, and nanodumbbells─into flexible chain-like superstructures. Remarkably, these NC chains exhibit a high degree of particle orientation even with an interparticle distance reaching up to 15 nm. Central to this oriented assembly method is the facet-selective adsorption of low-molecular-weight polyethylene glycol (PEG), such as PEG-400 (Mn = 400), onto specific facets of NCs. This regioselectivity is achieved by exploiting the lower binding affinity of OAH ligands on the (100) facets of rare earth NCs, enabling facet-specific ligand displacement and subsequent PEG attachment. By adjusting the solvent polarity, the linear assembly of NCs is induced by the solvophobic effect, which simultaneously promotes the formation of hydrogen-bonded PEG supramolecular bridges. These supramolecular bridges effectively connect NCs and exhibit sufficient robustness to maintain the structural integrity of the chains, despite the large interparticle spacing. Notably, even when coassembling different types of NCs, the resulting multicomponent chains still feature highly selective facet-to-facet connections. This work not only introduces a versatile method for fabricating well-aligned linear superstructures but also provides valuable insights into the fundamental principles governing the facet-selective assembly of NCs in solution.

Dynamic Transformation of High-Architectural Nanocrystal Superlattices upon Solvent Molecule Exposure.

The cluster-based body-centered-cubic superlattice (cBCC SL) represents one of the most complicated structures among reported nanocrystal assemblies, comprised of 72 truncated tetrahedral quantum dots per unit cell. Our previous report revealed that truncated tetrahedral quantum dots within cBCC SLs possessed highly controlled translational and orientational order owing to an unusual energetic landscape based on the balancing of entropic and enthalpic contributions during the assembly process. However, the cBCC SL's structural transformability and mechanical properties, uniquely originating from such complicated nanostructures, have yet to be investigated. Herein, we report that cBCC SLs can undergo dynamic transformation to face-centered-cubic SLs in response to post-assembly molecular exposure. We monitored the dynamic transformation process using in situ synchrotron-based small-angle X-ray scattering, revealing a dynamic transformation involving multiple steps underpinned by interactions between incoming molecules and TTQDs' surface ligands. Furthermore, our mechanistic study demonstrated that the precise configuration of TTQDs' ligand molecules in cBCC SLs was key to their high structural transformability and unique jelly-like soft mechanical properties. While ligand molecular configurations in nanocrystal SLs are often considered minor features, our findings emphasize their significance in controlling weak van der Waals interactions between nanocrystals within assembled SLs, leading to previously unremarked superstructural transformability and unique mechanical properties. Our findings promote a facile route toward further creation of soft materials, nanorobotics, and out-of-equilibrium assemblies based on nanocrystal building blocks.

Flexible multiple-stimulus-responsive photonic films based on layer-by-layer assembly of cellulose nanocrystals and deep eutectic solvents

Photonic crystal materials responding to environmental stimuli are important in sensors, intelligent detection, and anti-counterfeiting. However, traditional photonic materials usually lack tunable color and sufficient color suppleness, hindering their practical applications. Here, we report a facile strategy to achieve mechanical and color-tunable photonic films by doping deep eutectic solvents (DES) into cellulose nanocrystals (CNC) using layer-by-layer assembly. The amount of DES and several assembly layers were vital in determining the structure color and mechanical and response properties in the CNC photonic films. The experimental results revealed that DES could endow CNC suspension systems with high zeta potential, high viscoelasticity, and low transmittance. The tiny DES compensated for the insufficient flexibility of the CNC film, resulting in a wide color range, high solvent discrimination ability, and multi-color at several view angles. Moreover, photonic crystal film also played an important role in intelligent display and could be applied to traffic reflective signs to remind pedestrians and drivers of road safety and as smart labels for indoor humidity detection. These characteristics of the CNC photonic films could provide a promising strategy for developing advanced intelligent sensors, detection, and anti-counterfeiting materials.

Oriented Assembly of Lead Halide Perovskite Nanocrystals.

Cesium lead halide nanostructures have highly tunable optical and optoelectronic properties. Establishing precise control in forming perovskite single-crystal nanostructures is key to unlocking the full potential of these materials. However, studying the growth kinetics of colloidal cesium lead halides is challenging due to their sensitivity to light, electron beam, and environmental factors like humidity. In this study, in situ observations of CsPbBr3-particle dynamics were made possible through extremely low dose liquid cell transmission electron microscopy, showing that oriented attachment is the dominant pathway for the growth of single-crystal CsPbBr3 architectures from primary nanocubes. In addition, oriented assembly and fusion of ligand-stabilized cubic CsPbBr3 nanocrystals are promoted by electron beam irradiation or introduction of polar additives that both induce partial desorption of the original ligands and polarize the nanocube surfaces. These findings advance our understanding of cesium lead halide growth mechanisms, aiding the controlled synthesis of other perovskite nanostructures.

Chiral Assembly of Perovskite Nanocrystals: Sensitive Discrimination of Amino Acid Enantiomers.

Chirality is a widespread phenomenon in nature and in living organisms and plays an important role in living systems. The sensitive discrimination of chiral molecular enantiomers remains a challenge in the fields of chemistry and biology. Establishing a simple, fast, and efficient strategy to discriminate the spatial configuration of chiral molecular enantiomers is of great significance. Chiral perovskite nanocrystals (PNCs) have attracted much attention because of their excellent optical activity. However, it is a challenge to prepare perovskites with both chiral and fluorescence properties for chiral sensing. In this work, we synthesized two chiral fluorescent perovskite nanocrystal assembly (PNA) enantiomers by using l- or d-phenylalanine (Phe) as chiral ligands. PNA exhibited good fluorescence recognition for l- and d-proline (Pro). Homochiral interaction led to fluorescence enhancement, while heterochiral interaction led to fluorescence quenching, and there is a good linear relationship between the fluorescence changing rate and l- or d-Pro concentration. Mechanism studies show that homochiral interaction-induced fluorescence enhancement is attributed to the disassembly of chiral PNA, while no disassembly of chiral PNA was found in heterochiral interaction-induced fluorescence quenching, which is attributed to the substitution of Phe on the surface of chiral PNA by heterochiral Pro. This work suggests that chiral perovskite can be used for chiral fluorescence sensing; it will inspire the development of chiral nanomaterials and chiral optical sensors.

Pressure‐Induced Inversion of Chiroptical Properties in Cholesteric Assembled Cellulose Nanocrystals

AbstractDynamic manipulation of the chiroptical effect, particularly the inversion of chiral signal, has attracted broad attention, but still remains challenging, Here, stepwise tuning of the helicoidal assembly and chiroptical properties of the cellulose nanocrystal (CNC) films utilizing high pressure are demonstrated. With in situ monitoring, the changes of Fourier‐transform infrared (FTIR) spectra and evaluating the corresponding applied energy, three distinctive stages of chiroptical properties are clearly identified. In these stages, the photonic bandgap of the CNC film exhibits a fast‐slow–fast alteration over different energy imposed. The three stages are associated sequentially with interlayer space reduction, hydrogen bonding reconfiguration, and covalent bands changing. A switch of chiral signal from left‐ to right‐handedness is observed in the third stage, and the handedness of CD spectra can be recovered upon release, which is barely observed. This unique property is suspected to be the change in CNCs assembly induced by molecular‐level conformational change. This work sheds light on the fundamental understanding of how pressure can trigger the change from molecular‐level to hierarchical assembly and corresponding chiroptical performance, facilitating the design of chiral assembly with pre‐programmed triggering chiroptical properties of bio‐photonic materials.

Exciton-carrier coupling in a metal halide perovskite nanocrystal assembly probed by two-dimensional coherent spectroscopy

The surface chemistry and inter-connectivity within perovskite nanocrystals play a critical role in determining the electronic interactions. They manifest in the Coulomb screening of electron–hole correlations and the carrier relaxation dynamics, among other many-body processes. Here, we characterize the coupling between the exciton and free carrier states close to the band-edge in a ligand-free formamidinium lead bromide nanocrystal assembly via two-dimensional coherent spectroscopy. The optical signatures observed in this work show: (i) a nonlinear spectral lineshape reminiscent of Fano-like interference that evidences the coupling between discrete electronic states and a continuum, (ii) symmetric excited state absorption cross-peaks that suggest the existence of a coupled exciton-carrier excited state, and (iii) ultrafast carrier thermalization and exciton formation. Our results highlight the presence of coherent coupling between exciton and free carriers, particularly in the sub-100 femtosecond timescales.

Dark‐Bright Exciton Splitting Dominates Low‐Temperature Diffusion in Halide Perovskite Nanocrystal Assemblies

AbstractSemiconductor nanocrystals can replace conventional bulk materials completely in displays and light‐emitting diodes. Exciton transport dominates over charge carrier transport for materials with high exciton binding energies and long ligands, such as halide perovskite nanocrystal films. Here, how beneficial superlattices – nearly perfect 3D assemblies of nanocrystals ‐ are to exciton transport is investigated. Surprisingly, the high degree of order is not as crucial as the individual nanocrystal size, which strongly influences the splitting of the excitonic manifold into bright and dark states. At very low temperatures, the energetic splitting is larger for the smallest nanocrystals, and dark levels with low oscillator strength effectively trap excitons inside individual nanocrystals, suppressing diffusion. The effect is reversed at elevated temperatures, and the larger nanocrystal size becomes detrimental to exciton transport due to enhanced exciton trapping and dissociation. The results reveal that the nanocrystal size must be strongly accounted for in design strategies of future optoelectronic applications.

Observation of Quasi-Invariant Photocarrier Lifetimes in PbS Nanocrystal Assemblies Coupled to Resonant and Nonresonant Arrays of Optical Antennas

Observation of Quasi-Invariant Photocarrier Lifetimes in PbS Nanocrystal Assemblies Coupled to Resonant and Nonresonant Arrays of Optical Antennas