Mesoscopic Order Research Articles

Elasticity Mapping of Colloidal Glasses Reveals the Interplay between Mesoscopic Order and Granular Mechanics.

Colloidal glasses (CGs) made of polymer (polymethylmethacrylate) nanoparticles are promising metamaterials for light and sound manipulation, but fabrication imperfections and fragility can limit their functionality and applications. Here, the vibrational mechanical modes of nanoparticles are probed to evaluate the nanomechanical and morphological properties of various CGs architectures. Utilizing the scanning micro-Brillouin light scattering (µ-BLS), the effective elastic constants and nanoparticles' sizes is determined as a function of position in a remote and non-destructive manner. This method is applied to CG mesostructures with different spatial distributions of their particle size and degree of order. These include CGs with single-sized systems, binary mixtures, bilayer structures, continuous gradient structures, and gradient mixtures. The microenvironments govern the local mechanical properties and highlight how the granular mesostructure can be used to develop durable functional polymer colloids. A size effect is revealed on the effective elastic constant, with the smallest particles and ordered assemblies forming robust structures, and classify the various types of mesoscale order in terms of their mechanical stiffness. The work establishes scanning µ-BLS as a tool for mapping elasticity, particle size, and local structure in complex nanostructures.

Al/SBA-15 Mesoporous Material: A Study of pH Influence over Aluminum Insertion into the Framework.

Herein, ordered mesoporous materials like SBA-15 and Al/SBA-15 were prepared using the pH adjustment method. Thus, these materials were developed in different pH of synthesis, from the pH adjustment method using a KCl/HCl solution and varying the Si/Al molar ratio (5, 25, and 75). All the ordered mesoporous materials were characterized by FRX, 27Al NMR, SEM, XRD, N2 adsorption/desorption, and CO2 adsorption. From the applied method, it was possible to obtain SBA-15 and Al/SBA-15 with high mesoscopic ordering based on the XRD patterns, independent of the pH employed. From the chemical composition, the insertion of higher amounts of Al into the synthesis caused a progressive improvement in the structural and textural properties of the ordered mesoporous materials. Thus, the chosen synthesis conditions can lead to different aluminum coordination (tetrahedral and octahedral), which gives these materials a greater potential to be applied. The presence of Al in high amounts provides material with the ability to form micropores. Finally, the proposed method proved to be innovative; low-cost; less aggressive to the environment, with efficient insertion of aluminum in the framework of SBA-15 mesoporous material; and practical, based on only one step.

Dissymmetric Triaryltriazines: Small Mass Columnar Glasses.

Columnar liquid crystals with very small molecular masses that form anisotropic glasses well above room temperature are obtained by mixed dissymmetric substitution of sym-triazine with ester-bearing phenyl and phenanthryl or tetrahelicenyl moieties. The combination of low molecular symmetry with configurational flexibility and short polar ester moieties stabilizes the mesophase over large temperature ranges and induces pronounced calorimetric glass transitions within the anisotropic fluid despite the smallness of the molecules. In contrast to more symmetrical homologs, no ester tails longer than ethyl are necessary to induce the liquid crystalline state, allowing for the near-absence of any insulating and weight-increasing alkyl periphery. Films drop-cast from solution show in all cases emission spectra that do not show significant change of fluorescence emission upon annealing, indicating that the columnar hexagonal mesoscopic order is obtained directly upon deposition from solution and is resistant to crystallization upon annealing.

Highly homogeneous multicomponent mesoporous catalysts: Defective amorphous vs. nanocrystalline CeO2 structure towards CO-PROX reaction

Mesoporous multicomponent materials with uniform pore sizes and well-defined network geometries are viewed as highly attractive candidates in the catalysis field. However, their synthesis at a high homogeneity level is considered quite challenging. Herein, alumina based mixed oxides (Al/Ce/Cu or Fe) are produced through a facile evaporation-induced-self-assembly route and tested towards preferential oxidation of CO in H2-rich gas. The effect of several synthetic parameters is investigated, with citric acid addition identified as a key factor in view of obtaining high mesoscopic order and notable homogeneity, particularly at high dopant amounts. Following thermal aging at 900 °C, metal oxides distribution and nanoporous nature are well-preserved with a parallel nucleation of ceria nanoparticles into the semi-crystalline inorganic framework. CO-PROX assessment of the aged samples reveals a drastic enhancement in catalytic activity, especially for the ternary Cu–Ce–Al system, associated with material's structural reconstruction strongly affecting metal–support interaction.

Synthesis of Ruthenium-Promoted ZnO/SBA-15 Composites for Enhanced Photocatalytic Degradation of Methylene Blue Dye

Synthetic organic pigments like xanthene and azo dyes from the direct discharge of textile effluents are considered colossal global issues and attract the concern of scholars. Photocatalysis continues to be a very valuable pollution control method for industrial wastewater. Incorporations of metal oxide catalysts such as zinc oxide (ZnO) on mesoporous Santa Barbara Armophous-15 (SBA-15) support to improve catalyst thermo-mechanical stability have been comprehensively reported. However, charge separation efficiency and light absorption of ZnO/SBA-15 continue to be limiting its photocatalytic activity. Herein, we report a successful preparation of Ruthenium-induced ZnO/SBA-15 composite via conventional incipient wetness impregnation technique with the aim of boosting the photocatalytic activity of the incorporated ZnO. Physicochemical properties of the SBA-15 support, ZnO/SBA-15, and Ru-ZnO/SBA-15 composites were characterized by X-ray diffraction (XRD), N2 physisorption isotherms at 77 K, Fourier-transform infrared (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray (EDS), and transmission electron microscopy (TEM). The characterization outcomes exhibited that ZnO and ruthenium species have been successfully embedded into SBA-15 support, andtheSBA-15 support maintains its structured hexagonal mesoscopic ordering in both ZnO/SBA-15 and Ru-ZnO/SBA-15 composites. The photocatalytic activity of the composite was assessed through photo-assisted mineralization of aqueous MB solution, and the process was optimized for initial dye concentration and catalyst dosage. 50 mg catalyst exhibited significant degradation efficiency of 97.96% after 120 min, surpassing the efficiencies of 77% and 81% displayed by 10 and 30 mg of the as-synthesized catalyst. The photodegradation rate was found to decrease with an increase in the initial dye concentration. The superior photocatalytic activity of Ru-ZnO/SBA-15 over the binary ZnO/SBA-15 may be attributed to the slower recombination rate of photogenerated charges on the ZnO surface with the addition of ruthenium.

Electron-Beam Induced Emergence of Mesoscopic Ordering in Layered MnPS3.

Ordered mesoscale structures in 2D materials induced by small misorientations have allowed for a wide variety of electronic, ferroelectric, and quantum phenomena to be explored. Until now, the only mechanism to induce this periodic ordering was via mechanical rotations between the layers, with the periodicity of the resulting moiré pattern being directly related to twist angle. Here we report a fundamentally distinct mechanism for emergence of mesoscopic periodic patterns in multilayer sulfur-containing metal phosphorus trichalcogenide, MnPS3, induced by the electron beam. The formation under the beam of periodic hexagonal patterns with several characteristic length scales, nucleation and transitions between the phases, and local dynamics are demonstrated. The associated mechanisms are attributed to the relative contraction of the layers caused by beam-induced sulfur vacancy formation with subsequent ordering and lattice parameter change. As a result, the plasmonic response of the system is locally altered, suggesting an element of control over plasmon resonances by electron beam patterning. We pose that harnessing this phenomenon provides both insight into fundamental physics of quantum materials and enables device applications by enabling controlled periodic potentials on the atomic scale.

Synthesis of sulfonic SBA-15 by co-condensation and soxhlet extraction: optimization by shortening the preparation time

Propyl sulfonic SBA-15 catalysts are of great interest in several fields of chemistry and have exhibited high activity towards numerous reactions. Nonetheless, the incorporation of these functional groups on SBA-15 silica poses several challenges. Grafting techniques may conduct to a non-uniform dispersion of the functional groups on the surface. Co-condensation of the functional precursor during the synthesis of the silica overcomes this drawback, but requires longer syntheses and it has the disadvantage that removal of surfactant cannot be done by calcination because of the thermal stability of the functional groups present on the surface. Thus, the detemplation is limited in this case to extraction by standard procedures which generally involve large amounts of solvent per gram of catalyst, long contact time and limited yield of the template removal. The aims of this work were, on the one hand, to study the reduction of the ripening time for catalysts prepared by co-condensation with sulfonic groups and, on the other hand, to develop a standard procedure which allows achieving a high yield of detemplation and optimizes the amount of solvent needed and the time required, as well as employ a commercially available solvent. Different characterization techniques allowed to conclude that the obtained materials exhibited high surface area and a good degree of mesoscopic order, comparable with materials obtained by traditional procedures. Also, a high degree of template removal was achieved and the sulfonic groups were preserved in functionalized materials. These results are relevant for a further scale-up of the catalysts production.

Lithium insertion in hard carbon as observed by 7Li NMR and XRD. The local and mesoscopic order and their relevance for lithium storage and diffusion

The storage mechanism of lithium in hard carbon was investigated by 7Li NMR and 2D-XRD methods. Lithium was found to fill disordered sites first and then fill the ordered sites of graphitic character arranged in a distinct mesoscopic order.

Few‐Unit‐Cell MFI Zeolite Synthesized using a Simple Di‐quaternary Ammonium Structure‐Directing Agent

AbstractSynthesis of a pentasil‐type zeolite with ultra‐small few‐unit‐cell crystalline domains, which we call FDP (few‐unit‐cell crystalline domain pentasil), is reported. FDP is made using bis‐1,5(tributyl ammonium) pentamethylene cations as structure directing agent (SDA). This di‐quaternary ammonium SDA combines butyl ammonium, in place of the one commonly used for MFI synthesis, propyl ammonium, and a five‐carbon nitrogen‐connecting chain, in place of the six‐carbon connecting chain SDAs that are known to fit well within the MFI pores. X‐ray diffraction analysis and electron microscopy imaging of FDP indicate ca. 10 nm crystalline domains organized in hierarchical micro‐/meso‐porous aggregates exhibiting mesoscopic order with an aggregate particle size up to ca. 5 μm. Al and Sn can be incorporated into the FDP zeolite framework to produce active and selective methanol‐to‐hydrocarbon and glucose isomerization catalysts, respectively.

Few-Unit-Cell MFI Zeolite Synthesized using a Simple Di-quaternary Ammonium Structure-Directing Agent.

Synthesis of a pentasil‐type zeolite with ultra‐small few‐unit‐cell crystalline domains, which we call FDP (few‐unit‐cell crystalline domain pentasil), is reported. FDP is made using bis‐1,5(tributyl ammonium) pentamethylene cations as structure directing agent (SDA). This di‐quaternary ammonium SDA combines butyl ammonium, in place of the one commonly used for MFI synthesis, propyl ammonium, and a five‐carbon nitrogen‐connecting chain, in place of the six‐carbon connecting chain SDAs that are known to fit well within the MFI pores. X‐ray diffraction analysis and electron microscopy imaging of FDP indicate ca. 10 nm crystalline domains organized in hierarchical micro‐/meso‐porous aggregates exhibiting mesoscopic order with an aggregate particle size up to ca. 5 μm. Al and Sn can be incorporated into the FDP zeolite framework to produce active and selective methanol‐to‐hydrocarbon and glucose isomerization catalysts, respectively.

Very Slow Phase Transition from the Liquid to Mesophase and Phase-Coexistence in the Ionic Liquid [C8mim]BF4

Abstract The room temperature ionic liquid, 1-methyl-3-octylimidazolium tetrafluoroborate, abbreviated as [C8mim]BF4, has been known as a good glass-former, which can be cooled or heated at normal scanning rates without any phase transition. However, after cooling to 183 K, just below the glass transition temperature, 190 K, followed by heating to 223 K, Tg + 33 K, a novel phase transition from the supercooled liquid to a partially ordered phase was observed by X-ray diffractometry during a slow isothermal annealing at that temperature. The XRD profiles showed that the ordered phase is not crystal, but a smectic-A phase of a bilayer structure as seen in typical lamellar phases of surfactant solutions or lipid polymers. It is remarkable that the liquid phase still remains even after the existence of the ordered SmA phase for more than 90 hours, which is supposed to be the coexistence, or partial ordering, of the liquid and liquid crystalline. This cannot be seen in conventional one-component systems, such as ordinary molecular liquids. The ionic liquid structure is expected to be very stable due to the original mesoscopic order, which is predicted by MD simulation, Raman spectroscopy and neutron scattering.

Phase stability condition and liquid–liquid phase separation under mesoscale confinement

Here we establish the thermodynamic phase stability condition under mesoscale confinement, which is essential in elucidating how the confinement of solutions inside a droplet, cell or liposome may influence phase separation. To clarify how phase stability is affected by external conditions, a formal analogy between a partially open ensemble and a mesoscopic system will be exploited, through which the nonnegligible role of the system boundary will be identified as the crucial difference from the macroscopic stability condition. The thermodynamic stability condition extended for mesoscale is shown to involve several different orders of magnitude that are all considered to be O(1) at a macroscopic limit. Phase instability in mesoscale is shown to ensue when the difference between self-association (relative self-fluctuation of particle number) and mutual association (relative number correlation between different species) reaches the mesoscopic order of magnitude, in contrast to the divergence of particle number fluctuation (namely, reaching a macroscopic order of magnitude) required in macroscale. Thus, confinement may enhance phase instability.

Unravelling the impact of thiophene auxiliary in new porphyrin sensitizers for high solar energy conversion

The performance of conjugated donor-π-Acceptor (D-π-A) sensitizers with the modification of thiophene auxiliary acceptors depends critically on their mesoscopic ordering that enables improved photon harvesting and charge transfer processes. This idea has been implemented here by reporting photocatalytic hydrogen production performance in the incremental order of 2691, 6641 and 7396 μmol g−1 h−1 by altering thiophene (LG-5) to thieno-thiophene (LG-tT) to dithieno- thiophene (LG-DtT) auxiliaries. New sensitizers, LG-tT and LG-DtT are making it possible to achieve an impressive power conversion efficiency of (PCE) of 8.25 % and 7.05 %, respectively in dye-sensitized solar cell applications. The high onset of Q-band absorption of both sensitizers (720−750 nm) is resulting in effective harvesting of sunlight. DFT studies suggest the photoexcited electron transfer process took place intramolecularly from donor phenothiazine to acceptor cyanoacrylic acid via porphyrin macrocycle. This strategy of molecular engineering at donor and acceptor fragments led to competitive results compared to many reported sensitizers for both DSSC and photocatalytic hydrogen generation.

Enhanced sampling of cylindrical microphase separation via a shell-averaged bond-orientational order parameter.

The formation of a hexagonal phase from disordered phase is one of the typical order-disorder transitions (ODTs) observed in asymmetric diblock copolymer systems. In order to drive this transition in a particle-based simulation, we introduce a shell-based bond-orientational order parameter that selectively responds to the mesoscopic order of the hexagonal cylinder phase. From metadynamics simulations in a bond-free particle model system, the characteristic pathway involved with the underlying free energy surface is deduced for the disordered-to-hexagonal transition. It is shown consecutively that the transition pathway and the metastable state are reproduced in dissipative particle dynamics simulations for the corresponding transition in a bulk asymmetric block copolymer melt system. These agreements suggest that efficient strategies for enhanced sampling with particle-based simulations of block copolymer systems can be devised using coarse-grained pictures of the mesoscopic order.

Self-organization of silicates on different length scales exemplified by amorphous mesoporous silica and mesoporous zeolite beta using multiammonium surfactants.

In this study the structure directing effect of a gemini-type piperidine-based multi-ammonium surfactant during hydrothermal zeolite synthesis was investigated for two cases: with and without a source of aluminum. The absence of an aluminum source led to the formation of an amorphous mesoporous MCM-48 type silica material, while the presence of aluminum guaranteed the formation of zeolite beta with a hierarchical pore system. The two opposing cases were studied in a time and temperature-dependent manner. The mobility and through space interaction of these large surfactant molecules were studied by liquid state nuclear magnetic resonance (NMR) at a temperature relevant to hydrothermal synthesis (363 K) in pure water and upon addition of an aluminum and silicon source. In the gel state, at different stages of aging and hydrothermal synthesis, low angle X-ray diffraction (XRD) and solid state magic angle spinning nuclear magnetic resonance (1H MAS NMR) spectrometry determined the developing order within the system. At each of these different synthesis steps the respective intermediate materials were calcined. Transmission electron microscopy then allowed closer inspection of the locally developing mesoscopic order, while N2 physisorption was used to follow the evolution of porosity.

Dynamics of mesoscopic polarization in the uniaxial tetragonal tungsten bronze (SrxBa1−x)Nb2O6

The high-frequency dielectric behavior of uniaxial tungsten-bronze strontium barium niobate crystals with various Sr/Ba ratios, including both ferroelectric and relaxor compositions, have been studied in a broad frequency range (${10}^{4}$ to ${10}^{13}\phantom{\rule{0.16em}{0ex}}\mathrm{Hz}$) and temperature interval 100--500 K in order to thoroughly understand the evolution of the relaxation dynamics across the ferroelectric phase transition. The dielectric response along the polar axis consists of three relaxations corresponding to polarization mechanisms related to several correlation lengths of mesoscopic order. All of them show dissimilar behaviors with temperature, pointing out to their distinct nature. A temperature-dependent central mode at THz frequencies and a relaxation above 10 GHz are accompanied by the slowing down of a relaxation in the MHz range. This response reveals the complex mechanism of the phase transition and supports the coexistence of displacive and order-disorder scenarios. Relaxor and ferroelectric compositions surprisingly reveal similar qualitative behavior within the frequency window used. However, relaxor crystals display relaxations at higher frequency because of the smaller extent of the polar fluctuations and ferroelectric regions, which coexist in almost all the compositions. The presence of two different ferroelectric subsystems in the structure agrees with the existence of several polarization mechanisms involved in the complex dielectric and ferroelectric response.

Tunable assembly of truncated nanocubes by evaporation-driven poor-solvent enrichment

Self-assembly of nanocrystals is extensively used to generate superlattices with long-range translational order and atomic crystallographic orientation, i.e. mesocrystals, with emergent mesoscale properties, but the predictability and tunability of the assembly methods are poorly understood. Here, we report how mesocrystals produced by poor-solvent enrichment can be tuned by solvent composition, initial nanocrystal concentration, poor-solvent enrichment rate, and excess surfactant. The crystallographic coherence and mesoscopic order within the mesocrystal were characterized using techniques in real and reciprocal spaces, and superlattice growth was followed in real time by small-angle X-ray scattering. We show that formation of highly ordered superlattices is dominated by the evaporation-driven increase of the solvent polarity and particle concentration, and facilitated by excess surfactant. Poor-solvent enrichment is a versatile nanoparticle assembly method that offers a promising production route with high predictability to modulate and maximize the size and morphology of nanocrystal metamaterials.

Building ferroelectric from the bottom up: The machine learning analysis of the atomic-scale ferroelectric distortions

Recent advances in scanning transmission electron microscopy (STEM) have enabled direct visualization of the atomic structure of ferroic materials, enabling the determination of atomic column positions with approximately picometer precision. This, in turn, enabled direct mapping of ferroelectric and ferroelastic order parameter fields via the top-down approach, where the atomic coordinates are directly mapped on the mesoscopic order parameters. Here, we explore the alternative bottom-up approach, where the atomic coordinates derived from the STEM image are used to explore the extant atomic displacement patterns in the material and build the collection of the building blocks for the distorted lattice. This approach is illustrated for the La-doped BiFeO3 system.

Local Ordering of Lattice Self-Assembled SDS@2β-CD Materials and Adsorbed Water Revealed by Vibrational Sum Frequency Generation Microscope.

VSFG (vibrational sum frequency generation) microscopy was used to study the SDS@2β-CD system, a synthetic capsid-like self-assembled material. We found because of strong hydrogen-bond interactions between water and the assemblies, water molecules are template to adopt the local mesoscopic ordering of the self-assemblies, which allows VSFG to probe water on nonflat interfaces. We show that the origin of the VSFG signal from the self-assembly is a combination of individual molecular chirality and highly coordinated ordering of the self-assembly, which gives rise of anisotropic signals, e.g., under SSS polarization. A similar strategy could be applied to other self-assembled materials composed by molecules without inversion symmetry. Using an imaging process, VSFG spectra of different self-assembly sheets were spatially resolved. We found heterogeneity among different domains, which can be attributed to variations in the hydration level of different domains. Since the SDS@2β-CD system is a synthetic lattice self-assembly, such heterogeneity could also exist in other natural lattice assemblies such as a virus and tubulin.

Chiral Excitonic Organic Photodiodes for Direct Detection of Circular Polarized Light

AbstractA facile route to soft matter self‐powered bulk heterojunction photodiode detectors sensitive to the circular polarization state of light is shown based on the intrinsic excitonic circular dichroism of the photoactive layer blend. As light detecting materials, enantiopure semiconducting small molecular squaraine derivates of opposite handedness are employed. Via Mueller matrix ellipsometry, the circular dichroism is proven to be of H‐type excitonic nature and not originating from mesoscopic structural ordering. Within the green spectral range, the photodiodes convert circular polarized light into a handedness‐dependent photocurrent with a maximum dissymmetry factor of ±0.1 corresponding to 5% overall efficiency for the polarization discrimination under short circuit conditions. On the basis of transfer matrix optical simulations, it is rationalized that the optical dissymmetry fully translates into a photocurrent dissymmetry for ease of device design. Thereby, the photodiode's ability to efficiently distinguish between left and right circularly polarized light without the use of external optical elements and voltage bias is demonstrated. This allows a straightforward and sustainable future design of flexible, lightweight, and compact integrated platforms for chiroptical imaging and sensing.