Dispersed Crystal Research Articles

Importance of surface modification of γ-alumina in creating its nanostructured composites with zeolitic imidazolate framework ZIF-67

Application of zeolitic imidazolate framework-67 (ZIF-67) as an adsorbent has been greatly hindered by slow mass transfer of adsorbate molecules due to its inherent microporosity. To address this limitation, we have developed binary nanostructures composed of ZIF-67 and γ-alumina (GA) containing respectively micropores and large mesopores. The nanostructured composites were successfully prepared by coupling ZIF-67 and GA with and without surface modification with imidazole silane that mimics the building blocks of ZIF-67 to obtain GA-Im-ZIF-67 (with imidazole silane) and GA-ZIF-67 (without imidazole silane). The sizes of ZIF-67 crystals in these composites were smaller as compared to those of pure ZIF-67, and the textural properties of these composites with and without surface modification were quite similar. However, the surface grafting of alumina with imidazole silane played an important role in improving interfacial coupling between GA and ZIF-67, which resulted in significant changes in the dispersion of ZIF-67 crystals and better adsorption properties. The presence of large mesopores in the alumina-based composites containing smaller ZIF-67 crystals improved their adsorption properties toward dyes such as Rhodamine B (RhB). The RhB adsorption capacity of GA-Im-ZIF-67 was much higher than that of GA-ZIF-67, suggesting that the imidazole silane modification of GA before its coupling with ZIF-67 and the GA mesoporosity were essential for a substantial increase in the adsorption capacity of RhB.

Preparation of temperature-response fibers with cholesteric liquid crystal dispersion

Cholesteric liquid crystal (CLC) dispersion was prepared using the mixed emulsifiers composed of Tween 20 and Span 80. The effects of preparation parameters on mean particle size and particle size distribution of CLC dispersion were investigated, demonstrating that the CLC mixture was better dispersed and stabilized above the phase transition temperature, and keeping the HLB at 11.7, emulsifier amount at 1.0%, dispersing speed at 5000 rpm for 60 min, the CLC particle in the dispersion were spherical and had a reversible thermochromic property. This dispersion was then used in the preparation of temperature-response PVP/CLC fibers in a water-based system by electrospinning. Polarized optical microscopy and scanning electron microscopy image reveal that CLC particles were incorporated into the PVP/CLC fibers, protecting the CLC from leaking out. The PVP/CLC fibers exhibited an optical temperature response in the temperature range from 25 to 60 °C.

Single-Cycle Terahertz Pulse Generation from OH1 Crystal via Cherenkov Phase Matching

OH1 crystal is an organic nonlinear optical crystal with a large nonlinear optical constant. However, it has dispersion of refractive indices in the terahertz (THz) frequency. This limits the frequencies that satisfy the phase matching conditions for THz wave generation. In this study, we addressed the phase matching conditions for THz wave generation by combining an OH1 crystal with prism-coupled Cherenkov phase matching. We observed the generation of single-cycle THz pulses with a spectrum covering a frequency range of 3 THz. These results prove that combining prism-coupled Cherenkov phase matching with nonlinear optical crystals yields a THz wave generation method that is insusceptible to crystal dispersion.

Ab Initio Molecular Dynamics and Lattice Dynamics-Based Force Field for Modeling Hexagonal Boron Nitride in Mechanical and Interfacial Applications.

Hexagonal boron nitride (hBN) is an up-and-coming two-dimensional material, with applications in electronic devices, tribology, and separation membranes. Herein, we utilize density-functional-theory-based ab initio molecular dynamics (MD) simulations and lattice dynamics calculations to develop a classical force field (FF) for modeling hBN. The FF predicts the crystal structure, elastic constants, and phonon dispersion relation of hBN with good accuracy and exhibits remarkable agreement with the interlayer binding energy predicted by random phase approximation calculations. We demonstrate the importance of including Coulombic interactions but excluding 1-4 intrasheet interactions to obtain the correct phonon dispersion relation. We find that improper dihedrals do not modify the bulk mechanical properties and the extent of thermal vibrations in hBN, although they impact its flexural rigidity. Combining the FF with the accurate TIP4P/Ice water model yields excellent agreement with interaction energies predicted by quantum Monte Carlo calculations. Our FF should enable an accurate description of hBN interfaces in classical MD simulations.

Raman inactive phonon-polariton dispersion in quantum paraelectric SrTiO3 crystals studied by FTIR

ABSTRACTThe dispersion relation of Raman inactive phonon-polaritons with T1u symmetry was studied in quantum paraelectric SrTiO3 with centrosymmetric Pm3¯m in which no Raman active mode is allowed. The reflectivity in the far- and mid-IR regions was measured using a [001] crystal plate by the reflection FT-IR spectroscopy, and the complex refractive index was determined in the broadband frequency range between 30 and 1200 cm−1. Using these values the dispersion relation of phonon-polariton frequency was discussed using the real and imaginary parts of a polariton wave vector considering the spacial decay of polariton.

Symmetry Breaking in Photonic Crystals: On-Demand Dispersion from Flatband to Dirac Cones.

We demonstrate that symmetry breaking opens a new degree of freedom to tailor energy-momentum dispersion in photonic crystals. Using a general theoretical framework in two illustrative practical structures, we show that breaking symmetry enables an on-demand tuning of the local density of states of the same photonic band from zero (Dirac cone dispersion) to infinity (flatband dispersion), as well as any constant density over an adjustable spectral range. As a proof of concept, we demonstrate experimentally the transformation of the very same photonic band from a conventional quadratic shape to a Dirac dispersion, a flatband dispersion, and a multivalley one. This transition is achieved by finely tuning the vertical symmetry breaking of the photonic structures. Our results provide an unprecedented degree of freedom for optical dispersion engineering in planar integrated photonic devices.

Analysis of Crystal Size Dispersion Effects in a Continuous Coiled Tubular Crystallizer: Experiments and Modeling

Continuous processing gains importance in the fine chemical and pharmaceutical industries where crystallization is an important downstream operation. Seeded cooling crystallization of the l-alanine/water system was investigated under similar conditions, i.e., temperature interval, cooling rate, and seed material, both in a stirred batch vessel and in a continuous plug flow crystallizer in the coiled flow inverter (CFI) design with horizontal helical tube coils (ID = 4 mm) and frequent 90° bends of the coils. Short-cut calculations based on characteristic time scales and the Damkohler number allow for comparing the batch and continuous crystallization processes. The experimental results reveal crystal growth and growth rate dispersion to be dominating on the product crystal size distribution (CSD). However, at low flow rates of approximately 31 g min–1, a moving sediment flow of the slurry was present in the CFI crystallizer, resulting in further size dispersion effects. Elevated flow rates of approximatel...

Aggregation-free sensitizer dispersion in rigid ionic crystals for efficient solid-state photon upconversion and demonstration of defect effects

Accommodation of ionic sensitizers into emitter ionic crystals allows aggregation-free sensitizer dispersion and efficient photon upconversion.

Coupling free energy and surface anchoring mechanism in gold nanorod–nematic liquid crystal dispersions

Dependence of both the induced optical birefringence signals and simulated free energy ftotal with the pump H.

Realization of conical dispersion and zero-refractive-index in graphene plasmonic crystal

Dirac cones discovered in classical periodic systems such as photonic and phononic crystals have exhibited many interesting properties, particularly conical dispersion at the Brillouin zone center can be related to a zero-refractive-index. Here, we theoretically and numerically explore the conical dispersion in plasmonic crystal of graphene nanodisks arranged in triangular lattice. We show that the plasmonic crystal of Dirac-like cone resulted from three-fold accidental degeneracy can be mapped to a zero-refractive-index medium around the Dirac-like point frequency of 65.5 THz. The isotropic behavior of Dirac-like point formed by a monopole and two dipoles is observed by calculating isofrequency contours. Furthermore, numerical simulations including cloaking, focusing and unidirectional transmission are implemented to demonstrate the zero-index characteristics of the graphene plasmonic crystal.

The enhanced hydrogen separation performance of mixed matrix membranes by incorporation of two-dimensional ZIF-L into polyimide containing hydroxyl group

This paper reports the preparation of mixed matrix membranes (MMMs) by incorporating a two-dimensional zeolitic imidazolate framework-L (ZIF-L) into a highly gas permeable hydroxyl group-containing polyimide (PI) for hydrogen separation. ZIF-L has a leaf-shaped morphology with excellent CO2 adsorption properties due to strong interaction between ZIF-L and CO2 molecules. The dispersion of ZIF-L crystals in the polymer phase increased CO2 adsorption and restricted CO2 transport through MMMs, resulting in a significant increase of H2 selectivity over CO2. The gas transport properties of MMMs with a ZIF-L loading up to 20wt% were investigated, and the results showed such MMMs had a H2 permeability of 260 Barrers and ideal H2/CO2 selectivity of 13.4 at room temperature. The membranes presented here have the potential for large-scale fabrication for hydrogen separation applications.

Synthesis of highly disperse tetragonal BaTiO3 nanoparticles with core–shell by a hydrothermal method

In order to synthesize of high-dispersion and tetragonal BaTiO3 (BT) nanoparticle, a hydrothermal method is used in a mixture of chloride metal sources and KOH with polyvinylpyrrolidone (PVP). The properties of BT–PVPs prepared by different reaction temperature and time are investigated via XRD, FE-SEM, DLS, FT-IR, and TEM to clarify the changes of the crystal phase, dispersion, and particle structure. The reaction is finished at 230 °C for 24 h and the critical reaction condition for that the crystal phase of the obtained BT particle changed from the cubic to the tetragonal is found to be 190 °C fixed in reaction time 24 h, and 9 h. During reaction the PVP on the BT surface decomposed to different form, and the PVP plays the role of dispersant in aqueous solution. By the hydrothermal condition of 230 °C for 24 h almost monodisperse BT–PVP with sizes of 83 nm and tetragonality (c/a) of 1.0062 were synthesized. The structure of nanoparticle, core (BT)–shell (PVP) was investigated by FT-IR and direct observed by TEM and the mechanism of particle growth and dispersion was discussed.

Heat-Resistant and Microwaveable Poly(lactic acid) by Quantum-Dot-Promoted Stereocomplexation

Nanofiller-tailored stereocomplexation signifies a promising and feasible pathway to develop heat-resistant poly(lactic acid) (PLA) materials. However, this pathway is thwarted by the potential adverse environmental issues of traditional nanofillers and the challenges in facilitating the nanofiller dispersion and selective formation of stereocomplex crystals (SCs). Here we unravel a microwave-assisted approach to exploit biobased quantum dots (QDs) featuring excellent capability to preferably nucleate PLA SCs. The combination of ultrasmall dimension and high oxygenation degree of QDs conferred intimate interactions with stereocomplexed PLA chains, readying complete exfoliation and uniform dispersion of QDs to promote stereocomplexation. The well-dispersed QDs provided perfect UV shielding for PLA composites, while sustaining high transmission to visible light comparable to pure PLA. Strong interfacial interactions and high concentration of SCs were created around the nanoscale surfaces of QDs, accounting ...

Ice cream structure modification by ice-binding proteins

Ice-binding proteins (IBPs), also known as antifreeze proteins, were added to ice cream to investigate their effect on structure and texture. Ice recrystallization inhibition was assessed in the ice cream mixes using a novel accelerated microscope assay and the ice cream microstructure was studied using an ice crystal dispersion method. It was found that adding recombinantly produced fish type III IBPs at a concentration 3 mg·L−1 made ice cream hard and crystalline with improved shape preservation during melting. Ice creams made with IBPs (both from winter rye, and type III IBP) had aggregates of ice crystals that entrapped pockets of the ice cream mixture in a rigid network. Larger individual ice crystals and no entrapment in control ice creams was observed. Based on these results a model of ice crystals aggregates formation in the presence of IBPs was proposed.

Effect of setting accelerator to the initial strength of mortar with blast furnace slag cement

Effect of three types of setting accelerators such as calcium nitrous, calcium nitrate and C-S-H micro crystal dispersion on early strength enhancement of mortar with blast furnace slag cement were investigated. As a result, it was confirmed that compressive strength of mortar at early age had been enhanced by each accelerator, among them, the accelerator of C-S-H type showed the highest promoting effect. Furthermore, it was found that when the dosage is 4% or more, the initial strength designated by construction procedure can be secured and the productivity of construction work can also be improved.

Liquid crystal dispersions containing nanoparticles of different anisometry: carbon nanotubes and organomodified laponite

Liquid crystal dispersions containing nanoparticles of different anisometry: carbon nanotubes and organomodified laponite

Photonic-crystal waveguide for the second-harmonic generation

The possibility of efficient second-harmonic generation in the optical range in a planar dielectric waveguide with the active region in the form of a one-dimensional photonic crystal has been theoretically shown. The true phase matching can be achieved by controlling wave dispersion in the photonic crystal. The dispersion equations for the photonic crystal and three-layer waveguide have been self-consistently solved. It is shown that the coherence length may exceed 10 mm.

Broadband second-harmonic generation in APPLN with group-velocity matching

In this paper, we present a method to increase the acceptance bandwidth of second harmonic generation (SHG) with 5 mol% MgO-doped aperiodically poled lithium niobate (APPLN) when the conditions of quasi-phase-matching and group-velocity matching are satisfied simultaneously. The APPLN, with a length of 10 mm, has 3333 uniform domains, with the polarization directions of each domain optimized by a genetic algorithm, to obtain the profile of nonlinear coefficients in the communication band. By adjusting the positions and quantities of the fundamental wavelengths appropriately, the evolution of bandwidths is investigated theoretically. The simulation results show that the acceptance bandwidth of SHG is approximately 243.3 nm for type-I (o+o→e) interaction around the wavelength of zero-group-velocity dispersion in crystal, which is enhanced by 4.5 times that of periodic structures.

CoMn2O4 Anchored on N-Doped High-Dimensional Hierarchical Porous Carbon Derived from Biomass for Bifunctional Oxygen Electrocatalysis

There is an emerging interest in developing bifunctional oxygen electrocatalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), being key electrochemical reactions that govern the overall performance of unitized regenerative fuel cells and rechargeable metal-air batteries. However, such undertaking has been a huge challenge due to the high cost of noble metals (e.g. Pt, Ir) and their stability when used as catalysts. Herein, we report CoMn2O4 embedded on three-dimensional (3D) hierarchical porous carbon (HPC) derived from waste corn cobs as a possible noble metal-free bifunctional electrocatalyst. The hybrid catalyst is fabricated by solvothermal reaction of as-prepared N-doped 3DHPC and CoMn2O4. The template-free approach in preparing N-3DHPC ensures ample nitrogen doping using melamine to improve electronic conductivity of carbon and formation of three-dimensional, interconnected pore network, which is favorable for CoMn2O4 crystal dispersion. The same hybrid material also presents good OER activity, rendering an active and inexpensive dual-function electrocatalyst.

Mixtures of 4-pentyl-4'-cyanobiphenyl and photosensitive azoxy nematics as hosts forliquid crystal dispersions of carbon nanotubes

Mixtures of 4-pentyl-4'-cyanobiphenyl and photosensitive azoxy nematics as hosts forliquid crystal dispersions of carbon nanotubes