Dispersed Crystal Research Articles

Chiroptical anisotropy of crystals and molecules.

Optical activity, a foundational part of chemistry, is not restricted to chiral molecules although generations have been instructed otherwise. A more inclusive view of optical activity is valuable because it clarifies structure-property relationships however, this view only comes into focus in measurements of oriented molecules, commonly found in crystals. Unfortunately, measurements of optical rotatory dispersion or circular dichroism in anisotropic single crystals have challenged scientists for more than two centuries. New polarimetric methods for unpacking the optical activity of crystals in general directions are still needed. Such methods are reviewed as well as some of the 'nourishment' they provide, thereby inviting to new researchers. Methods for fitting intensity measurements in terms of the constitutive tensor that manifests as the differential refraction and absorption of circularly polarized light, are described, and examples are illustrated. Single oriented molecules, as opposed to single oriented crystals, can be treated computationally. Structure-property correlations for such achiral molecules with comparatively simple electronic structures are considered as a heuristic foundation for the response of crystals that may be subject to measurement.

Characterization of Lignocellulosic Fibers Reinforced with Poly(vinyl alcohol)

The demands for materials made of plastics are rapidly increasing, especially in food packaging application. Recently, attention has been drawn to the use of bio-reinforced composites in packaging, automotive, medical and construction applications due to increased concern for environmental sustainability. Poly(vinyl alcohol) (PVA) films reinforced with crystals (unbleached) prepared by solution casting method possessed significantly improved properties compared to film reinforced with cellulose (bleached). From the results, PVA films with the addition of 4% (w/w) of crystalline cellulose exhibited best combination of properties. In addition to good mechanical properties, this composite has good water resistance and biodegradability. The water absorption of biocomposite was found to be 22.63%. From X - ray diffraction (XRD) analysis, diffraction peaks of biocomposite was observed at 2θ = 22.4384. From scanning electron microscopy (SEM) analysis it was found that fractures at surfaces of biocomposite film were smooth and even without any porosity and uniform dispersion of jute crystals in the matrix.

Tunable protein crystal size distribution via continuous slug-flow crystallization with spatially varying temperature

Under appropriate buffer and pH conditions, the magnitude and dispersion of the product protein crystals were reproducibly manipulated by controlling the spatial temperature along the tube in a continuous tubular crystallizer.

Adsorption and Lubrication of α-Gel (α-Form Hydrated Crystal) Dispersion at Solid/Liquid Interfaces.

We characterized the adsorption and desorption of α-gel (α-form hydrated crystal) dispersions in aqueous media using a quartz crystal microbalance with dissipation monitoring (QCM-D) technique. The α-gel was formed from a mixture of N-[3-(dimethylamino)propyl]docosanamide (APA-22) L-lactic acid salt, 1-octadecanol (C18OH), and water. The solid substrate employed in this study as a model for hair was silica. The QCM-D measurements revealed that the α-gel dispersions yielded a rigid adsorption film on the negatively charged silica surface. The adsorption mass decreased with decreasing domain size (on the micrometer scale) of the α-gel dispersions. The adsorption film highly restricted the desorption of the α-gel from the silica surface even after rinsing with water. The adsorption film also exhibited excellent lubrication ability in aqueous media both before and after rinsing with water. We expect that the α-gel formed by APA-22 L-lactic acid is a potential ingredient for formulating an environment-friendly hair conditioner owing to its high adsorption, limited desorption, and excellent lubrication abilities on the solid surface.

Aging effect on the co-crystallization behavior of the donor and acceptor crystals in aqueous dispersions

CT co-crystals and “phase-separated” crystals were prepared separately by the mixing of donor and acceptor crystal dispersions.

Chirality-Induced Phonon Dispersion in a Noncentrosymmetric Micropolar Crystal.

Features of the phonon spectrum of a chiral crystal are examined within the micropolar elasticity theory. This formalism accounts for not only translational micromotions of a medium but also rotational ones. It is found that there appears the phonon band splitting depending on the left- and right-circular polarization in a purely phonon sector without invoking any outside subsystem. The phonon spectrum reveals parity breaking while preserving time-reversal symmetry, i.e., it possesses true chirality. We find that hybridization of the microrotational and translational modes gives rise to the acoustic phonon branch with a "roton" minimum reminiscent of the elementary excitations in the superfluid helium-4. We argue that a mechanism of this phenomena is in line with Nozières' reinterpretation P. Nozières, [J. Low Temp. Phys. 137, 45 (2004)JLTPAC0022-229110.1023/B:JOLT.0000044234.82957.2f] of the rotons as a manifestation of an incipient crystallization instability. We discuss a close analogy between the translational and rotational micromotions in the micropolar elastic medium and the Bogoliubov quasiparticles and gapful density fluctuations in ^{4}He.

Features of dielectric properties of medical thermal indicators based on dispersions of cholesteric liquid crystals in the polymer matrix

Within the frequency range 10…106 Hz, the frequency dependences of the real (ε') and imaginary (ε") components of the complex dielectric permittivity of medical thermal indicators based on polyvinyl acetate and mixtures of cholesteric liquid crystals have been studied. In them, the selective reflection of electromagnetic waves visible to the human eye occurs at normal (36.6 °C) and elevated (38.2 °C) human body temperatures. Being based on the comparison of the ε' frequency dependences for the studied in this work dispersions of nematic liquid crystals prepared using the same technology and with the same polymer, it has been shown that, already on the basis of analysis of frequency dependences for ε', it is possible to ascertain the difference in characteristics for two types of thermal indicators. From the comparison of frequency dependences for ε", the main reasons of a difference between dielectric properties of the investigated medical thermal indicators for various temperatures of a human body have been ascertained.

Antiscalants in the Process of Reverse Osmosis: Antiscaling Mechanism and Modern Problems of Application

Despite the available long-term experience in the practical application of antiscalants for preventing the depositions on membranes during the reverse osmosis of sparingly soluble inorganic compounds of generally crystalline nature (scaling, inorganic fouling), the studies on the antiscaling mechanism, the development of express methods for estimating the optimal dose of antiscalants, and the creation of new efficient and environmentally friendly reagents still remain relevant. In this paper, the contemporary scientific studies concerning the mechanism of the action of scaling inhibitors and the topical problems of their practical application in reverse osmosis process are analyzed. The key role of the selective sorption of antiscalants on the surface of the particles of formed sparingly soluble compounds in their inhibiting efficiency at substoichiometric doses is described as exhibited in the change in nucleation and crystal growth kinetics, the morphological and structural transformation of crystals, and the change in the capability of particles for agglomeration and interaction with the surface of membranes. The relevance of the development of new efficient, non-toxic, non-bioaccumulated, and biodegradable antiscalants for avoiding the environmental risks upon the discharge of concentrates into the environment is shown, and the currently most promising types of “green” scaling inhibitors are considered. The results of studying the action of both traditional and “green” antiscalants by modern methods of analysis (scanning electron microscopy, X-ray diffraction, dynamic light scattering, fluorescent tagging) are given to confirm the “threshold effect” and the crystal deformation and dispersion effects in the process of scaling inhibition. The priority problems of fundamental and applied studies for improving the efficiency and environmental friendliness of the application of antiscalants in reverse osmosis processes are specified.

Dispersion engineering of W2 steeple-house-defect waveguide photonic crystal

An epitome for dispersion and buffering in a photonic crystal was set forth. Slots in the form of a line of contacted steeple-houses are implanted in a two-line photonic crystal waveguide (2LPCW) to form an irregular slot of steeple-house defect PCW (SDPCW) to realize bandwidth expanding and a significant regulator for group delay (GD), group velocity dispersion (GVD) and group delay dispersion (GDD) effects. The SDPCW was compared with other types of defects reported in this study and in the literature previously, we fulfilled the highest favorable value of buffering capacity about 210.256 bits. Furthermore, low GDD is achieved in the range from 1ps2to 10ps2 for 1 mm delay line length. The SDPCW may be appropriate for the workable application, which has a utility in coupling enhancement between the cavities as it was observed from the field distribution detected over confined spatial light along the propagation path for enhancing the transmission bandwidth, buffering properties and outstanding tolerance to fabrication errors. Moreover, stopping and/or slowing the light has an excessive advantage in the store of quantum states of light for an adequately long time to make quantum operations. Besides, the SDPCW achieved high electro-optical (EO) sensitivity about 244.42 nm/RIU. Thus, the proposed SDPCW can be used for enhancing the interaction between light and the sensing medium.

Design and Characterization of Glyceryl Monooleate-Nanostructures Containing Doxorubicin Hydrochloride.

Glyceryl monooleate (GMO) is one of the most popular amphiphilic lipids, which, in the presence of different amounts of water and a proper amount of stabilizer, can promote the development of well defined, thermodynamically stable nanostructures, called lyotropic liquid crystal dispersions. The aim of this study is based on the design, characterization, and evaluation of the cytotoxicity of lyotropic liquid crystal nanostructures containing a model anticancer drug such as doxorubicin hydrochloride. The drug is efficiently retained by the GMO nanosystems by a remote loading approach. The nanostructures prepared with different non-ionic surfactants (poloxamers and polysorbates) are characterized by different physico-chemical features as a function of several parameters, i.e., serum stability, temperature, and different pH values, as well as the amount of cryoprotectants used to obtain suitable freeze-dried systems. The nanostructures prepared with poloxamer 407 used as a stabilizer show an increased toxicity of the entrapped drug on breast cancer cell lines (MCF-7 and MDA-MB-231) due to their ability to sensitize multidrug-resistant (MDR) tumor cells through the inhibition of specific drug efflux transporters. Moreover, the interaction between the nanostructures and the cells occurs after just a few hours, evidencing a huge cellular uptake of the nanosystems.

Triggering and acceleration of xylitol crystallization by seeding and shearing: Rheo-optical and rheological investigation

The present study investigates the triggering and acceleration of xylitol crystallization for its use as a short-term TES. The combined effect of seeding and the action of shear on xylitol crystallization at a supercooled temperature has been investigated by direct observations under shear (rheo-optical approach) and by rheometry. The initial seed is an agglomerate of crystals of xylitol. In addition to the more classical erosion and rupture mechanisms leading to the dispersion of crystals, shear has shown to induce the detachment of crystalline dust adhered to the initial seed into the supercooled xylitol. These crystal fragments then serve as sites for secondary nucleation and subsequent crystallization. Rheo-optical observations have allowed the determination of shear conditions to control the size of crystals by dispersion. A second part has been dedicated to the effect of shear on crystallization of xylitol by seeding by means of rheology. The measurements, although not reproducible, clearly show that seeding in presence of shear (for the investigated conditions) is very efficient to trigger and accelerate the crystallization of xylitol. Post-mortem DSC and XRPD analyses of the final crystallized seeded and sheared samples have not shown any effect on the xylitol crystallinity degree.

Влияние трегалозы на дисперсность кристаллов льда и консистенцию низкожирного мороженого

Introduction. The research objective was to establish the effect of the complete and partial replacement of sucrose by trehalose on the dispersion of ice crystals in ice cream with a low mass fraction of fat and solids. 
 Study objects and methods. The present research featured three test samples of ice cream with a 3% mass fraction of fat: one with a complete replacement of sucrose (15.5%) and two with a partial replacement of 7.5% and 3%. In the control sample, the mass fraction of sucrose was 15.5%. To control the dynamic viscosity indicator of consistency, the research employed such an advanced method as rotational viscometry. Microstructure methods were used to determine the dispersion of ice crystals and the air phase.
 Results and discussion. The usage of trehalose in the production of low-fat ice cream in the amounts of 3.0%, 7.5%, and 15% increased the dispersion of ice crystals and preserved it during storage. After three months of storage, most ice crystals in the test ice cream samples had a size of ≤ 45 μm with an organoleptic sensibility of ≤ 50 μm, while in the control sample (15.5% of sucrose) it did not exceed 60 μm. The experiment determined the effect of trehalose on the consistency of ice cream according to the following indicators: dynamic viscosity, overrun, and dispersion of the air phase. 15.5% of trehalose increased the dynamic viscosity of ice cream mix by 1.2 times as compared to the sample with the same concentration of sucrose. According to the average diameter of air bubbles, trehalose helped to preserve the dispersion of the air phase during storage. After three months, Sample 1 with 15.5% of trehalose demonstrated the maximum dispersion, which was 17% higher than in the control sample with a sucrose mass fraction of 15.5%.
 Conclusion. The complete (15.5%) and partial (3% and 7.5%) sucrose replacement by trehalose in low-fat ice cream increased the dispersion of ice crystals and improved its consistency. Unlike the sample with 15.5% of sucrose, samples with trehalose had smaller ice crystals, which remained the same after three months. The trehalose samples had a better dynamic viscosity and air saturation. The research requires a further study of dispersion of ice crystals after 12 months of storage.

Controlling phonon lifetimes via sublattice disordering in AgBiSe2

Due to their ability to convert thermal gradients into useful electrical energy, thermoelectrics are promising for energy efficiency uses. Thermoelectric conversion rates are driven by the ratio of electrical to thermal conductivity in the material, thus substantial research focuses on balancing these competing mechanisms. Here the authors use state-of-the-art neutron scattering and computational modeling to investigate the temperature dependence of the crystal structure, phonon dispersions, and phonon lifetimes to provide new microscopic insight to thermal conductivity suppression in AgBiSe2, a thermoelectric exhibiting a cationic sublattice disordering at high temperature. These combined efforts enable the authors to definitively describe contributions to the thermal conductivity arising from a step-like change in phonon scattering rates directly originating from the combined effects of mass and force-constant disorder due to cation disorder at the structural phase transition. This study highlights the potential of tunable microstructures to control phonon scattering rates in real materials, a necessary component for rational material design, particularly for thermoelectrics.

Synthesis and catalytic performance of zeolite-Y supported on silicon carbide in n-heptane cracking

In this work, we demonstrate a facile approach for the synthesis of zeolite-Y crystals (size, ca. ∼400 nm) supported on silicon carbide (SiC) with the assistance of the cationic template (polydiallyldimethylammonium chloride, PDDA). The polymeric cationic template used to treat SiC particles induces a positive charge on SiC surface which electrostatically attracts negatively charged aluminosilicate seeds and promotes the growth of zeolite (ZY) particles over SiC, thus leading to the formation of stable ZY@SiC supported catalysts. The supported ZY catalysts with different weight ratio of ZY and SiC were synthesized and characterized by various techniques such as XRD, SEM, SEM-EDX, SEM-mapping, TEM, STEM, FT-IR, 27Al MAS NMR and N2 sorption. The characterization of the supported ZY catalysts suggests the uniform growth of ZY particles over SiC together with the creation of hierarchical micro-mesopores assembly. In the catalytic cracking of n-heptane, the catalyst ZY@SiC-50 displayed a remarkable improvement in reaction rate when compared to commercial zeolite-Y (CBV-600) amounting to 3.5 folds enhancement. Interestingly, the light olefins yield is also substantially improved. At WHSV of 8 h−1 and 475 °C, the highest light olefin yield (24–36 %) was achieved over ZY@SiC-50 whereas the reference catalyst, CBV-600 produced lower light olefins yield (7–17 %). Moreover, the supported ZY catalyst exhibited less deactivation rates. This improved performance is attributed to the hierarchical micro-mesopores assembly created by the homogeneous dispersion of zeolite crystals on SiC which offers fast diffusion pathways for the reactants and enhanced accessibility to active sites thus leading to higher observed reaction rates and fast diffusion of products thus minimizing the occurrence of side reactions.

Foams of vegetable oils containing long-chain triglycerides

HypothesisCan vegetable oils containing long-chain triglycerides be aerated to yield stable oil foams? This is based on the idea that cooling of vegetable oil results in the formation of crystals of certain triglyceride chain lengths and composition dispersed in liquid oil of other chain lengths and composition. Do such oleogels allow the formation of oil foams stabilised by adsorbed crystals? ExperimentsUsing two vegetable oils, the temperatures for crystal formation are determined. Crystal dispersions were characterised using rheology and optical microscopy. Oleogels were aerated using a double beater and the effects of temperature and aeration time were investigated. The stability and microstructure of the oil foams were studied visually and using microscopy. A stable oil foam was progressively destabilised on heating. FindingsUpon cooling/warming vegetable oils, crystals of high melting triglyceride form in a low melting liquid oil - an oleogel. Such oleogels can be whipped to fabricate oil foams stabilised by fat crystals. Optimum foaming yields an over-run of ~ 40% for peanut oil and ~ 110% for olive oil. Oil foams which do not exhibit drainage, coarsening or coalescence result. We show that high melting triglyceride crystals possess a higher fraction of saturated fatty acids than the original oil. Ultra-stable oil foams can be rendered unstable by heating upon approaching the melting point of the crystals.

Electro-optical effects of organic N-benzyl-2-methyl-4-nitroaniline dispersion in nematic liquid crystals

The dispersion of organic N-benzyl-2-methyl-4-nitroaniline (BNA) in nematic liquid crystals (LCs) is studied. BNA doping decreases the threshold voltage of cell because of the reduced splay elastic constant and increased dielectric anisotropy of the LC mixture. When operated in the high voltage difference condition, the BNA-doped LC cell has a fall time that is five times faster than that of the pure one because of the decrements in the threshold voltage of the cell and rotational viscosity of the LC mixture. The additional restoring force induced by the BNA’s spontaneous polarization electric field (SPEF) also assists to decrease the fall time of the LC cell. The decreased viscosity can be deduced from the decrements in phase transition temperature and associated order parameter of the LC mixture. Density functional theory calculation demonstrates that the BNA dopant strengthens the absorbance for blue light, enhances the molecular interaction energy and dipole moment, decreases the molecular energy gap, and thus increases the permittivity of the LC mixture. The calculation also shows that the increased dipole moment, polarizability, and polarizability anisotropy increase the dielectric anisotropy of the LC mixture, which agrees with the experimental results well. BNA doping has a promising application to the fields of LC devices and displays.

Size-Dependent Liquid Crystal Behavior of Graphene Oxides for Preparation of Highly Ordered Graphene-Based Films

We report the preparation of a highly-oriented graphene-based film prepared from liquid crystal dispersion of graphene oxides (GOs). We observed that the liquid crystal behavior of GOs is highly affected by the lateral size of GO flakes: the critical concentration for liquid crystal formation decreased with the increase of the lateral size of GO flakes, which is in a good agreement with Onsager’s theory. As a result, we were able to obtain highly-ordered graphene assemblies with large-sized GO flakes (150 ± 29 μm) at relatively low concentrations. By applying the shear force, we were able to obtain highly-oriented films from liquid crystal GO flakes. After hydrogen iodide (HI) reduction, GO films showed excellent mechanical strength and electrical conductivity, which were 278% and 283% higher, respectively, than those of films made from smaller sized GO flakes (28 ± 24 μm).

RESEARCH OF THE EFFECT OF AGING PROCESS ON DISPERSION OF AIR PHASE AND ICE CRYSTALS IN MILK ICE CREAM

In this research the results of analytical studies are presented, which prove the lack of data on influence of aging process on dispersion of structural elements in ice cream with fat mass fraction of 6% or less, and experimental studies on definition of dispersion of air phase and ice crystals in milk ice cream. It was found that the process of the mix aging doesn’t significantly affect the dispersion of air phase and ice crystals in ice cream with fat mass fraction of 3%. In ice cream with fat mass fraction of 6%, made from a mix, the dispersion of the air phase increased along with the aging process, and the size of almost all air bubbles were less than 50 microns. At the same time the dispersion of ice crystals increased by no more than 10%. The decrease in dispersion of the air phase during the storage period was observed, mostly in ice cream with a fat mass fraction of 6% produced of the cured mix. The research results have the practical importance as they justify the need for the aging process in the production of ice cream with a low mass fraction of fat and determine the necessity of further research in this area.

Fabry\u2013P\xe9rot modes associated with hyperbolic-like dispersion in dielectric photonic crystals and demonstration of a bending angle sensor at microwave frequencies

The dispersion properties of metamaterials and photonic crystals (PhCs) lead to an intensive research in the development of cavity resonators for the confinement of electromagnetic (e-m) radiation. In this work, we investigate the formation of Fabry–Pérot (FP) modes associated with hyperbolic-like dispersion (HLD) regimes in two-dimensional dielectric PhCs. Conventionally, FP modes are formed using an optical etalon, in which electromagnetic (e-m) waves reflecting from a partially reflecting mirror separated by a distance can interfere constructively and form a resonating mode. The FP mode observed in dielectric PhCs is formed due to the interference of cylindrical wavefronts inside the PhC interface at HLD frequencies. The FP modes in PhCs are surface localized, in which maxima/minima of the electric field lies along the air–PhC interface as a standing wave pattern and decays in air medium. Projected bandstructure, Eigen Frequency Contours (EFC), phase and group index calculations are carried out to explain the formation of FP modes in PhCs under different coupling cases. By varying the PhC dimension, FP modes with different spatial profiles are witnessed and the role of source position in exciting specific mode is demonstrated. The observed FP modes in PhCs are compared with the FP mode in an ideal indefinite slab. Based on the FP resonance in PhCs, a sensing device capable of detecting a bending angle less than 0.05^circ is demonstrated numerically. The FP modes in PhCs are scalable to other parts of e-m spectra so that the bending angle sensing can be extendable to terahertz and optical domains.

Crystal chemistry characteristics and dispersion performance of Ca-montmorillonite with different layer charge density

The correlation between crystal chemistry characteristics and dispersion performance of Ca-montmorillonite with different layer charge density was studied. The four kinds of purified montmorillonite were characterized by XRD, XRF, FTIR, SEM, TEM, BET, TG-DTG, Zeta potential, and Molecular dynamics simulation (MD). The XRD analysis results show that the d(001) value of the four kinds of Ca-montmorillonite are 1.51 nm, 1.51 nm, 1.53 nm, and 1.50 nm, respectively, and the calculation results of layer charge density show that the semi-unit cell charge density are 0.38, 0.53, 0.61, and 0.69, respectively. The charge density is positively correlated with the mass content of MgO. The FTIR analysis results show that with the increase of layer charge density, the couple vibration wave number of Si–O–Mg and Mg–O move towards the high frequency region, from 464.70 cm−1 to 466.36 cm−1 and from 517.12 cm−1 to 520.41 cm−1. The SEM analysis results show that the higher layer charge density of montmorillonite, the worse exfoliation between layers and the thicker layer thickness, The images of TEM show that montmorillonites are mainly composed of a clearly layered structure. The results of BET show that with the increase of charge density, the BET surface area, micropore area and total pore volume gradually increase from 32.69 m2 g−1 to 64.50 m2 g−1, from 4.87 m2 g−1 to 18.24 m2 g−1, and from 0.06 cm3 g−1 to 0.12 cm3 g−1 , respectively, while PSDs and pore diameter decrease from 7.88 nm to 1.74 nm, and from 7.65 nm to 5.47 nm. The results of TG and DTG show that with the increase of charge density, the removal temperature of free water and inter-layer water increase from 80 °C to 100 °C and 139 °C to 155 °C, respectively. The simulation results of MD show that with the increase of layer charge density, the number of hydrogen bonds increase from 186 to 271 and the adsorption energy increases from −1467.11 to −1874.32 kcal mol−1. The particle size increases from 701 nm(Mt1) to 1576 nm(Mt4) with the layer charge density, and the absolute value of Zeta potential, colloidal value and expansion capacity of montmorillonites suspension decrease with the increase of the layer charge density, which further indicates that the dispersion of montmorillonites decrease with the increase of layer charge density.