Neat Crystals Research Articles

Flexoelectricity and piezoelectric effects in poly (vinyl alcohol)-SrTiO3 nanocomposites

This work investigates the structural, dielectric, mechanical, and apparent piezoelectric properties of PVA-SrTiO3 nanocomposite films by varying the concentration of SrTiO3 nanoparticles. It was shown that the piezoelectric coefficient d33, dielectric constant, elastic modulus, and hardness strongly depend upon nanoparticle concentration; the strong molecular interaction between constituents leads to the formation of an interface layer between PVA matrix and SrTiO3. We propose that the apparent piezoelectric coefficient relates to the converse flexoelectric effect and Maxwell stress induced by an electric field. The proper interface layer formation strongly depends upon nanoparticle concentration; when the concentration increases, their agglomeration drives the destruction of the interface such that the properties of the nanocomposites are diminished. By fine-tuning the interface layer of PVA nanocomposite with nanoparticles functionalizing by polyvinylpyrrolidone, the films exhibit an unexpectedly high apparent piezoelectric coefficient (d33=35 pC/N); this value is higher than neat SrTiO3 crystals and polymer composites with flexoelectric properties.

Hydrate vs Anhydrate under a Pressure-(De)stabilizing Effect of the Presence of Water in Solid Forms of Sulfamethoxazole

An understanding of the structure–properties relationship of crystals is one of the principles of crystal engineering. It is well established that the physicochemical properties of solids, such as their temperature and pressure stability, can be modified by the diversification of the chemical composition: i.e., by the synthesis of multicomponent crystals. This method is widely used in the pharmaceutical industry in the search for novel crystal forms providing higher bioavailability and better processability during the manufacturing process. It is also crucial to thoroughly study, analyze, and compare multicomponent crystals with neat crystals to assess to what extent their properties were altered. In this work we investigate the effect of the presence of water molecules on the pressure stability of crystals, on an example of an antibiotic sulfamethoxazole in its neat form (polymorph I, SMX I) and as a hemihydrate (SMX·0.5H2O). The crystals were investigated under high pressure in a series of hydrostatic media up to ca. 4 GPa. SMX I was established to be the preferred and stable solid form of sulfamethoxazole under the studied conditions, while the compression of crystals of SMX·0.5H2O above 3.7 GPa led to a reversible isostructural solid-to-solid phase transition to phase II (named SMX hemihydrate-II). The difference between SMX hemihydrates I and II and a comparison of the pressure stability of the investigated forms of SMX are discussed in terms of intermolecular interactions, Full Interaction Maps (FIMs), structural voids, and changes in crystal density. It has been shown that lower density and less ordered molecular arrangement in crystals of SMX hemihydrate, a direct effect of the presence of water molecules, contribute to its lower pressure stability in comparison to crystals of SMX I.

Deep‐Blue Ultralong Room‐Temperature Phosphorescence from Halogen‐Free Organic Materials through Cage Effect for Various Applications

AbstractOrganic room‐temperature phosphors with high performances are of great importance for broad range of potential applications. Herein, a new concept of cage effect is proposed to effectively promote room‐temperature phosphorescence (RTP) property of organic materials. A novel phosphor, bearing electron‐donating carbazole and electron‐accepting boronate ester moieties (CBBU) is designed and synthesized. CBBU crystals show multiple photoluminescence including concomitant fluorescence, thermally activated delayed fluorescence (TADF), and RTP. Further doping CBBU in boronate ester crystals (DB/CBBU) boosts remarkably deep‐blue RTP emission with CIE coordinates (0.15, 0.09) and a lifetime of 3.69 s, which is longer by four orders of magnitude than that of neat CBBU crystals. To the best of knowledge, it is the longest deep‐blue organic RTP materials reported so far. To understand this phenomenon, cage effect in terms of bending, twisting, and crowding degrees, as well as interaction of chromophores with cages has been taken into consideration. The results demonstrate that the strong cage effect alleviates effectively molecular motion of chromophores and then promotes simultaneously their RTP efficiency and lifetime. Similar results have also been found in a series of boronate ester derivatives. Furthermore, applications of the efficient RTP materials for temperature measurements, thermal transition detection, and UV sensing are exploited.

A Novel DR/NIR T-Shaped AIEgen: Synthesis and X-Ray Crystal Structure Study

We developed a new benzodifuran derivative as the condensation product between 2,6-diamino-4-(4-nitrophenyl)benzo[1,2-b:4,5-b’]difuran-3,7-dicarboxylate and 3-hydroxy-2-naphthaldehyde. The intramolecular hydrogen-bond interactions in the terminal half-salen moieties produce a sterically encumbered highly conjugated main plane and a D-A-D (donor-acceptor-donor) T-shaped structure. The novel AIEgen (aggregation-induced enhanced emission generator) fulfils the requirement of RIR (restriction of intramolecular rotation) molecules. DR/NIR (deep red/near infrared) emission was recorded in solution and in the solid state, with a noteworthy photoluminescence quantum yield recorded on the neat crystals which undergo some mechanochromism. The crystal structure study of the probe from data collected at a synchrotron X-ray source shows a main aromatic plane π-stacked in a columnar arrangement.

Tunable Diffraction Gratings in Copolymer Network Liquid Crystals Driven with Interdigitated Electrodes

The diffraction behavior of a polymer network liquid crystal (PNLC) was studied in in-plane switching (IPS) test cells and compared to the behavior seen in a neat liquid crystal. Due to the presence of polymer, the diffraction behavior was varied drastically: PNLCs are composites, which possess a specific domain size. The size of such polymer-induced domains was investigated with polarized optical microscopy and scanning electron microscopy. PNLCs are capable of continuous optical-phase modulation. It was found that electrical addressing with nonhomogenous electric fields can be useful to vary the phase modulation profile as compared to a neat LC. The diffraction patterns seen in a nematic LC were influenced by the applied addressing voltage and showed some limited tunability already. However, in the PNLC, the diffraction patterns were drastically varied as compared to a neat nematic LC. These gratings showed responses localized to the electrodes, had higher tuneability, and could also be useful to partially suppress the zeroth-diffraction order. Depending on the applied voltage, the diffraction efficiency could be tuned, efficiently. The presented results are instructive to understand the impact of a polymer network on the field-dependent reorientation of the liquid crystal director: if addressed with the same electric field profile, the responses were much more localized than in a neat nematic LC. In a straightforward numerical approach, domains in the PNLC samples were described by using cuboids. Diffraction patterns were then calculated based on the director reorientations seen and compared to the experimental data.

The Effect of Bulky Substituents on Two π-Conjugated Mesogenic Fluorophores. Their Organic Polymers and Zinc-Bridged Luminescent Networks.

From a dicyano-phenylenevinylene (PV) and an azobenzene (AB) skeleton, two new symmetrical salen dyes were obtained. Terminal bulky substituents able to reduce intermolecular interactions and flexible tails to guarantee solubility were added to the fluorogenic cores. Photochemical performances were investigated on the small molecules in solution, as neat crystals and as dopants in polymeric matrixes. High fluorescence quantum yield in the orange-red region was observed for the brightest emissive films (88% yield). The spectra of absorption and fluorescence were predicted by Density Functional Theory (DFT) calculations. The predicted energy levels of the frontier orbitals are in good agreement with voltammetry and molecular spectroscopy measures. Employing the two dyes as dopants of a nematic polymer led to remarkable orange or yellow luminescence, which dramatically decreases in on-off switch mode after liquid crystal (LC) order was lost. The fluorogenic cores were also embedded in organic polymers and self-assembly zinc coordination networks to transfer the emission properties to a macro-system. The final polymers emit from red to yellow both in solution and in the solid state and their photoluminescence (PL) performance are, in some cases, enhanced when compared to the fluorogenic cores.

A Novel Complex of Chitosan⁻Sodium Carbonate and Its Properties.

Chitosan has excellent properties, as it is nontoxic, mucoadhesive, biocompatible, and biodegradable. However, the poor water solubility of chitosan is a major disadvantage. Here, a novel chitosan-sodium carbonate complex was formed by adding a large amount of sodium carbonate to a chitosan/acetic acid solution, which is water-soluble. Fourier transform infrared spectroscopy, energy dispersive spectrometry, scanning electron microscopy, and solid-state nuclear magnetic resonance techniques were used to detect and characterize the aforementioned complex, which appeared to be a neat flake crystal. Solid-state nuclear magnetic resonance (SSNMR) was used to verify the connections between carbonate, sodium ions, and the protonated amino group in chitosan on the basis of 13C signals at the chemical shift of 167.745 ppm and 164.743 ppm. Further confirmation was provided by the strong cross-polarization signals identified by the SSNMR 2D 13C–1H frequency-switched Lee–Goldberg heteronuclear correlation spectrum. The cytotoxicity of a film prepared using this complex was tested using rat fibroblasts. The results show that the film promoted cell proliferation, which provides evidence to support its nontoxicity. The ease of film-forming and the results of cytocompatibility testing suggest that the chitosan-sodium carbonate complex has the potential for use in tissue engineering.

Nanostructured Oil in Cosmetic Paraffin Waxes

This work examines the oil-binding behavior of cosmetic paraffin wax–mineral oil systems using powder X-ray diffraction (XRD), differential scanning calorimetry (DSC), and pulsed nuclear magnetic resonance (pNMR). Neat paraffin wax crystals and paraffin wax oleogels crystallized into the same polymorphic forms; however, the oleogels had a larger lamellar thickness and crystal domain size. This increase in lamellar size could indicate that the oil was structured in between individual wax crystalline lamellae (i.e., nanostructured oil). The amount of crystalline material determined by pNMR of wax oleogels increased with temperature below their melting point, because interlamellar nanostructured oil lost some mobility and displayed solid-like behavior. These results provide experimental evidence for the existence of nanostructured oil, in support of simulation studies in the literature, and shed light into the oil-binding mechanism of some materials.

Pressure-induced preference for solvation of 5,6-dimethylbenzimidazole

5,6-Dimethylbenzimidazole (C9H9N2) crystallizes exclusively in the unsolvated form from an aqueous solution up to 0.25 GPa and from methanol, ethanol or their mixed solutions up to 0.6 GPa. At still higher pressures, solvated crystals with water, methanol and ethanol are formed depending on the solvent used for recrystallization. The NH⋯N bonds of the neat crystals are replaced by NH⋯OH⋯N bonds in the solvates. This preference for high-pressure solvation has been rationalized in terms of changed hydrogen bonds as well as volume balance between neat and solvated compounds. The methanol solvate C9H9N2·MeOH undergoes a pressure-induced phase transition at 1.40 GPa, lowering its symmetry from monoclinic space group P21/c (phase α) to triclinic space group P (high-pressure phase β) and ordering the H-atoms in hydrogen bonds NH⋯OH⋯N, disordered in phase α.

Poly(acrylic acid) to induce competitive crystallization of a theophylline/oxalic acid cocrystal and a theophylline polymorph

Polymeric additives to induce competitive crystallization of pharmaceutical compounds were explored. A cocrystal of theophylline and oxalic acid was used as a model system, and poly(acrylic acid), poly(caprolactone), and poly(ethylene glycol) were the additives. The cocrystal formation was selectively hindered with addition of poly(acrylic acid). First the size of the cocrystals were reduced, and eventually the cocrystallization was inhibited to generate neat theophylline crystals. The theophylline crystals were of a distinctively different crystal structure from known polymorphs, based on powder X-ray diffraction. They were also obtained in nanoscale size, when millimeter-scale crystals formed without poly(acrylic acid). Polymeric additives that could form specific interactions with crystallizing compounds seem to be useful tools for the phase and size control of pharmaceutical crystals.

Photochromism in a New Light: Temperature-Dependent in situ Photocrystallography

Organic photochromic molecules including diarylethenes are of particular interest for their potential applications in fields of high density optical data storage and light-activated switches, among many others. However, one of the limitations in diarylethene-based systems has been the low photoconversion observed in neat single crystals which is often less than 20%. The low conversion is typically believed to be the result of screening effects in which the photoisomerized molecules at the surface absorb incident light preventing full isomerization of the crystal. To assess the effect of screening on a model diarylethene system, photocrystallographic experiments on microcrystals of the compound were performed using synchrotron radiation at the Advanced Photon Source at Argonne National Labs. During the course of the study, we discovered that the photoconversion of the diarylethene crystals exhibits highly unusual temperature dependent behavior which is incongruent with current computational models of diarylethene photochemistry. Herein we report the first temperature-dependent `constant irradiation' in situ photocrystallography experiments performed on a photochromic system. Through the application of this technique, combined with spectroscopic analysis, we demonstrate that the steady-state population arising from the photo-cyclization reaction shows a temperature dependence which has been heretofore unobserved. Possible explanations for this anomalous behavior and its role in the photochemical reactivity of this and other diarylethene systems will be presented.

Classification and Morphological Structure of Scale in the Process of Alumina Production High Pressure Digestion

The chemical composition, phase component and morphology characteristics of scale were researched by chemical analysis, XRD, SEM and TEM. The results show that the scale can be divided into iron minerals, silicon minerals, Ca-Ti-Mg minerals and aluminum hydroxide. Alumogoethite and micro-fine sodium-silicon slag fill in the gaps between the neat and bulky hematite crystals. Microgranular hydrated garnet and olivine fill in the gaps between the goethite crystals with a dense layered structure, accompanied by a small amount of galena and apatite precipitation particles. Perovskite and magnesium hydroxide have five periodic sedimentary cycles, forming an alternating sedimentary layer structure. Aluminum hydroxide forms thick scale and presents two kinds of typical structures, spherulitic and laminated. The research provides the theoretical basis for preventing and controlling scale in high-pressure digester group.

Dendritic Morphology Composed of Stacked Single Crystals in Poly(ethylene succinate) Melt-Crystallized with Poly(p-vinyl phenol)

Dendritic morphology with stacked single crystals of poly(ethylene succinate) (PESu) melt-crystallized in the presence of amorphous poly(p-vinyl phenol) (PVPh) were observed and analyzed using optical microscopy (OM), atomic force microscopy (AFM), and transmission electron microscopy (TEM). At higher temperatures, the fluffy dendritic morphology was a transition in melt-crystallized PESu/PVPh from originally compact crystals at lower crystallization temperature. The addition of amorphous and strongly interacting PVPh polymer, confinement in thin films, and high crystallization temperature were considered as the main factors of the crystals transition from compact crystals to dendritic crystals. Single crystals of PESu were proven by AFM in the PESu/PVPh blend especially when confined in films of above 500 nm, melt-crystallized at Tc = 70 °C or above. The electron diffraction pattern of TEM result further confirmed the formation of PESu single crystals. The combination of thin film thickness, high crystallization temperature, and strong interaction between two polymers were believed to be the main factors for melt-crystallized PESu single crystals. In the single crystals with spiral arrays, the PESu chains, though achiral, tend to exhibit paired-up crystal entities resembling “identical twins” but with opposite helical directions. The single-layer thickness is almost equal between the paired-up lozenge lamellae screwing clockwise or counterclockwise. The PESu single crystals in PESu/PVPh blend were melt-grown, and electron diffraction patterns proven in this study are in agreement with the literature for neat PESu single crystals grown in dilute solutions.

Experimental assessment of quasi-binary picture of thermotropics: Induced smectic A phase in 7CB–n-heptane system

Quasi-binary (QB) picture of thermotropics, which regards a neat thermotropic liquid crystal as a binary system consisting of (semi)rigid core and molten alkyl chain, was assessed experimentally for the most famous (and representative) thermotropic mesogenic series nCB. By adding n-heptane as solvent, the smectic A phase was induced in 7CB-n-heptane system. Small angle x-ray diffraction showed that the QB picture holds not only in the phase behavior but also in the structure. It is suggested that the melting of 8CB and 9CB to isotropic liquid via smectic and nematic liquid crystals can be understood as a thermotropic-lyotropic crossover.

Control of Surface Wettability and Photomicropatterning with a Polymorphic Diarylethene Crystal upon Photoirradiation

A photochromic diarylethene crystal of 1,2-bis(2-methyl-6-nitro-1-benzothiophen-3-yl)perfluorocyclopentene (1 a) was found to undergo a thermodynamic phase transition at 180 °C to form a needle-like crystal, designated as 1 a-γ. The phase transition involves melting of the initial α-crystal and growth of the γ-crystal. The phase transition temperature decreased with the presence of the closed-ring isomer (1 b) in the crystal because of the decrease in the melting temperature. Upon irradiation with ultraviolet (UV) light, compound 1 a in the α-crystal was converted into 1 b to an extent of 20 %. Consequently, the α-crystal containing 20 % of 1 b underwent the phase transition accompanied by melting of the crystal and growth of the γ-crystal even at 170 °C. Photomicropatterning by the phase transition upon irradiation with UV light using a photomask, followed by heating at 170 °C, was successfully accomplished with a resolution in the microcrystalline pattern of about 20 μm. The contact angle with water on the γ-microcrystalline phase on a glass substrate was larger than that on the α-microcrystalline phase by 20°. This can be ascribed to a difference in the roughness of the surface. Furthermore, the γ-microcrystal was also found to be formed upon heating an amorphous film of 1 a in poly(methyl methacrylate) for 2 min at 130 °C. The crystallized area exhibited a higher water contact angle than the amorphous area. Upon irradiation of the amorphous film with UV light, such crystallization did not take place because of the impurity effect of 1 b in 1 a. Photomicropatterning by the crystallization in the polymer showed a pattern with a higher resolution of about 4 μm, which was much better than that of the neat crystal. This photopatterning process represents a useful tool for controlling the surface wettability in relevant applications.

Identification on the Fuse Fracture Properties of Electro thermal Apparatus

In the fire scene, the fracture trails of fuse were often found. There are various reasons of fracture, such as outside mechanical force, melting fracture due to overheating, short-circuit and high temperature of fire. By the fuse fracture experiments of daily electrothermal apparatus and corresponding trace analysis; this paper summarizes an identification method of fuse fracture properties, which can provide technical support for the investigators to identify the cause of the fire. Trace traits can be applied to the macro method and metallographic method. By macro method it is seen that the cut edge of mechanical force and tensile fracture is right or sharp-angled form. Traces ends formed under the condition of short-circuit are most spherical. The shape of trace formed by high temperature of fire is between the traces shapes of the above, a smooth, but less spherical shape. Using metallographic method, untouched region by the temperature of ruptured fuse by mechanical force is observed with the ferrite microspheres small equiaxial crystal. Deformation organization is noticed of tensile fracture and cut of fuse fracture place. While the microstructure in the high temperature effect is the equiaxial crystal, and the microstructures of short-circuit fusing in molten mark end (or local) show big grain boundaries, inner of which still has not neat columnar crystal, in addition, there is an obvious transition region between the melting parts and matrix.

Time-resolved synchrotron diffraction and theoretical studies of very short-lived photo-induced molecular species

Definitive experimental results on the geometry of fleeting species are at the time of writing still limited to monochromatic data collection, but methods for modifications of the polychromatic Laue data to increase their accuracy and their suitability for pump-probe experiments have been implemented and are reviewed. In the monochromatic experiments summarized, excited-state conversion percentages are small when neat crystals are used, but are higher when photoactive species are embedded in an inert framework in supramolecular crystals. With polychromatic techniques and increasing source brightness, smaller samples down to tenths of a micrometre or less can be used, increasing homogeneity of exposure and the fractional population of the excited species. Experiments described include a series of transition metal complexes and a fully organic example involving excimer formation. In the final section, experimental findings are compared with those from theoretical calculations on the isolated species. Qualitative agreement is generally obtained, but the theoretical results are strongly dependent on the details of the calculation, indicating the need for further systematic analysis.

Coordination polymers derived from a bis-pyridyl-bis-amide ligand: Supramolecular structural diversities and anion binding properties

Abstract Six new coordination polymers namely [{Cu(μ- L1 )(CH 3 COO) 2 }] ∝ 1a , [{Cu(μ- L1 ) 2 (CH 3 COO) 2 ] ∝ 1b , [{Cu(μ- L1 ) 2 (H 2 O) 2 }(NO 3 ) 2 ] ∝ 2 , [{Cu(μ- L1 ) 2 (H 2 O) 2 }(ClO 4 ) 2 ] ∝ 3 , [{Cu(μ- L1 )(H 2 O) 2 (μ-SO 4 )}·3H 2 O] ∝ 4a and [{Cu(μ- L1 ) 2 SO 4 }·X] ∝ 4b ( L1 = N,N ′-bis-(3-pyridyl)terephthalamide) have been synthesized. Single crystal structures of five coordination polymers namely 1a , 2–4b and the free ligand L1 are discussed in the context of the effect of conformation dependent ligating topology of the ligands, hydrogen bonding backbone, counter anions on the resultant supramolecular structures observed in these coordination polymers. It was revealed from the single crystal X-ray structure analysis that conformation dependent ligating topology of the bis-amide ligand L1 , counter anion’s ligating strength dependent metal: ligand ratio, hydrogen bonding ability of the ligand as well as counter anions are responsible for the formation of 1D zigzag, 1D looped chain, 2D corrugated sheet in 1a , 2–3 , 4a − 4b , respectively. By following in situ coordination polymer crystallization technique, anion binding and separation studies have also been performed; nitrate anion has been separated as neat coordination polymer crystals from a complex mixture of anions.

Determination of Structure and Phase Transition of Light Element Nanocomposites in Mesoporous Silica: Case study of NH3BH3 in MCM-41

Nanocomposition of molecular crystal ammonia borane (AB) by embedding it in mesoporous silica leads to a remarkable enhancement of the hydrogen storage properties. To investigate the nature of a nanophase AB, we used atomic pair distribution function (PDF) analysis of synchrotron X-ray powder diffraction data to follow the structural evolution of AB embedded within MCM-41 at temperatures ranging from 80 to 300 K. We found that the nanophase AB residing within the mesoporous scaffold does not undergo the structural phase transition at 225 K that was observed in the neat molecular crystal. Rather, it stays in the tetragonal phase over a wide temperature range of 110 to 240 K and starts to lose structural correlation above 240 K. This finding strongly suggests that nanoconfinement of AB within mesoporous scaffolds stabilizes the high-temperature disordered tetragonal phase at a much lower temperature. PDF analyses of composite materials composed of excess AB (i.e., AB:MCM-41 > 1:1) indicates that the excess AB forms aggregates outside the mesoporous scaffold and that these aggregates have structural properties similar to neat AB, that is, the orthorhombic-to-tetragonal structural phase transition is observed at 225 K upon warming. These results may provide important insight into the mechanism behind the enhanced hydrogen storage properties of this system.

Carbazole-Based Organogel as a Scaffold To Construct Energy Transfer Arrays with Controllable Fluorescence Emission

A diaryldiketopyrrolopyrrole derivative functionalized with phenothiazine moieties (DPPP) was synthesized and introduced into the ordered 4-(3,6-di-tert-butyl-9H-carbazol-9-yl)benzamide (TBCB) organogel system. It was found that TBCB-based gel became a scaffold to make DPPP molecules line up along the gel fibers, resulting in new self-assembled arrays, whose XRD patterns were quite different from those of the neat TBCB gel and DPPP crystal. In the composite gel, the occurrence of a partial energy transfer from the excited light-harvesting antenna of TBCB to the DPPP acceptor was confirmed on the basis of time-dependent and time-resolved fluorescence investigations. Remarkably, the composite gel could emit intense red light or purplish white light by tuning the excitation wavelength. Such ordered soft materials with color-tunable emission may possess potential applications in sensor and photonic devices.