A new equilibrium form of zircon crystal

The surface tensions of the {100}, {110}, {101} and {211} faces are calculated by using Machenzie's method. A new equilibrium form of zircon crystal is then derived on the basis of Wulf's Law. This theoretic form consists of {100} prismatic faces and {211} pyramidal faces, which is different from that of the prediction by the periodic bond chain theory. The discovery of the equilibrium form of zircon crystal provides a clue for understanding of the morphology of zircon crystals formed in deep magma chamber, indicating that zircon morphology is an indicator of crystallization conditions.     

Isothermal crystallization of poly(vinylidene fluoride) in the presence of high static electric fields. II. Effect of crystallization temperature and electric field strength on the crystal phase content and morphology

The melt crystallization of poly(vinylidene fluoride) in a static electric field was studied for different fields strengths and undercooling conditions. The γ-phase nucleation process was examined directly by polarized optical microscopy and indirectly by small-angle light scattering. The crystal phase content was assessed by differential scanning calorimetry. It is shown that the γ-phase nucleation density and γ-phase content increase with field strength and that the higher the crystallization temperature, the larger the effect of the field. These experimental results confirm the predictions of the model of nucleation in an electric field that we published previously. It is also noted that the degree of crystallinity and the perfection of crystal orientation along the γ-phase spherulite radical direction decrease with field strength. The homogeneity of morphology resulting from the crystallization in the field is also examined by polarized optical microscopy on specimens microtomed across their thickness. When the crystallization is carried out under high field (E ≈ 0.1 MV/cm) and high temperature (T > 166°C) a nonuniform morphology results, characterized by a higher nucleation density at the positive electrode than at the negative electrode. Near the negative electrode very large disklike spherulites are seen to grow parallel to the substrate.     

Structure and Crystallization of Glasses in the MnNbOF<Subscript>5</Subscript>–BaF<Subscript>2</Subscript>–InF<Subscript>3</Subscript> System

Glasses of the MnNbOF₅–BaF₂–InF₃ system were prepared. The structure, thermal behavior, and crystallization of these glasses were studied by IR and Raman spectroscopy, differential scanning calorimetry (DSC), X-ray powder diffraction, and microscopy. The \(\rm{NbO}_2\rm{F}_4^{3-}\) and \(\rm{InF}_6^{3-}\) ions form a mixed glass network. Glass crystallization occurs in one or two steps depending on the component ratio. The major crystal phases are Ba₃In₂F₁₂ and BaNbOF₅. The obtainability of transparent crystal-glass samples in MnNbOF₅–BaF₂–InF₃ glasses via heat treatment is shown.     

Mechanisms of thermal transformation of zinc blende to [NaCl] in MnS crystals

Single crystals of zinc blende phase MnS transform at 200°C to single crystals of [NaCl] phase by single diffusive jumps of the cations. Dimensional changes cause random distortion of the crystal. Evidence is also presented for a second structural correspondence in which {111} zinc blende planes become {100} [NaCl] planes. The corresponding deformational mechanism might be favored at low temperatures.     

Guided self-assembly of electrostatic binary monolayers via isothermal-isobaric control

Self-assembly of a binary monolayer of charged particles is modeled using molecular dynamics and statistical mechanics. The equilibrium phase diagram for the system has three distinct phases: an ionic crystal; a geometrically ordered crystal with disordered charges; and a fluid. We show that self-assembly occurs near the phase transition between the ionic crystal and the fluid, and that the rate of ordering is sensitive to the applied pressure. By assuming an Arrhenius form for the rate of ordering, an optimality condition for the temperature and pressure is derived that maximizes the rate. Using the Clausius-Clapeyron equation, the optimal point on the phase boundary is expressed in terms of the thermodynamic changes in state variables across the boundary. The predicted optimal temperature and pressure conditions are in good agreement with numerical simulations and result in self-organization rates five times that of a simulation without applied pressure.     

Direct Observation of Singlet ππ* and nπ* Equilibrium State in 2-Amino-1,3,5-triazine Solution

1,3,5-Triazine molecules represent a class of molecules that may have been prebiotic information carriers in a primordial soup in early Earth and their excited state dynamics has received attention in recent years. In our previous study, one component with lifetime longer than 100 ps was discovered in 2-amino-1,3,5-trainzine (2-AT), but its nature has not been revealed. In this study, excited state dynamics of 2-AT is studied in different solvents by using femtosecond time-resolved transient absorption and fluorescence up-conversion spectroscopy. Interestingly, an equilibrium state consisting of the bright \begin{document}$ \pi\pi.* $\end{document} and dark n\begin{document}$ \pi.* $\end{document} states in 2-AT is directly observed in aqueous solution and its dynamics is solvent sensitive. The whole picture of the excited state deactivation mechanism of 2-AT is proposed based on our spectroscopy results.     

Blue or green glowing crystals of the cation [Au{C(NHMe)2}2]+. Structural effects of anions, hydrogen bonding, and solvate molecules on the luminescence of a two-coordinate gold(I) carbene complex

Depending upon the crystallization conditions, [Au{C(NHMe) 2} 2](AsF 6) forms colorless crystals that display a blue or green luminescence. The difference involves the type of solvate molecule that is incorporated into the crystal and the structure of the chains of cations that are formed upon crystallization. The crystallographically determined structures of blue-glowing [Au{C(NHMe) 2} 2](AsF 6).0.5(benzene), blue-glowing [Au{C(NHMe) 2} 2](AsF 6).0.5(acetone), green-glowing [Au{C(NHMe) 2} 2](AsF 6).0.5(chlorobenzene), and blue-glowing, solvate-free [Au{C(NHMe) 2} 2](EF 6), E = P, As, Sb are reported. All pack with the cations forming extended columns, which may be linear or bent, but all show significant aurophilic interactions. The blue-glowing crystals have ordered stacks of cations with some variation in structural arrangement whereas the green-glowing crystals have disorder in their stacking pattern. Although there is extensive hydrogen bonding between the cations and anions in all structures, in the solvated crystals, the solvate molecules occupy channels but make no hydrogen-bonded contacts. The emission spectra of these new salts taken at 298 and 77 K are reported.     

(Liquid + liquid) equilibria of methanol + ethylbenzene + isooctane + methy <Emphasis Type="Italic">tert</Emphasis>-butyl ether quaternary system at <Emphasis Type="Italic">T</Emphasis> = 303.15 K

Tie line data of {methanol + methyl tert-butyl ether + isooctane} ternary systems were obtained at T = 303.15 K, while data for {methanol + ethylbenzene + isooctane} were taken from literature. The ternary system {methanol + methyl tert-butyl ether + ethylbenzene} and {methyl tert-butyl ether + ethylbenzene + isooctane} were completely miscible. A quaternary system {methanol + ethylbenzene + isooctane + methyl tert-butyl ether} was also studied at the same temperature. In order to obtain equilibium data of the quaternary system, four quaternary sectional planes with several methyl tert-butyl ether/methanol ratios were studied. The effect of the addition of methyl tert-butyl ether on the liquid-liquid equilibrium data of {methanol + ethylbenzene + isooctane} ternary system has been investigate at the same temperature. The distribution curves for ternary and quaternary system was analysed. For the quaternary system {methanol + ethylbenzene + isooctane + methyl tert-butyl ether}, experimental data demonstrated that the distribution coefficient of ethylbenzene between the hydrocarbon and methanol phase on a methyl tert-butyl ether–free basis slightly increases with the increase of methyl tert-butyl ether/methanol ratio. Ternary experimental results were correlated with the UNIQUAC and NRTL equation. The NRTL equation is more accurate than the UNIQUAC equation for the ternary systems studied here. The equilibrium data of three ternary systems were used for determining interactions parameters for the UNIQUAC equation. The UNIQUAC equation fitted to the experimental data appeared to be more accurate than the UNIFAC method for the same quaternary system.     

Structural and aromatic aspects for tautomerism of (Z)-6-((4-bromophenylamino)methylene)-2,3-dihydroxycyclohexa-2,4-dienone

The molecular and crystal structure of (Z)-6-((4-bromophenylamino)methylene)-2,3-dihydroxycyclohexa-2,4-dienone were determined by single crystal X-ray diffraction and spectroscopic methods. Molecules of the compound can be regarded as a resonance hybrid of cis-keto tautomer and zwitterionic form. Pairs of molecules of the compound generate pseudocyclic centrosymmetric R₂² (10) R_{2}^{2} (10) supramolecular synthons with the aid of O–H···O type intermolecular H-bonds. Stacking of R₂² (10) R_{2}^{2} (10) synthons along b-axis is stabilized by π···π interactions. Changes in both covalent topology and molecular geometry of the compound accompanying proton transfer were monitored by a relaxed PES scan with respect to hydroxyl bond length used as redundant internal coordinate. Quantum chemical studies at 6-311 + G(d,p) level reveal that bond lengths which are indicative to tautomerization process cannot reach their expected values even if proton transfer occurs in gas phase and pseudo-aromatic chelate ring formation has primary effect on the stabilization of NH tautomer. Resonance-assisted intramolecular H-bond affects the electronic state of its neighboring aromatic fragments.     

Environment-induced morphological changes of polyethylene lamellae during crystallization in solution

Polyethylene (PE) lamellar crystals were grown by two dual-staged crystallization methods: (1) Fractionated PE was first crystallized from n-octane by the self-seeding method, the solvent of the resulting suspension of crystals was exchanged for p-xylene, and thereafter, the suspension was mixed with a solution in p-xylene at various temperatures so that PE grew from p-xylene onto the lamellae pregrown from n-octane, and (2) according to the similar procedure, PE lamellae were first grown from p-xylene and subsequently, PE was deposited from n-octane onto the lamellae pre-grown from p-xylene. In the crystallization procedure (1), triangular lamellae with the 〈010〉 chain folding developed randomly on the {100} lateral surfaces of truncated parent lamellae so that the surfaces were serrated, and otherwise, thin daughter lamellae bordered the parent lamellae along the {110} surfaces, retaining the flat growth fronts with the 〈110〉 folding. In the procedure (2), the {100} sectors with the 〈010〉 folding developed at the apexes of the long diagonal of lozengeshaped parent lamellae, and consequently, their morphology was transfigured into a truncated crystal. These morphological transformations are discussed on the basis of the change in the interfacial free energy between the parent crystal and the surrounding phase due to the substitution of solvent. © 1994 John Wiley & Sons, Inc.     

Elucidating the effect of additives on the growth and stability of Cu2O surfaces via shape transformation of pre-grown crystals

A new strategy of using pre-grown crystals to study preferential adsorption of various additives is demonstrated for the electrocrystallization of Cu2O. In this method, micron-size Cu2O crystals with well-defined cubic and octahedral shapes were first electrochemically grown, and their crystallization was resumed in a medium containing the additive to be investigated (e.g., Na+, NH4+, SO42-, Cl-, dodecyl sulfate). This method makes it possible to systematically study the interaction of additives with specific planes (e.g., {100} of a cube and {111} of an octahedron) already present. By observing shape transformation over time, the relative stabilities of {100}, {111}, and {110} planes of Cu2O in various growth media could be determined. During this study, a general scheme of forming new crystal shapes containing crystallographic planes that cannot be directly stabilized by preferential adsorption alone was also established (i.e., rhombicuboctahedral shape of Cu2O containing {110} planes). This method can be extended to other crystal systems, which will enable us to classify common features of additives (e.g., charges, type of atoms) and crystallographic planes (e.g., atomic arrangement, surface termination, surface charge) required to allow for strong preferential adsorption.     

Crystallization of CaCO3 in the presence of sulfate and additives: experimental and molecular dynamics simulation studies

The effects of sulfate and BHTPMP (Bis (hexamethylene) triaminepentakis (methylene phosphonic acid)) on the crystallization rate, phase composition and morphology of calcium carbonate have been studied. It was observed that sulfate reduces the nucleation rate and favors the formation of aragonite form in the calcium carbonate precipitate. Moreover, in the presence of sulfate the rhombohedral morphology of the calcite crystals is modified, and during the formation of calcite, the development of {104} faces are more significantly prohibited than {110} faces. In the presence of sulfate together with BHTPMP, the crystallization process is inhibited and the modified morphology and the dominant calcite form are observed in the solid. The results from molecular dynamics simulations show the more strong combination of sulfate with calcite surface, in particular the {104} face, in comparison with the aragonite surface. The strong interaction of BHTPMP with sulfate and the aragonite surface favors the formation of the dominant calcite phase in the precipitate.     

Effects of temperature and water on the γ → α crystalline transition of nylon 6 caused by stretching in the chain direction

The effects of temperature and water on the crystal transition of nylon 6 from the γ phase to the α phase, which is caused by stretching along the chain direction, were investigated. The γ-phase fibers with high crystallite orientation were stretched at constant load under various conditions. An inversion of the effect of water on the transition occurs at about ?60°C. Stretching in the wet state is more effective for the transition at higher temperature. In contrast, at low temperatures water in the crystalline regions actsasa cohesive agent for the chains and increases the activation energy for the transition. Thus, dry stretching is more effective than wet stretching at very low temperature. The fraction of transformed α-phase crystallites increases abruptly over a narrow range of stress. Thus the critical stress can be determined for the transition. The critical stress changes appreciably with temperature; the higher the temperature, the lower the critical stress. The relation between stretching temperature and critical stress was analyzed by Flory's equation for the shift of transition temperature by stress. About 220°C. was estimated as the zero-stress transition temperature. The heat content of the γ-phase crystal was estimated to be smaller by 500 cal./mole than that of the α-phase crystal. This result suggests that the free energy of the γ-phase crystal is lower than that of the α-phase crystal at temperatures lower than the transition point. The irreversible strain of a sample in which the crystal transition has taken place is very small at low temperature. This small extension of the sample is evidence that the γ → α transition produced by stretching along the chain axis is a crystal-crystal transition.     

The role of a liquid crystal oligomer in stabilizing blue phases

A novel liquid crystal oligomer, 4‐(4‐cyanophenyl)phenyl 4‐octyloxy‐2‐{7‐{4‐[4‐(4‐hexylphenyl)‐2,3‐difluorophenyl]phenyloxy}heptanoyloxy}benzoate, was prepared and found to exhibit a wide temperature range of a nematic phase in spite of being far from a rod‐like structure. Furthermore, the compound induced blue phases in the mixture with a chiral smectic liquid crystal. The molecular shape and its 2,3‐difluorophenyl unit play a role in stabilizing the blue phases.     

Application of the log-normal model for long term high affinity antibody/antigen interactions using Bio-Layer Interferometry

For more than 50 years, optical biosensors have been used to measure bio-molecular interactions. The most frequently applied binding model to fit biosensor data is the simple 1:1 binding model which requires the stabilization of the association phase to the equilibrium Req and the stabilization of the dissociation phase to the equilibrium zero. However, due to technical limitations many published biosensor measurements are finished before these requirements are fulfilled. In the present study, a long term binding interaction analysis with a monoclonal antibody, namely IgG 2F5 and UG37 a specific antigen with a promising biosensor platform, the Bio-Layer Interferometry, was performed. Data fitting with the simple 1:1 binding model to the association phase was inappropriate and the fitted parameters varied with the concentration and time, which contradicts the theory of the simple 1:1 binding model. Furthermore, extrapolation of the fits with individual times spans compared to 100 % of the obtained data systematically underestimated the actual observed binding curve. Interestingly, an alternative model based on the cumulative distribution function of the log-normal probability distribution remedied the aforementioned problems allowing $\hbox {K}_\mathrm{L}$ (which is the analog to the affinity constant $\hbox {K}_\mathrm{D}$ ) to be estimated. We further demonstrate that this model fits the biosensor data far better and is essentially less affected by the stabilization of the association phase to the equilibrium (Req) and the stabilization of the dissociation phase to the equilibrium zero. Finally, extrapolation with the log-normal model predicts the actually observed binding curve in a proper manner.     

Deformation morphology of polyester single crystals

Truncated, six-sided single crystals of a 10–16 linear polyester were grown from dilute solution in hexanol, deposited onto Mylar film, and uniaxially deformed at room temperature. For elongations below 10%, the crystals deform uniformly; however, above 20% elongation many cracks spanned by fibrils of 300 Å diameter develop approximately normal to the applied stress direction. Depending on the position of the crystal relative to the draw direction, lateral buckling pleats and cleavage cracks can also occur. Collapse of the nonplanar crystals onto the substrate with a resulting nonuniform adherence of the crystal influences the deformation. The deformation morphology is compared to that of truncated sixfold sector polyethylene crystals. Most notably, in contrast to polyethylene, {010} fold sectors do not deform differently from {110} fold sectors and phase boundaries between {110} and {010} fold sectors do not fracture easily.     

Rotational Spectra of 2,3,6-Trifluoropyridine: Effect of Fluorination on Ring Geometry

The ground state rotational spectrum of 2, 3, 6-trifluoropyridine has been investigated in the 2.0\begin{document}$ - $\end{document}20.0 GHz region by pulsed jet Fourier transform microwave spectroscopy. The experimental rotational constants are \begin{document}$ A $\end{document} = 3134.4479(2) MHz, \begin{document}$ B $\end{document} = 1346.79372(7) MHz, and \begin{document}$ C $\end{document} = 941.99495(6) MHz. The transitions are so intense that rotational transitions of all mono-\begin{document}$ ^{13} $\end{document}C and \begin{document}$ ^{15} $\end{document}N isotopologues are measured in natural abundance. The semi-experimental equilibrium rotational constants of the 7 isotopologues were derived by taking account of the anharmonic vibrational corrections, which allowed a semi-experimental determination of the equilibrium structure of 2, 3, 6-trifluoropyridine.     

Mimicking the biomolecular control of calcium oxalate monohydrate crystal growth: effect of contiguous glutamic acids

Scanning confocal interference microscopy (SCIM) and molecular dynamics (MD) simulations were used to investigate the adsorption of the synthetic polypeptide poly(l-glutamic acid) (poly-glu) to calcium oxalate monohydrate (COM) crystals and its effect on COM formation. At low concentrations (1 μg/mL), poly-glu inhibits growth most effectively in ?001? directions, indicating strong interactions of the polypeptide with {121} crystal faces. Growth in ?010? directions was inhibited only marginally by 1 μg/mL poly-glu, while growth in ?100? directions did not appear to be affected. This suggests that, at low concentrations, poly-glu inhibits lattice-ion addition to the faces of COM in the order {121} > {010} ≥ {100}. At high concentrations (6 μg/mL), poly-glu resulted in the formation of dumbbell-shaped crystals featuring concave troughs on the {100} faces. The effects on crystal growth indicate that, at high concentrations, poly-glu interacts with the faces of COM in the order {100} > {121} > {010}. This mirrors MD simulations, which predicted that poly-glu will adsorb to a {100} terrace plane (most calcium-rich) in preference to a {121} (oblique) riser plane but will adsorb to {121} riser plane in preference to an {010} terrace plane (least calcium-rich). The effects of different poly-glu concentration on COM growth (1-6 μg/mL) may be due to variations between the faces in terms of growth mechanism and/or (nano)roughness, which can affect surface energy. In addition, 1 μg/mL might not be adequate to reach the critical concentration for poly-glu to significantly pin step movement on {100} and {010} faces. Understanding the mechanisms involved in these processes is essential for the development of agents to reduce recurrence of kidney stone disease.