Crystal Unit Cell Research Articles

Determining the nanostructure and main axis of gly-his-gly fibrils using the amide I’ bands in FTIR, VCD, and Raman spectra

The zwitterionic tripeptide glycyl-histidine-glycine (GHG) has been shown to self-assemble into visible crystalline fibrils that form a gel-supporting network with a very high storage modulus. Here we elaborate on the theory and experimental setup behind our novel approach employed to determining the main fibril axis for these gel-forming fibrils by simulating the amide I band profile for infrared absorption (IR), vibrational circular dichroism (VCD), and visible Raman scattering. We also highlight that combining these three vibrational spectroscopies can help in validating structures that are solved using powder x-ray diffraction analysis (PXRD). The PXRD analysis yielded a GHG fibril unit cell with P21 symmetry containing two peptide monomers and two water molecules. The monomers adopt a conformation reminiscent of the distorted polyproline II conformation obtained for tri-lysine in aqueous solution. Stabilization occurs primarily through peptide-peptide intermolecular hydrogen bond interactions, while the role of water in peptide hydration is minimal. The comparison of simulated and experimental amide I’ band profiles suggests that the xz plane of the crystal unit cell is being predominantly probed in the experimental IR and VCD spectra, with the x axis of the unit cell pointing in the direction of the main fibril axis. The monomer peptide in the unit cell interacts with six adjacent peptides forming hydrophobic channels by edge-to-face and parallel-displaced ππstacking in the y direction. These cores are further stabilized by a plethora of intermolecular interactions in the x and z directions. Our result suggests that the hydrophobic xz-surfaces would be a good target for the adsorption of hydrophobic drugs.

Phase Equilibria in the Cu2Se–Cu8SiSe6–Cu8GeSe6 System

Phase equilibria in the Cu2Se–Cu8SiSe6–Cu8GeSe6 area of the Cu2Se–SiSe2–GeSe2 system have been studied using differential thermal analysis (DTA), X-ray powder diffraction analysis (XRD), scanning electron microscopy (SEM), and energy-dispersive spectroscopy (EDX). The results served to plot a Т–х diagram of the Cu8SiSe6–Cu8GeSe6 boundary system, a series of polythermal sections, and a 300-K isothermal section of the phase diagram and a liquidus surface projection for the title system. The primary crystallization and homogeneity fields of phases, and the characters and temperatures of invariant and monovariant equilibria have been determined. In the Cu8SiSe6–Cu8GeSe6 boundary system, continuous solid solutions have been found to exist between the high-temperature phases of the terminal compounds and extensive homogeneity area based on their low-temperature phases were found. The crystal lattice types and unit cell parameters have been determined for the terminal compounds and both phases of solid solutions using X-ray powder diffraction data. The prepared phases of variable composition are of interest as environmentally friendly functional materials.

Accurate computational design of three-dimensional protein crystals.

Protein crystallization plays a central role in structural biology. Despite this, the process of crystallization remains poorly understood and highly empirical, with crystal contacts, lattice packing arrangements and space group preferences being largely unpredictable. Programming protein crystallization through precisely engineered side-chain-side-chain interactions across protein-protein interfaces is an outstanding challenge. Here we develop a general computational approach for designing three-dimensional protein crystals with prespecified lattice architectures at atomic accuracy that hierarchically constrains the overall number of degrees of freedom of the system. We design three pairs of oligomers that can be individually purified, and upon mixing, spontaneously self-assemble into >100 µm three-dimensional crystals. The structures of these crystals are nearly identical to the computational design models, closely corresponding in both overall architecture and the specific protein-protein interactions. The dimensions of the crystal unit cell can be systematically redesigned while retaining the space group symmetry and overall architecture, and the crystals are extremely porous and highly stable. Our approach enables the computational design of protein crystals with high accuracy, and the designed protein crystals, which have both structural and assembly information encoded in their primary sequences, provide a powerful platform for biological materials engineering.

Biomineralization of mantis shrimp dactyl club following molting: Apatite formation and brominated organic components

The stomatopod Odontodactylus scyllarus uses weaponized club-like appendages to attack its prey. These clubs are made of apatite, chitin, amorphous calcium carbonate, and amorphous calcium phosphate organized in a highly hierarchical structure with multiple regions and layers. We follow the development of the biomineralized club as a function of time using clubs harvested at specific times since molting. The clubs are investigated using a broad suite of techniques to unravel the biomineralization history of the clubs. Nano focus synchrotron x-ray diffraction and x-ray fluorescence experiments reveal that the club structure is more organized with more sub-regions than previously thought. The recently discovered impact surface has crystallites in a different size and orientation than those in the impact region. The crystal unit cell parameters vary to a large degree across individual samples, which indicates a spatial variation in the degree of chemical substitution. Energy dispersive spectroscopy and Raman spectroscopy show that this variation cannot be explained by carbonation and fluoridation of the lattice alone. X-ray fluorescence and mass spectroscopy show that the impact surface is coated with a thin membrane rich in bromine that forms at very initial stages of club formation. Proteomic studies show that a fraction of the club mineralization protein-1 has brominated tyrosine suggesting that bromination of club proteins at the club surface is an integral component of the club design. Taken together, the data unravel the spatio-temporal changes in biomineral structure during club formation. Statement of significanceMantis shrimp hunt using club-like appendages that contain apatite, chitin, amorphous calcium carbonate, and amorphous calcium phosphate ordered in a highly hierarchical structure. To understand the formation process of the club we analyze clubs harvested at specific times since molting thereby constructing a club formation map. By combining several methods ranging from position resolved synchrotron X-ray diffraction to proteomics, we reveal that clubs form from an organic membrane with brominated protein and that crystalline apatite phases are present from the very onset of club formation and grow in relative importance over time. This reveals a complex biomineralization process leading to these fascinating biomineralized tools.

Low-Frequency Vibrations of Saccharides Using Terahertz Time-Domain Spectroscopy and Ab-Initio Simulations

The vibrational properties of molecular crystals in the terahertz range are controlled by the interplay of intermolecular and intramolecular interactions. The resulting delocalized normal modes span a substantial number of atoms within the unit cell of the molecular crystals and cannot be easily attributed to a specific stretching or bending mode. Several compounds were studied to understand the nature of normal modes. However, a systematic analysis of saccharides is still missing. This study investigates the terahertz vibrational properties of various saccharides, including glucose, galactose, lactose, cellobiose, and cellulose. The terahertz spectra were measured using terahertz time-domain spectroscopy. The samples were carefully characterized, and the residual Fabry–Perot oscillations were removed to obtain the absorption coefficient and refractive index of the saccharides. Density functional theory simulations were used to obtain theoretical terahertz spectra, considering hydrogen bonding interactions with an enhanced version of the van der Waals non-local density functional. The results revealed differences in low-energy vibrational modes frequencies, influenced by molecular structure properties, hydrogen bonding networks, and water content. Librations and internal vibrations were identified as dominant dynamics in the saccharides, with significant mixing between intermolecular and intramolecular vibrations. This comprehensive analysis sheds light on the vibrational behavior of saccharides in the terahertz range.

Towards Anticancer and Antibacterial Agents: Design and Synthesis of 1,2,3-Triazol-quinobenzothiazine Derivatives.

In this paper, we describe a new method for synthesizing hybrid combinations of 1,2,3-triazoles with a tetracyclic quinobenzothiazinium system. The developed approach allowed for the production of a series of new azaphenothiazine derivatives with the 1,2,3-triazole system in different positions of the benzene ring. In practice, the methodology consists of the reaction of triazole aniline derivatives with thioquinanthrenediinium bis-chloride. The structure of the products was determined by 1H-NMR, 13C-NMR spectroscopy, and HR-MS spectrometry, respectively. Moreover, the spatial structure of the molecule and the arrangement of molecules in the crystal (unit cell) were determined by X-ray crystallography. The anticancer activity profiles of the synthesized compounds were tested in vitro against human cancer cells of the A549, SNB-19, and T47D lines and the normal NHDF cell line. Additional tests of antibacterial activity against methicillin-sensitive and methicillin-resistant staphylococci, vancomycin-sensitive and vancomycin-resistant enterococci, and two mycobacterial strains were also performed. In fact, the dependence of anticancer and antibacterial activity on the substituent type and its position in the quinobenzothiazinium system was observed. Furthermore, the distance-guided property evaluation was performed using principal component analysis (PCA) and hierarchical clustering analysis (HCA) on the pool of the calculated descriptors. Finally, the theoretically approximated partition coefficients (clogP) were (inter-)correlated with each other and cross-compared with the empirically specified logPTLC parameters.

Deep learning aided topology optimization of phononic crystals

In this work, a novel approach for the topology optimization of phononic crystals based on the replacement of the computationally demanding traditional solvers for the calculation of dispersion diagrams with a surrogate deep learning (DL) model is proposed. We show that our trained DL model is ultrafast in the prediction of the dispersion diagrams, and therefore can be efficiently used in the optimization framework.The main novelty of the proposed approach relies on the use of non-uniform rational basis spline (NURBS) curves instead of pixels and/or mesh elements to control the shape of the unit cells of phononic crystals. The surrogate DL model is combined with a genetic algorithm serving as a topology optimization tool. The validity of the approach is shown in the case of phononic crystals made of a continuous matrix with cavities. Several objective functions have been tested as an alternative to the most common gap to mid-gap ratio. This allowed us to obtain interesting phononic crystal geometries which can be easily additively manufactured.The proposed method applies to problems involving inverse design and can open new avenues in the design of computer-assisted periodic structures.

A combined theoretical and experimental study of the D-2-aminobutyric acid L-norvaline single crystal for efficient third-order nonlinear optical (NLO) applications

Here we report, the formation of an optically active single crystal of D-2-aminobutyric acid L-Norvaline (ABANV) by the slow evaporation technique by co-crystallization of amino acids D-2-aminobutyric acid (ABA) and L-Norvaline together in water. An X-ray diffraction technique has been used to determine the dimensions of the single crystal unit cells. The functional group of ABANV crystal was studied using FTIR spectroscopy in order to determine its chemical structure. The FT NMR spectrum was conducted to analyze the carbon and hydrogen environments of the grown crystal. In optical absorption studies, the crystal was shown to be transparent in the visible region with a lower cut off wavelength of 236 nm, which led to an optical band gap energy Eg of 5.25 eV. In addition, using TG/DSC techniques, we have investigated the thermal stability of the grown ABANV single crystal as well as their accurate melting point. A HOMO and LUMO analysis were performed to determine the electronic charge distribution and reactivity of the molecules within the crystal. First-order molecular hyperpolarizality (β) properties of the grown crystal have been determined using the B3LYP method. The scatter graph provides an explanation of the chemical bonding of ELF and LOL, as well as the inter and intra fragment interactions.

Base pairs with 5-chloroorotic acid and comparison with the natural nucleobase. Structural and spectroscopic study, and three suggested antiviral modified nucleosides

A structural and spectroscopic study of 5-chloroorotic acid (5-ClOA) biomolecule was carried out by IR and FT-Raman and the results obtained were compared to those achieved in 5-fluoroorotic acid and 5-aminoorotic acid compounds. The structures of all possible tautomeric forms were determined using DFT and MP2 methods. To know the tautomer form present in the solid state, the crystal unit cell was optimized through dimer and tetramer forms in several tautomeric forms. The keto form was confirmed through an accurate assignment of all the bands. For this purpose, an additional improvement in the theoretical spectra was carried out using linear scaling equations (LSE) and polynomic equations (PSE) deduced from uracil molecule. Base pairs with uracil, thymine and cytosine nucleobases were optimized and compared to the natural Watson-Crick (WC) pairs. The counterpoise (CP) corrected interaction energies of the base pairs were also calculated. Three nucleosides were optimized based on 5-ClOA as nucleobase, and their corresponding WC pairs with adenosine. These modified nucleosides were inserted in DNA:DNA and RNA:RNA microhelices, which were optimized. The position of the -COOH group in the uracil ring of these microhelices interrupts the DNA/RNA helix formation. Because of the special characteristic of these molecules they can be used as antiviral drugs. Communicated by Ramaswamy H. Sarma

A comprehensive study on intrinsic alpha corpuscular radiation damage in monazite crystals using picometer-scale imaging, coupled with SCXRD and Raman spectroscopy

We have investigated monazite crystals, known to experience lattice distortions due to alpha particle emission from their atomic nuclei. Our aim in this investigation is to study the complex relationship between the lattice parameters and Raman spectra of monazite crystals. Through this study, we seek to understand the interdependency between these physical parameters and their influence on one another for an improved understanding of radiation-induced damage in these crystals. In addition to this, we also attempted to establish a correlation between these properties and their picometer-scale images to gain a deeper understanding of the structural changes that occur at the atomic scale. We conducted our study on four monazite samples withstanding intrinsic alpha decay radiation, denoted as M1, M2, M3, and M4, with crystal unit cell volume ranging from 299.961 Å3 to 301.96 Å3. Our Pearson statistical analysis revealed a correlation R2 (0.96) between the SCXRD-derived Ce–P Distance of monazite and the FWHM of PO4 band active mode in Raman spectra. This indicated lattice distortions due to alpha decay radiation impacting the Raman spectra. While Raman PO4 band broadening can be a consequence of impurities, dopants, and radiation damage, HRTEM scrutiny of the samples at picometer scales revealed the presence of point defects, plane rotation, and lattice distortions within the samples, suggesting the impact of alpha decay on the crystal lattice. HRTEM analysis has added additional confirmation that the major contribution to PO4 band broadening is due to alpha radiation damage in these samples. Through our study, we conclude a multiple-approach correlation is necessary to accurately study radiation damage dynamics at atomic scales.

Investigation on growth, crystal structure, third-order optical nonlinearity properties and DFT computational studies of novel proton transfer 3-aminopyridine P-nitrobenzoate P-nitrobenzoic acid (3APPNB) single crystal for third-order NLO applications

A new organic single crystal of 3-aminopyridine p-nitrobenzoate p-nitrobenzoic acid (3APPNB) with a size of 8 × 4 × 2 mm3 was grown by slow evaporation solution growth technique at room temperature using methanol solvent. The lattice parameter values were evaluated with the help of single crystal XRD and it confirms that the 3APPNB crystal belongs to triclinic crystal structure and the space group P-1. Crystal unit cell parameters are a = 9.3384(5) Å, b = 10.0403(5) Å, c = 11.094(6) Å, α = 109.4940(10)°, β = 93.964(2)°, γ = 99.890(2)° and V = 957.03 (9) (Å3) were determined. The 3APPNB crystal crystallizes in a centrosymmetric nature, triclinic system and space group P-1. SCXRD study shows that both the anion and the cation are interlinked to each other by two types of symmetrical intermolecular C–H…O and N–H···O hydrogen bonds. The crystalline nature and hkl phases have been determined using Powder XRD studies. The presence of different vibrational groups in the 3APPNB compound is examined by employing Fourier transform infrared (FT-IR) spectral analysis. UV–Vis-DRS spectral analysis signifies that the 3APPNB has a wide transmittance (98 %) and a cut-off wavelength of around 317 nm. The etch pit density (EDP) of 3APPNB crystal was examined by a chemical etching analysis. The thermal studies expose that 3APPNB is thermally stable up to 172 °C. The surface morphology of the 3APPNB is analyzed by SEM. The nonlinear properties like β, n2 and χ(3) were measured through the Z-scan analysis and the values were calculated to be 5.78 × 10−5 m/W, 8.05 × 10−12 m2/W) and χ(3) = 8.936 × 10−9. The third-order nonlinear optical (TONLO) χ(3) values are higher. The achieved TONLO χ(3) value when compared to other similar constituents is owing to the tarnish movement of π-electron configuration from the donor to an acceptor that makes the molecules highly polarized. The results reveal that the 3APPNB crystal finds applications in devices like optical switching and optical limiting. The quantum-chemical theoretical analyses are performed to measure the intrinsic properties of the 3APPNB molecules using DFT calculation. The band gap, orbital energy and second hyperpolarizability are also studied using changing the applied field. Furthermore, Quantum chemical calculations are used to obtain the MESP, HOMO-LUMO and first-order hyperpolarizability for the 3APPNB compound.

Yuchuanite-(Y), Y2(CO3)3·H2O, a new hydrous yttrium carbonate mineral from the Yushui Cu deposit, South China

Abstract A new mineral species, yuchuanite-(Y), ideally Y2(CO3)3·H2O, has been discovered and characterized in the Yushui Cu deposit in South China. The mineral occurs in bedded/massive ore and is associated with bornite, chalcopyrite, galena, sphalerite, bastnäsite-(Y), xenotime-(Y), anhydrite, and quartz. Individual crystals range in size from 30 to 300 μm. No twinning is observed. The mineral is colorless and transparent with a vitreous luster. The calculated density is 3.62 g/cm3. An electron microprobe analysis yields the empirical formula (based on 10 O apfu), (Y1.61Yb0.11Er0.11Dy0.08Ho0.03 Gd0.02Tm0.02)Σ1.99(CO3)3·H2O. Yuchuanite-(Y) is triclinic, with space group P1 (#2), Z = 6, and unit-cell parameters a = 6.2134(3) Å, b = 8.9697(3) Å, c = 19.9045(7) Å, α = 91.062(3)°, β = 90.398(3)°, γ = 91.832(3)°, and V = 1108.54(8) Å3. The structure is constructed from (110) sheets of eight-coordinated Y polyhedra and C trigonal planar groups. All Y polyhedra are linked by shared edges. The Y atoms occupy six independent crystallographic sites of two different coordination types: [YO7(H2O)] and [YO8]. The chemical composition of yuchuanite-(Y) is similar to tengerite-(Y), Y2(CO3)3·2–3H2O, but is distinct in the crystal structure, such as crystal system, space group, and unit cell, from that of tengerite-(Y). The Y polyhedra of tengerite-(Y) are nine-coordinated, while those of yuchuanite-(Y) are eight-coordinated. Moreover, their structures could be both described as sheet structures built up from Y polyhedra and CO3 trigonal planar groups but link together in significantly different ways. Thus, yuchuanite-(Y) is not a polytype of tengerite-(Y) but is an independent mineral species.

Efficient removal of antimony from aqueous solution using Al-doped Fe3O4 nanoparticles: adsorption behavior and kinetics study

ABSTRACT Fe3O4 magnetic nanoparticles have been employed as a cost-effective adsorbent for removing Sb from aqueous solutions. However, the widespread application is limited by its finite adsorption capacity and aggregation nature. In this study, Al-doped Fe3O4 nanoparticles were prepared via a facile solvothermal method to break through the current obstacle. Al-doped Fe3O4 nanoparticles were fully characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Scanning Electron microscopy (SEM), and infrared spectroscopy (FTIR). The results confirmed that Al atoms had been successfully doped into Fe3O4 crystal unit cells, resulting in smaller particle size, larger surface area, and higher isoelectric point. These changes led to the formation of more hydroxyl groups on the surface of Al-doped Fe3O4 nanoparticles. Compared to pristine Fe3O4, the maximum adsorption capacity toward Sb(III) and Sb(V) increased from 111.695 to 197.034 mg/g and from 34.479 to 187.459 mg/g at neutral pH, respectively. The doping of Al also had some negative impact on the original magnetic strength but still maintained a sufficient magnetic separation potential. These results indicated that Al-doped Fe3O4 nanoparticles could be employed as a promising adsorbent for removing Sb(III) and Sb(V) from wastewater.

Atomic-thin VN layer@N-doped carbon as efficient oxygen reduction reaction electrocatalysts

The defect engineering is of vital importance for electrocatalysts because it can provide an additional yet advanced tier to further boost catalysis, especially for ultrathin nanosheets of transitional metal compounds with a high surface to bulk ratio and more importantly the ability to engineer the defect along the longitudinal direction of the grain boundaries. Herein, we developed super-thin and ordered face-centered cubic VN nanosheets with grain boundaries using a new facile and in-situ method. The structural and morphological properties of the prepared samples were investigated, finding that the temperature has significant effects on the distribution of sheets. The thickness of nanosheets is only 1.3 nm the same as that of three cubic VN crystal unit cells, which is pivotal to the electrochemical reaction. The detailed electrocatalysts results show that the VN nanosheets (NSs) exhibit interesting ORR performance with the onset potential of 0.93 V and a half-wave potential of 0.86 V. The evenly distributed VN NSs display the highest durability with only 5% attenuation after 50000s operation for the oxygen reduction reaction. We provide a new strategy to synthesize super-thin nitrides nanosheet structure, highlighting the strong correlation between surface engineering and the performance of electrocatalysts for potential practical oxygen reactions.

Research on cobalt-doping sites in g-C3N4 framework and photocatalytic reduction CO2 mechanism insights

The novel Co-doping combined with mesoporous g-C3N4-based photocatalyst was constructed, and the Co-CN showed impressive photocatalytic reduction CO2 activity. Employing the DFT computation, we discussed the possible Co doping sites on g-C3N4 framework, as well as the effects of band gaps, optical properties, and various densities of state (DOS) on photocatalytic activity. The adsorption energy calculation proved that the substitution and interstitial doping Co atoms in g-C3N4 crystal unit cell was the stable configuration. The coexistence substitution and substitution the monolayer g-C3N4 showed serious deformation. It indicated that the introduction of Co atoms leads g-C3N4 molecular orbital redistribution and Co tends to occupy the conduction band, due to its weak electronegativity. Moreover, the DFT and experiment results pointed out that the doped-Co narrowed g-C3N4 bandgap and increased light absorption from 450 to 800 nm, the improved charge carrier separation efficiency was originated from Co atom the unfilled 4 f and the empty 5d orbital act as electron capturing center. This research indicates the availability of transition metal g-C3N4 with conducive photocatalytic activity.

Multispectral transmission through phoxonic crystal slot-waveguide at midwave infrared frequencies

We design a multispectral transmission waveguide based on phoxonic crystals at midwave infrared (MWIR) frequencies. The phoxonic crystal slot-waveguide architecture is realized using a germanium (Ge)-slot waveguide, surrounded by a supercell array of oxide holes in silicon–germanium (SiGe) membrane tailored photonic and phononic crystal bandgap. The plane wave simulations for both photonic and phononic crystal unit cells were performed to confirm the geometry of the phoxonic supercell. The bandgap analysis shows the capability of the proposed architecture to confine photons of the terahertz frequency range within the slot waveguide by isolating them from the phonons of gigahertz frequency range. The phononic and photonic bandgaps were simultaneously engineered by varying the periodic variation of the density function and dielectric permittivity, respectively. The computational approach shows the suppression in photon-phonon scattering as validated by a uniform transmission of ∼99.8 % over a broad range of 3 to 5 μm wavelengths. The designed phoxonic crystal waveguide can be fabricated with planar processing technology and used in many applications where multispectral control of mid-IR signals is required.

Crystal Structure L-Asparagine Potassium Nitrate Single Crystals

The elemental analysis of the compound confirms the ratio of the compound. The sharp and well defined Bragg peaks obtained in the powder X-ray diffraction pattern confirm the crystalline nature of the compound. The single crystal unit cell parameters of the compound show that the grown crystal belongs to orthorhombic system with space group P. The optical property of the compound was ascertained through UV-visible spectral analysis. The various characteristics absorption bands in the compound were assigned through Fourier transform infra-red (FTIR) spectroscopy. Thenonlinear optical property study indicates that the compound has SHG efficiency 0.50 times greater than that of standard potassium dihydrogen phosphate (KDP).

Computer simulation of clusters in doped crystals of lithium niobite

Using as a structural unit (“unit cell”) a MeO6 oxygen-octahedral cluster crystal (Me: Nb, Li, vacancy, impurity element) and a semiclassical atomistic approach, computer simulation of large clusters in the structure of a lithium niobate (LiNbO3) crystal doped with trivalent metal. This approach makes it possible to avoid, unavoidable when using a crystal unit cell as a structural unit, the loss of discontinuity and electroneutrality of oxygen octahedra O6 at the edges of the cluster under study, and also allows you to move away from traditional vacancy split models.

Inorganic ferrite brown; transformation towards a versatile pigment for energy efficient constructions

The present work demonstrates a multifunctional brown inorganic ferrite pigment series, which is free of highly toxic elements, via solid-state ceramic method. Partial replacement of chromophore Fe3+ by Al3+ in the pigment composition (ZnFe1.9Al0.1O4) brought structural distortion in its octahedral geometry that further induced compressive stress inside the crystal unit cell. The introduction of even 5 mol% of Al3+ ions incorporated in place of Fe3+ could able to promote the pigment reflectance profile 25 units higher compared to parent system, particularly with significant colour improvement. Acrylic coating of the pigment on Al substrate was equally well in displaying good colour strength and temperature shielding ability (∼2 °C) with respect to ZnFe2O4. The pigment stands out with its promising anticorrosive performance over the commercial toxic candidates, chromates and phosphates, exhibiting excellent Rct = 4.1 × 109 Ωcm2. The durability of 20 wt% pigment loaded epoxy coating on steel activates through combined action of Zn(OH)2 and FeOOH film mechanism. Since, the pigment exhibits intense colour, high NIR solar reflectance and robust corrosion resistance properties, their use as a high-performance multifunctional pigment is indispensable.

Nucleation Assisted through the Memory of a Polymer Melt: A Different Polymorph Emerging from the Melt of Another One

We present investigations of the intricate crystallization and melting behavior of an alternating copolymer synthesized by photopolymerization of 2,2′-dimercaptodiethyl sulfide with di(ethylene glycol)divinyl ether. Upon increasing temperature, we observed the succession of two distinctly separated melting processes, which we related to the sequential formation and disappearance of two crystalline polymorphs. Due to their well-separated melting temperatures Tm1 and Tm2, we labeled these polymorphs as LOW-Tm-form and HIGH-Tm-form, respectively. X-ray diffraction results confirmed differences in the parameters of the crystal unit cells. However, upon cooling from the isotropic melt, we never obtained the HIGH-Tm-form and could only generate the LOW-Tm-form characterized by spherulitic crystals that melted completely at Tm1. Surprisingly, simultaneously everywhere within these molten spherulites, a large number of needle-like crystals were growing as a function of the time the sample was kept (well) above Tm1. All crystals exhibited an orientation largely following the radial direction of the initial spherulites. This observation suggests that molten polymer chains remembered for some time their previous alignment within the crystalline LOW-Tm-form. This memory assisted the nucleation and thus exclusively enabled the formation of the HIGH-Tm-form. Only when partially crystallizing a sample aboveTm1 in the HIGH-Tm-form and subsequently cooling it below Tm1 allowed to achieve coexistence of both polymorphs. When heating such a sample of coexisting crystalline structures above Tm1, only the LOW-Tm-form melted and the HIGH-Tm-form remained. The generality of our findings has been demonstrated by similar results obtained for complementary alternating copolymers. Our study suggests that the otherwise impossible nucleation of polymorphs with a high melting temperature can be enabled by prior orientation of chains within another easily established polymorph characterized by a lower melting temperature.