Long-term stabilized amorphous calcium carbonate-an ink for bio-inspired 3D printing.

Biominerals formed by organisms in the course of biomineralization often demonstrate complex morphologies despite their single-crystalline nature. This is achieved owing to the crystallization via a predeposited amorphous calcium carbonate (ACC) phase, a precursor that is particularly widespread in biominerals. Inspired by this natural strategy, we used robocasting, an additive manufacturing three-dimensional (3D) printing technique, for printing 3D objects from novel long-term, Mg-stabilized ACC pastes with high solids loading. We demonstrated, for the first time, that the ACC remains stable for at least a couple of months, even after printing. Crystallization, if desired, occurs only after the 3D object is already formed and at temperatures significantly lower than those of common postprinting sintering. We also examined the effects different organic binders have on the crystallization, the morphology, and the final amount of incorporated Mg. This novel bio-inspired method may pave the way for a new bio-inspired route to low-temperature 3D printing of ceramic materials for a multitude of applications.

Modifying hydrophilic properties of polyurethane acryl paint substrates by atomic layer deposition and self-assembled monolayers.

A process of atomic layer deposition (ALD) combined with self-assembled monolayers (SAMs) was used to investigate the possible modification of the wetting properties of polyurethane (PUR) paint surfaces without altering their original hue. First, we used an ALD process to produce thin and uniform Al2O3 coatings of these surfaces at temperatures as low as 80 °C. We then successfully achieved the addition of 16-phosphono-hexadecanoic acid (16-PHA) SAMs to the Al2O3-coated paint samples. Given initial hydrophobicity, which however was not stable over time, Al2O3 coatings reduced the contact angle of the PUR surfaces from 110 to 10°. Addition of SAMs on the Al2O3 coatings induced a sustained reduction in their contact angles to 60-70°, and aging of the samples revealed a further decrease to 25-40°. Testing of the Al2O3/16-PHA coating in a Weather-Ometer (WOM) revealed its durability even under harsh outdoor conditions. These experimental results show that by combining ALD with SAMs it is possible to produce durable coatings with modified hydrophilic/hydrophobic properties that are stable over time. The use of SAMs with different end-groups may allow fine-tuning of the coating's wetting properties.

Structural analysis and optical properties of the Bi2-x Y x WO6 system.

Photocatalytic conversion of solar energy into chemical energy has attracted considerable interest for several decades. One compound already reported as a visible-light-active photocatalyst for water splitting is BiYWO6, a member of the Bi2-x Y x WO6 family of compounds. The structural and optical properties of other members of this family have not been reported to date. In this work, we synthesized various compositions of Bi2-x Y x WO6, studied their optical properties, and report their structural parameters obtained by utilizing powder diffraction coupled with Rietveld refinement.

Multilevel hierarchy of fluorinated wax on CuO nanowires for superoleophobic surfaces.

We demonstrate the multilevel hierarchy of nanoscale wax crystals on nanowire (NW) structures that strongly repels not only water but also olive oil and hexadecane. We deposited C24F50-fluorinated wax (F-wax) using thermal evaporation on the surface of CuO NWs. Fluorinated wax crystals are self-assembled on the CuO NWs forming three-dimensional hierarchical structures. The achieved multilevel hierarchy has strongly repelled water, glycerol, ethylene glycol, and olive oil with contact angles (CAs) exceeding 160°. When sufficient F-wax is crystallized on the CuO NWs, crystals that are assembled perpendicularly to the longitudinal NW axis form a re-entrant curvature allowing superoleophobic characteristics with strong repellence of hexadecane with CAs of ∼150° and a small contact angle hysteresis of <10°. Furthermore, the surfaces can repel extremely small water droplets (∼100 pL), an indication of an ability to withstand condensation. These types of multilevel hierarchies can be formed on numerous roughened surfaces as the wax can be easily applied to various substrates without affecting the mechanical integrity of base structures.

Protein-induced, previously unidentified twin form of calcite.

Using single-crystal x-ray diffraction, we found a formerly unknown twin form in calcite crystals grown from solution to which a mollusc shell-derived 17-kDa protein, Caspartin, was added. This intracrystalline protein was extracted from the calcitic prisms of the Pinna nobilis shells. The observed twin form is characterized by the twinning plane of the (108)-type, which is in addition to the known four twin laws of calcite identified during 150 years of investigations. The established twin forms in calcite have twinning planes of the (001)-, (012)-, (104)-, and (018)-types. Our discovery provides additional evidence on the crucial role of biological macromolecules in biomineralization.

On the structure of aragonite.

High-resolution synchrotron powder diffraction measurements were carried out at the 32-ID beamline of the Advanced Photon Source of Argonne National Laboratory in order to clarify the structure of geological aragonite, a widely abundant polymorph of CaCO(3). The investigated crystals were practically free of impurity atoms, as measured by wavelength-dispersive X-ray spectroscopy in scanning electron microscopy. A superior quality of diffraction data was achieved by using the 11-channel 111 Si multi-analyzer of the diffracted beam. Applying the Rietveld refinement procedure to the high-resolution diffraction spectra, we were able to extract the aragonite lattice parameters with an accuracy of about 20 p.p.m. The data obtained unambiguously confirm that pure aragonite crystals have orthorhombic symmetry.

Depth-resolved strain measurements in polycrystalline materials by energy-variable X-ray diffraction.

An energy-variable synchrotron diffraction technique is being established as a novel method for the depth-resolved measurement of residual strains in polycrystalline structures. An analytic expression for the diffraction profile is obtained by taking into account the instrument misalignment, change of the height of an incident X-ray beam with energy, and penetration of X-rays into the sample depth. It is shown that the maximum diffraction intensity recorded in the detector is coming from a certain depth beneath the surface of the sample, the depth being energy-dependent. This finding opens a way for precise strain measurements with high depth resolution by changing the X-ray energy in small enough steps. An experimental example, residual strain measurements across an alumina/zirconia multilayer, demonstrates the capability of the method.