Strategy for Hydroxide Exclusion in Nanocrystalline Solid-State Metathesis Products

We demonstrate a simple strategy to either prevent or enhance hydroxide incorporation in nanocrystalline solid-state metathesis reaction products prepared in ambient environments. As an example, we show that ZnCO3 (smithsonite) or Zn5(CO3)2(OH)6 (hydrozincite) forms extremely rapidly, in less than two minutes, to form crystalline domains of 11 ± 2 nm and 6 ± 2 nm, respectively. The phase selectivity between these nanocrystalline products is dominated by the alkalinity of the hydrated precursor salts, which may in turn affect the availability of carbon dioxide during the reaction. Thus, unlike traditional aqueous precipitation reactions, our solid-state method offers a way to produce hydroxide-free, nanocrystalline products without active pH control

Roughness effects on contact angle measurements

We have developed a simple and economical procedure to demonstrate the effects of roughness and wetting fraction on the equilibrium contact angles of liquid droplets on solid surfaces. Contact angles for droplets placed on a rough surface, which wet only a portion of the surface, are larger than the contact angles of droplets formed by condensation of steam, which wet the surface more completely. These contact angle data facilitate assessments of changes in true surface area, due to surface roughening, as well as changes in the fractional contact areas of the water droplets, due to the formation of air pockets between the rough surface and the droplet

Flipping materials analysis on its head: what materials science can learn from archaeology

Materials scientists are trained to understand that high-quality data require high-quality samples. Archaeology shows a different and very powerful way to approach the analysis of materials

Frequency-Dependent Impedance Responses of ZnO Using UV Light

Impedance spectroscopy data show that polycrystalline ZnO films can show either increases or decreases in their effective resistances after UV exposure, depending on the frequency of the applied AC excitation. Simple equivalent circuit models, based on resistance (R) and capacitance (C) in parallel, are sufficient to confirm the observed experimental trends. Simulated data demonstrate that that arbitrary R and C values will not produce the sign change, but that typical resistance and capacitance characteristics for photoconductive semiconductors like ZnO can cause the sign change. These results suggest that it could be desirable to manipulate the R and C values of photodetector materials to either control – or eliminate – such frequency-dependent UV responses

Incorporating Far-Infrared Data into Carbonate Mineral Analyses

Polycrystalline carbonate minerals (including calcite, Mg-calcite, and aragonite) can show distinctive variations in their far-infrared (FIR) spectra. We describe how to identify mixed-phase samples by correlating FIR spectral changes with mid-infrared spectra, X-ray diffraction data, and simple peak overlap simulations. Furthermore, we show how to distinguish portlandite-containing (Ca(OH)2) mixtures that are common in heated calcium carbonate samples. Ultimately, these results could be used for tracking how minerals are formed and how they change during environmental exposure or processing after extraction

Electrodeposited Zn for Water-Repellent Coatings

We show that mildly alkaline electrolytes can be used to produce Zn coatings that improve the water repellent properties of stainless steel. Optimal Zn deposits were prepared under potentiostatic conditions from electrolytes that contained ZnCl2, NH4Cl, and a surfactant (polyethyleneimine). After deposition, the Zn electrodeposit was capped with stearic acid to prevent oxidation and to provide a lower surface energy. The capped electrodeposits display an impressive degree of water repellency, including extremely poor water droplet adhesion. We discuss the range of deposition parameters (electrolyte composition, pH, and applied potential) that produce the best water-repellent electrodeposits

Probing the structure of electrochemically-aggregated collagen

The internal structure of porous materials and membranes plays a critical role in their mechanical and biochemical properties, especially if they are targeted for cell growth in tissue healing and regeneration applications. Collagenous membranes are a class of proteinaceous materials that has been targeted for cell scaffolding studies because collagen is a structural protein found in many tissues. Collagen’s aggregation in a hierarchical fibrillar structure can be stimulated and controlled in vitro to create products that function similarly to those produced in vivo. This can be accomplished merely by changing pH and temperature, even in the absence of growth factors and enzymes that are present during in vivo growth. Scaffolds can interact with cells by serving as a structure for their attachment, or as a matrix for introducing nutrients, antibiotics, and other molecules to the cells. In this way, the 3D structure and mechanical properties of a scaffold can influence how cells move within and interact with it. In earlier work, we showed that electrochemically produced type I collagenous membranes can control cell proliferation to mimic their behaviour in vivo, unlike collagen fibrilized by standard thermal methods.[1,2] Furthermore, the electrochemically assembled collagen has proven to be a better matrix for osteoblast differentiation relative to other types of common scaffold materials. Since these findings show that matrix composition alone does not explain cell response, we continue to study the 3D structure of the electrochemically produced collagen scaffold prepared under different conditions. It is challenging to assess the internal structure of a membrane, such as the sizes and connectivity of its pores, since traditional optical or scanning probe imaging methods do not allow access to internal voids within the material. SPT is a passive microrheological technique [3] that we used to follow the diffusion of individual fluorescent particles that were suspended in the collagen membrane during its electrochemical formation. Each sphere samples its local rheological environment, which makes SPT well-suited for assessing the degree of heterogeneity in a system. While there have been bulk rheological studies of collagen-based matrices and at least one diffusion study within individual collagen fibrils, there is a surprising absence of microrheological studies of collagen-based scaffolds. Earlier work from our group showed that preparing these membranes in the presence of different cations led to different degrees of collagen fibrillation and aggregation as well as differences in membrane stiffness.[4] Our preliminary SPT results show that all of these electrochemically produced collagen membranes have a very compartmentalized structure, regardless of their stiffness. Our findings suggest that electrochemically induced aggregation can independently affect the structure, stiffness, and fluid viscosity of collagen membranes, which offers interesting future opportunities in cell scaffold design. [1] Gendron, R.; Kumar, M. R.; Paradis, H.; Martin, D.; Ho, N.; Gardiner, D.; Merschrod S., E. F.; Poduska, K. M. Controlled cell proliferation on an electrochemically engineered collagen scaffold. Macromol. Biosci. 2012, 12, 360–366. [2] Nino-Fong, R.; McDuffee, L. A.; Esparza Gonzalez, B. P.; Kumar, M. R.; Merschrod S., E. F.; Poduska, K. M. Scaffold Effects on Osteogenic Differentiation of Equine Mesenchymal Stem Cells: An In Vitro Comparative Study. Macromol. Biosci. 2013, 13, 348–355. [3] Oppong, F. K.; Rubatat, L.; Frisken, B. J.; Bailey, A. E.; de Bruyn, J. R. Microrheology and structure of a yield-stress polymer gel. Phys. Rev. E 2006, 73, 041405. [4] Kumar, M. R.; Merschrod S., E. F.; Poduska, K. M. Correlating Mechanical Properties with Aggregation Processes in Electrochemically Fabricated Collagen Membranes. Biomacromol. 2009, 10, 1970–197

Graphite oxidation chemistry is relevant for designing cleaning strategies for radiocarbon dating samples

We demonstrate that mixtures of graphite and lab-oxidized graphenic carbon materials can be separated into three individual components (graphite, graphene/graphite oxide (GO) and oxidative debris (OD)) by a series of aqueous treatments. Our results show that a key part of this separation procedure involves a water treatment and sonication near neutral pH in order to separate GO from OD. We show that the relative proportions of OD and GO – independent of any humic substances – can affect the ability of oxidized graphite to be suspended in water, which can influence the efficiency of the separation procedures we describe. We compare and contrast our protocol with others that are widely used for cleaning archaeological charcoal prior to radiocarbon dating. Our protocol has potential applications for tailored cleaning procedures for graphenic carbon materials, including the possibility of separating GO from both OD and graphite, for radiocarbon dating purposes

Tuning magnetic hysteresis of electrodeposited Fe 3 O 4

We demonstrate that changes in electrolyte composition and applied potential during aqueous electrodeposition can be used to tune the magnetic hysteresis response of thin-film Fe3O4 (magnetite) on polycrystalline metal substrates. X-ray diffraction data confirmed that magnetite formation in electrolytes containing KCH3COO (0.04–2.0 M) and Fe(SO4)2(NH4)2 (0.01M) required temperatures between 60 and 85 °C, and deposition potentials between −0.300 and −0.575 V or galvanostatic current densities between 50 and 88 μA/cm2. Scanning electron microscopy studies show that magnetite crystallites tend to adopt different habits depending on the electrolyte composition. Room-temperature magnetic hysteresis responses (squareness and coercivity) are dependent upon the crystal habit of deposits, implying that the electrolyte’s acetate concentration influences the magnetic domain structure of the resulting magnetite deposits. Magnetite crystallites grown from electrolytes with low acetate concentrations showed pseudo-single-domain magnetic response, while magnetite grown from acetate-enriched electrolytes showed multidomain magnetic response

ANALYSIS OF LANDAU–LIFSHITZ AND NEO-HOOKEAN MODELS FOR STATIC AND DYNAMIC ACOUSTOELASTIC TESTING

A comparison of three different isotropic non-linear elastic models uncovers subtle but important differences in the acoustoelastic responses of a material slab that is subjected to dynamic deformations during a pump-probe experiment. The probe wave deformations are small and are superimposed on larger underlying deformations using three different models: Landau–Lifshitz (using itsfourth-order extension), compressible neo-Hookean model(properly accountingfor volumetric deformations), and an alternative neo-Hookeanmodel(fully decoupled energies due to distortional isochoric and volumetric deformations). The analyses yield elasticity tensors and respective expressionsfor the propagation speeds of P-wave and S-wave probesfor each model. Despite having many similarities, the different models give different predictions of which probe wave types will have speeds that are perturbed by different pump wave types. The analyses also show a conceptual inconsistency in the Landau–Lifshitz model, that a simple shear deformation induces a stress and a shear wave probe speed that depend on the second-order elastic constantλ, which controls resistance to volumetric changes and thus should not be present in the expressionsfor shear stress and shear wave probe speeds. Thus, even though the Landau–Lifshitz model is widely used, it may not always be the best option to model experimental data