Effects of gelatin on mechanical properties of hydroxyapatite-gelatin nano-composltes

A biomimetic reactor has been developed to synthesize hydroxyapatite- gelatin (HAP-GEL) nanocomposites that mimic ultra-structures of natural bone. We hypothesize that in the reactor, gelatin concentration controls morphology and packing structures of HAP crystals. To test the hypothesis, three types of mechanical tests were conducted, including nanoindentation, compression, and fracture tests. Nanoindentation tests in conjunction with computer modeling were used to assess effects on gelatin-induced microstructures of HAP. The results showed that increasing gelatin content increased both the plane strain modulus and the fracture toughness. The gelatin appeared to shorten the HAP crystal distance, which consolidated the internal structure of the composite and made the material more rigid. The fracture toughness KIC increased partially due to the effect of fiber bridging between gelatin molecules. The highest fracture toughness (1.12 MPa·1/2) was equivalent to that of pure hydroxyapatite. The compressive strength of the HAP-GEL (107.7±26.8 MPa) was, however, less sensitive to microstructural changes and was within the range of natural cortical bone (human 170 MPa, pig: 100 MPa). The compression strength was dominated by void inclusions while the nanoindentation response reflected ultra-structural arrangement of the crystals. The gelatin concentration is likely to modify crystal arrangement as demonstrated in TEM experiments but not void distribution at macroscopic levels. © 2006 Materials Research Society.

Fabrication of excitonic luminescent inorganic-organic hybrid nano- and microcrystals

Inorganic-organic (IO) hybrid nano- and microcrystals are fabricated by a low-cost, environmentally friendly and easily scaled-up route. Lead(II) iodide (PbI 2) nano/microcrystals are obtained by solvothermal techniques and subsequent IO hybrid (C 12H 25NH 3) 2PbI 4 crystals are produced by intercalation of the organic moiety. The hexagonally shaped crystals obtained range in size from 20 nm to ∼7 μm. Sequential stacking of inorganic/organic layers in these IO hybrid crystals results in strong room-temperature exciton photoluminescence, wherein the excitons are confined within the inorganic sheets. © 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

Electrorheologic liquid crystals in microsystems: model and measurements

Fluids with a controllable viscosity gained a lot of interest throughout the last years. One of the advantages of these fluids is that they allow to fabricate hydraulic components such as valves with a very simple structure. Although the properties of these fluids are very interesting for microsystems, their applicability is limited at microscale since the particles suspended in these fluids tend to obstruct microchannels. This paper investigates the applicability of electrorheologic Liquid Crystals (LCs) in microsystems. Since LC's do not contain suspended particles, they show intrinsic advantages over classic rheologic active fluids in microapplications. As a matter of fact, LC molecules are usually only a few nanometers long, and therefore, they can probably be used in systems with sub-micrometer channels or other nanoscale applications. This paper presents a novel model describing the electrorheologic behavior of these nanoscale molecules. This model is used to simulate a microvalve controlled by LC's. By comparing measurements and simulations performed on this microvalve it is possible to prove that the model developed in this paper is very accurate. In addition, these simulations and measurements revealed other remarkable properties of LC's, such as high bandwidths and high changes in flow resistance. © 2006 IEEE.

Characterisation of carbon nano-onions using Raman spectroscopy

Characteristics of the Raman spectrum from carbon onions have been identified in terms of the position of the G peak and appearance of the transverse optic phonon peaks. Five new peaks were observed in the low wavenumber region, at about 1100, 861, 700, 450 and 250 cm(-1). The origins of these peaks are discussed in terms of the phonon density of states (PDOS) and phonon dispersion curves of graphite. The curvature of the graphene planes is invoked to explain the relaxation of the Raman selection rules and the appearance of the new peaks. The Raman spectrum of carbon onions is compared with that of highly oriented pyrolytic graphite (HOPG). The strain of graphene planes due to curvature has been estimated analytically and is used to account for the downward shift of the G peak. (C) 2003 Elsevier Science B.V. All rights reserved.

Formation of metastable liquid catalyst during subeutectic growth of germanium nanowires.

Lattice-resolved, video-rate environmental transmission electron microscopy shows the formation of a liquid Au-Ge layer on sub-30-nm Au catalyst crystals and the transition of this two-phase Au-Ge/Au coexistence to a completely liquid Au-Ge droplet during isothermal digermane exposure at temperatures far below the bulk Au-Ge eutectic temperature. Upon Ge crystal nucleation and subsequent Ge nanowire growth, the catalyst either recrystallizes or remains liquid, apparently stabilized by the Ge supersaturation. We argue that there is a large energy barrier to nucleate diamond-cubic Ge, but not to nucleate the Au-Ge liquid. As a result, the system follows the more kinetically accessible path, forming a liquid even at 240 degrees C, although there is no liquid along the most thermodynamically favorable path below 360 degrees C.

Strong flexoelectric behavior in bimesogenic liquid crystals

In this paper, we demonstrate strong flexoelectric coupling in bimesogenic liquid crystals. This strong coupling is determined via the flexoelectro-optic effect in chiral nematic liquid crystals based on bimesogenic mixtures that are doped with low concentrations of high twisting power chiral additive. Two mixtures were examined: one had a pitch length of p∼300nm, the other had a pitch length of p∼600nm. These mixtures exhibit enantiotropic chiral nematic phases close to room temperature. We found that full-intensity modulation, that is, a rotation of the optic axis of 45° between crossed polarizers, could be achieved at significantly lower applied electric fields (E<5Vμm -1) than previously reported. In fact, for the condition of full-intensity modulation, the lowest electric-field strength recorded was E=2Vμm-1. As a result of a combination of the strong flexoelectric coupling and a divergence in the pitch, tilt angles of the optic axis up to 87°, i.e., a rotation of the optic axis through 174°, were observed. Furthermore, the flexoelastic ratios, which may be considered as a figure-of-merit parameter, were calculated from the results and found to be large, ranging from 1.3to2C/Nm for a temperature range of up to 40°C. © 2006 American Institute of Physics.

Structure-flexoelastic properties of bimesogenic liquid crystals

In this paper, we report on the flexoelastic and viscoelastic ratios for a number of bimesogens compounds with the same generic structure. Values are obtained indirectly by measuring the flexoelectro-optic response in the chiral nematic phase. By varying the molecular structure we alter the bend angle, transverse dipole moment, and length of the molecule. First, to examine the influence of the bend angle we use a homologous series whereby the only alteration in the molecular structure is the number of methylene units in the aliphatic spacer, n. Results show that the flexoelastic ratio, e K, and the effective flexoelectric coefficient, e, both exhibit an odd-even effect with values for n=odd being greater than that for n=even. This is understood in terms of an increase in the bend angle of the molecule and an increase in the transverse dipole moment. Second, in order to investigate the impact of the dipole moment, we have altered the mesogenic units so as to vary the longitudinal dipole moment and used different linkages in the aliphatic spacer in an attempt to alter the transverse dipole moment. Qualitatively, the results demonstrate that the odd-spaced bimesogen with larger transverse dipole moments exhibit larger flexoelastic ratios. © 2007 The American Physical Society.

Spark plasma sintering of TiNi nano-powders for biological application

Nano-sized TiNi powder with an average size of 50nm was consolidated using spark plasma sintering (SPS) at 800 °C for 5min. A layer of anatase TiO 2 coating was formed on the sintered TiNi by chemical reaction with a hydrogen peroxide (H2O2) solution at 60 °C followed by heat treatment at 400 °C to enhance the bioactivity of the metal surface. Cell culture using osteoblast cells and a biomimetic test in simulated body fluid proved the biocompatibility of the chemically treated SPS TiNi. © IOP Publishing Ltd.

Resonant Raman characterisation of ultra-thin nano-protective carbon layers for magnetic storage devices

Carbon thin films are very important as protective coatings for a wide range of applications such as magnetic storage devices. The key parameter of interest is the sp3 fraction, since it controls the mechanical properties of the film. Visible Raman spectroscopy is a very popular technique to determine the carbon bonding. However, the visible Raman spectra mainly depend on the configuration and clustering of the sp2 sites. This can result in the Raman spectra of different samples looking similar albeit having a different structure. Thus, visible Raman alone cannot be used to derive the sp3 content. Here we monitor the carbon bonding by using a combined study of Raman spectra taken at two wavelengths (514 and 244 nm). We show how the G peak dispersion is a very useful parameter to investigate the carbon samples and we endorse it as a production-line characterisation tool. The dispersion is proportional to the degree of disorder, thus making it possible to distinguish between graphitic and diamond-like carbon. © 2003 Elsevier B.V. All rights reserved.