Materials2016, 9(9), 733; doi:10.3390/ma9090733 (registering DOI) - published 27 August 2016 Show/Hide Abstract
Abstract: In order to investigate the effects of microwave curing on the microstructure of the interfacial transition zone of mortar prepared with a composite binder containing glass powder and to explain the mechanism of microwave curing on the improvement of compressive strength, in this study, the compressive strength of mortar under microwave curing was compared against mortar cured using (a) normal curing at 20 ± 1 °C with relative humidity (RH) > 90%; (b) steam curing at 40 °C for 10 h; and (c) steam curing at 80 °C for 4 h. The microstructure of the interfacial transition zone of mortar under the four curing regimes was analyzed by Scanning electron microscopy (SEM). The results showed that the improvement of the compressive strength of mortar under microwave curing can be attributed to the amelioration of the microstructure of the interfacial transition zone. The hydration degree of cement is accelerated by the thermal effect of microwave curing and Na+ partially dissolved from the fine glass powder to form more reticular calcium silicate hydrate, which connects the aggregate, calcium hydroxide, and non-hydrated cement and glass powder into a denser integral structure. In addition, a more stable triangular structure of calcium hydroxide contributes to the improvement of compressive strength.
Materials2016, 9(9), 732; doi:10.3390/ma9090732 (registering DOI) - published 26 August 2016 Show/Hide Abstract
Abstract: Tin clathrate-II framework-substituted compositions are of current interest as potential thermoelectric materials for medium-temperature applications. A review of the literature reveals different compositions reported with varying physical properties, which depend strongly on the exact composition as well as the processing conditions. We therefore initiated an approach whereby single crystals of two different (K,Ba)16(Ga,Sn)136 compositions were first obtained, followed by grinding of the crystals into fine powder for low temperature spark plasma sintering consolidation into dense polycrystalline solids and subsequent high temperature transport measurements. Powder X-ray refinement results indicate that the hexakaidecahedra are empty, K and Ba occupying only the decahedra. Their electrical properties depend on composition and have very low thermal conductivities. The structural and transport properties of these materials are compared to that of other Sn clathrate-II compositions.
Materials2016, 9(9), 731; doi:10.3390/ma9090731 (registering DOI) - published 26 August 2016 Show/Hide Abstract
Abstract: A series of alkyl chain modified graphene oxides (AmGO) with different alkyl chain length and content was fabricated using a reducing reaction between graphene oxide (GO) and alkyl amine. Then AmGO was used as a graphene-based particle emulsifier to stabilize Pickering emulsion. Compared with the emulsion stabilized by GO, which was oil-in-water type, all the emulsions stabilized by AmGO were water-in-oil type. The effects of alkyl chain length and alkyl chain content on the emulsion properties of AmGO were investigated. The emulsions stabilized by AmGO showed good stability within a wide range of pH (from pH = 1 to pH = 13) and salt concentrations (from 0.1 to 1000 mM). In addition, the application of water-in-oil emulsions stabilized by AmGO was investigated. AmGO/polyaniline nanocomposite (AmGO/PANi) was prepared through an emulsion approach, and its supercapacitor performance was investigated. This research broadens the application of AmGO as a water-in-oil type emulsion stabilizer and in preparing graphene-based functional materials.
Materials2016, 9(9), 727; doi:10.3390/ma9090727 (registering DOI) - published 26 August 2016 Show/Hide Abstract
Abstract: Hydrogels from self-assembling ionic complementary peptides have been receiving a lot of interest from the scientific community as mimetic of the extracellular matrix that can offer three-dimensional supports for cell growth or can become vehicles for the delivery of stem cells, drugs or bioactive proteins. In order to develop a 3D “architecture” for mesenchymal stem cells, we propose the introduction in the hydrogel of conjugates obtained by chemoselective ligation between a ionic-complementary self-assembling peptide (called EAK) and three different bioactive molecules: an adhesive sequence with 4 Glycine-Arginine-Glycine-Aspartic Acid-Serine-Proline (GRGDSP) motifs per chain, an adhesive peptide mapped on h-Vitronectin and the growth factor Insulin-like Growth Factor-1 (IGF-1). The mesenchymal stem cell adhesion assays showed a significant increase in adhesion and proliferation for the hydrogels decorated with each of the synthesized conjugates; moreover, such functionalized 3D hydrogels support cell spreading and elongation, validating the use of this class of self-assembly peptides-based material as very promising 3D model scaffolds for cell cultures, at variance of the less realistic 2D ones. Furthermore, small amplitude oscillatory shear tests showed that the presence of IGF-1-conjugate did not alter significantly the viscoelastic properties of the hydrogels even though differences were observed in the nanoscale structure of the scaffolds obtained by changing their composition, ranging from long, well-defined fibers for conjugates with adhesion sequences to the compact and dense film for the IGF-1-conjugate.
Materials2016, 9(9), 726; doi:10.3390/ma9090726 - published 25 August 2016 Show/Hide Abstract
Abstract: A series of carbon-based superconductors XC6 with high Tc were reported recently. In this paper, based on the first-principles calculations, we studied the mechanical properties of these structures, and further explored the XC12 phases, where the X atoms are from elemental hydrogen to calcium, except noble gas atoms. The mechanically- and dynamically-stable structures include HC6, NC6, and SC6 in XC6 phases, and BC12, CC12, PC12, SC12, ClC12, and KC12 in XC12 phases. The doping leads to a weakening in mechanical properties and an increase in the elastic anisotropy. C6 has the lowest elastic anisotropy, and the anisotropy increases with the atomic number of doping atoms for both XC6 and XC12. Furthermore, the acoustic velocities, Debye temperatures, and the electronic properties are also studied.
Materials2016, 9(9), 728; doi:10.3390/ma9090728 - published 25 August 2016 Show/Hide Abstract
Abstract: A study of PDMS (polydimethylsiloxane) sol-gel–coated channels fabricated using soft lithography and a laser direct writing technique is presented. PDMS is a biocompatible material that presents a high versatility to reproduce several structures. It is widely employed in the fabrication of preclinical devices due to its advantages but it presents a rapid chemical deterioration to organic solvents. The use of sol-gel layers to cover the PDMS overcomes this problem since it provides the robustness of glass for the structures made with PDMS, decreasing its deterioration and changing the biocompatibility of the surface. In this work, PDMS channels are coated with three different kinds of sol-gel compositions (60MTES/40TEOS, 70MTES/30TISP and 80MTES/20TISP). The endothelial cell adhesion to the different coated devices is evaluated in order to determine the most suitable sol-gel preparation conditions to enhance cellular adhesion.