Frontiers of Materials Science (v.4, #1)

Diamond is one of the most important functional materials for film applications due to its extreme physical and mechanical properties, many of which depend on the crystallographic texture. The influence of various deposition parameters matters to the texture formation and evolution during chemical vapor deposition (CVD) of diamond films. In this overview, the texture evolutions are presented in terms of both simulations and experimental observations. The crystallographic textures in diamond are simulated based on the van der Drift growth selection mechanism. The film morphology and textures associated with the growth parameters α (proportional to the ratio of the growth rate along the 〈100〉 direction to that along the 〈111〉 direction) are presented and determined by applying the fastest growth directions. Thick films with variations in substrate temperature, methane concentration, film thickness, and nitrogen addition were analyzed using high-resolution electron back-scattering diffraction (HR-EBSD) as well as X-ray diffraction (XRD), and the fraction variations of fiber textures with these deposition parameters were explained. In conjunction with the focused ion beam (FIB) technique for specimen preparation, the grain orientations in the beginning nucleation zones were studied using HR-EBSD (50 nm step size) in another two sets of thin films deposited with variations in methane concentration and substrate material. The microstructures, textures, and grain boundary character were characterized. Based on the combination of an FIB unit for serial sectioning and HR-EBSD, diamond growth dynamics was observed using a 3D EBSD technique, with which individual diamond grains were investigated in 3D. Microscopic defects were observed in the vicinity of the high-angle grain boundaries by using the transmission electron microscopy (TEM) technique, and the advances of TEM orientation microscopy make it possible to identify the grain orientations in nano-crystalline diamond.
Keywords: CVD diamond films; deposition parameters; texture; EBSD; van der Drift growth selection mechanism

Diameters of single-walled carbon nanotubes (SWCNTs) and related nanochemistry and nanobiology by Jie Ma; Jian-Nong Wang; Chung-Jung Tsai; Ruth Nussinov; Buyong Ma (17-28).
We reviewed and examined recent progresses related to the nanochemistry and nanobiology of signal-walled carbon nanotubes (SWCNTs), focusing on the diameters of SWCNTs and how the diameters affect the interactions of SWCNT with protein and DNA, which underlay more complex biological responses. The diameters of SWCNTs are closely related to the electronic structure and surface chemistry of SWCNTs, and subsequently affect the interaction of SWCNTs with membrane, protein, and DNA. The surfaces of SWCNT with smaller diameters are more polar, and these with large diameters are more hydrophobic. The preference of SWCNT to interact with Trp/Phe/Met residues indicates it is possible that SWCNT may interfere with normal protein-protein interactions. SWCNT-DNA interactions often change DNA conformation. Besides the promising future of using SWCNTs as delivering nanomaterial, thermal therapy, and other biological applications, we should thoroughly examine the possible effects of carbon nanotube on interrupting normal protein-protein interaction network and other genetic effects at the cellular level.
Keywords: carbon nanotube (CNT); nanobiology; protein; DNA; toxicity; cancer

Electrospun nanofibers: Work for medicine? by Susan Liao; Casey K. Chan; S. Ramakrishna (29-33).
Attempts have been made to fabricate nanofibrous scaffolds to mimic the chemical composition and structural properties of the extracellular matrix (ECM) for tissue/organ replacement. Nanofiber scaffolds with various patterns have been successfully produced from synthetic and natural polymers through a relatively simple technique of electrospinning. The resulting patterns can mimic some of the diverse tissue-specific orientation and three-dimensional (3D) fibrous structures. Studies on cell-nanofiber interactions, including studies on stem cells, have revealed the importance of nanotopography on cell adhesion, proliferation and differentiation. Furthermore, clinical application of electrospun nanofibers including wound healing, tissue regeneration, drug delivery and stem cell therapy are highly feasible due to the ease and flexibility of fabrication of making nanofiber with this cost-effective method using electrospinning. In this review, we have highlighted the current state of the art and provided future perspectives on electrospun nanofiber in medical applications.
Keywords: biomimetic materials; nanofiber; electrospinning; stem cell; medicine

The potential of Zr-based bulk metallic glasses as biomaterials by Qi Chen; Lin Liu; Sheng-Min Zhang (34-44).
Zr-based bulk metallic glasses (BMGs) are a new type of metallic materials with disordered atomic structure that exhibit high strength and high elastic strain, relatively low Young’s modulus, and excellent corrosion resistance and biocompatibility. The combination of these unique properties makes the Zr-based BMGs very promising for biomaterials applications. In this review article, the authors give an overview of the recent progress in the study of biocompatibility of Zr-based BMGs, especially the relevant work that has been done in the metallic glasses group in Huazhong University of Science and Technology (HUST), including the development of Ni-free Zr-based BMGs, the mechanical and wear properties, the bio-corrosion resistance, the in vitro and in vivo biocompatibility and the bioactive surface modification of these newly developed BMGs.
Keywords: Zr-based bulk metallic glasses; biocompatibility; bioactive surface modification

Properties, synthesis, and characterization of graphene by Liang-Xu Dong; Qiang Chen (45-51).
Graphene is a wonder material that attracts great interests in materials science and condensed matter physics. It is the thinnest material and also the strongest material ever measured. Its distinctive band structure and physical properties determine its bright application prospects. This review introduces briefly the properties and applications of graphene. Recent synthesis and characterization methods are summarized in detail, and the future research direction is also pointed out in this paper.
Keywords: graphene; properties; synthesis; characterization

Fabrication of mesoporous silica/carbon black nanospheres and load-sensitive conducting rubber nanocomposites by En-Rong Li; Qian-Jun Zhang; Wei Wang; Qing-Wen Zhu; Long Ba (52-56).
Mesoporous silica nanospheres (MSNs) with regular pores have been fabricated using cetyltrimethylammonium bromide (CTAB) as surfactant in high pH solution. The average size of the MCM-41 silica nanospheres was reduced from 95 to 48 nm, while the concentration of CTAB increases from 7.7 to 11.5 mmol/L. Carbon black was deposited on MSNs using hexane as the carbon source. By mixing such materials with silicone rubber, the composites become conducting when equivalent carbon volume fraction is higher than a certain region, which is less sensitive to the morphology of the deposited carbon. The improved piezoresistance repeatability has been found on the composite sample of MSNs/carbon plus extra high conducting carbon black. The load and strain sensitive range up to 0.35 MPa and 0.10, respectively, with less resistance fluctuation during multiple press loading cycles.
Keywords: nanomaterials; mesoporous silica; conducting rubber; piezoresistance

Silk fibroin film (SFF) has been widely used in biomaterials. SFF is usually prepared from a regenerated silk aqueous solution and its properties depend remarkably on the preparation conditions. However, the effect of the silk fibroin concentration (C 0) on the SFF surface properties as well as the cytocompatibility has rarely been investigated. In this work we prepared a series of Bombyx mori SFFs by casting SF aqueous solutions with the concentration from 10° to 102 mg/mL on TCPS substrate at 60°C. The test results of atomic force microscopy, attenuated total reflection Fourier transform infrared and contact angles analysis showed that the film surface roughness and β-sheet structure increased with the increase of C 0, whereas the surface hydrophilicity increased with the decrease of C 0. The in vitro clotting time measurement results revealed that the SFFs prepared from the thinner solution showed a longer APTT (activated partial thromboplastin time) and TT (thrombin time). The results of microscopy and MTT assay also revealed that cell adhesion and growth were enhanced on the SFF cast from lower C 0 for fibroblasts. In contrast, endothelial cells showed a similar behavior on all those films that were prepared from the solution in different concentrations.
Keywords: silk fibroin films (SFFs); solution concentrations; surface property; clotting time; cytocompatibility

Preparation and characterization of composite fibers from organic-soluble chitosan and poly-vinylpyrrolidone by electrospinning by Gui-Ping Ma; Dong-Zhi Yang; Bin-ling Chen; Shu-Min Ding; Guo-Qiang Song; Jun Nie (64-69).
Ultrafine composite fibers were fabricated by electrospinning of chloroform solutions of organic-soluble chitosan (O-CS) and poly-vinylpyrrolidone (PVP). The composite fibers were subjected to detailed analysis by Fourier transformed infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM). The FT-IR showed that the composite fibers contained the two polymers. The SEM image results confirmed that the morphology and diameter of the fibers were remarkably affected by the process and the parameters of the electrospinning. The governing parameters included the applied voltage, the viscosity of the electrospun solution and tip-to-collector distance, and were further investigated.
Keywords: organic-soluble chitosan (O-CS); polyvinylpyrrolidone (PVP); electrospinning; composite fibers

A kind of novel three-dimensional crosslinked hydrogel was synthesized via Michael-type addition reaction of dithiothreitol (DTT) as a crosslinker/extender towards the self-assembly of α-cyclodextrins (α-CDs) with acryloyl end capped 3-arm PEG. The supramolecular structure of the resulting hydrogels was characterized by using FT-IR, TGA, XRD and DSC measurements. The effect of varying the amount of α-CDs was studied on the crosslinking process. Interestingly, this conjugation reaction is smoothly carried out at physiological temperature and pH in the absence of any sensitizer or catalyst. It appears that these chemically crosslinked hydrogels have the potential to be used as carriers for drug controlled release and scaffolds for injectable tissue engineering.
Keywords: α-cyclodextrin (α-CD); dithiothreitol (DTT); Michael-type addition reaction; self-assembly; supramolecular structured hydrogel

The non-isothermal and isothermal degradation behaviors and kinetics of poly(L-lactide) (PLLA) were studied by using thermogravimetry analysis (TGA) in nitrogen and air atmosphere, respectively. At lower heating rate ((5–10)°C/min), PLLA starts to decompose in air at lower temperature than those in nitrogen atmosphere; however, at higher heating rate ((20–40)°C/min), the starting decomposition temperature in air are similar to those in nitrogen atmosphere, not only showing that PLLA has better thermal stability in nitrogen than in air atmosphere, but also suggesting that the faster heating rate will decrease the decomposition of PLLA in thermal processing. Whether in air or in nitrogen atmosphere, the decomposition of PLLA has only one-stage degradation with a first-order decomposed reaction, suggesting that the molecular chains of PLLA have the similar decomposed kinetics. The average apparent activation energy of nonisothermal thermal degradation (Ē non) calculated by Ozawa theory are 231.7 kJ·mol−1 in air and 181.6 kJ·mol−1 in nitrogen; while the average apparent activation energy of isothermal degradation (Ē iso) calculated by Flynn method are 144.0 kJ·mol−1 in air and 129.2 kJ·mol−1 in nitrogen, also suggesting that PLLA is easier to decompose in air than in nitrogen. Moreover, the decomposed products of PLLA are also investigated by using thermogravimetry-differential scanning calorimetry-mass spectrometry (TGDSC-MS). In air atmosphere the volatilization products are more complex than those in nitrogen because the oxidation reaction occurring produces some oxides groups.
Keywords: poly(L-lactide) (PLLA); degradation; kinetics; TG; apparent activation energy

Effect of AAc-GA content on swelling behaviors of temperature-sensitive PNIPAAm-based hydrogels by You-Yu Dong; Xiao-Ling He; Li Chen; Fan-Yong Yan; Hao-Jie Li (84-89).
A series of temperature-sensitive poly (NIPAAm-co-AAc-GA) hydrogels were synthesized by the copolymerization of glycyrrhetinic acid with vinyl monomer (AAc-GA) and N-isopropylacrylamide (NIPAAm) in N, N-dimethylformamide (DMF). Since GA has the specific binding capacity to asialoglycoprotein receptors on the membrane of hepatocyte, the hydrogel with GA could be expected as good candidate for hepatic cell culture. The results showed that macroporous and channel network structure was formed in the hydrogel matrix. With increasing the AAc-GA content, the swelling ratios of hydrogels and lower critical solution temperature (LCST) increased because of the hydrophilic group of AAc-GA and the macroporous structure. In addition, the prepared hydrogels could respond quickly to temperature and exhibited good reversible temperature-responsive characteristics.
Keywords: glycyrrhetinic acid; temperature-responsive; N-isopropylacrylamide (NIPAAm); hydrogel

A novel blue emitting phosphor NaBa0.98Eu0.02PO4 and the improvement of its luminescence properties by Juan Gu; Bo Yue; Guang-Fu Yin; Xiao-Ming Liao; Zhong-Bing Huang; Ya-Dong Yao; Yun-Qing Kang (90-94).
A novel blue-emitting phosphor NaBa0.98Eu0.02PO4 was synthesized by conventional solid state reaction, and it exhibits efficient blue emission under near-ultraviolet (n-UV) excitation. The emission spectrum shows a single band centered at about 440 nm, which corresponds to the 4f65d1-4f7 transition of Eu2+. The excitation spectrum is a broad band in the wavelength range between 200 and 450 nm, which can match the emission of white light emitting diodes (LEDs) by the method of n-UV conversion. The Ca2+, Sr2+ and Mg2+ were co-doped into NaBa0.98Eu0.02PO4 respectively. Special attention was paid to the sample co-doped with Ca2+ that could possess a higher luminous efficacy than the analogs co-doped with Sr2+ and Mg2+. With the co-doping of Ca2+, the enhanced intensity of the excitation and emission band appears. The optimum co-doping concentration of Ca2+ is 7 mol.%. The emission intensity of NaBa0.91Ca0.07Eu0.02PO4 phosphoris about 1.68 times than that of NaBa0.98Eu0.02PO4 phosphor. The as-prepared phosphors are the potential blue phosphors for application in white LEDs.
Keywords: inorganic compound; luminescence; crystal field; phosphate; light emitting diode (LED)

Nano-sized monodisperse gold particles (AuNPs) have received significant attention in the past decade, due to their unique physical properties and good chemical stability, which can lead to a wide variety of potential applications. In this work, TEG-derived PAMAM dendrimers with amine-terminating groups were synthesized and characterized by 1H NMR and FT-IR. These dendrimers were investigated as the templates for preparation of gold nanoparticles through the reduction of HAuCl4 by NaBH4 in water. Stable gold nanoparticles with diameters around 10 nm were obtained in the presence of G2.0–G5.0 dendrimers and characterized by UV-Vis spectroscopy, transmission electron microscopy (TEM) and dynamic light scattering (DLS). The particle size of the produced AuNPs decreased with increasing dendrimer generations. A dendrimer of higher generation has a rigid structure with many end groups on the surface and may play a powerful role in the growth of the AuNPs, as well as having a solid stabilization effect on the AuNPs.
Keywords: gold nanoparticles; polyamidoamine (PAMAM) dendrimer; triethylene glycol (TEG); interaction

Effects of high magnetic field on thermodynamic properties of pure Fe and Cu by Na-Qiong Zhu; Lin Li; Yan-Lin He; Guang-Jie Shao; Mei-Bo Tang; Jing-Tai Zhao (100-102).
By the use of PPMS (Physics Property Measurement System), specific heat values of pure Cu at 2–300 K were determined under the magnetic field of 0, 3, 6 and 9 T, respectively. Magnetization curves of pure Fe under the magnetic field of 0–9 Twere obtained at different temperature ranging from 5 to 300 K. Analyses of the experimental results indicate that below 300 K, magnetic fields have no effects on the specific heat values of diamagnetic Cu and very little effects on those of ferromagnetic Fe.
Keywords: specific heat; magnetization curve; magnetic field

Analysis of fluid flow in centrifugal casting by K. S. Keerthi Prasad; M. S. Murali; P. G. Mukunda (103-110).
Centrifugal casting process is a fast process with melt, cast and moulds being opaque. It is almost impossible to observe the melt behavior during casting. Cold modeling experiments were conducted using horizontal transparent moulds and transparent fluids of different viscosities to study the effect of different process variables on the flow pattern. Effects of the thickness of fluid cylinder, viscosity of the fluid, diameter of the mould, and rotational speed of the mould on the formation of complete hollow fluid cylinder are investigated. The influence of rotational speed has been studied in aluminum casting. The cylinders are cast at different rotational speed with varying thickness. It is observed that the speed required to form uniform cylinder increases with the increase in thickness of a fluid cylinder. As rotational speed is increased the hardness of the cast cylinder also increases. The flow patterns seen in cold modeling experiments and actual castings agree reasonably well.
Keywords: cold modeling experiment; aluminum; fluid flow