Advanced Materials Research Vols. 306-307

Abstract: In this paper, the atomic magnetic moments and spin-splittings of the six-member ring N2C4 cluster with planar and folding configurations in DNA bases are studied, respectively. The results show that the surprising interplay between the molecular structure and their magnetic property. In the planar configuration, the cluster exhibits antiferromagnetism and ferromagnetism in the ground state and metastable state, respectively. In the folding configuration, it exhibits antiferromagnetism and ferrimagnetism in the ground state and metastable state, respectively.

Abstract: Deproteinization of natural rubber was achieved in the latex stage. The structure of deproteinized natural rubber (DPNR) was characterized by fourier transform infrared spectroscopy (FTIR). The thermo degradation of DPNR was studied by thermogravimetry analysis (TG) under air atmosphere and nitrogen atmosphere. The kinetic parameters apparent activation energies (Ea) of the thermal decomposition reaction been calculated from the TG curves using the method described by Broido. And the results were compared with the thermo degradation of natural rubber (NR) under the same conditions. The effect of proteins in natural rubber latex on thermal/ thermo-oxidative stability of NR was discussed. The results show that: the absorptions of the proteins in DPNR at 1546 ㎝^-1, compared to NR, become significantly weaker, nearly disappear, which indicates most of proteins has been removed from NR. The thermo degradation of DPNR in nitrogen atmosphere is a one-step reaction. The initial degradation temperature (T₀) 、the maximum degradation temperature（T_p） and the final degradation temperature（T_f）as well as the Ea of DPNR are higher than those of NR, which indicates that DPNR represents a better thermal stability than NR under nitrogen atmosphere. Thermo-oxidative degradation of DPNR and NR are two-step reaction. The characteristic temperatures (T₀, T_p and T_f) of DPNR are lower than those of NR. The Ea during the First Step of Thermooxidative Degradation of DPNR are also lower than those of NR. These results prove that the thermo-oxidative stability of DPNR is worse than that of NR. Protein is the key role to the thermal stability of natural rubber.

Abstract: In this research, we aimed to develop a new type of core-shell electrospun fiber, possessing “short” length (core) and “concentrated” polymer brush (shell). We prepared electrospun fibers with initiating moiety for surface-initiated atom transfer radical polymerization (SI-ATRP), one of living radical polymerizations. Then we grafted poly(sodium styrene sulfonate) (PSSNa) on the fibers by SI-ATRP. After the polymerization, we mechanically cut the electrospun fibers with a homogenizer, yielding regulated shortened fibers. Our ultimate goal is to make a novel shortened nanofibril biomaterial with concentrated brush as cell growth scaffolds. Therefore we expect that this unprecedented short nanofiber can be broadly applied as a biomaterial owing to the unique structures and properties of the concentrated brush. The details will be discussed.

Abstract: In the present study, a simple method of regenerating microstructure of human tooth under near-physiological conditions (pH 7.0, 37 °C, 1 atm) was developed. Commercial gelatin was used as matrix materials in this method, which nucleated the formation of fluorapatite (FA) nanocrystals and regulated the growth of nanocrystals. As a result, the resulting thin FA coatings had been prepared on human tooth slices and sintered hydroxyapatite disks, which were in tight contact with the substrates. Besides, the morphologies of FA nanocrystals changed from acicular to hexagonal with the exchange cycle of gel increased. Electron dispersive spectrometer analysis indicated that some sodium and carbonate ions were incorporated into the FA crystal lattices and the calcium to phosphorus ratio was approximate 1.58. The mechanical properties of the resulting FA coating were investigated through nanoindentation system, which showed the similar hardness with dentin. In conclusion, this method demonstrated a potential application to repair tooth damage in dental clinics.

Abstract: Multi-walled carbon nanotubes (MWNTs) reinforced hydroxyapatite (HA) composite was fabricated by in-situ method and followed by hot-pressing sintering; the influence of MWNTs’ content on the mechanical and microstructure properties was explored. The results show that adding MWNTs within a certain range could enhance the mechanical properties of HA matrix significantly. The maximal increment of the bending strength and fracture toughness of the composites, compared with the pure HA, were 157% and 171% respectively. XRD and TEM showed that the primary crystal phase of the composite was HA together with the diffraction peaks of carbon nanotube. By SEM, we found that MWNTs are homogeneously dispersed within grains or at grain boundaries of the HA matrix in composites which MWNTs’ content was not more than 15vol%, otherwise MWNTs tended to be agglomerated. The reinforcement mechanism was discussed based on the microstructure investigation. The broken nanotubes and pullout of MWNTs at interfaces were efficient in transferring the load from the HA matrix to the nanotubes, leading to the improvement of the mechanical properties.

Abstract: For bone implant NiTi foams with a structure (69.3-69.9% porosity and 150-400μm pore size) were fabricated by CIP and sintering with NaCl space-holders. A maximum compressive strength of 30.90Mpa and a ultimate compressive ductility of 33.5% were obtained. Moreover, 81-89% of the strain recovered after inducing shape-memory effect. In particular, the pores completely replicate the shape and size of the NaCl powders. It provides a powerful tool to tailor the pore structure and mechanical properties of NiTi foams to match the demand of bone implant. Simple processing route and low cost allow these foams to be a suitable candidate for bone implant applications.

Abstract: A polysaccharide based bioplolymer, chitosan was grafted with polyaniline through a simple room temperature oxidative-radical copolymerization method employing CuSO4 as a polymerizing agent. The grafting conditions were optimized by varying different parameters. The optimized experimental findings have been discussed and proposed a probable mechanism for the graft copolymerization. The representative sample of chitosan-graft-polyaniline (CHIT-g-PANI) was characterized using UV-vis, FTIR, X-ray diffraction and Scanning electron microscopy techniques taking chitosan as reference material. The result revealed the formation of grafted composite. Which exhibited highly improved electrical conductivity , in the order of ~ 10 -6 times due to the grafting of PANI onto chitosan backbone. Further , composite was found responsive in nature for H+ ion , which will be a suitable properties for its use in fabrication of bio-sensor.

Abstract: A two-step fermentation procedure for maize straw hydrolysis by Phanerochaete chrysosporium, Trichoderma and Aspergillus niger were investigated in this study. 2 mL of P. chrysosporium (10⁷spores/mL) was added to 50 mL medium for the first fermentation stage. The optimal culture conditions were 28°C of culture temperature, 4.0 of pH, 8 days of culture time, 2 mL of Trichoderma suspensions (10⁷spores/mL) and 1 mL of A. niger suspensions (10⁷spores/mL) of the inoculums size on the second fermentation stage. Under the optimal conditions, the crude degradation rate achieved 48.2%. Via sulfonation, oxidate-lignosulfonate alkali lignin (OLAL) was achieved from maize straw hydrolysate(MSH).OLAL and MSH can be partial substitution for common water reducers and OLAL was more efficient compared to that of MSH.

Abstract: Isothermal oxidation behavior of the AISI430 stainless steel was investigated at 900°C and 950°C in air. Isothermal themogravimettric analyses were performed at high-temperature for 360ks (kilo-seconds). The microstructures of the oxide films on the stainless steel were characterized by SEM and chemical analyses were performed by EDS and X-ray diffraction. The oxide film included outer layer and inner one. The outer layer was magnetite and hematite oxides with no significant amounts of chromium and the inner one was formed by iron and chromium spinel. Significantly accelerated and anomalous oxidation was observed with the stainless steel AISI430 in air at 900°C.

Abstract: In the present work, the rheological model for semisolid metal slurries (SSMS) is constructed and then applied to the Al-6.5wt%Si alloy to investigate its rheological behavior at transient state during isothermal shearing and isothermal resting. Firstly, the present study shows that the agreement of the variation of viscosity and the average agglomerate size with shearing time and resting time shows that the microstructure of SSMS determines its rheological behavior. Secondly, the deagglomeration of particles is about two orders of magnitude faster than agglomeration, which is in agreement with the experimental measurement. Finally, the Al-6.5wt%Si alloy at transient state has the behavior of “shear-thinning”, but not “shear-thickening” predicted in the documents.