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关键词： Graphite-exfoliation   XRD   RAMAN   DFT   gamma-Irradiation   Ultrasonication   Liquid nitrogen quenching  

摘要： Two-dimensional (2D) nanomaterials, especially graphene, have received increasing attention due to their mechanical, electronic, optical, chemical, and thermal properties. A set of physical-chemical techniques was applied to increase the exfoliation effect's promotion and characterization over the natural graphite flakes. More than 30 natural impurities were determined in raw graphite flakes by instrumental neutron activation analyses. A possible graphite exfoliation mechanism combining ultrasonication and low temperatures in liquid nitrogen was postulated using density functional theory (DFT) calculation. The sonication shock waves act on the graphite surfaces resulting in compressive stress propagating throughout the graphite bulk. The most observed effect was the corner's damage, promoting gas interlayer adsorption pathways, followed by explosive desorption. The applied sequence of treatments results in an increasing defect level. Intense exfoliation was observed with several graphite layers, visible after gamma radiation treatment in doses ranging from 0.1 MGy to 6.0 MGy on standard ambient temperature and pressure. The increasing irradiation dose mostly affects the surface of the flakes. The pristine Graflake shows a homogeneous carbon surface with no signs of oxidation. At the presence of oxygen peroxide under oxygen atmosphere, samples irradiated at 0.3 MGy already show more brick surface signs. The irradiation dose associated with the oxidation generates a much less homogeneous surface, the result is a more bricked and somehow smaller flakes. Under the same oxidizing atmosphere at a higher irradiation dose, the effect has mostly increased in all surfaces compromised by oxidation, favoring the flakes' dispersion. The treatment association results in a bricked surface with much smaller particles of the original Graflake, favoring the exfoliation.

关键词： Foaming ability   Foaming stability   Egg white   Lysozyme   Protein interaction  

摘要： Lysozyme separated from egg white has high economic value and plays an important role in biochemistry, medicine and other fields. The role of lysozyme in the foaming properties of egg white was investigated in this study. After lysozyme being removed, the foaming ability (FA) and the foaming stability (FS) of egg white decreased by 45.1% and 35.3%, respectively, while restored again with lysozyme rejoining. In the absence of lysozyme, the particle size decreased and electrostatic repulsion increased, which resulted in a reduction of the protein adsorption on the interface of foam. Meanwhile, FTIR analysis showed the decrease on the protein secondary structure of alpha-helix and beta-sheet. The reduction of hydrogen bonds played an adverse effect on the formation of stable interface. The decreased viscosity indicated the break of ovomucin-lysozyme complex, which was not conducive to the formation of viscoelastic film and leading to a reduction in FS. Furthermore, in the absence of lysozyme, the high surface tension value of the protein was harmful to the adsorption, stretching and rearrangement of protein molecules on the interface. This research provided a new opinion into the effect of lysozyme on the foaming properties of egg white.

关键词： Thiophene   Conductive polymer   Poly (pat)   Bandgap   Permittivity  

摘要： Although the use of conductive polymers has invaded the electronics industry, the insolubility parameter presents a major problem against their direct application on the surfaces of materials. Attachment of cyclic compounds to polymer chains is recommended to increase the solubility of conductive polymers. The aim of this study is to synthesize a new type of intrinsic conductive polymer, soluble in common solvents. The technique is based on the copolymerization of thiophene with a synthesized monomer phenylazepane-2-one. The reaction was catalyzed by a solid catalyst, prepared by the acid treatment of natural clay, generating active sites responsible for the adhesion of the thiophene and benzene rings. Proton and carbon nuclear magnetic resonances (H-1 NMR/C-13 NMR), ultraviolet spectroscopy (UV-Visible), infrared spectroscopy (IR) and differential scanning calorimetry (DSC) were used to identify the material obtained poly [(phenylazepane-2-one)-co-(thiophene)] abbreviated poly (PAT). Thermogravimetric analysis (TGA) showed the thermal stability of poly (PAT) before 200 degrees C. The solubility of poly (PAT) has been tested and confirmed in various common solvents. The indirect bandgap was calculated at 1.12 eV using Tauc formula. Ac electrical conductivity and dielectric permittivity have been studied versus frequency and temperature, showing the semiconductor character of poly (PAT). The results obtained showed that this novel polymer can play a pioneering role to replace conventional insoluble conducting polymers.

关键词： Rietveld refinement   SnO2 nanoparticles   dielectric properties   photoluminescence  

摘要： In the present report, Ce3+ modified SnO2 compositions [Sn(1-y)CeyO2, for y = 0, 0.05, and y = 0.10, where y is wt.% of Ce3+] were synthesized via co-precipitation and their physicochemical properties were investigated. Crystal structure studies were carried out by using Rietveld refinement which confirmed high phase-purity and rutile-type tetragonal crystallinity with a P4(2/)mnm space group (space group no. 136) for all samples. Fourier transform infrared (FTIR) spectroscopy depicted the antisymmetric vibrations of Sn-O-Sn and stretching vibration of Sn-O, which were confirmed by bends located at 636 cm(-1), and 460 cm(-1), respectively. All the compositions showed a strong hump at similar to 300 nm in the ultra-violet (UV) region and the peak shifts slightly towards the blue region with increasing Ce(3+)content. Transmission electron microscopy (TEM) micrographs depicted pseudospherical particles with an average particle diameter of 12.84 +/- 0.17 nm, 15.55 +/- 0.31 nm, and 16.52 +/- 0.36 nm for y= 0, 0.05, and 0.10, respectively. High-resolution transmission electron microscopy (HRTEM) images confirmed tetragonal crystallinity for all the compositions. Dielectric studies illustrated that on increasing the concentration of Ce3+ in the host SnO2, the value of dielectric permittivity increased. The value of tan delta is maximum for pristine SnO2. The variation of ac conductivity was due to Maxwell-Wagner type interfacial polarization. For all the compositions, a sharp hump centered at similar to 407 nm was observed in the photoluminescence spectrum, which may be attributed to the presence of oxygen anion vacancies.

关键词： Peptide hydrogel   Composite   Graphene   Oxide   Self-assembly  

摘要： Hydrogels based on short peptide molecules are interesting biomaterials with wide present and prospective use in biotechnologies. A well-known possible drawback of these materials can be their limited mechanical performance. In order to overcome this problem, we prepared Fmoc-Phe3self-assembling peptides by a biocatalytic approach, and we reinforced the hydrogel with graphene oxide nanosheets. The formulation here proposed confers to the hydrogel additional physicochemical properties without hampering peptide self-assembly. We investigated in depth the effect of nanocarbon morphology on hydrogel properties (i.e. morphology, viscoelastic properties, stiffness, resistance to an applied stress). In view of further developments towards possible clinical applications, we have preliminarily tested the biocompatibility of the composites. Our results showed that the innovative hydrogel composite formulation based on FmocPhe3 and GO is a biomaterial with improved mechanical properties that appears suitable for the development of biotechnological applications.

关键词： carbon sorbents   lactic acid   lysozyme   N-vinylpyrrolidone   betulin   medical-biological properties  

摘要： By means of chemical modification of the surface of a mesoporous carbon material (300-400 m(2)/g) biologically active substances (lactic acid, lysozyme, N-vinylpyrrolidone, betulin) new sorbents for medical purposes have been obtained. Their structural and morphological characteristics have been determined, and their antioxidant and biospecific properties have been evaluated.

关键词： fluid substitution   elasticity moduli   carbonates   petroleum rheology   non-Newtonian flow in porous media.  

摘要： The mechanical nature of fluid-substitution models has always been recognized as a major cause of their limited predictive power. For instance, saturants are typically treated as simple fluids characterized only by their densities, viscosities, and moduli of elasticity;their chemistry is just ignored, even when that fluid is crude oil. However, crude oil is a complex mixture of several thousand organic compounds characterized by a variety of molecular weights, polarities, and polarizabilities, and the response of its rheological behavior to acoustic wave propagation is difficult to predict, especially when it resides in the pore space of rocks. We have performed ultrasonic-velocity measurements on carbonate core plugs saturated with a brine and with a light crude oil that are mechanically similar (i.e., having comparable densities, viscosities, and moduli of elasticity) and that show a significant and consistent excess of hardening when the saturant is oil. Dispersion and wettability are excluded as explanations for the data. We hypothesize that asphaltene aggregation and adsorption as well as paraffin-wax crystallization (and possibly volumetric expansion) combine to cause crude oil to exhibit a dilatant-like behavior within the pore space of carbonates at ultrasonic frequencies. In general, the observed effect would be similar to the hardening of ooblek at high deformation rates. This hypothesis could be tested in the future by an adequate combination of high-resolution imaging and microfluidic setups. This and similar studies would be beneficial in developing physical fluid-substitution models with a more consistent predictive power.

关键词： heparin   hydrogels   poly(2-alkyl-2-oxazolines)   thermoresponsiveness  

摘要： Poly(ethylene glycol) (PEG)-glycosaminoglycan (GAG) hydrogel networks are established as very versatile biomaterials. Herein, the synthetic gel component of the biohybrid materials is systematically varied by combining different poly(2-alkyl-2-oxazolines) (POx) with heparin applying a Michael-type addition crosslinking scheme: POx of gradated hydrophilicity and temperature-responsiveness provides polymer networks of distinctly different stiffness and swelling. Adjusting the mechanical properties and the GAG concentration of the gels to similar values allows for modulating the release of GAG-binding growth factors (VEGF165 and PDGF-BB) by the choice of the POx and its temperature-dependent conformation. Adsorption of fibronectin, growth of fibroblasts, and bacterial adhesion scale with the hydrophobicity of the gel-incorporated POx. In vitro hemocompatibility tests with freshly drawn human whole blood show advantages of POx-based gels compared to the PEG-based reference materials. Biohybrid POx hydrogels can therefore enable biomedical technologies requiring GAG-based materials with customized and switchable physicochemical characteristics.

关键词： Colour change   enzymatic browning   flavour   high pressure processing   physicochemical properties  

摘要： The study aimed to investigate the mechanism of the colour change of carambola puree by high pressure processing (HPP), and the effects on its flavour, antioxidant properties and other physicochemical properties. The results showed that the colour change of carambola puree after HPP (200, 400, 600 and 800 MPa, for 15 min at 25 degrees C) was caused by both the enzymatic browning inhibition and the beta-carotene release promotion. The physical and chemical properties also varied after HPP treatment, in which the potential of hydrogen (pH) value and the total soluble solids decreased with the pressure. With the increase of pressure, the content of total phenols and flavonoids increased to a certain extent, and the antioxidant activity also increased. HPP could destroy the cell structure and form microscopic pores in the tissue, which might cause changes in physical and chemical properties. Compared with untreated samples, HPP could improve the characteristic flavour and quality of the sample itself, and it has a great application prospect in the production of carambola puree.

关键词： Ovalbumin   Alkali treatment   Textural properties   Morphological transformation   Degradation  

摘要： Different alkalinity could impart certain desirable properties to ovalbumin (OVA), such as improving gel texture or solidification time. In this study, the physicochemical properties, structural changes, and peptide-based quantitative analysis during degradation of OVA treated with 1.25%, 1.5% and 1.75% NaOH solutions at different time were investigated. With the extension of time, the hardness, water holding capacity, particle size, surface hydrophobicity of OVA gel and the number of peptides increased dramatically, and then decreased gradually regardless of alkalinity. By contrast, the pH and springiness of OVA gel exhibited a steady downward trend. Rheological behavior revealed that the OVA gel network degraded from a high viscosity semi-fluid to an aqueous sol. The ordered gel structure was mainly contributed by beta-sheets, accompanied by constantly conversion of alpha-helices, while the liquefaction was caused by the destruction of those regular secondary structures. LC-MS/MS showed that only a small number of common peptides were obtained at different time of protein degradation, and more similar sequences were observed in peptides generated in one day. In summary, it was concluded that although alkali-induced OVA showed a definite gel-sol transformation, the underlying mechanism could not be precisely expressed by degradation into peptides of specific sequences.