This is an editorial article. It has no abstract.
A novel double response surface model is used first time to optimize a regioselective process to prepare spherical dialdehyde cellulose nanocrystals (SDACN) and rod-like dialdehyde cellulose nanocrystals (RDACN) via one-step sodium periodate (NaIO4) oxidation. The influence of four preparation factors (solid-liquid ratio, NaIO4 concentration, reaction time and temperature) on the yields and aldehyde contents of the final products were evaluated. For comparison, rod-like cellulose nanocrystals (CN-M and CN-S) were prepared by hydrochloric/formic acid hydrolysis and sulfuric acid hydrolysis, respectively. The RDACN shows high crystallinity of 82%, while SDACN presents low crystallinity due to the high degree of oxidation. Thus, SDACN has poorer thermal stability than RDACN and CN-M, but higher than CN-S. Compared to CN-M, SDACN with higher aldehyde contents as templates is beneficial to deposit more Ag nanoparticles with diameters of 30±4 nm and the resultant nanohybrids exhibit good antibacterial activities against both Gram-negative E. coli and Gram-positive S. aureus.
A cycloolefin copolymer matrix was melt mixed with exfoliated graphite nanoplatelets (xGnP) and the resulting nanocomposites were foamed by supercritical carbon dioxide. The density of the obtained foams decreased with the foaming pressure. Moreover, xGnP limited the cell growth during the expansion process thus reducing the cell diameter (from 1.08 to 0.22 mm with an XGnP amount of 10 wt% at 150 bar) and increasing the cell density (from 12 to 45 cells/mm2 with a nanofiller content of 10 wt% at 150 bar). Electron microscopy observations of foams evidenced exfoliation and orientation of the nanoplatelets along the cell walls. Quasi-static compressive tests and tensile creep tests on foams clearly indicated that xGnP improved the modulus (up to a factor of 10 for a xGnP content of 10 wt%) and the creep stability.
A dual channel fluorescence system that combines the optical properties of silicon quantum dots–polysilane nanocomposites with those of 2-(4-chlorophenyl)-6-(thiophen-2-yl)pyridine, a fluorescent cytotoxic agent, is presented. The system is capable to alternatively trigger emission signals at two different wavelengths by excitation at a single wavelength. For this purpose a highly stable colloidal dispersion of silicon quantum dots–polysilane nanocomposite is prepared by a one-pot synthetic method using microwave-activated Wurtz coupling of organochlorosilanes. The size and shape of the silicon quantum dots within the polysilane thin film are studied by TEM. The colloidal dispersions are investigated by SAXS, which evidences that polysilane plays also a role as stabilizing agent to prevent aggregation. UV-vis spectrophotometry of the silicon quantum dots–polysilane nanocomposites in the presence of 2-(4-chlorophenyl)-6-(thiophen-2-yl)pyridine is used to define the active wavelength range and establish the fluorescence detection method.
Ultra-violet (UV) laser assisted stereolithography is used to print graded interpenetrating polymer networks (IPNs) by controlling network formation. Unlike the traditional process where structural change in IPNs is achieved by varying the feeding ratio of monomers or polymer precursors, in this demonstration property is changed by controlled termination of network formation. A photo-initiated process is used to construct IPNs by a combination of radical and cationic network formation in an acrylate/epoxy system. The extent of the cationic network formation is used to control the final properties of the system. Rapid-Scan Fourier Transformation Infrared Spectroscopy (RS-FTIR) is used to track the curing kinetics of the two networks and identify key parameters to control the final properties. Atomic force microscopy (AFM) and differential scanning calorimetry (DSC) confirm the formation of homogenous IPNs, whereas nano-indentation indicates that properties vary with the extent of cationic network formation. The curing characteristics are used to design and demonstrate printing of graded IPNs that show two orders of magnitude variation in mechanical properties in the millimeter scale.
Cyanate ester/epoxy resin (CE/EP) carbon fibre reinforced composites consisting of diglycidyl ether of bisphenol A (DGEBA) and novolac type cyanate ester (CE) were prepared and reactively flame retarded using epoxy functional adduct of DGEBA and 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide (DOPO). Effect of cyanate ester and flame retardant (FR) ratio was determined on matrix viscosity, matrix and composite glass transition temperature (Tg), as well as composite mechanical properties including storage modulus, tensile, bending, interlaminar shear and Charpy impact properties. Although the epoxy resin (EP) and FR decreased the Tg, even the flame retarded CE/EP blends had at least 22 °C higher Tg than the benchmark DGEBA composite. As for the mechanical properties, as a result of higher interlaminar shear strength suggesting better fibre-matrix adhesion, the CE/EP blends managed to over-perform the reference CE in most cases: The 2% phosphorus (P)-containing CE/EP composite had 25% higher tensile strength than the CE reference. The bending strength of the blends remained in the same range as the reference, while the impact resistance significantly increased in comparison to CE, especially in flame retarded composites.
Copolymerization of 4-methyl-1-pentene (4M1P) with 9-decen-1-ol (9D1O) or 4-penten-1-ol (4P1O) was conducted by using metallocene catalysts. The activity could be improved under the higher polymerization temperature. The dyad distribution of poly(4M1P-co-4P1O) was presented. The results showed that 4P1O was uniformly distributed in the copolymer chain. The melting temperature (Tm) of the copolymer was lower than that of poly(4M1P), and was decreased with the increase of the incorporation of comonomer. Tm of poly(4M1P-co-4P1O) was determined as 185 °C, even the incorporation of 4P1O was high as 15.0 mol%. WAXD (wide-angle X-ray diffraction) results showed that the poly(4M1P) was observed as crystalline form II, and turned to form I when the incorporation of α,ω-alkenols were high. Some new peaks, which were never observed in the previous researches, appeared in the X-ray diffraction profiles for poly(4M1P-co-4P1O). It is inferred that the similar chain length of 4P1O and 4M1P may be the key factor.
Epoxy-Graphene (E/G) nanocomposites with different loading of graphene were prepared via in situ prepolymerization and evaluated as protective coating for Stainless Steel 304 (SS304). The prepolymer composites were spin coated on SS304 substrates and thermally cured. Transmission Electron Microscopy (TEM) and Scanning Electron Microscopy (SEM) were utilized to examine the dispersion of graphene in the epoxy matrix. Epoxy and E/G nanocomposites were characterized using X-ray diffraction (XRD) and Fourier Transform Infrared (FTIR) techniques and the thermal behavior of the prepared coatings is analyzed using Thermogravimetric analysis (TGA) and Differential scanning calorimetry (DSC). The corrosion protection properties of the prepared coatings were evaluated using Electrochemical Impedance Spectroscopy (EIS) and Cyclic Voltammetry (CV) measurements. In addition to corrosion mitigation properties, the long-term adhesion performance of the coatings was evaluated by measuring the adhesion of the coatings to the SS304 substrate after 60 days of exposure to 3.5 wt% NaCl medium. The effects of graphene loading on the impact resistance, flexibility, and UV stability of the coating are analyzed and discussed. SEM was utilized to evaluate post adhesion and UV stability results. The results indicate that very low graphene loading up to 0.5 wt % significantly enhances the corrosion protection, UV stability, and impact resistance of epoxy coatings.