Effect of nanoparticulate incorporation on processability, chemistry and thermal properties of high temperature resin systems

Processability, curing dynamics, network formation, and thermal stability of cyanate ester resin (CY) nanocomposites with triSilanolphenyl polyhedral oligomeric silsesquioxane (POSS), natural montmorillonite clay (Na+), MT2EtOH (methyl, tallow, bis-2-hydroxyethyl, ternary ammonium) modified clay (30B), 2M2HT (dimethyl, dihydrogenatedtallow, quaternary ammonium) modified clay (20A), carbon nanotubes (CNTs) were studied by means of differential scanning calorimetry (DSC), modulated temperature differential scanning calorimetry (MTDSC), X-ray diffraction (XRD), field emission gun scanning electron microscopy (FEG-SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) and Raman spectroscopies. For comparison, the influence of the nanofillers on processability, curing dynamics, network formation, and thermal stability of a benzoxazine resin (BEN) were studied as well. [Continues.

Effect of polyhedral oligomeric silsesquioxane nanoparticles on thermal decomposition of cyanate ester resin

A series of cyanate ester resin (CY)/polyhedral oligomeric silsesquioxane (POSS) nanocomposites were prepared successfully. Morphology and thermal stability of the CY and its nanocomposites with POSS were studied by means of scanning electron microscopy (SEM) and Thermogravimetric Analysis (TGA). With the addition of POSS, the thermal stability of CY is dramatically improved. Under air atmosphere, the full decomposition temperature increased by 146 °C, with incorporation of only 1 wt% POSS. The heat generated by the thermal degradation of the CY/POSS nanocomposites is around 4 times less than that of the neat CY. Under nitrogen atmosphere, the char yield of the CY increased up to 15 wt% with addition of the POSS. Besides, the heat required for the degradation of the CY/POSS nanocomposites was much higher than that of the neat CY. These results reveal that the incorporation of the POSS resulted in change of the degradation mechanism of CY. The breakdown of POSS/CY network retarded the breakdown of the triazine rings of CY hence the thermal stability of POSS/CY nanocomposites were improved comparing to that of pristine CY. Furthermore, the formation of char retarded the degradation of benzene rings as well

Effect of graphene oxide sheet size on the curing kinetics and thermal stability of epoxy resins

This work revealed the influences of graphene oxide (GO) sheet size on the curing kinetics and thermal stability of epoxy resins. A series of GO/epoxy nanocomposites were prepared by the incorporation of three different sized GOsheets, namely GO-1, GO-2 and GO-3, the average size of which was 10.79 μgm, 1.72 μgmand 0.70 μgm, respectively. The morphologies of the nanocomposites were observed by field emission gun scanning electron microscope. The dispersion quality of each sized GO was comparable in the epoxy matrix. The curing kinetics was investigated by means of differential scanning calorimetry and analyzed based on kinetics model. Addition of a small amount of GO (0.1 wt%) exhibited strong catalytic effect on the curing reaction of epoxy resin. The activation energy was reduced by 18.9%, 28.8% and 14.6% with addition of GO-1, GO-2 and GO-3, respectively. GO-2 with medium size (1.72 μgm) showed the most effective catalysis on the cure. The thermal stability of the cured resins was evaluated based on thermogravimetric analysis. GO/epoxy nanocomposites showed improved thermal stability in the range of 420 °C-500 °C, compared with the pure resin. A∼4%more residue was obtained in each of the incorporated system. The variations of GOsheet size did not influence the enhancement effect on the thermal stability

A study of crystallisation of poly (ethylene oxide) and polypropylene on graphene surface

Crystallisation behaviour of poly (ethylene oxide) (PEO) and isotactic polypropylene (iPP) on graphene surface was investigated by means of polarized microscopy, wide angle X-ray diffraction (WAXD), and Raman techniques. Results indicated that graphene influences the crystallisation and crystal structure of iPP and PEO. WAXD peaks shifting toward lower diffraction angle, i.e. increase in d-pacing, was observed in both PEO and iPP crystallised on the surface of graphene. The change of d-spacing of both PEO and iPP could result from the compressive stress caused by graphene. A shift of 2D band in graphene was observed from Raman spectra. The Raman spectra indicated the big shift in the 2D band is due to the presence of stress induced strain in the polymer attached graphene. The residual stress was generated during crystallization of the polymers on the surface of graphene. Due to the interactions between the graphene and the polymers, the stress was transferred to the graphene which leads to a strain of the graphene. Raman spectra proved the presence of stress generated by the crystallization of the polymers on the surface of graphene

A study of crystallisation of poly (ethylene oxide) and polypropylene on graphene surface

Crystallisation behaviour of poly (ethylene oxide) (PEO) and isotactic polypropylene (iPP) on graphene surface was investigated by means of polarized microscopy, wide angle X-ray diffraction (WAXD), and Raman techniques. Results indicated that graphene influences the crystallisation and crystal structure of iPP and PEO. WAXD peaks shifting toward lower diffraction angle, i.e. increase in d-pacing, was observed in both PEO and iPP crystallised on the surface of graphene. The change of d-spacing of both PEO and iPP could result from the compressive stress caused by graphene. A shift of 2D band in graphene was observed from Raman spectra. The Raman spectra indicated the big shift in the 2D band is due to the presence of stress induced strain in the polymer attached graphene. The residual stress was generated during crystallization of the polymers on the surface of graphene. Due to the interactions between the graphene and the polymers, the stress was transferred to the graphene which leads to a strain of the graphene. Raman spectra proved the presence of stress generated by the crystallization of the polymers on the surface of graphene

Preparation and characterization of benzoxazine based nanocomposites: comprehensive study in curing kinetics and enhanced thermal stabilities

Several bisphenol-A benzoxazine (BEN) based nanocomposites incorporated with several polyhedral oligomeric silsesquioxane (POSS), carbon nanotubes (CNTs), and clays, were prepared successfully. The influences of the nanofillers on curing kinetics, network formation, and thermal stability of the BEN were investigated comprehensively. The addition of the nanofillers showed different influence on curing kinetics of BEN. Furthermore, the incorporation of the nanofillers showed good improvement on thermal stability of BEN. An increase of 70 and 336°C at the onset and the half-life decomposition temperature were observed with the addition of 5 wt % 30B clay in nitrogen atmosphere. With the incorporation of 5 wt % POSS, the half-life of decomposition and char yield enhanced by 280°C and 13 wt % in nitrogen atmosphere. For the 4 wt % MWCNT-COOH/BEN nanocomposite, the half-life of decomposition and char yield at 800°C increased by 286°C and 14 wt % in nitrogen atmosphere, respectively

A Computational Framework for Preserving Privacy and Maintaining Utility of Geographically Aggregated Data: A Stochastic Spatial Optimization Approach

Geographically aggregated data are often considered to be safe because information can be published by group as population counts rather than by individual. Identifiable information about individuals can still be disclosed when using such data, however. Conventional methods for protecting privacy, such as data swapping, often lack transparency because they do not quantify the reduction in disclosure risk. Recent methods, such as those based on differential privacy, could significantly compromise data utility by introducing excessive error. We develop a methodological framework to address the issues of privacy protection for geographically aggregated data while preserving data utility. In this framework, individuals at high risk of disclosure are moved to other locations to protect their privacy. Two spatial optimization models are developed to optimize these moves by maximizing privacy protection while maintaining data utility. The first model relocates all at-risk individuals while minimizing the error (hence maximizing the utility). The second model assumes a budget that specifies the maximum error to be introduced and maximizes the number of at-risk individuals being relocated within the error budget. Computational experiments performed on a synthetic population data set of two counties of Ohio indicate that the proposed models are effective and efficient in balancing data utility and privacy protection for real-world applications.</p

Preparation of pristine graphene sheets and large-area/ultrathin graphene films for high conducting and transparent applications

An effective and scalable exfoliation route has been developed to prepare high quality pristine graphene sheets. A remarkable yield of 55 wt % was achieved at a high solvent concentration of 20 mg/mL, with the application of only 1 h ultrasonication in total. The exfoliation process was achieved by synergistic effect of intercalation, self-assemblage, and further expansion. The successful exfoliation was proved by means of X-ray diffraction (XRD) patterns, Raman spectra, transmission electron microscopy (TEM), and scanning electron microscopy (SEM). Furthermore, preparation of large-area and ultrathin pristine graphene films were demonstrated by a facile, rapid, and scalable electrophoretic deposition approach. The pristine graphene sheets which are extremely sensitive to the applied electric field were arrayed in strict order to form the high-quality graphene films. The resultant graphene films exhibit a high electrical conductivity of ∼1 × 105 S/m. Raman spectroscopy analysis reflected bilayer morphology of the graphene film. The simple and rapid processing route and the high transparency and conductivity of the graphene films suggest their potential applications in electrical and optical fields

Effect of carbon nanotubes on the curing dynamics and network formation of cyanate ester resin

The effect of a pristine carbon nanotube (CNT), and three functionalised carbon nanotubes on the curing dynamics and network formation of a cyanate ester resin (CY), was investigated by means of differential scanning calorimetry (DSC), modulated temperature differential scanning calorimetry (MTDSC), field emission gun scanning electron microscopy (FEGSEM), Fourier transform infrared (FTIR) and Raman spectroscopies. Incorporation of the various carbon nanotubes showed different accelerating effects on cure of the CY. Addition of the pristine multi-walled carbon nanotube (MWCNT) did not show a prominent accelerating effect, whilst a carboxyl group functionalised multi-wall nanotube (MWCNT-COOH) displayed the greatest accelerating effect. For a hydroxyl group functionalised multi-walled carbon nanotube (MWCNT-OH)/CY system, the most pronounced accelerating effect was observed when 1 wt% to 2 wt% MWCNT-OH was added. Nano-scale dispersion of both the pristine and the functionalised multi-walled carbon nanotubes in the CY matrix was observed by using FEG-SEM. In contrast, micro-scale aggregation happened in a SWCNT-OH/CY system. The FTIR spectra monitored the formation of triazine rings in the CY and its composites with CNTs. The FTIR results indicated that the CNTs reacted with the cyanate groups of the CY to form oxime C=N-O bonds. The up-shifting of the bands for CNTs in Raman spectra confirmed nano-scale dispersion of MWCNTs in the CY matrix and strong interaction between the MWCNTs and the CY

Plant Interactions Alter the Predictions of Metabolic Scaling Theory

<div><p>Metabolic scaling theory (MST) is an attempt to link physiological processes of individual organisms with macroecology. It predicts a power law relationship with an exponent of −4/3 between mean individual biomass and density during density-dependent mortality (self-thinning). Empirical tests have produced variable results, and the validity of MST is intensely debated. MST focuses on organisms’ internal physiological mechanisms but we hypothesize that ecological interactions can be more important in determining plant mass-density relationships induced by density. We employ an individual-based model of plant stand development that includes three elements: a model of individual plant growth based on MST, different modes of local competition (size-symmetric vs. -asymmetric), and different resource levels. Our model is consistent with the observed variation in the slopes of self-thinning trajectories. Slopes were significantly shallower than −4/3 if competition was size-symmetric. We conclude that when the size of survivors is influenced by strong ecological interactions, these can override predictions of MST, whereas when surviving plants are less affected by interactions, individual-level metabolic processes can scale up to the population level. MST, like thermodynamics or biomechanics, sets limits within which organisms can live and function, but there may be stronger limits determined by ecological interactions. In such cases MST will not be predictive.</p></div