Jason Robert Tavares

Synthesis of cubic-structured monocrystalline titanium nitride nanoparticles by means of a dual plasma process

Titanium nitride has long been used for its favourable mechanical and chemical properties and it has been demonstrated that monocrystallinity in thin films enhances these properties. While the synthesis of monocrystalline thin films is well documented, common synthesis processes for titanium nitride nanoparticles yield only polycrystalline, spherically shaped powders. The process presented here allows for the synthesis of monocrystalline, cube-shaped nanoparticles by means of a dual plasma process. Pulsed electric arc erosion of a Ti cathode in a N-rich atmosphere produced by a radio-frequency discharge is used for the synthesis of the TiN nanoparticles. Electron microscopy revealed the cubic morphology of the synthesized powders and electron diffraction patterning confirmed the crystalline structure of the TiN nanoparticles.

Improved Dual-Plasma Process for the Synthesis of Coated or Functionalized Metal Nanoparticles

An improved dual-plasma process for the synthesis of nonagglomerated, organic layer-coated metal nanoparticles is presented. Nanoparticle synthesis is achieved by means of pulsed arc erosion of a copper cathode. Particles are coated in-flight through RF plasma polymerization of ethane. The axially symmetric geometry takes advantage of the initial nanoparticle trajectories and charging effects within the RF plasma, thus enhancing particle collection efficiency.

Charge effect of superparamagnetic iron oxide nanoparticles on their surface functionalization by photo-initiated chemical vapour deposition

Diverse applications of superparamagnetic iron oxide nanoparticles (SPIONs) in the chemical and biomedical industry depend on their surface properties. In this paper, we investigate the effect of initial surface charge (bare, positively and negatively charged SPIONs) on the resulting physicochemical properties of the particles following treatment through photo-initiated chemical vapour deposition (PICVD). Transmission electron microscopy shows a nanometric polymer coating on the SPIONs and contact angle measurements with water demonstrate that their surface became non-polar following functionalization using PICVD. FTIR and XPS data confirm the change in the chemical composition of the treated SPIONs. Indeed, XPS data reveal an initial charge-dependent increase in the surface oxygen content in the case of treated SPIONs. The O/C percentage ratios of the bare SPIONs increase from 1.7 to 1.9 after PICVD treatment, and decrease from 1.7 to 0.7 in the case of negatively charged SPIONs. The ratio remains unchanged for positively charged SPIONs (1.7). This indicates that bare and negatively charged SPIONs showed opposite preference for the oxygen or carbon attachment to their surface during their surface treatment. These results reveal that both the surface charge and stereochemical effects have determinant roles in the polymeric coating of SPIONs with PICVD. Our findings suggest that this technique is appropriate for the treatment of nanoparticles.Graphical Abstract

Photo initiated chemical vapour deposition to increase polymer hydrophobicity

Apple growers face new challenges to produce organic apples and now many cover orchards with high-density polyethylene (HDPE) nets to exclude insects, rather than spraying insecticides. However, rainwater- associated wetness favours the development of apple scabs, Venturia inaequalis, whose lesions accumulate on the leaves and fruit causing unsightly spots. Treating the nets with a superhydrophobic coating should reduce the amount of water that passes through the net. Here we treat HDPE and polyethylene terephthalate using photo-initiated chemical vapour deposition (PICVD). We placed polymer samples in a quartz tube and passed a mixture of H2 and CO through it while a UVC lamp (254 nm) illuminated the surface. After the treatment, the contact angle between water droplets and the surface increased by an average of 20°. The contact angle of samples placed 70 cm from the entrance of the tube was higher than those at 45 cm and 20 cm. The PICVD-treated HDPE achieved a contact angle of 124°. Nets spray coated with a solvent-based commercial product achieved 180° but water ingress was, surprisingly, higher than that for nets with a lower contact angle.

Large-Scale Plasma Waste Gasification

The plasma resource recovery system is a two-stage plasma gasification and vitrification system used to process municipal solid waste. A transferred arc discharge is used to generate syngas from the waste, and an air plasma torch is used to polish the gasification products. Online syngas monitoring can be employed to compensate for variations in waste feed, thus maintaining both the syngas composition (quality) and production rate.

Rheological behavior of cellulose nanocrystal suspensions in polyethylene glycol

The rheological behavior of cellulose nanocrystals (CNCs) in polar media based on polyethylene glycol (PEG) was investigated from aqueous suspensions to nanocomposites. The aim of this work is to improve our knowledge on the CNC behavior in polymer media and develop rheological indices to characterize the dispersion of nanoparticles in polymer matrices. CNCs were obtained from sulfuric acid hydrolysis of wood pulp and supplied after a spray- or freeze-drying process. Ultrasonication was used to break agglomerates and disperse CNCs in aqueous suspensions before mixing with an aqueous PEG solution at room temperature. The samples were subsequently dried and compression molded. From capillary and oscillatory shear rheology, no adsorption of PEG chains on CNCs could be detected, as many had previously hypothesized. The increase of PEG concentration in aqueous suspension favored the gelation by depletion effect and suggested CNC orientation. Viscoelastic properties and transmission electronic images of PEG/CNC nanocomposites highlighted the formation of a percolated network of CNCs for low concentrations ≥ 0.15 vol. %. From the model of Shih et al., a fractal dimension of 2 was obtained for these percolated nanocomposites, suggesting a 2D network of CNCs in the PEG matrix.

Ultrasonication of spray- and freeze-dried cellulose nanocrystals in water

The structural and rheological properties of aqueous suspensions of spray-dried cellulose nanocrystals (CNCs) were investigated and compared to those of freeze-dried. The cellulose nanocrystals were obtained from sulfuric acid hydrolysis of wood pulp. Ultrasonication was used to disperse cellulose nanocrystals in Milli-Q water and the power applied during ultrasonication was shown to be the controlling parameter for their dispersion, more than total energy. Dynamic light scattering measurements showed a decrease of the average hydrodynamic diameter down to the same limiting value, i.e. ∼75 nm, for both spray and freeze-dried cellulose nanocrystals. Since the same maximum dispersion state was reached for both CNC types, it indicated that the spray drying process did not limit dispersion, provided that sufficient ultrasonication was provided. Moreover, no desulfation occurred during ultrasonication at ambient temperature. Strong ultrasonication also caused a decrease of intrinsic viscosity, along with an increase in maximum packing concentration. These properties were correlated to agglomerates break-up, which released both ions and water in suspension. The ionic strength increase may lead to a thinner electrostatic double layer surrounding the cellulose nanocrystals, reducing their apparent concentration.

The structural amphiphilicity of cellulose nanocrystals characterized from their cohesion parameters

Cellulose nanocrystals (CNCs), usually considered as isotropically polar nanoparticles, are sheet-like crystalline assemblies of cellulose chains. Here, we link the anisotropy of the CNC structure to an amphiphilic behavior in suspension. The Hansen solubility parameters (HSP: δD;δP;δH) of wood-based H2SO4-hydrolyzed CNCs were measured from sedimentation tests in a wide set of 59 solvents and binary mixtures. Two sets of cohesion parameters corresponding to a polar surface (18.1; 20.4; 15.3) ± (0.5; 0.5; 0.4) MPa1/2 and to a mildly non-polar one (17.4; 4.8; 6.5) ± (0.3; 0.5; 0.6) MPa1/2 were determined, with respective solubility radii of 7.8 and 2.1 MPa1/2. The polar sphere is thought to correspond to the (110) & (11¯0) surfaces of cellulose Iβ nanocrystals, while the smaller non-polar sphere is coherent with the exposure of (200) surfaces. The HSP graph provides new insights on the amphiphilic nature of CNCs and a mapping of their chemical affinity for solvents and polymer matrices.

Surface engineering of wood substrates to impart barrier properties: a photochemical approach

In this study, sugar maple and white pine, two species of wood commonly used in indoor and outdoor applications, were treated by photo-initiated chemical vapor deposition to impart barrier properties. After treatment, wood wettability decreased significantly, as evidenced by water contact angle measurements (from 50° to 113° for sugar maple and 87° to 172° for white pine). Further, beyond being able to repel water, the coating shows the ability to breathe, evidenced by standardized vapor sorption tests. However, accelerated weathering via ASTM G155 testing determined that the treatment could not protect the wood from photo-degradation, or retain its properties post-weathering. This treatment could therefore be best suited for wood pre-treatment in combination with other coatings.

Large-Scale Encapsulation of Magnetic Iron Oxide Nanoparticles via Syngas Photo-Initiated Chemical Vapor Deposition

Photo-initiated chemical vapor deposition (PICVD) has been adapted for use in a jet-assisted fluidized bed configuration, allowing for the encapsulation of magnetic iron oxide nanoparticles on a larger scale than ever reported (5 g). This new methodology leads to a functional coating with a thickness of 1.4–10 nm, confirmed by HRTEM and TGA. XPS and TOF-SIMS characterization confirm that the coating is composed of both aliphatic and polymerized carbon chains, with incorporated organometallic bonds and oxygen-containing moieties. UV-Vis absorbance spectra show that the coating improved dispersion in non-polar solvents, such as n-dodecane. This process represents a first step towards the large-scale, solvent-free post-synthesis processing of nanoparticles to impart a functional coating.