I. Sandu

The influence of gravity on the distribution of the deposit formed onto a substrate by sessile, hanging, and sandwiched hanging drop evaporation

The focus of the present article is the study of the influence of gravity on the particle deposition profiles on a solid substrate during the evaporation of sessile, hanging and sandwiched hanging drops of colloidal particle suspensions. For concentrations of nanoparticles in the colloidal solutions in the range 0.0001-1 wt.%, highly diluted suspensions will preferentially form rings while concentrated suspensions will preferentially form spots in both sessile and hanging drop evaporation. For intermediary concentrations, the particle deposition profiles will depend on the nanoparticle aggregation dynamics in the suspension during the evaporation process, gravity and on the detailed evaporation geometry. The evaporation of a drop of toluene/carbon nanoparticle suspension hanging from a pendant water drop will leave on the substrate a circular spot with no visible external ring. By contrast, a clear external ring is formed on the substrate by the sessile evaporation of a similar drop of suspension sandwiched between a water drop and the substrate. From the application viewpoint, these processes can be used to create preferential electrical conductive carbon networks and contacts for arrays of self-assembled nanostructures fabricated on solid substrates as well as on flexible polymeric substrates.

Voltage and Temperature Coefficients of Resistance of Polyethylene/ Nanocarbon-Based Thick Film Composites: Melt-Mixing Versus Melt-Infiltration Synthesis

Carbon-composed resistors, thick film resistors, and chip resistors are commonly used in Electronics. They are prepared by mixing carbon-based materials with metal oxides or polymers and present not only some clear advantages such as low cost and easy processing, but also some unwanted characteristics such as voltage and temperature dependence of the electrical properties. Considering that the polymer-carbon mixing process induces high values for the voltage and temperature resistance coefficients (VCR, TCR) of the composites, we have developed a new method for preparing polymer/nanocarbon thick films (the melt-infiltration method) which minimizes these values. Direct current electrical measurements show VCR values of almost two orders of magnitude lower for polyethylene/nanocarbon thick film composites prepared by melt-infiltration than for composites prepared by melt-mixing (—0.04%/V and —2.5%/V, respectively).

Nanocarbon Film as a Percolation Network for Nanocarbon/Polymer Composites

Starting with a nanocarbon film, which has some special characteristics, the present study uses this film as a cluster of connected particles that induces the percolation of electrical carrier in composites. The composite is formed through the free infiltration of the polymer through the filler’s aggregates. This method forms nanocarbon/polymer composites which have an electrical conductivity more than three orders of magnitude greater than those prepared by mixing.

Carbon nanostructures by gas-phase laser pyrolysis

Carbon-made materials have been the field of major discoveries with the identification of new phases, which have stimulated a huge effort to understand their properties. Laser pyrolysis of hydrocarbons is based on a high temperature C/H/O/... system of well-established composition and allows obtaining carbon nanostructures from the almost amorphous carbon and particles with a turbostratic structure up to those characterized by a high degree of curvature. The variation of the gas composition and experimental parameters controls the final particle morphology providing useful functional properties. Gas-phase hydrocarbons were used either in resonant or non-resonant laser pyrolysis processes. The formation of different nanostructures is related to the presence of heteroatom in the reactants. Focusing, in the context of necessary presence of this heteroatom in the gas composition, on the present questions concerning the rational synthesis of nanostructures with controlled dimensionality, size and potentially properties, the work presents some significant changes in soot morphology produced by the variation of the experimental parameters and these, sometimes unavoidable, heterogeneous atoms.