Sputtering onto liquids: how does the liquid viscosity affect the formation of nanoparticles and metal films?

This paper reports on the effect of the solvent viscosity on the formation of gold nanoparticles (Au NPs) during the sputtering onto liquid (SoL) process. All other parameters related to the plasma and the host liquid are kept constant. SoL is a simple highly reproducible approach for the preparation of colloidal dispersions of small naked NPs. The properties of the final product are determined by both the sputtering parameters and the host liquid characteristics. As a model system we chose to sputter a gold target by a direct-current magnetron discharge onto a line of polymerized rapeseed oils having similar surface tension (32.6-33.1 mJ m-2 at RT). It was found that well-dispersed Au NPs grow in the bulk solution of oils with low viscosities (below 630 cP at 25 °C), while a gold film forms onto the surface of high viscosity liquids (more than 1000 cP at 25 °C). The mean diameter of the individual Au NPs is in the range of about 2.1-2.5 nm according to transmission electron microscopy.

Microwave Atmospheric Plasma: A Versatile and Fast Way to Confer Antimicrobial Activity toward Direct Chitosan Immobilization onto Poly(lactic acid) Substrate.

In this study, a simple method to immobilize chitosan on a poly(lactic acid) (PLA) surface was developed in a fast manner. The immobilization was realized in two steps. First, an atmospheric plasma (MWAP) torch was used to modify the PLA surface in less than 5 min in order to create enough activated sites toward the chitosan adhesion, followed by a direct dip coating to spread and immobilize chitosan on this MWAP-modified PLA surface. The modification of the PLA surface properties was confirmed by X-ray photoelectron spectroscopy (XPS), water contact angle, and atomic force microscopy. It resulted that the activated species derived from the plasma torch, i.e., hydroxyl and carboxylic acid moieties, enabled an increase of the hydrophilicity of the PLA surface. Interestingly, this activated surface allows a good spreading of chitosan solution from dip coating and leads to a homogeneous stable coating. Our XPS results bring us the hypothesis that the stabilization of the chitosan layer is mainly induced by noncovalent interactions such as hydrogen bonding and electrostatic interactions. A first insight into the biological properties of theses surfaces was assessed in terms of the antimicrobial activity of the here-designed surfaces.

Simple method for gas temperature determination in CO2-containing discharges.

A simple gas temperature determination method based on the line ratio between two rotational peaks from the CO Angstrom rotational emission band is reported. A formula based on CO spectral synthesis provides a way for temperature control in plasmas containing CO molecules. This approach is validated in a CO2 flowing gas surfaguide microwave discharge operating at 2.45 GHz. The gas temperature results are compared with the ones obtained using a Boltzmann plot approach, as well as using direct comparison of measured and calculated rotational spectra of the same rotational band.

Functionalization of MWCNTs with atomic nitrogen.

In this study of the changes induced by exposing MWCNTs to a nitrogen plasma, it was found by HRTEM that the atomic nitrogen exposure does not significantly etch the surface of the carbon nanotube (CNT). Nevertheless, the atomic nitrogen generated by a microwave plasma effectively grafts amine, nitrile, amide, and oxime groups onto the CNT surface, as observed by XPS, altering the density of valence electronic states, as seen in UPS.