Temporal evolution of roughness development on polymer surfaces exposed to non-thermal plasma

Brazilian agencies: CNPq and CAPES/PRINTUFSC, 2019Processes such as ablation, erosion and corrosion generally create roughness patterns on solid surfaces. Despite the randomness of this phenomenon, some patterns can be described mathematically by studying statistically the mechanisms behind them. This paper reports an experimental study on the temporal evolution of the roughness development of polymer surfaces exposed to argon non-thermal plasma under reduced pressure of 5 mbar and 65 W of applied power. The substrates studied were polypropylene, high density polyethylene, polyamide-6 and poly(ether ether)ketone. The mean roughness data as well as the saturation roughness values showed differences between polyolefin and polymers containing heteroatoms and notably the dependence of the etching on the packing density of the polymer chains. The plasma-etched surfaces were described statistically as self-affine surfaces using scaling law analysis, exhibiting roughness exponents of α ca.0.73 ± 0.2 and growth exponents of β ca. 1.0 ± 0.1. The roughness increases and decreases successively during treatment although presenting a general linear behavior in a non-monotonous way, as a function of time. The models for the shadowing and redistribution of active species can be complemented with the transient crosslinking model of the observed flattening stages.publishersversionpublishe

A simple and low-cost method of sulfur functionalization and aqueous dispersion of graphene driven by gas-liquid non-thermal plasma discharge

Graphene is a 2D nanomaterial that has received increasing attention due to its remarkable properties, such as high electric and thermal conductivity and good mechanical properties. The insertion of heteroatoms onto graphene enables the control of various properties of the material, such as dispersion, catalysis and band gap. Among the heteroatoms studied, sulfur is attractive due to its versatility, being part of functional groups that enhance dispersion and enable further modification. Various methods of sulfur functionalization were studied, and non-thermal plasma distinguishes itself due to its energy efficiency, ease of operation, and low heating of the treated material. However, existing non-thermal plasma methods are limited due to the expense of the equipment, energy consumption due to vacuum conditions and limited treated mass.In this work, we present a brand new simple, low-cost method for sulfur functionalization of graphene by argon non-thermal plasma discharged over an aqueous medium containing potassium thiocyanate, operating at ambient pressure and temperature. The modified graphene obtained was analyzed by Raman, XPS, FTIR, zeta potential and thiol quantification. The results showed an increase in graphene dispersion in water caused by the insertion of sulfonic acid and thiol functional groups onto the graphene structure, while maintaining the pristine qualities of the starting material

Non-Thermal Plasma Induced Total Mineralization of Glyphosate in Water in the Presence of Iron II Ions

<div><p>The present work focused on the mineralization of herbicide glyphosate (N-(phosphonomethyl) glycine) (C3H8NO5P) in aqueous phase by Glidarc plasma following the orthophosphates released and the reduction of the total organic carbon (TOC). Furthermore, the effect of initial concentration, pH and the degradation process of glyphosate in the presence of Fe2+ were also examined. The results showed that the efficiency of degradation increased with the presence of ferrous ions as catalysts in aqueous medium and also the release of orthophosphate is more efficient in acid medium with pH range of 3.5-6.3. The kinetics of the release of orthophosphate and the TOC removal obey the first order rate law. The ninhydrin and orthophosphates tests showed that the degradation of glyphosate in water by Glidarc plasma was mainly by OH and NO attacked with C–N and C–P bond cleavage leading to complete mineralization.</p></div