Maurizio Sansotera

Hydrophobic carbonaceous materials obtained by covalent bonding of perfluorocarbon and perfluoropolyether chains

Perfluorocarbon residues, i.e. perfluoroethyl (PFE), CF3CF2–, perfluoro-n-propyl (PFnP), CF3CF2CF2–, perfluoro-isopropyl (PFiP), (CF3)2CF–, and perfluoropolyether (PFPE) chains, e.g. (CF2CF2O)m(CF2O)n, were covalently bonded on the surface of carbon black (CB) and diamond-like carbon (DLC) using PFPE and perfluorodiacyl (PFDA) peroxides. The thermal decomposition of the peroxidic moieties of these perfluorinated peroxides generated reactive perfluorinated radicals. The perfluorinated free radicals could directly bond to the sp2 sites avoiding any spacer, which usually decreases both thermal and chemical stabilities of the resulting materials. The effects of chemical treatment on the carbonaceous materials were studied using X-ray Photoelectron Spectroscopy (XPS), Scanning Electron Microscopy (SEM) and Contact Angle (CA) measurements. The surface areas of CB powders were determined by the BET technique; the morphology of the DLC coatings was evaluated by Atomic Force Microscopy (AFM) and the friction forces were measured by means of Lateral Force Microscopy (LFM).

Italian WEEE management system and treatment of end-of-life cooling and freezing equipments for CFCs removal

This study presents and analyzes the data of the Italian system for take-back and recovery of waste electrical and electronic equipments (WEEEs) in the start-up period 2008-2010. The analysis was focused particularly on the data about the treatment of end-of-life cooling and freezing equipments. In fact, the wastes of cooling and freezing equipments have a high environmental impact. Indeed, in their compressor oil and insulation polyurethane (PU) foams chlorofluorocarbon (CFC) ozone-depleting gases are still present. In the period 2001-2004 Northern Italy resulted the main source in Europe of CFCs. The European Directive on WEEE management was enacted in 2002, but in Italy it was implemented by the legislative Decree in 2005 and it became operational in 2008. Actually, in 2008 the national WEEE Coordination Centre was founded in order to organize the WEEE pick-up process and to control collection, recovery and recycling targets. As a result, in 2010 the average WEEE collection per capita exceeded the threshold of more than 4 kg per inhabitant, as well as cooling and freezing appliances represented more than one fourth of the Italian WEEE collection stream. During the treatment of end-of-life cooling and freezing equipments, CFCs were recovered and disposed principally by burner methods. The analyses of defined specimens collected in the treatment facilities were standardized to reliably determine the amount of recovered CFCs. Samples of alkaline solid salt, alkaline saline solution, polyurethane matrix and compressor oil collected during the audit assessment procedure were analyzed and the results were discussed. In particular, the analysis of PU samples after the shredding and the warm pressing procedures measured a residual CFCs content around 500-1300 mg/kg of CFCs within the foam matrix.

Micromanufacturing in Fused Silica via Femtosecond Laser Irradiation Followed by Gas-Phase Chemical Etching

Femtosecond laser irradiation followed by chemical etching (FLICE) with hydrogen fluoride (HF) is an emerging technique for the fabrication of directly buried, three-dimensional microfluidic channels in silica. The procedure, as described in literature, consists of irradiating a silica slab followed by chemical etching using hydrogen fluoride. With aqueous HF the etching process is diffusion-limited and is self-terminating, leading to maximum microchannel lengths of about 1.5 mm, while the use of low-pressure gaseous HF etchant can quickly produce 3 mm long channels with an aspect ratio (Length/Diameter) higher than 25. By utilizing this methodology the aspect ratio is not constant, but depends on the length of the channel. When the microchannel is short the aspect ratio increases quickly until it reaches a maximum length at around 1400 µm. Thereafter the aspect ratio starts to decrease slowly. In this paper we present a variation of the low-pressure gaseous HF etching method, which is based on the dynamic displacement of the etchant. This method results in a 13% increase in the aspect ratio (L/D = 29) at the expense of a low etching speed (4 µm/min).

Comparison of Branched and Linear Perfluoropolyether Chains Functionalization on Hydrophobic, Morphological and Conductive Properties of Multi-Walled Carbon Nanotubes

The functionalization of multi-walled carbon nanotubes (MW-CNTs) was obtained by generating reactive perfluoropolyether (PFPE) radicals that can covalently bond to MW-CNTs’ surface. Branched and linear PFPE peroxides with equivalent molecular weights of 1275 and 1200 amu, respectively, have been thermally decomposed for the production of PFPE radicals. The functionalization with PFPE chains has changed the wettability of MW-CNTs, which switched their behavior from hydrophilic to super-hydrophobic. The low surface energy properties of PFPEs have been transferred to MW-CNTs surface and branched units with trifluoromethyl groups, CF3, have conferred higher hydrophobicity than linear units. Porosimetry discriminated the effects of PFPE functionalization on meso-porosity and macro-porosity. It has been observed that reactive sites located in MW-CNTs mesopores have been intensively functionalized by branched PFPE peroxide due to its low average molecular weight. Conductivity measurements at different applied pressures have showed that the covalent linkage of PFPE chains, branched as well as linear, weakly modified the electrical conductivity of MW-CNTs. The decomposed portions of PFPE residues, the PFPE chains bonded on carbon nanotubes, and the PFPE fluids obtained by homo-coupling side-reactions were evaluated by mass balances. PFPE-modified MW-CNTs have been characterized by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), thermogravimetric analysis (TGA), static contact angle (SCA), surface area, and porosity measurements.

Perfluoropolyether-Functionalized Carbon-Based Materials and Their Applications

In the last decade, several carbon-based materials have been covalently functionalized with perfluoropolyethers (PFPEs) moieties, and the properties of these PFPE-functionalized materials have been characterized to outline their possible applications. PFPE fluids are perfluorinated polymeric compounds which exhibit exceptional thermooxidative stability and chemical resistance, high gas permeability, low surface energy, good lubricity characteristics, and extended bioinertness. The covalent functionalization with PFPE chains modified the carbon-based materials and some of the typical properties of PFPEs, such as low surface energy and high gas permeability, were conferred to the functionalized surface. In addition, PFPE-functionalized materials remained thermally and chemically resistant, thanks to the stability of both starting materials. On the basis of these features, several applications of PFPE-functionalized carbon-based materials have been developed in the field of electrochemical devices such as fuel cells and lithium batteries, in self-lubricating surfaces and polymer formulation. Other applications in the field of separation techniques are based on the fluorous effect ascribable to PFPE chains.

Chapter 7:The Role of Perfluoropolyethers in the Development of Polymeric Proton Exchange Membrane Fuel Cells

In the field of renewable energy, proton exchange membrane fuel cells (PEMFCs) are the devices that have most benefited from the unique characteristics of fluorinated materials. Fluorinated polymers are present in many parts of the cell, such as the membrane, the catalytic layers and the gas diffusion layers (GDLs). In particular, GDLs promote the distribution of the gaseous reagents from the bipolar plates to the catalyst layer and regulate the correct water management that is necessary to avoid drying of the membrane and accumulation of liquid water inside the cell. Therefore, the conductive carbonaceous materials composing GDLs are usually treated with a hydrophobic material. An innovative methodology to confer stable hydrophobicity on carbonaceous materials involves the use of perfluoropolyethers (PFPEs). PFPEs can either be deposited as a neutral or functional polymer on the surface of carbonaceous materials or linked by thermal treatment with PFPE peroxide. PFPE chains have the typical properties of perfluorinated polymers, such as chemical stability, thermal stability and high hydrophobicity, but also some peculiar features such as a liquid physical form and high gas permeability. The application of PFPEs can be exploited in order to develop conductive hydrophobic composite materials with high performance in PEMFCs.