1,720,975 research outputs found
Novel hybrid fluoro-carboxylated copolymers deposited by initiated chemical vapor deposition as protonic membranes
No full textCopolymers of 1H, 1H, 2H, 2H,-perfluorodecyl acrylate and methacrylic acid are synthesized by initiated chemical vapor deposition (iCVD) to serve as proton exchange membranes for potential application in miniaturized fuel cells. The copolymerization of hydrophobic and hydrophilic monomers is difficult by conventional liquid-phase technique. We demonstrate that the use of iCVD is very promising for the synthesis of these membranes. Changing the monomer feed ratio we have a systematical control over the copolymer composition. The calculation of the copolymer ratios shows a moderate alternate composition of the copolymer which is advantageous to obtain highly conductive (acid functionalities) and stable (hydrophobic functionalities) membrane in the operating conditions of the fuel cells. The copolymers show a high degree of chain mobility when passing from dry to hydrated state as demonstrated by XPS analysis and by the high water contact angle hysteresis measured (>30°). An ionic conductivity of 70 mS/cm is obtained in conditions of highest percentage of hydrophobic functionalities. This conductivity value is comparable with the ionic conductivity of commercial Nafion®. © 2012 Elsevier Ltd. All rights reserved
Water entry and fall of hydrophobic and superhydrophobic Teflon spheres
No full textHydrophobic and superhydrophobic solid Teflon spheres have been observed while settling in water under the action of gravity, starting from different initial conditions, and have been followed until the steady-state is reached. The superhydrophobic sphere features a nano/microtextured surface and advancing and receding water contact angles equal to, respectively, [Formula: see text] and [Formula: see text]. When impacting water from air, both spheres can entrap a conspicuous amount of air deriving from the sealing of a macro-sized air cavity formed upon impact (air cavity trapping) and standing at the rear part of the settling sphere. It is shown that this air amount, like a spindle, reduces the force coefficient exerted on the sphere, basically acting on the pressure drag. However, the air cavity trapping occurs above a critical impact velocity which for the superhydrophobic spheres is significantly lower than that pertaining to the hydrophobic one; thus a certain range of impact velocities exists at which the superhydrophobic sphere experiences a lower pressure drag and a higher mean velocity. As soon as the air cavity vanishes, the dynamics of the superhydrophobic sphere becomes indistinguishable from that of the hydrophobic one, in spite of the persistence of air within the surface micro-texture
Surface and bulk hydrophobic cement composites by tyre rubber addition
Full text linkRubber addition increases porosity, nevertheless it can hinder liquid water entrance.
Abstract
Penetration of water in cement composites, porous and hydrophilic materials, is cause of progressive deterioration and failure. Standard procedures for protecting building structures generally involve uniquely the modification of the surface by coating or impregnation procedures.
In this work, the addition of tyre rubber (TR) to the cement paste is demonstrated to be effective for developing mortars with a pronounced hydrophobic behavior in every part of their structure. Hydrophobic performances are better in the case of finer TR grains size and for larger TR volume addition. TR mortars show higher porosity than the conventional ones, nevertheless the effect of the low rubber surface energy prevails, and the absorption of water drops is almost completely abated. These lightweight materials result to be very competitive for non-structural applications and are in agreement with the environmentally sustainable policies finalized to convert a synthetic waste to an engineering resourc
On the “growth” of nano-structures on c-silicon in self-masked plasma etching processes.
No full textPlasma etching is emerging as reliable top-down self-masked approach for nanotexturing on a
wafer-scale the surface of crystalline silicon. Differently sized and shaped nano-bumps can be
obtained as a function of plasma parameters and, accordingly, different optical and
optoelectronic effects have been already reported. In this work, we utilize a combination of
techniques such as transmission electron microscopy, X-ray photoelectron spectroscopy, field
emission gun scanning electron microscopy, in order to enlighten on structure, composition,
and topography of these nano-objects. The results indicate that they present a composite
structure, with a crystalline conic base and an amorphous
extension with inclusion of metallic nano-crystals. These
and other evidences suggest that the structures are partly
formed by the sculpting action typically ascribed to the
etching process, partly due to a deposition of amorphous
composite matter, likely aggregated by a catalytic action of
the metal particles
Water absorption in rubber-cement composites: 3D structure investigation by X-ray computed-tomography
No full textPlasma Nanostructuring of Polymers: Different Routes to Superhydrophobicity
No full textIn this paper, we review different plasma processes developed in our laboratory to obtain nanostructured superhydrophobic polymer surfaces. All methods consist of a single step and lead to functional materials which combine a fluorinated chemistry with unique surface
morphologies. The transition from sticky to slippery
superhydrophobicity, crucial for several applications ranging from microfluidics to outdoor self-cleaning surfaces, is found by properly
tuning process parameters. Methods are compared
in terms of process time-scale and compatibility
to different substrates
Tuning the Acid/Base Surface Character of Carbonaceous Materials by Means of Cold Plasma Treatments
No full textCarbonaceous materials, in the form of flat graphite slabs and carbon black granules, are surface-modified in radio frequency (RF, 13.56 MHz) glow discharges fed with NH3/O-2 mixtures at different power values, in order to graft oxygen-containing and/or nitrogen-containing chemical groups. In this way, it is possible to adjust the acid/base character of the material surfaces in a predictable way, as a function of the feed composition and of the power. A plasma reactor equipped with a rotating vacuum chamber and internal glass wings is used to keep the granular materials homogeneously stirred and to modify the surface of both graphite slabs and carbon black granules. The chemical modifications have been evaluated using X-ray photoelectron spectroscopy. Water contact angle measurements have been carried out on flat graphite, with water solutions at different pH, in order to study the acid/base character imparted to the functionalized surface. Scanning electron microscopy analysis has been performed to check the effects of plasma treatments on the morphology of the substrates
Soft matter laser micro-texturing for friction reduction: An experimental investigation
No full textIn this paper, a femtosecond laser manufacturing process is effectively employed to produce a pattern of micro dimples on a fluoroelastomer. To quantify the microtexture tribological performance, two configurations are implemented: non-conformal and conformal contacts are tested on a pin-on-disk tribometer. Due to the reduced number of dimples engaged in the contact region, no significant friction enhancement is obtained in the non-conformal configuration. On the contrary, in the case of conformal contacts, outstanding outcomes in terms of friction reduction - up to 60% - can be achieved by a properly designed micro-texture. Such a result is obtained by improving the wear debris entrapment and the cavitation respectively at low and high speed, without increasing significantly the occurrence of flow eddies
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