Constantinos A. Charitidis

Plasma micro-nanotextured, scratch, water and hexadecane resistant, superhydrophobic, and superamphiphobic polymeric surfaces with perfluorinated monolayers.

Superhydrophobic and superamphiphobic toward superoleophobic polymeric surfaces of polymethyl methacrylate (PMMA), polyether ether ketone (PEEK), and polydimethyl siloxane (PDMS) are fabricated in a two-step process: (1) plasma texturing (i.e., ion-enhanced plasma etching with simultaneous roughening), with varying plasma chemistry depending on the polymer, and subsequently (2) grafting of self-assembled perfluorododecyltrichlorosilane monolayers (SAMs). Depending on the absence or not of an etch mask (i.e., colloidal microparticle self-assembly on it), random or ordered hierarchical micro-nanotexturing can be obtained. We demonstrate that stable organic monolayers can be grafted onto all these textured polymeric surfaces. After the monolayer deposition, the initially hydrophilic polymeric surfaces become superamphiphobic with static contact angles for water and oils>153°, for hexadecane>142°, and hysteresis<10° for all surfaces. This approach thus provides a simple and generic method to obtain superamphiphobicity on polymers toward superoleophobicity. Hydrolytic and hexadecane immersion tests prove that superamphiphobicity is stable for more than 14 days. We also perform nanoscratch and post nanoscratch tests to prove the scratch resistance of both the texture and the SAM and demonstrate lower coefficient of friction of the SAM compared to the uncoated surface. Scanning electron microscope observation after the nanoscratch tests confirms the scratch resistance of the surfaces.

Surface functionalization of carbon fibers with active screen plasma

The active screen plasma technology was used to functionalize carbon fibers and vitreous carbon disks. The plasma treatment conditions were mapped using optical emission spectroscopy and the functionalized surfaces were analyzed using scanning electron microscopy and atomic force microscopy, x-ray photoelectron spectroscopy, and contact angle measurements. A relationship was found between the active species in the plasma and the functional groups attached to the carbon surfaces, which provides valuable information for the optimization of the active screen plasma treatment. Moreover, the surface analyses were repeated over a period of 28 days to study the aging of the functionalized surfaces in air. The hydrophobic recovery was modeled using a surface restructuring theory which revealed a mean lifetime of 3.4 days for the functional groups.

Nanomechanical Properties and Deformation Mechanism in Metals, Oxides and Alloys

Metals, oxides and alloys are widely used in transport and industry-engineering applications, due to their functionality. In this work, the nanomechanical properties (namely hardness and elastic modulus) and nanoscale deformation of metals, oxides and alloys (elastic and plastic deformation at certain applied loads) are investigated, together with pile-up/sink-in deformation mechanism analysis, subjected to identical condition parameters, by a combined Nanoindenter—Scanning Probe Microscope system. The study of discrete events including the onset of dislocation plasticity is recorded during the nanoindentation test (extraction of high-resolution load–displacement data). A yield-type pop-in occurs upon low applied load representing the start of phase transformation, monitored through a gradual slope change in the load–displacement curve. The ratio of surface hardness to hardness in bulk is investigated, revealing a clear higher surface hardness than bulk for magnesium alloys, whereas lower surface hardness than bulk for aluminium alloys; for metals and oxides, the behavior varied. The deviation from the case of Young’s modulus being equal to reduced modulus is analyzed, for all three categories of materials, along with pile-up/sink in deformation mechanism. Evidence of indentation size effect is found and quantified for all three categories of materials.

Carbon nanofibers functionalized with active screen plasma-deposited metal nanoparticles for electrical energy storage devices

Supercapacitors are energy storage devices with higher energy densities than conventional capacitors but lower than batteries or fuel cells. There is a strong interest in increasing the volumetric and gravimetric capacitance of these devices to meet the growing demands of the electrical and electronic sectors. The capacitance depends largely on the electrode material, and carbon nanofibers (CNFs) have attracted much attention because of their relatively low cost, large surface area, and good electrical conductivity as well as chemical and thermal stability. The deposition of metal nanoparticles on CNFs is a promising way to increase their surface properties and, ultimately, the capacitance of the devices. In this study, nickel and silver nanoparticles were deposited on CNFs using the active screen plasma technology. The CNFs were characterized, and their electrochemical performance was assessed in a three-electrode cell. The results show significant improvements over the untreated CNFs, particularly after functionalization with silver nanoparticles.