Alexandre Fassini Michels | Universidade de Caxias do Sul (original) (raw)

Papers by Alexandre Fassini Michels

ACS Applied Materials & Interfaces, 2019

Journal of Nanophotonics, 2013

A self-assembled polytetrafluoroethylene (PTFE) nanostructure is deposited on microcrystalline di... more A self-assembled polytetrafluoroethylene (PTFE) nanostructure is deposited on microcrystalline diamond (MCD) films, by use of physical and chemical vapor deposition in a two-step process, to produce (fully) superhydrophobic surfaces: high water contact angle (static, 165 AE 2 deg), very low hysteresis (dynamic, ∼4 deg), and associated sliding angle (1 deg 5 0 AE 15 0), thus combining the diamond infrared transparency and self-cleaning properties. These are interpreted in light of Wenzel and Cassie-Baxter wetting models, associated with structural microscopy of nano-micro rough PTFE/MCD surfaces, and present a promising perspective for self-cleaning infrared optics applications.

Surface and Coatings Technology, 2013

The wet ability of micro and nanocrystalline diamond films (MCD and NCD) coated with PTFE was inv... more The wet ability of micro and nanocrystalline diamond films (MCD and NCD) coated with PTFE was investigated. The diamond films were grown by microwave plasma CVD with and without nitrogen addition. Both surfaces of the diamond films were evaluated by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Apparent, advancing and receding water contact angles (WCA) were measured before and after the PTFE coating. The roughness of the microcrystalline diamond films together with the nanostructured PTFE coating resulted in super hydrophobic surfaces with water contact angle of 165°± 2°and very low hysteresis (4°). For nanocrystalline diamond films, the contact angle was also very high (149°± 2°) but the hysteresis remained above 90°.

AIP Advances

Lateral force microscopy (LFM) is an established technique to assess friction forces at the nanos... more Lateral force microscopy (LFM) is an established technique to assess friction forces at the nanoscale. Nanoindentation followed by unidirectional sliding (NUS) is also used to evaluate friction forces at the micro/nanoscale. However, comparative studies between NUS and LFM evaluating the experimental results at different scales are still missing. In this work, a-C:D/H and a-C:H thin films with different [D]/[C] and [H]/[C] contents were used to analyze the friction forces by NUS and LFM. The results show that the friction behavior assessed by these two techniques in different scales is the same. The correlation between friction forces measured by NUS and LFM depends mainly on a contact area factor that makes invariant the friction force from nanoscale to microscale. Such behavior suggests a similar damping mechanism, probably phonon-coupling phenomena, for the friction force origin.

Optical interferometric monitoring during spin coating (optospinography) of fluid coatings has al... more Optical interferometric monitoring during spin coating (optospinography) of fluid coatings has allowed close observation of their temporal evolution (typically at 700-3000 rpm, 1KHz microcomputer-assisted data acquisition). When the fluids are non-volatile, kinematic viscosity data can be determined using a simple analytical model. Validity of the method was tested with a standard (mineral oil OP20) with nominal kinematic viscosity ν = 37 + 1 cS (temperature fluctuation of + 0.5 o C), for which the optospinography method, combined with Abbe refractometry, provided ν = 36.1 + 0.1 cS (angular speed uncertainty of + 5 rpm). This is an indication that we now have available an absolute, contactless optical viscometry method for thin (thickness less than 10 µm) fluid films in small samples.

Abstract. Optical interferometric monitoring of spin coating (optospinography) has allowed close ... more Abstract. Optical interferometric monitoring of spin coating (optospinography) has allowed close observation of the temporal evolution of a thin silicate sol film (typically at 2000 rpm, 100 Hz data acquisition). The kinematic viscosity data obtained, using a simple analytical model, are validated with those from a mineral oil standard, with agreement well within the experimental uncertainties. For spin coating in open air, the influence of variations in refractive index, rheological properties and air flow are discussed. Inflections in the temporal evolution of the optical thickness of silicate sol films are analyzed, which indicate the usefulness of optospinography, particularly when applied in the proximity of the rotation axis and evaporation is minimized, to monitor time variations in the kinematic viscosity of these sols during spin coating.

Cerâmica

This work presents a study to evaluate the process of producing internal holes in ceramic disks p... more This work presents a study to evaluate the process of producing internal holes in ceramic disks produced by low pressure injection molding (LPIM) process. Two process conditions defined as pre-injection and post-injection were used to test the proposition. In the first one the pin cores that produce the holes were positioned in the cavity before the injection of the feedstock; and in the second one, the pin cores were positioned in the cavity, just after the feeding phase of the injection mold. An experimental injection mold designed and manufactured to test both processes was developed to produce ceramic disk with Ø 50 x 2 mm with four holes of Ø 5 mm, equally and radially distributed through the disk. The feedstock was composed of 86 wt% alumina (Al2O3) and 14 wt% organic vehicle based on paraffin wax. Heating and cooling systems controlled by a data acquisition system were included in the mold. The results showed that there were no welding lines with the post-injection process, p...

Composites Part B: Engineering

Ultra-high molecular weight polyethylene (UHMWPE) is widely used in bearing components. However, ... more Ultra-high molecular weight polyethylene (UHMWPE) is widely used in bearing components. However, in this type of application, wear issues leading to formation of debris in regions near the implant may arise, causing inflammation of the tissue. Due to this, this paper seeks to improve surface properties by the deposition of Ti, Zr and Ta thin films on the surface of UHMWPE by magnetron sputtering. It was possible to define which of the deposited films presented better results. Metallic coatings with thicknesses ranging from 288 to 440 nm showed a significant improvement in wettability, hardness, toughness and roughness. In addition, they showed excellent adhesion strength front to pull-off and nanoscratch tests, and no contaminants in the compositional analyzes performed by Rutherford backscatter spectrometry (RBS). From an electrochemical viewpoint, the order of choice for metal coating over UHMWPE would be Ta, Ti, and Zr, respectively. Overall, these coatings offer an improved surface for biomedical applications, especially when mechanical stresses are required.

Journal of Materials Science

Physical chemistry chemical physics : PCCP, Jan 9, 2018

Hydrogenated amorphous carbon (a-C:H) thin films have a unique combination of properties that are... more Hydrogenated amorphous carbon (a-C:H) thin films have a unique combination of properties that are fundamental in mechanical and electromechanical devices aimed at energy efficiency issues. The literature brings a wealth of information about the ultra-low friction (superlubricity) mechanism in a-C:H thin films. However, there is persistent controversy concerning the physicochemical mechanisms of contact mechanics at the atomic/molecular level and the role of electrical interactions at the sliding interface is still a matter of debate. We find that the hydrogenation of the outermost nanostructured surface atomic layers of a-C:H thin films is proportional to the surface potential and also to the friction forces arising at the sliding interface. A higher hydrogen-to-carbon ratio reduces the surface potential, directly affecting frictional forces by a less effective long-term interaction. The structural ultra-low friction (superlubricity) is attributed to a lower polarizability at the ou...

Recueil des Travaux Chimiques des Pays-Bas

... Soluble dans les solutions de HCI et de Na,S,O,. produit de couleur brun-clair. Pas explosif.... more ... Soluble dans les solutions de HCI et de Na,S,O,. produit de couleur brun-clair. Pas explosif. Solubilite: voir Ie precedent. produit: jaune clair. Sableux, pas explosif. ... Pour cette reaction ( 1 ) des considerations thermodynamiques demon-trent que la reaction est improbable. ...

Proceedings of Spie the International Society For Optical Engineering, 1999

First results are presented of optical interferometric monitoring during dip coating in real time... more First results are presented of optical interferometric monitoring during dip coating in real time, as applied to mineral oil OP10 and multi-component zirconyl chloride aqueous solution films. Resulting new perspectives are considered.

Recueil des Travaux Chimiques des Pays-Bas, 1961

O processo de dip coating é largamente usado na indústria na produção de filmes, cuja espessura é... more O processo de dip coating é largamente usado na indústria na produção de filmes, cuja espessura é geralmente medida com precisão micrométrica por métodos capacitivos. Neste trabalho, são apresentados resultados pioneiros de análise da monitoração óptica do processo, que permite acompanhar, em tempo real, a evolução da espessura de filmes de óleos minerais newtonianos e não-voláteis de distintas viscosidades e velocidades de retirada. O experimento consiste da análise de um feixe de um laser, neste caso com comprimento de onda λ=660 nm, refletido no filme líquido escoando sobre o substrato de vidro. O feixe do laser incide perpendicularmente sobre a amostra. A luz refletida pela amostra é comparada a sinal de referência e depois é processada, a uma taxa de 3, 5 KHz, por um amplificador lock-in e um microcomputador, equipado com um conversor A/D. O adequado alinhamento do sistema óptico, que ilumina uma área pequena (diâmetro < 0,5 µm) da amostra, e um sistema com alta taxa de aquisição são elementos essenciais para que seja possível acompanhar em detalhe o processo do dip coating.Foi considerado um modelo teórico simples, acrescido de uma constante multiplicativa, associada a efeitos de tensão superficial, a qual se mostrou consistente com relatos anteriores. Foi obtida muito boa concordância com os resultados experimentais, após os instantes iniciais do processo, dentro da incerteza experimental de ±0,007 µm. Esta alta precisão possibilita aplicabilidade a filmes líquidos de espessura interferométrica. (PIBIC/CNPq-UFRGS).