Alexandre F. Michels

Micro and Nano-Texturization of Intermetallic Oxide Alloys by a Single Anodization Step: Preparation of Artificial Self-Cleaning Surfaces

Micro- and nanostructures of Ti-γCu (γ = 0, 30, 50, 70, and 100 wt %) intermetallic alloys were produced through a single anodization step. It was found that the original alloy composition influences the final oxide morphology obtained after anodization which presented formation of a microstructure with nanotubes, nanoparticles or nanopillars on the surface. Pure Ti and Cu oxide metals and their alloys presented hydrophilic or superhydrophilic properties immediately after anodization. When the anodized pure metal and/or Ti-γCu surfaces were functionalized with trimethoxypropylsilane (TPMSi), by dipping and coating with a thin perfluorinated layer, the treated substrates became in all cases superhydrophobic (water contact angles in the range of 152-166°), showing excellent self-cleaning properties with hysteresis below 3°. These results can be explained by a combination of nanomicro morphologies with low surface energy compounds in the topmost monolayers. The decrease in hysteresis was associated with a higher M-OH bond concentration on the anodized surfaces, which allowed for more complete TMPSi coating coverage. This study also indicates that easy and effective fabrication of superhydrophobic surfaces in pure metals and alloys is possible without involving traditional multistep processes.

Interferometric monitoring of dip coating

Dip-coated films, which are widely used in the coating industry, are usually measured by capacitive methods with micrometric precision. For the first time to our knowledge, we have applied an interferometric determination of the evolution of thickness in real time to nonvolatile Newtonian mineral oils with several viscosities and distinct dip withdrawing speeds. The evolution of film thickness during the process depends on time as t(-1/2), in accordance with a simple model. Comparison with measured results with an uncertainty of +/- 0.007 microm) showed good agreement after the initial steps of the process had been completed.

Optically monitored dip coating as a contactless viscometry method for liquid films

Real-time interferometric monitoring of the dip coating process is applied to the study of properties of flowing liquids. Nonvolatile Newtonian oils are considered, allowing validity of a simple model after the steady state is reached where film physical thickness depends on time as t(-1/2). Measurement of two distinct mineral oil standards, under several withdrawing speeds, resulted in kinematic viscosities of 1.17+/-0.03 and 9.9+/-0.2 S (1S = 1 cm2/s). Agreement of these results with nominal values from the manufacturer suggests that interferometric monitoring of dip coating may become a valuable method for accurate, contactless viscometry of liquid films. Advantages and present limitations are discussed.

Double optical monitoring of dip coating with a time-varying refractive index

A brief overview of optical monitoring for vacuum and wet-bench film-deposition processes is presented. Interferometric and polarimetric measurements are combined with regard to simultaneous monitoring of refractive index and physical thickness in real time. Monitoring stability and accuracy are verified during dip coating with a transparent oil standard. This double optical technique is applied to dip coating with a multicomponent zirconyl chloride aqueous solution, whose resulting temporal refractive-index and physical-thickness curves indicate good reproducibility as well as significant sensitivity to changes of film-flow properties during the dip-coating process.

Optical Viscometry of Spinning Sol Coatings

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.

Analysis of dip coating processing parameters by double optical monitoring

Double optical monitoring is applied to determine the influence of main process parameters on the formation of sulfated zirconia and self-assembled mesoporous silica solgel films by dip coating. In addition, we analyze, for the first time to the best of our knowledge, the influence of withdrawal speed, temperature, and relative humidity on refractive-index and physical thickness variations (uncertainties of +/-0.005 and +/-7 nm) during the process. Results provide insight into controlled production of single and multilayer films from complex fluids by dip coating.

Real-time interferometric monitoring of dip coating

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.

Real-time interferometric analysis of spinning liquid films

Optical interferometric monitoring of spin coating (optospinography) has allowed close observation of a thin liquid film temporal evolution (at 500 -2500 rpm, 100 Hz data acquisition), from which its kinematic viscosity can be determined. The data obtained from this procedure is in good agreement with known values for two oil standards, indicating that the method is valid in the range of approx. 0.4 to 150 Stokes. Advantages and limitations are discussed.

High Infrared Transmittance, Superhydrophobic Coatings

Surface structures, using PTFE self-assembly and silica nanoparticle aggregates much smaller than infrared wavelengths, have allowed both self-cleaning and graded-index antireflection. Examples are shown on glass and on microcrystalline diamond.

Nano-microstructured, superhydrophobic, and near-infrared antireflective thin films on glass

Superhydrophobic surfaces were produced on glass with self-cleaning and wide-angle anti-reflection in the near-infrared (1.0-2.1μm). These properties resulted from a combination of surface energy and nano/micro-structured topology based on silica nanoparticles (NPs), index grading and interference. In a two-layer approach (glass/silica NPs/PTFE), a water contact angle (WCA) of 169°±2°was attained with very low hysteresis (≤ 2°), as well as high transmittance (93-94% at normal incidence). In a three-layer approach (glass/silica NPs/silica aerogel/PTFE), surfaces were produced with WCA of 158°±2°, also very low hysteresis (< 5°), and significant antireflection. This allowed for a normal transmittance of 99.5% or higher, which decreased less than 2% at +20° incidence. These results show that pronounced wide-angle antireflection and self-cleaning properties can be simultaneously attained by proper glass coating. Present advantages and limitations for potential applications are discussed.