Interferometric monitoring of dip coating

Abstract

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 Ϫ1͞2 , in accordance with a simple model. Comparison with measured results with an uncertainty of Ϯ0.007 m͒ showed good agreement after the initial steps of the process had been completed.

Analysis of dip coating processing parameters by double optical monitoring

“…As the withdrawal speed increases, so does the mass drain in the same time interval. On the other hand, a larger film thickness adheres to the substrate for a faster withdrawal speed, as indicated by the equation that describes physical thickness evolution during the drainage stage [1,6]:…”

“…Once known the constant refractive index by Abbe refractometry, interferometric monitoring provided temporal evolution of optical thickness, thus allowing determination of physical thickness evolution in real time. Predictions of a simple theoretical model of drainage for Newtonian fluids could then be successfully tested [6,7].…”

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

“…As in interferometric optospinography, 3,4 the reflected light at normal incidence is compared with a reference signal that is later processed by a lock-in amplifier and by a computer with an analog-to-digital converter. 12,13 In the polarimetric measurement the laser light, polarized in the plane of incidence, impinges onto the sample at a variable angle. 16 The high acquisition rate, typically of the order of 3.5 kHz, and the proper alignment of the optical system, leading to a small illuminated spot on the sample (diameter of less than 0.5 mm) at x ϭ x 0 , were carefully maintained for detailed monitoring of the dip-coating process.…”

“…11 This allowed the application of a simple model to compare theoretical and experimental results of temporal physical-thickness evolution. 12 The agreement that was reached made possible contactless monitoring of liquid film-flow properties during the dip-coating process. 13 However, significant refractive-index variation made explicit interpretation difficult for dip coating with a multicomponent zirconyl chloride aqueous solution.…”

Synthesis, Characterization and Properties of Zirconium Oxide (ZrO2)-Doped Titanium Oxide (TiO2) Thin Films Obtained via Sol-Gel Process

“…Vd is the deposition rate, k is the empirical factor depending on the viscosity, surface tension and density of the solution used and a is the exponent with 2/3 value according to Landau and Levich [62], and 1/2 according to Michels et al [63] or even proportionately at the speed of dipping Hewak et al [64].…”