초록(영문)
Suspension coating, a coating technique where a suspension containing small particles is poured onto a surface and the solvent is dried
to coat the surface only with the particles, promises to be significantly enhanced in the future. However, the technique requires extensive
control because the flow of the solvent in the coating process causes unevenness which influences the physical properties of the coating
film after desiccation. In this study, we quantitatively analyzed the amount of coffee ringing effect after desiccation of the suspension
while varying the type and concentration of the particles in the suspension. We compared the suspensions containing spherical particles
(aspect ratio = 1) and non-spherical particles (aspect ratio = 4) and each suspension was prepared at 1% and 2% concentration by mass.
Drying behavior of the suspensions were analyzed using multi-speckle diffusing-wave spectroscopy (MSDWS) powered by a LSC
-based camera and a CCD -based camera. Both cameras captured speckle variation of the light scattered back from the moving particles.
The drying process was monitored at baseline and after 3, 6, 9, and 12 minutes of drying time. The correlation function was plotted and
grouped together at the same time for comparison among different suspensions. The relaxation time was calculated from the time-series
of the correlation function. In order to test the validity of MSDWS -based quantitative analysis of the coffee ringing effect, the surface
and cross-section of each suspension were photographed by SEM to correlate the visual appearance of the particles and MSDWS -based
quantification.