Undercut defects of color filter (CF) layers, which inevitably occur in UV curing and development processes for liquid crystal displays and white organic light‐emitting diodes, should be elucidated to ensure product quality and processability. The dynamic changes of the green CF layer are investigated during the baking process by examining the motion of pigment particles within the thin CF layer via multi‐speckle diffusing wave spectroscopy (MSDWS). Autocorrelation functions and characteristic times for the α‐relaxation, which are determined using light intensities scattered from the CF layer, directly indicate thermal melting and curing stages in the process. It is confirmed that MSDWS is a reliable non‐contact measurement tool for quantitatively analyzing the initial change of the CF layer during the baking process.
Particle motion and coffee ring patterns in water-borne suspensions of polystyrene (PS) particle added with small amounts of secondary hydrophobic decalin are investigated during the drying of the suspension droplets, mainly employing light scattering methods. Very tiny secondary fluid insertions via high-speed agitation effectively link the particles through hydrophobic dissolution leading to the formation of multimodal particulate clusters, with resistance to the outward capillary flow and suppression of coffee ring formation after drying. The impact of decalin on particles is corroborated by actual images acquired from an optical profiler and a scanning electron microscope (SEM). The average particle motion inside the suspension changed by decalin was expressed in terms of mean square displacement (MSD) based on diffusing wave spectroscopy (DWS). Employing multispeckle diffusing wave spectroscopy (MSDWS), the rapid motion or -relaxation of particles in various suspensions with and without decalin is quantified in early lag time during the drying of droplets. The change in particle dynamics during suspension drop drying, when adding a small secondary fluid, plays a key role in tuning coffee ring patterns.
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