김형수 교수

Surface coatings and patterning technologies are essential for various physicochemical applications. In this Letter, we describe key parameters to achieve uniform particle coatings from binary solutions. First, multiple sequential Marangoni flows, set by solute and surfactant simultaneously, prevent nonuniform particle distributions and continuously mix suspended materials during droplet evaporation. Second, we show the importance of particle-surface interactions that can be established by surfa

We investigate experimentally and theoretically how a droplet of a binary mixture evaporates when placed on a solid substrate. Our focus is the limit at which the two liquid components have different vapour pressures. Using physicochemical effects, we directly visualize the selective evaporation of the more volatile component and so document the space and time dependence of the chemical distribution in the droplet. In particular, we observe that a mixture consisting of an organic solvent and dei

Interfacial polymerization (IP) provides a versatile platform for fabricating defect-free functional nanofilms for various applications, including molecular separation, energy, electronics, and biomedical materials. Unfortunately, coupled with complex natural instability phenomena, the IP mechanism and key parameters underlying the structural evolution of nanofilms, especially in the presence of surfactants as an interface regulator, remain puzzling. Here, we interfacially assembled polymer nano

Two 3D-3C velocimetry techniques for micro-scale measurements are compared: tomographic particle image velocimetry (Tomo-PIV) and 3D particle-tracking velocimetry (3D-PTV). Both methods are applied to experimental data from a confined shear-driven liquid droplet over a moving surface. The droplet has 200 μm height and 2 mm diameter. Micro 3D-PTV and Tomo-PIV are used to obtain the tracer particle distribution and the flow velocity field for the same set of images. It is shown that the reconstruc

We show that in addition to the surface tension of the volatile liquid, the vapor concentration also influenced the local surface tension along the interface, which in turn changed the internal flow velocity. To predict the flow velocity and oscillatory frequency of the solutal Marangoni flow, we developed a theoretical model based on scaling analysis that showed a good agreement with the experimental results. We believe that the current study will motivate low-cost and portable sample flow cont

We investigate the flow patterns created when a liquid drop contacts a reservoir liquid, which has implications on various physicochemical and biochemical reactions including mixing in microfluidic systems. The localized vortical flow spontaneously triggered by the difference of surface tension between the two liquids is studied, which is thus termed the Marangoni vortex. To quantitatively investigate the strength of vortices, we performed particle image velocimetry (PIV) experiments by varying

We describe a tomographic PIV system for the measurement of the internal flow in a droplet over a stagnant and a moving surface. The flow condition is representative of the flow in an immersion droplet applied in a liquid immersion lithography machine. We quantify the accuracy and reliability of the measurements and compare the shape of the reconstructed measurement volume to shape measurements by means of shadowgraphy. First results indicate the internal flow pattern near the receding contact l

Currently, quantum dot light-emitting diodes (QD-LEDs) are receiving extensive attention. To maximize their luminous performance, the uniformity of the QD-LEDs is crucial. Although the spontaneously self-induced solutal Marangoni flow of an evaporating binary mixture droplet has been widely investigated and used to suppress coffee-ring patterns in ink-jet printing technology, unfortunately, ring shapes are still present at the edges, and the Marangoni flow generated by the selective evaporation

It has been shown that many proteins, when converted into partially unfolded structures, interact strongly with a lipid bilayer. SecA protein of Escherichia coli is an unusual water-soluble protein which, in the native form, can readily penetrate the membrane and lipid bilayer. In order to see whether the native SecA exhibits partially unfolded characteristics, the stability and solvent accessibility of SecA were studied using various spectroscopic and hydrogen-exchange methods. The results are

Gallium-based liquid metal micro- and nanodroplets are being extensively explored in innumerable emerging technologies. Although many of these systems involve the interfaces of liquid metal with a continuous phase liquid (<i>e.g.,</i> microfluidic channels and emulsions), the static or dynamic phenomena at the interface have been scarcely discussed. In this study, we begin by introducing the interfacial phenomena and characteristics observed at the interface between a liquid metal and continuous

Surface-coating technologies are important for a variety of applications, e.g. ink-jet printing, micro-electronic engineering and biological arrays. In this study, we introduce a novel idea to obtain uniform patterns with multi-component solution in a confined geometry. When a droplet of the multi-component liquid evaporates in the confined area, the evaporated vapors are stagnated inside the confined chamber where the evaporated liquid molecule is much heavier than the ambient air. These vapors

A multicomponent droplet evaporation problem has widely been investigated due to diverse industrial applications, including ink-jet printing, surface coating and patterning, medical diagnosis, spraying cooling, and fuel combustion. During evaporation, the Marangoni flow caused by selective evaporation should be observed, and it plays an important role in determining the drying process and the final dried deposit pattern. However, most of the works focused on measuring the internal flow field alt