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Prof. Shin Develops High-precision Coating Technology Using Surf...
  • Writer : Communications Team
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  • Date : 2017-04-19

Prof. Shin Develops High-precision Coating Technology Using Surfactant-like Polymers
New applications expected in automobile painting and biosensors 



 L-R: Prof. Sehyun Shin (corresponding author), Cha
▲ L-R: Prof. Sehyun Shin (corresponding author), Changdeok Seo (first author), and Daeho Jang (first author)



A research team led by Prof. Sehyun Shin of the School of Mechanical Engineering at Korea University succeeded in developing microparticle coating technology able to coat surfaces uniformly with microparticles using surfactant-like polymer solutions.

* Surfactant: Compounds exhibiting both water-insoluble hydrophobic and water-soluble hydrophilic properties; widely used as soap and detergent.
* Polymer solution: A solution in which polymers, comprised of chemically bonded molecules, have dissolved; widely used in cosmetics and coating industries.



The study, supported by the Ministry of Science, ICT and Future Planning and the National Research Foundation of Korea, was published in Scientific Reports on March 29.
- Title: Altering the coffee-ring effect by adding a surfactant-like viscous polymer solution 
- Authors: Prof. Sehyun Shin (corresponding author, Korea University), Changdeok Seo (co-first author, Korea University), Daeho Jang (co-first author, Korea University)



High-precision coating is important in the fields of biomedicine, automobile coating, and printed electronics. When the coating solution evaporates in the coating process, microparticles contained in the solution becomes focused towards the edges, and this coffee-ring effect negatively affects coating quality.
* Coffee-ring effect: The formation of ring-like deposits along the edges after drops of a substance evaporate. 

The team reduced the coffee-ring effect by adding a small amount of surfactant-like polymer solution to the coating solution. The biocompatible polymer solution can not only be used in general coating processes, but also enhance the sensitivity of cancer diagnosis sensors that involve the coating of cancer-detecting microparticles on biosensors.



Prof. Shin said, “Our study enables the uniform coating of microparticles contained in droplets. We started off with the purpose of reducing the coffee-ring effect, so as to allow more effective detection of cancerous materials that exist in small traces in blood. By applying our findings to the coating of cancer-detecting microparticles, it is possible to significantly improve the sensitivity of sensors used in cancer diagnosis. Moreover, our results can be easily applied to most industrial coating processes, including automobile coating, printed electronics, and droplet-based coating, such as sprays and inkjets.





1. Scientific Reports - An online journal published by the prestigious Nature Publishing Group

2. Coffee-ring effect - This refers to the formation of ring-like deposits along the edges after drops of coffee spilled on a table evaporate. The coffee-ring phenomenon is caused naturally by the induced flow during the  evaporation of microparticles.
3. Tears of wine - This refers to a ring of liquid from which droplets form a few seconds after a glass of is shaken in a circular motion. Alcohol evaporates faster than water, and the surface tension draws up the surrounding liquid. The droplets then drop back into the wine due to gravity.

4. Liquid biopsy - A term that contrasts tissue biopsy, involves tests on blood samples to detect cancerous cells, DNA and exosomes in the blood.



Description of Figures:

Fig. 1


       [Water]                [Water and surfactant]            [Water and PEG]





(Fig.) Images following the evaporation of particle-containing droplets; distribution of surface thickness
Figures (a) and (d) show a standard coffee-ring effect with particles focused near the edge. Figures (b) and (d) show the results for surfactant-containing water. The coffee-ring effect is reduced, but the particles are focused in the central area. Figures (c) and (f), the main findings of this study, show that PEG-added solutions produce rings distributed from the edge to the center while reducing the coffee-ring effect.

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