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Iridescent cellulose nanocrystal films with tunable reflection wavelength for colorimetric sensors
양하경,최송이,김진웅 한국공업화학회 2018 한국공업화학회 연구논문 초록집 Vol.2018 No.0
We introduce a new colorimetric display technology in which cellulose nanocrystals (CNCs) self-assemble in suspension to form iridescent chiral nematic films. Iridescent CNC films reflect circularly polarized light at specific wavelengths in the dried film state. The chiral nematic pitch is tunable depending on the applied external energy during the suspension procedure, i.e., ultrasound. The reflection wavelength is electrostatic in nature, thus meaning that the electrostatic repulsion between CNCs is essential for determination of reflection wavelength. To figure out the underlying mechanism exactly, we controlled the surface charge density of CNCs by using 2,2,6,6-tetramethylpiperidine-1-oxyl radical mediated oxidation and explained how the electrostatic repulsion between CNCs could span the reflection wavelength in the film. Even more intriguing, the film was found to exhibit a shift of the Bragg reflection band when exposed to specific environment.
양하경,최송이,한상우,김진웅 한국공업화학회 2017 한국공업화학회 연구논문 초록집 Vol.2017 No.1
This study introduces a new colorimetric display technology in which cellulose nanoscrystals (CNCs) self-assemble in suspension to form iridescent chiral nematic films. Utilization of CNCs is truly intriguing since they reflect circularly polarized light at specific wavelengths in the dried film state. The chiral nematic pitch is tunable depending on how much external energy is applied during the suspension procedure, i.e., ultrasound. The reflection wavelength is electrostatic in nature, thus meaning that the electrostatic repulsion between CNCs is essential for regulation of reflection wavelength. In order to exactly figure out the underlying mechanism, we controlled the surface charge density of CNCs by using 2,2,6,6-tetramethylpiperidine-1-oxyl radical mediated oxidation and demonstrated how the electrostatic repulsion between CNCs could span the reflecton wavelength in the film.
Color-spectrum-broadened ductile cellulose films for vapor-pH -responsive colorimetric sensors
양하경,최송이,김도연,박대환,이두호,최선영,남윤성,김진웅 한국공업화학회 2019 Journal of Industrial and Engineering Chemistry Vol.80 No.-
We introduce a smart colorimetric sensor platform, in which iridescent chiral nematicfilms composed ofoxidized cellulose nanocrystals (OxCNCs) exhibit pH-responsive color changes. To provide dried OxCNCfilms with the controlled reflection of circularly polarized lights at specific wavelengths, we manipulatedthe half-pitch distance from 145 to 270 nm by adjusting the surface charges of OxCNCs during 2,2,6,6-tetramethylpiperidine-1-oxyl-radical-mediated oxidation. Utilizing the controlled electrostatic repul-sion generated by the difference in the surface charge of OxCNCs, the reflection wavelengths of thefilmscould be tuned across a broad color spectrum. In addition, we improvedflexibility or ductility of OxCNCcompositefilms by coassembly with a hygroscopic polymer, polyethylene glycol, while maintaining theiriridescent colors. Wefinally demonstrated that the OxCNC compositefilms could show reversible colorchanges in response to vapors of aqueous solutions with different pH values, thus enabling thedevelopment of a vapor-pH-responsive colorimetric sensor technology.
이우진,김보현,한상우,서민정,최송이,양하경,김신현,정소희,김진웅 한국공업화학회 2018 Journal of Industrial and Engineering Chemistry Vol.68 No.-
This work offers a promising approach for development of a temperature-responsive colorimetric display platform. For this purpose, uniform thermochromic microcapsules consisting of a cholesteric liquid crystal (CLC) core and a thin polyurethane shell layer were fabricated by conducting in-situ condensation polymerization at the interface of monodisperse CLC-in-water emulsion drops. Colloidal packing-driven microcapsule registry led to exact 2-dimensional positioning of CLC microcapsules into a holes-patterned flexible film stencil. Furthermore, we showed that the designated registry of different color types of CLC microcapsules on the stencil enabled development of a microwriting display technology capable of reversible text representation according to temperature change.