Kyung Moon Choi

A multifunctional and high-efficiency microfluidic device for droplet generation and fusion is presented. Through unique design of the micro-channels, the device is able to alternately generate droplets, generating droplet ratios ranging from 1 ratio 5 to 5 ratio 1, and fuse droplets, enabling precise chemical reactions in several picoliters on a single chip. The controlled fusion is managed by passive control based on the channel geometry and liquid phase flow. The synthesis of CdS nanoparticles utilizing each fused droplet as a microreactor for rapid and efficient mixing of reagents is demonstrated in this paper. Following alternating droplet generation, the channel geometry allows the exclusive fusion of alternate droplets with concomitant rapid mixing and produces supersaturated solution of Cd2+ and S2- ions to form CdS nanoparticles in each fused droplet. The spectroscopic properties of the CdS nanoparticles produced by this method are compared with CdS prepared by bulk mixing.

The photopolymerization kinetics of typical dental dimethacrylate monomers were studied by differential photocalorimetry. Increasing proportions of the low-viscosity diluent monomer triethylene glycol dimethacrylate (TEGDMA) were added to either Bis-GMA (2,2-bis[p-(2‘-hydroxy-3‘-methacryloxypropoxy)phenylene]propane), EBADMA (ethoxylated bisphenol A dimethacrylate), or UDMA (1,6-bis(methacryloxy-2-ethoxycarbonylamino)-2,4,4-trimethylhexane) to provide three base resins that differed in their hydrogen-bonding potential and, therefore, resulted in compositions covering a broad range of viscosities. When compared at similar diluent concentrations, UDMA resins were significantly more reactive than Bis-GMA and EBADMA resins. At higher diluent concentrations, EBADMA resins provided the lowest photopolymerization reactivities. Optimum reactivities in the UDMA and EBADMA resin systems were obtained with the addition of relatively small amounts of TEGDMA, whereas the Bis-GMA/TEGDMA resin system required near equivalent mole ratios for highest reactivity. The hydrogen-bonding interactions, which substantially influence the Bis-GMA and UDMA resin series, were examined by Fourier transform infrared spectroscopy and resin viscosity. Synergistic effects of base and diluent monomer on the polymerization rate and the final conversion were found for the two base resins having hydrogen-bonding interactions. The structures of the individual monomers and, consequently, the resin viscosities of the comonomer mixtures strongly influence both the rate and the extent of conversion of the photopolymerization process.

Patterning techniques that rely on high-resolution elastomeric elements such as stamps, molds, and conformable photomasks are operationally simple methods for nanofabrication that may find applications in areas such as molecular and organic electronics. The resolution of these "soft" lithographic procedures is often limited by the mechanical properties of the elastomers. We introduce here a chemically modified poly(dimethylsiloxane) material that is designed and optimized specifically for soft lithography, particularly in the nanometer regime. We demonstrate its use for nanopatterning tasks that are challenging with the commercially available elastomers that have been used in the past.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTPolymerization mechanism and physicochemical properties of electrochemically prepared polyindole tetrafluoroborateKyung Moon Choi, Chung Yub Kim, and Keu Hong KimCite this: J. Phys. Chem. 1992, 96, 9, 3782–3788Publication Date (Print):April 1, 1992Publication History Published online1 May 2002Published inissue 1 April 1992https://pubs.acs.org/doi/10.1021/j100188a040https://doi.org/10.1021/j100188a040research-articleACS PublicationsRequest reuse permissionsArticle Views438Altmetric-Citations59LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAmorphous Polysilsesquioxanes as a Confinement Matrix for Quantum-Sized Particle Growth. Size Analysis and Quantum Size Effect of CdS Particles Grown in Porous PolysilsesquioxanesKyung Moon Choi and K. J. SheaCite this: J. Phys. Chem. 1994, 98, 12, 3207–3214Publication Date (Print):March 1, 1994Publication History Published online1 May 2002Published inissue 1 March 1994https://pubs.acs.org/doi/10.1021/j100063a026https://doi.org/10.1021/j100063a026research-articleACS PublicationsRequest reuse permissionsArticle Views273Altmetric-Citations54LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts