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Self-assembled hydrophobic surface generated from a helical nanofilament (B4) liquid crystal phase
Kim, Hanim,Yi, Youngwoo,Chen, Dong,Korblova, Eva,Walba, David M.,Clark, Noel A.,Yoon, Dong Ki The Royal Society of Chemistry 2013 Soft matter Vol.9 No.10
<P>Hydrophobic air/liquid crystal (LC) surfaces exhibiting self-assembled dual scale roughness have been made by simple cooling of a bent-core mesogen from its high temperature isotropic melt through two liquid crystal phases. The transition to the fluid smectic B2 phase generates micron-scale toric focal conic domains (TFCDs) at the surface. Upon further cooling into the hexatic smectic B4 phase these TFCD structures are preserved and become textured by the nanometer-sized helical nanofilaments (HNFs) of the B4. The resulting TFCD/HNF surface is hydrophobic and shows clear evidence for surface tension reduction characteristic of dual-scale roughness, suggesting a simple self-assembly-based approach to low surface tension surfaces using LC morphology.</P> <P>Graphic Abstract</P><P>Hydrophobic air/liquid crystal (LC) surfaces exhibiting self-assembled dual scale roughness have been made by simple cooling of a bent-core mesogen from its high temperature isotropic melt through two liquid crystal phases. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3sm27221d'> </P>
Multistep hierarchical self-assembly of chiral nanopore arrays
Kim, Hanim,Lee, Sunhee,Shin, Tae Joo,Korblova, Eva,Walba, David M.,Clark, Noel A.,Lee, Sang Bok,Yoon, Dong Ki National Academy of Sciences 2014 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.111 No.40
<P><B>Significance</B></P><P>Bent-core mesogenic molecules form smectic liquid crystal phases in which the molecular layers are locally polar and chiral, and have a built-in tendency for saddle splay curvature, a combination that fills bulk neat bent-core smectics with self-assembled helical nanofilament bundles of twisted layers. This observation led us to explore the growth mode of such smectics under conditions of nanoconfinement and the remarkable observation reported here that single nanofilaments readily grow in linear nanoscale pores, generating a new motif of hierarchically self-assembled hybrid organic/inorganic structures for applications in chiral synthesis and separation.</P><P>A series of simple hierarchical self-assembly steps achieve self-organization from the centimeter to the subnanometer-length scales in the form of square-centimeter arrays of linear nanopores, each one having a single chiral helical nanofilament of large internal surface area and interfacial interactions based on chiral crystalline molecular arrangements.</P>
Kim, Dae Woo,Kim, Hanim,Jin, Ming Liang,Ellison, Christopher J. Elsevier 2019 Carbon Vol.148 No.-
<P><B>Abstract</B></P> <P>A highly impermeable gas barrier coating is developed by intercalating ethylenediamine (EDA) into the nanochannels of graphene oxide (GO). The diffusion of EDA is facilitated in aqueous GO liquid crystal (LC) scaffolds, and the intercalation can be achieved spontaneously in a few seconds. The intercalated EDA not only crosslinks GO but also induces chemical reduction of GO to RGO, making the RGO/EDA coating stable in water. Remarkably, the RGO/EDA coating exhibits extremely low gas permeability ranging from 0.006 to 0.02 barrer for He, H<SUB>2</SUB>, N<SUB>2</SUB>, and CO<SUB>2</SUB>, similar to that of a neat GO film and exceeding the barrier performance of conventional polymers or their composite materials with graphene or nanoclay. The excellent barrier properties can be attributed to the high tortuosity caused by the well-aligned structure of high-aspect-ratio graphene sheets. In addition, the viscoelastic rheological properties of the GOLC could be beneficial for coating RGO/EDA on various substrates with different geometries where gas barrier properties are needed.</P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Linkage-length dependent structuring behaviour of bent-core molecules in helical nanostructures
Kim, Hanim,Zep, Anna,Ryu, Seong Ho,Ahn, Hyungju,Shin, Tae Joo,Lee, Sang Bok,Pociecha, Damian,Gorecka, Ewa,Yoon, Dong Ki The Royal Society of Chemistry 2016 SOFT MATTER Vol.12 No.14
<P>We studied the correlation between the molecular structure and the formation of helical nanofilaments (HNFs) of bent-core dimeric molecules with varying linkage lengths. To obtain precise structural data, a single domain of HNFs was prepared under physical confinement using porous 1D nanochannels, made up of anodic aluminium oxide films. Electron microscopy and grazing incidence X-ray diffraction were used to elucidate the linkage length-dependent formation of HNFs.</P>
Kim, Kibeom,Kim, Hanim,Jo, Seong-Yong,Araoka, Fumito,Yoon, Dong Ki,Choi, Suk-Won American Chemical Society 2015 ACS APPLIED MATERIALS & INTERFACES Vol.7 No.40
<P>We prepared a nonchiral mixture of achiral bent-core molecules and photoresponsive rodlike liquid crystalline (LC) molecules. With the help of the isothermal photochemical nematic (N)-isotropic (Iso) phase transition of the photoresponsive rodlike LC molecules, the corresponding phase transition from a dark conglomerate BX phase to another distinguishable dark conglomerate B4 phase took place in the mixture. A large circular dichroism (CD) signal originating from supramolecular chirality was detected in the initial BX phase. On the other hand, the detected CD signal was decreased in the B4 phase after UV irradiation. Interestingly, the decreased CD signal could be reverted to the initial CD signal with visible irradiation. This chiroptical process revealed in this work was stable and reversible and thus opens up the possibility of practical applications such as rewritable optical storage.</P><P><B>Graphic Abstract</B> <IMG SRC='http://pubs.acs.org/appl/literatum/publisher/achs/journals/content/aamick/2015/aamick.2015.7.issue-40/acsami.5b07543/production/images/medium/am-2015-07543q_0006.gif'></P><P><A href='http://pubs.acs.org/doi/suppl/10.1021/am5b07543'>ACS Electronic Supporting Info</A></P>
Continuous ZIF-8/reduced graphene oxide nanocoating for ultrafast oil/water separation
Kim, Dae Woo,Eum, Kiwon,Kim, Hanim,Kim, Daeok,Mello, Matheus Dorneles de,Park, Kangho,Tsapatsis, Michael Elsevier 2019 CHEMICAL ENGINEERING JOURNAL -LAUSANNE- Vol.372 No.-
<P><B>Abstract</B></P> <P>Continuous ZIF-8/reduced graphene oxide (RGO) nanocoating is fabricated by growing ZIF-8 on RGO-coated polyurethane (PU) foam. Surface modification of PU foam can be easily achieved by immersing the PU foam in GO solution, followed by mild thermal treatment to turn the GO layer into RGO layer. Adhesion between polymer foam and ZIF-8 layer was enhanced by the inserted RGO layer because oxygen-containing groups of RGO could interact with Zn<SUP>2+</SUP> precursor of ZIF-8 localizing the layer growth preferentially on the surface of RGO. The synergetic hydrophobic/oleophilic properties of RGO and ZIF-8 enable selective oil absorption of PU foam with an absorption capacity of 15–35 g/g depending on the viscosity of organic solvents. Most of all, the ZIF-8/RGO coated PU foam can filter organic solvent selectively <I>via</I> vacuum filtration, showing ultrafast hexane flux up to 800,000 Lm<SUP>−2</SUP> h<SUP>−1</SUP> and no water flux.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A method to fabricate continuous hydrophobic/oleophilic RGO/ZIF-8 nanocoating on polymeric foam. </LI> <LI> Selective oil absorption with an absorption capacity of 15–35 g/g depending on the viscosity of organic solvents. </LI> <LI> Ultrafast hexane flux up to 800,000 Lm<SUP>−2</SUP> h<SUP>−1</SUP> and no water flux during vacuum filtration. </LI> <LI> Universal method to fabricate metal-organic frameworks on polymeric foam. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>