Moo Jin Kwak

One-Step Synthesis of Cross-Linked Ionic Polymer Thin Films in Vapor Phase and Its Application to an Oil/Water Separation Membrane

In spite of the huge research interest, ionic polymers could not have been synthesized in the vapor phase because the monomers of ionic polymers contain nonvolatile ionic salts, preventing the monomers from vaporization. Here, we suggest a new, one-step synthetic pathway to form a series of cross-linked ionic polymers (CIPs) in the vapor phase via initiated chemical vapor deposition (iCVD). 2-(Dimethylamino)ethyl methacrylate (DMAEMA) and 4-vinylbenzyl chloride (VBC) monomers are introduced into the iCVD reactor in the vapor phase to form a copolymer film. Simultaneously in the course of the deposition process, the tertiary amine in DMAEMA and benzylic chloride in VBC undergo a Menshutkin nucleophilic substitution reaction to form an ionic ammonium-chloride complex, forming a highly cross-linked ionic copolymer film of p(DMAEMA-co-VBC). To the best of our knowledge, this is the first report on the synthesis of CIP films in the vapor phase. The newly developed CIP thin film is further applied to the surface modification of the membrane for oil/water separation. With the hydrophilic and underwater oleophobic membrane whose surface is modified with the CIP film, excellent separation efficiency (>99%) and unprecedentedly high permeation flux (average 2.32 × 105 L m-2 h-1) are achieved.

A Simple, Cost-Efficient Method to Separate Microalgal Lipids from Wet Biomass Using Surface Energy-Modified Membranes

For the efficient separation of lipid extracted from microalgae cells, a novel membrane was devised by introducing a functional polymer coating onto a membrane surface by means of an initiated chemical vapor deposition (iCVD) process. To this end, a steel-use-stainless (SUS) membrane was modified in a way that its surface energy was systemically modified. The surface modification by conformal coating of functional polymer film allowed for selective separation of oil-water mixture, by harnessing the tuned interfacial energy between each liquid phase and the membrane surface. The surface-modified membrane, when used with chloroform-based solvent, exhibited superb permeate flux, breakthrough pressure, and also separation yield: it allowed separation of 95.5 ± 1.2% of converted lipid (FAME) in the chloroform phase from the water/MeOH phase with microalgal debris. This result clearly supported that the membrane-based lipid separation is indeed facilitated by way of membrane being functionalized, enabling us to simplify the whole downstream process of microalgae-derived biodiesel production.

A Superamphiphobic Sponge with Mechanical Durability and a Self-Cleaning Effect.

A robust superamphiphobic sponge (SA-sponge) is proposed by using a single initiated chemical vapor deposition (i-CVD) process. Poly(3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyl methacrylate) (PFDMA) is deposited on a commercial sponge by the polymerization of fluoroalkyl acrylates during the i-CVD process. This PFDMA is conformally coated onto both the exterior and interior of the sponge structure by a single step of the i-CVD process at nearly room temperature. Due to the inherent porous structure of the sponge and the hydrophobic property of the fluorine-based PFDMA, the demonstrated SA-sponge shows not only superhydrophobicity but also superoleophobicity. Furthermore, the fabricated SA-sponge is robust with regard to physical and chemical damage. The fabricated SA-sponge can be utilized for multi-purpose applications such as gas-permeable liquid separators.

A hydrogel-coated membrane for highly efficient separation of microalgal bio-lipid

A cross-linked hydrogel-coated membrane was fabricated to achieve simple but highly efficient separation of bio-lipids directly from an aqueous microalgal culture medium. The membrane is composed of a stainless steel membrane coated conformally with a cross-linked hydrogel, poly(2-hydroxyethyl methacrylate) (pHEMA), synthesized by a photo-initiated chemical vapor deposition (piCVD) process. The pHEMA-coated membrane has hydrophilicity and underwater-oleophobicity for efficient separation of a bio-lipid-in-hexane/water mixture by gravity. The conformal pHEMA film-coated membrane enables extremely high oil rejection performance with intrusion pressure of 6.1 kPa and water permeation flux of 6.5×103 L m-2 h-1, with excellent separation efficiency greater than 98.0%.

Solvent-Free Deposition of Ultrathin Copolymer Films with Tunable Viscoelasticity for Application to Pressure-Sensitive Adhesives

A new fabrication method for an ultrathin (500 nm thick) pressure-sensitive adhesive (PSA) was demonstrated by utilizing a series of in situ cross-linked viscoelastic copolymer films. Viscoelastic films composed of poly(2-hydroxyethyl acrylate- co-2-ethylhexyl acrylate) were synthesized successfully in a one-step manner by an initiated chemical vapor deposition (iCVD) process, where free-radical polymerization is triggered in the vapor phase either by heat or UV, or a combination of both. In particular, the photoinitiated chemical vapor deposition method generated a highly cross-linked polymer film, whereas cross-linking of the copolymer film was suppressed greatly in the conventional thermal iCVD method. A combination of thermal and photoinitiated chemical vapor deposition could regulate the cross-linking density of the copolymer films. We controlled the cross-linking density of the copolymer films to exhibit a viscoelastic property so that they would readily adhere to various kinds of substrates with only 500 nm thick copolymer PSA. The adhesion performance of the PSA was systematically optimized by tuning the copolymer composition as well as the cross-linking density, and consequently a high shear strength of more than 85.2 ± 5 N/cm2 was achieved despite the 500 nm thickness. In addition, the PSA was completely transparent. We expect that the ultrathin PSAs developed in this work will be utilized widely for the realization of various soft electronic devices, which usually require strong adhesion, tunable viscoelastic properties, and optical transparency.

Triboelectric energy harvester with an ultra-thin tribo-dielectric layer by initiated CVD and investigation of underlying physics in the triboelectricity

A thickness effect of a tribo-dielectric layer (TDL) made of ultra-thin polymer in a triboelectric energy harvester (TEH) is experimentally and comprehensively studied. The TDL was deposited by the initiated chemical vapor deposition (i-CVD) method and its thickness was precisely controlled to analyze the thickness effect. The correlation between the thickness of the TDL and the output performance is experimentally determined and analytically understood with the aid of the dynamic contact-separation model. In contrast to the conventional static contact-separation model, in this case the output performance increases as the thickness of the TDL increases owing to the dynamic behavior of the electron, which includes drift and recombination phenomenon in the TDL.