Hee Joong Kim

High-Performance Reverse Osmosis CNT/Polyamide Nanocomposite Membrane by Controlled Interfacial Interactions

Polyamide reverse osmosis (RO) membranes with carbon nanotubes (CNTs) are prepared by interfacial polymerization using trimesoyl chloride (TMC) solutions in n-hexane and aqueous solutions of m-phenylenediamine (MPD) containing functionalized CNTs. The functionalized CNTs are prepared by the reactions of pristine CNTs with acid mixture (sulfuric acid and nitric acid of 3:1 volume ratio) by varying amounts of acid, reaction temperature, and reaction time. CNTs prepared by an optimized reaction condition are found to be well-dispersed in the polyamide layer, which is confirmed from atomic force microscopy, scanning electron microscopy, and Raman spectroscopy studies. The polyamide RO membranes containing well-dispersed CNTs exhibit larger water flux values than polyamide membrane prepared without any CNTs, although the salt rejection values of these membranes are close. Furthermore, the durability and chemical resistance against NaCl solutions of the membranes containing CNTs are found to be improved compared with those of the membrane without CNTs. The high membrane performance (high water flux and salt rejection) and the improved stability of the polyamide membranes containing CNTs are ascribed to the hydrophobic nanochannels of CNTs and well-dispersed states in the polyamide layers formed through the interactions between CNTs and polyamide in the active layers.

Novel composite polymer electrolytes containing poly(ethylene glycol)-grafted graphene oxide for all-solid-state lithium-ion battery applications

A series of composite polymer electrolytes were prepared using an organic/inorganic hybrid branched-graft copolymer (BCP) based on poly(ethylene glycol) methyl ether methacrylate (PEGMA) and 3-(3,5,7,9,11,13,15-heptaisobutylpentacyclo-[9.5.1.13,9.15,15.17,13]octasiloxane-1-yl)propyl methacrylate (MA-POSS) as the polymer matrix and poly(ethylene glycol)-grafted graphene oxide (PGO) as the filler material, and they were applied as solid-state polymer electrolytes (SPEs) for lithium-ion battery applications. The ionic conductivity of the composite polymer electrolyte containing 0.2 wt% of PGO (2.1 × 10−4 S cm−1 at 30 °C) was found to be one order of magnitude higher than that of the BCP (1.1 × 10−5 S cm−1 at 30 °C); the pristine polymer matrix, because of the larger amount of lithium salt, can be dissociated in the composite polymer electrolyte by Lewis acid–base interactions between the PGO and lithium salt. The thermal and mechanical stabilities of the composite polymer electrolytes were also improved by introducing PGO fillers and reasonable storage modulus values were maintained even at elevated temperatures up to 150 °C. All-solid-state battery performance was evaluated with the composite polymer electrolyte containing 0.2 wt% of PGO, resulting in superior cycle performance compared to that of the BCP due to the enhanced ionic conductivity as well as additional ion-conducting paths provided by the PGO fillers.

High-performance reverse osmosis nanocomposite membranes containing the mixture of carbon nanotubes and graphene oxides

Polyamide reverse osmosis membranes containing carbon nanotubes with acidic groups (CNTa), graphene oxide (GO), and both CNTa and GO (CNTa–GO) were prepared by the interfacial polymerization of trimesoyl chloride solutions in hexane and m-phenylenediamine aqueous solutions containing carbon nanomaterials. All of the polyamide membranes containing the carbon nanomaterials showed considerably improved membrane performances, such as water flux, chlorine resistance, long-term durability, and mechanical properties, compared to the polyamide membrane without any of the carbon nanomaterials due to the advantageous properties of the CNT and GO as the filler materials. The largest improvement of membrane performances was observed in the polyamide membrane with CNTa–GO (the mixture of CNTa and GO). CNTa–GO can be more well-dispersed in the aqueous solution than the one-component carbon nanomaterials, such as CNTa and GO, due to the surfactant effects of GO, and then, the polyamide membrane with CNTa–GO can contain the largest amount of the carbon materials among the membranes and show the best membrane performances.

The improvement of antibiofouling properties of a reverse osmosis membrane by oxidized CNTs

Polyamide reverse osmosis (RO) membranes with deposited carbon nanotubes (CNTs) coated with poly(vinyl alcohol) (PVA) on the surface were prepared by interfacial polymerization followed by the deposition of oxidized CNTs and the coating of PVA on the surface. The polyamide membrane with the oxidized CNTs and PVA coating (PA–CNT–PVA membrane) showed much improved mechanical properties and durability compared with the polyamide membrane without CNTs (PA membrane). The PA–CNT–PVA membrane also exhibited much better antifouling properties than the PA membrane and the commercial RO membrane (LFC-1). The improved durability and antibiofouling performances of the PA–CNT–PVA membrane were possible when the CNTs were well-dispersed on the top of the polyamide active layers and stabilized by the thin crosslinked PVA coatings.

Polymer Composite Electrolytes Having Core–Shell Silica Fillers with Anion-Trapping Boron Moiety in the Shell Layer for All-Solid-State Lithium-Ion Batteries

Core-shell silica particles with ion-conducting poly(ethylene glycol) and anion-trapping boron moiety in the shell layer were prepared to be used as fillers for polymer composite electrolytes based on organic/inorganic hybrid branched copolymer as polymer matrix for all-solid-state lithium-ion battery applications. The core-shell silica particles were found to improve mechanical strength and thermal stability of the polymer matrix and poly(ethylene glycol) and boron moiety in the shell layer increase compatibility between filler and polymer matrix. Furthermore, boron moiety in the shell layer increases both ionic conductivity and lithium transference number of the polymer matrix because lithium salt can be more easily dissociated by the anion-trapping boron. Interfacial compatibility with lithium metal anode is also improved because well-dispersed silica particles serve as protective layer against interfacial side reactions. As a result, all-solid-state battery performance was found to be enhanced when the copolymer having core-shell silica particles with the boron moiety was used as solid polymer electrolyte.

2D boron nitride nanoflakes as a multifunctional additive in gel polymer electrolytes for safe, long cycle life and high rate lithium metal batteries

The multifunctional properties of 2D boron nitride nanoflakes (BNNFs) in gel polymer electrolytes (GPEs) are presented. A small addition (0.5 wt%) of BNNFs into the GPE substantially improves all the advantageous properties of the GPE including ionic conductivity, Li+ transference number, mechanical modulus, and dendrite-suppressing capability, thereby enabling high performance lithium metal batteries.

Synthesis and characterization of self-cross-linkable and bactericidal methacrylate polymers having renewable cardanol moieties for surface coating applications

Polymers containing a renewable cardanol moiety were prepared via radical polymerization of 2-hydroxy-3-cardanylpropyl methacrylate (HCPM) and methyl methacrylate (MMA), where HCPM was synthesized by a reaction of cardanol with glycidyl methacrylate in the presence of a base catalyst. Incorporation of the cardanol moiety into PMMA was found to increase the thermal and mechanical stability of the brittle PMMA. When the cardanol based polymers were irradiated with UV light, the mechanical stability increased further because cross-linked networks were formed between the double bonds in the cardanol moieties. Cross-linked polymer films containing the cardanol moiety exhibited high gloss and transparency to visible light. Cardanol-containing polymers with and without the cross-linked networks and other cardanol-based polymers such as poly(cardanyl acrylate) and poly(2-acetoxy-3-cardanylpropyl methacrylate) all showed high antibacterial activity against Escherichia coli (E. coli), indicating that the disappearance of double bonds and/or the structure changes of connecting groups do not diminish the intrinsic bactericidal properties of the cardanol moieties.

Thermo-responsive copolymers with ionic group as novel draw solutes for forward osmosis processes

Thermo-responsive copolymers containing ionic groups (P(MTxEOy), where x and y are the feed molar percent of [2-(methacryloyloxy)ethyl]trimethylammonium chloride (MTAC) and 2-(2-methoxyethoxy)ethyl methacrylate (MEO), respectively) were synthesized via free radical polymerization using MTAC and MEO as monomers, in order to use the copolymers as a draw solute in a forward osmosis (FO) system. The osmotic pressure and lower critical solution temperature (LCST) could be controlled by changing the composition of the copolymers. For example, P(MT25EO75) shows a relatively high osmotic pressure of 0.909 Osmol/kg at 0.2 g/mL, and P(MT5EO95) shows a LCST close to room temperature at 32 °C. When P(MT20EO80) was used as a draw solute in the FO system, a reasonable water permeation flux value of 5.45 Lm−2h−1 at 0.1 g/mL was observed and the draw solute (P(MT20EO80)) could be recovered with a very large draw solute recovery value of 99.80% from the draw solutions by heating to 70 °C, above the LCST, followed by a microfiltration process. Therefore, it is expected that such copolymer system could be a prospective candidate as a draw solute in the FO system.

Gel Polymer Electrolytes Containing Anion-Trapping Boron Moieties for Lithium-Ion Battery Applications

Gel polymer electrolytes (GPEs) based on semi-interpenetrating polymer network (IPN) structure for lithium-ion batteries were prepared by mixing boron-containing cross-linker (BC) composed of ethylene oxide (EO) chains, cross-linkable methacrylate group, and anion-trapping boron moiety with poly(vinylidene fluoride) (PVDF) followed by ultraviolet light-induced curing process. Various physical and electrochemical properties of the GPEs were systematically investigated by varying the EO chain length and boron content. Dimensional stability at high temperature without thermal shrinkage, if any, was observed due to the presence of thermally stable PVDF in the GPEs. GPE having 80 wt % of BC and 20 wt % of PVDF exhibited an ionic conductivity of 4.2 mS cm-1 at 30 °C which is 1 order of magnitude larger than that of the liquid electrolyte system containing the commercial Celgard separator (0.4 mS cm-1) owing to the facile electrolyte uptake ability of EO chain and anion-trapping ability of the boron moiety. As a result, the lithium-ion battery cell prepared using the GPE with BC showed an excellent cycle performance at 1.0 C maintaining 87% of capacity during 100 cycles.

Solid Polymer Electrolytes Based on Functionalized Tannic Acids from Natural Resources for All-Solid-State Lithium-Ion Batteries.

Solid polymer electrolytes (SPEs) for all-solid-state lithium-ion batteries are prepared by simple one-pot polymerization induced by ultraviolet (UV) light using poly(ethylene glycol) methyl ether methacrylate (PEGMA) as an ion-conducting monomeric unit and tannic acid (TA)-based crosslinking agent and plasticizer. The crosslinking agent and plasticizer based on natural resources are obtained from the reaction of TA with glycidyl methacrylate and glycidyl poly(ethylene glycol), respectively. Dimensionally stable free-standing SPE having a large ionic conductivity of 5.6×10(-4)  Scm(-1) at room temperature can be obtained by the polymerization of PEGMA into P(PEGMA) with a very small amount (0.1 wt %) of the crosslinking agent and 2.0 wt % of the plasticizer. The ionic conductivity value of SPE with a crosslinked structure is one order of magnitude larger than that of linear P(PEGMA) in the waxy state.