Sungsoo Han

The increase of antifouling properties of ultrafiltration membrane coated by star-shaped polymers

Star-shaped polymers were prepared by atom transfer radical polymerization (ATRP) using poly(ethylene glycol) methyl ether methacrylate (PEGMA) and methyl methacrylate (MMA) as monomers and polyhedral oligomeric silsesquioxane (POSS) as a core material. Linear copolymers from PEGMA and MMA were also prepared for comparison purposes. Polysulfone (PSf) ultrafiltration membranes coated with the star-shaped polymer showed larger fouling resistance and flux recovery than those coated with the linear-shaped polymer. The improved antifouling properties of the star-shaped polymer compared with those of the linear polymer were ascribed to its larger oxygen to carbon ratio and smaller interactive forces with proteins.

Dual Effective Organic/Inorganic Hybrid Star-Shaped Polymer Coatings on Ultrafiltration Membrane for Bio- and Oil-Fouling Resistance

Amphiphilic organic/inorganic hybrid star-shaped polymers (SPP) were prepared by atom transfer radical polymerization (ATRP) using poly(ethylene glycol) methyl ether methacrylate (PEGMA) and 3-(3,5,7,9,11,13,15-heptacyclohexyl-pentacyclo[9.5.1.1³,⁹.1⁵,¹⁵.1⁷,¹³]-octasiloxane-1-yl)propyl methacrylate (MA-POSS) as monomers and octakis(2-bromo-2-methylpropionoxypropyldimethylsiloxy)-octasilsesquioxane (OBPS) as an initiator. Star-shaped polymers (SPM) having PEGMA and methyl methacrylate (MMA) moieties were also prepared for comparative purposes. Polysulfone (PSf) ultrafiltration membranes coated with the SPP showed higher bio- and oil-fouling resistance and flux-recovery ability than the bare PSf membrane. Moreover, the SPP-coated membranes exhibited better antifouling properties than the SPM-coated membrane when they were used for oil/water emulsion filtration. The dual effective antifouling properties of the SPP were ascribed to the simultaneous enrichment of hydrophilic PEG and hydrophobic POSS moieties on the membrane surfaces resulting in the decrease in interactions with proteins and the increase in repellence to oils.

Layer-by-layer assembly of polyelectrolyte multilayers in three-dimensional inverse opal structured templates.

A novel means of layer-by-layer deposition (LbL) of polyelectrolyte multilayers on three-dimensionally porous inverse opal (3D-IO) structures is presented. The 3D-IO structures comprising UV-curable polymer are highly flexible and can be readily demonstrated as free-standing films with double-sided open porosity over a large scale. A conflict between the intrinsically hydrophobic polymeric structures and waterborne characteristics of the LbL deposition process is overcome by employing a mixed solvent system of water and alcohol. The deposition pH of the LbL assembly can strongly affect the charge density and the degree of entanglement of polyelectrolyte chains, resulting in contrastingly different film deposition and growth behaviors. Since this method utilizes a three-dimensionally structured surface as a deposition substrate, 3D-IO films with a thickness of tens of micrometers can be uniformly and completely deposited with polyelectrolyte multilayers using only several tens of bilayer depositions, which can offer a new pathway of fabricating functionalized polymeric films. Finally, the LbL treated 3D-IO films are applied to nanofiltration membranes for removing multivalent metallic cations. Due to the enhanced Donnan exclusion effect as a result of multiple interfaces formed inside the 3D-IO structures and the relatively large volumetric ratio of water-permeable polyelectrolyte complexes, outstanding membrane performance was observed. Specifically, a good rejection rate of metal ions was achieved even under highly diluted feed conditions without sacrificing the high permeation flux.

Evaluation of poly (aspartic acid sodium salt) as a draw solute for forward osmosis

Poly (aspartic acid sodium salt) (PAspNa) was evaluated for its potential as a novel draw solute in forward osmosis (FO). The inherent advantages of PAspNa, such as good water solubility, high osmotic pressure, and nontoxicity, were first examined through a series of physicochemical analyses and atomic-scale molecular dynamics simulations. Then, lab-scale FO tests were performed to evaluate its suitability in practical processes. Compared to other conventional inorganic solutes, PAspNa showed comparable water flux but significantly lower reverse solute flux, demonstrating its suitability as a draw solute. Moreover, fouling experiments using synthetic wastewater as a feed solution demonstrated that PAspNa reversely flowed to the feed side reduced inorganic scaling on the membrane active layer. The recyclability of PAspNa was studied using both nanofiltration (NF) and membrane distillation (MD) processes, and the results exhibited its ease of recovery. This research reported the feasibility and applicability of FO-NF or FO-MD processes using PAspNa for wastewater reclamation and brackish water desalination.

Nanomesh‐Structured Ultrathin Membranes Harnessing the Unidirectional Alignment of Viruses on a Graphene‐Oxide Film

DOI: 10.1002/adma.201305862 However, strong van der Waals interactions and subsequent irreversible aggregation of the nanomaterials makes it unlikely for the assembled system to exhibit unidirectional alignment. This limitation can be overcome by employing “intelligent” (i.e., responsive) and fl exible one-dimensionally structured biomaterials. [ 11,12 ] The self-assembled structures of M13 viruses are an example; their mechanical stiffness and structural characteristics are readily controlled by manipulating the environmental pH or the type of bonding with the underlying substrate. [ 13,14 ]

Photo-cross-linkable star-shaped polymers with poly(ethylene glycol) and renewable cardanol side groups: synthesis, characterization, and application to antifouling coatings for filtration membranes

Star-shaped polymers (SPCs) containing poly(ethylene glycol) (PEG) and renewable cardanol side groups were synthesized by atom transfer radical polymerization (ATRP). Water-soluble SPCs were turned into water-insoluble materials by self-cross-linking reaction of the unsaturated hydrocarbon chains of cardanol moieties upon UV irradiation. The SPC-coated membranes with UV curing exhibited noticeably higher bio- and oil-fouling resistance than the bare polysulfone (PSf) membrane during filtration experiments, whereas the SPC-coated membranes without UV curing showed a large flux-decline caused by fouling compared to that of the bare membrane, because SPCs were washed out during filtration. The enhanced antifouling properties of the SPC-coated membranes with UV curing were ascribed to a large quantity of PEG moieties on the surfaces stabilized by the cross-linked polymeric structure, leading to decreased interactions with proteins and oils.

Particle-nested inverse opal structures as hierarchically structured large-scale membranes with tunable separation properties.

A novel multiscale porous architecture where an individual particle is nested inside a hollow chamber of inverse-opal (IO) frame is created using a large scale self-assembly of core-shell structured colloidal particles and subsequent selective removal of the outer shells of the colloids. Since the nested particle is smaller than the size of individual IO chamber, the interconnected nanochannels are spontaneously formed within the structured frame. The size of internal nanochannels is readily tuned to have high permeability and size-selective separation capability, which is successfully tested for nanoparticle separation.

Multiscale Porous Interconnected Nanocolander Network with Tunable Transport Properties

A nanocolander network is developed by embedding mesoporous block copolymers inside the structural frame of a macroporous inverse-opal structure. Spontaneously formed macroconduits interconnecting the macropores are utilized as internal bypasses for enhancing the bulk transport properties. A demonstrative application for the membrane of the nanocolander network is of perfect size-selectivity for nanoparticle separation without compromising the high permeability of the transporting medium.

Nanoscale Electrical Degradation of Silicon–Carbon Composite Anode Materials for Lithium-Ion Batteries

High-performance lithium-ion batteries (LIBs) are in increasing demand for a variety of applications in rapidly growing energy-related fields including electric vehicles. To develop high-performance LIBs, it is necessary to comprehensively understand the degradation mechanism of the LIB electrodes. From this viewpoint, it is crucial to investigate how the electrical properties of LIB electrodes change under charging and discharging. Here, we probe the local electrical properties of LIB electrodes with nanoscale resolution by scanning spreading resistance microscopy (SSRM). Via quantitative and comparative SSRM measurements on pristine and degraded LIB anodes of Si-C composites blended with graphite (Gr) particles, the electrical degradation of the LIB anodes is visualized. The electrical conductivity of the Si-C composite particles considerably degraded over 300 cycles of charging and discharging, whereas the Gr particles maintained their conductivity.