The Experts below are selected from a list of 309 Experts worldwide ranked by ideXlab platform

Jennifer A Lewis - One of the best experts on this subject based on the ideXlab platform.

  • Cationic Comb Polymer superdispersants for colloidal silica suspensions.
    Langmuir : the ACS journal of surfaces and colloids, 2009
    Co-Authors: Summer K. Rhodes, Robert H. Lambeth, Jaime Gonzales, Jeffrey S. Moore, Jennifer A Lewis
    Abstract:

    We investigate the ability of a cationic Comb Polymer composed of a poly(trimethylammonium iodide ethyl methacrylate) (PTMAM) backbone and uncharged poly(ethylene glycol) (PEG) teeth to stabilize aqueous silica suspensions of varying ionic strength and pH. Both PTMAM-g-PEG and its homoPolymer backbone, PTMAM, are synthesized via reversible addition-fragmentation chain transfer followed by quaternization of the pendant amine groups with methyl iodide. Through a Combination of Polymer adsorption, zeta potential, and sedimentation measurements as well as confocal imaging of sediment structures, we find that PTMAM-g-PEG imparts stability over a broad range of solution conditions, where pure PTMAM fails.

  • Comb Polymer architecture ionic strength and particle size effects on the batio3 suspension stability
    Journal of the American Ceramic Society, 2009
    Co-Authors: Jun Yoshikawa, Jennifer A Lewis, Byongwa Chun
    Abstract:

    We investigate the stability of aqueous barium titanate suspensions as a function of dispersant architecture, ionic strength, counterion valency, and particle size. Both pure polyelectrolytes, poly(acrylic acid) and poly(methacrylic acid) (PMAA), and Comb Polymer dispersants composed of a PMAA backbone with methoxy-poly(ethylene oxide) (mPEO) teeth of varying molecular weights are studied. While each dispersant imparts stability to barium titanate suspensions at low ionic strength (<∼0.01M), only the PMAA–mPEO Comb Polymer with the longest teeth provides stability at higher ionic strengths independent of particle size and counterion valency. Our findings provide new insight into the design of Comb Polymer dispersants for stabilizing aqueous ceramic suspensions over a broad range of processing conditions.

  • Comb Polymer Architecture, Ionic Strength, and Particle Size Effects on the BaTiO3 Suspension Stability
    Journal of the American Ceramic Society, 2009
    Co-Authors: Jun Yoshikawa, Jennifer A Lewis, Byongwa Chun
    Abstract:

    We investigate the stability of aqueous barium titanate suspensions as a function of dispersant architecture, ionic strength, counterion valency, and particle size. Both pure polyelectrolytes, poly(acrylic acid) and poly(methacrylic acid) (PMAA), and Comb Polymer dispersants composed of a PMAA backbone with methoxy-poly(ethylene oxide) (mPEO) teeth of varying molecular weights are studied. While each dispersant imparts stability to barium titanate suspensions at low ionic strength (

  • Comb Polymer architecture effects on the rheological property evolution of concentrated cement suspensions
    Journal of the American Ceramic Society, 2004
    Co-Authors: Glen H Kirby, Jennifer A Lewis
    Abstract:

    We have studied the rheological behavior of concentrated cement suspensions in the absence and presence of Comb Polymers comprised of a polyacrylic acid (PAA) backbone and charge-neutral, poly(ethylene oxide) (PEO) teeth. These species possessed a uniform backbone molecular weight and graft density, with varying teeth molecular weight. Both PAA, a linear polyelectrolyte, and PAA/PEO Comb Polymers imparted initial stability to concentrated cement suspensions above a critical weight fraction, w* of 4 mg/(g of cement). Cement– PAA suspensions, however, set prematurely. Their rapid, irreversible stiffening stemmed from deleterious interactions between PAA and multivalent counterions in solution. Interestingly, the presence of PEO teeth comprised of only a few monomer units in length mitigated such interactions. The rheological property evolution of concentrated cement–PAA/ PEO suspensions exhibited complex behavior ranging from the reversible gel-like response observed at short teeth lengths to a remarkable gel-to-fluid transition observed during the deceleratory period for systems comprised of longer PEO teeth. At longer hydration times, all cement–PAA/PEO suspensions

  • Poly(acrylic acid)–Poly(ethylene oxide) Comb Polymer Effects on BaTiO3 Nanoparticle Suspension Stability
    Journal of the American Ceramic Society, 2004
    Co-Authors: Glen H Kirby, Daniel J. Harris, Jennifer A Lewis
    Abstract:

    We have studied the effects of poly(acrylic acid)–poly(ethylene oxide) (PAA–PEO) Comb Polymers on the stability of aqueous BaTiO3 nanoparticle suspensions over a wide pH range in the presence and absence of mono- and divalent salt species. The Comb Polymer architecture consists of charge-neutral PEO teeth attached at random intervals along an ionizable PAA backbone. Potentiometric titrations, light scattering, and turbidity measurements were conducted on pure PAA and PAA–PEO solutions to assess their degree of ionization, radius of hydration, and stability. Adsorption isotherm and rheological measurements were conducted on BaTiO3 nanoparticle suspensions to determine the effectiveness of both PAA and PAA–PEO dispersants. Our observations indicate that the presence of PEO teeth effectively shield the underlying PAA backbone from ion interactions, e.g., counterion-screening or ion-bridging effects, thereby allowing PAA–PEO dispersants to impart stability to BaTiO3 nanoparticle suspensions over a wide range of pH, ionic strength, and ion valency conditions where pure PAA fails.

Jong Hak Kim - One of the best experts on this subject based on the ideXlab platform.

  • flexible all solid state 1 4 v symmetric supercapacitors with high energy density based on Comb Polymer electrolyte and 1d hierarchical carbon nanotube electrode
    Journal of Power Sources, 2020
    Co-Authors: Chang Soo Lee, Sung Hoon Ahn, Dong Jun Kim, Jae Hun Lee, Arumugam Manthiram, Jong Hak Kim
    Abstract:

    Abstract A high-performance solid-state supercapacitor (ssSC) based on an amphiphilic Comb Polymer (CP) solid electrolyte and an electrode comprising porous one-dimensional (1D) hierarchical carbon nanotubes is reported. The solid electrolyte is prepared from the amphiphilic CP, poly(vinylidene fluoride-co-chlorotrifluoroethylene)-g-poly(oxyethylene methacrylate) (P(VDF-co-CTFE)-g-POEM) comprising hydrophobic P(VDF-co-CTFE) main chains and hydrophilic POEM side chains, which provide good mechanical strength and high ionic conductivity, respectively. Preferential interaction of POEM with the ionic liquid (IL) and microphase-separated structures of CP/IL electrolytes are demonstrated. Two types of 1D hierarchical carbon nanotubes are prepared by a metal–organic-framework-derived approach using 1D tellurium as the template. The ssSC fabricated with the CP electrolyte displays a high specific capacitance of 239.3 F g−1, which is much higher than that achieved with the widely used conventional poly(vinyl alcohol) electrolytes. The flexible ssSC fabricated with carbon cloth as electrode substrate exhibits a remarkable specific capacitance of 220.8 F g−1.

  • Antifouling poly(vinylidene fluoride) ultrafiltration membranes containing amphiphilic Comb Polymer additive Part B Polymer physics
    Journal of Polymer Science, 2010
    Co-Authors: Jong Kwan Koh, Yong Woo Kim, Sung Hoon Ahn, Byoung Ryul Min, Jong Hak Kim
    Abstract:

    An amphiphilic Comb Polymer consisting of poly(vinylidene fluoride-co-chlorotrifluoroethylene) [P(VDF-co-CTFE)] main chains and poly(oxyethylene methacrylate) (POEM) side chains was synthesized using direct initiation of the chlorine atoms in CTFE units through atom transfer radical Polymerization, as confirmed by ¹H NMR and FTIR spectroscopy. The P(VDF-co-CTFE)-g-POEM Comb Polymer was introduced as an additive to prepare poly(vinylidene fluoride) antifouling ultrafiltration membranes. As the contents of Comb Polymer increased, the mechanical properties of membranes slightly decreased due to the decreased crystallinity of the membranes, as revealed by universal testing machine and X-ray diffraction. However, water contact angle measurement and X-ray photoelectron spectroscopy showed that the hydrophilic POEM segments spontaneously segregated on the membrane surfaces. As a result, the antifouling property of the membranes containing P(VDF-co-CTFE)-g-POEM Comb Polymer was considerably improved with a slight change of water flux.

  • Antifouling poly(vinylidene fluoride) ultrafiltration membranes containing amphiphilic Comb Polymer additive
    Journal of Polymer Science Part B: Polymer Physics, 2009
    Co-Authors: Jong Kwan Koh, Yong Woo Kim, Sung Hoon Ahn, Byoung Ryul Min, Jong Hak Kim
    Abstract:

    An amphiphilic Comb Polymer consisting of poly(vinylidene fluoride-co-chlorotrifluoroethylene) [P(VDF-co-CTFE)] main chains and poly(oxyethylene methacrylate) (POEM) side chains was synthesized using direct initiation of the chlorine atoms in CTFE units through atom transfer radical Polymerization, as confirmed by 1H NMR and FTIR spectroscopy. The P(VDF-co-CTFE)-g-POEM Comb Polymer was introduced as an additive to prepare poly(vinylidene fluoride) antifouling ultrafiltration membranes. As the contents of Comb Polymer increased, the mechanical properties of membranes slightly decreased due to the decreased crystallinity of the membranes, as revealed by universal testing machine and X-ray diffraction. However, water contact angle measurement and X-ray photoelectron spectroscopy showed that the hydrophilic POEM segments spontaneously segregated on the membrane surfaces. As a result, the antifouling property of the membranes containing P(VDF-co-CTFE)-g-POEM Comb Polymer was considerably improved with a slight change of water flux. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 183–189, 2010

  • Graft Polymerization of poly(epichlorohydrin-g-poly((oxyethylene) methacrylate)) using ATRP and its Polymer electrolyte with KI
    Ionics, 2009
    Co-Authors: Kyung Ju Lee, Byoung Ryul Min, Jung Tae Park, Joo Hwan Koh, Jong Hak Kim
    Abstract:

    This contribution demonstrates a synthesis of Comb Polymer consisting of a poly(epichlorohydrin) (PECH) backbone and poly(oxyethylene methacrylate) side chains. Atom transfer radical Polymerization (ATRP) was used to directly initiate the chlorine atoms of PECH macroinitiator. The structure of Comb Polymer was characterized by nuclear magnetic resonance (^1H nuclear magnetic resonance) and Fourier transform infrared (FT-IR) spectroscopy, presenting the successful “grafting from” method using ATRP. The Comb Polymer was used as a Polymer matrix for dissolving potassium iodide (KI) to prepare solid Polymer electrolyte. FT-IR spectroscopy indicates that the potassium salts are dissolved in the Polymeric matrix due to coordination interaction with the ether oxygens of graft coPolymer. Differential scanning calorimetry showed that glass transition temperature ( T _g) of Polymer electrolytes continuously increased with increasing salt concentration up to 15 wt.%, mostly due to coordinative interactions between the potassium ions and the ether oxygens of Polymer matrix. Ionic conductivity at room temperature increased with increasing salt concentrations up to 5 wt.% (maximum ionic conductivity ~3.7 × 10^−5 S/cm), after which it gradually decreased.

Ashutosh Chilkoti - One of the best experts on this subject based on the ideXlab platform.

  • Fabrication of biofunctionalized quasi-three-dimensional microstructures of a nonfouling Comb Polymer using soft lithography
    Advanced Functional Materials, 2005
    Co-Authors: Hongwei Ma, Thomas P. Beebe, Zhanping Zhang, Jinho Hyun, Ashutosh Chilkoti
    Abstract:

    This paper describes a simple set of patterning methods that are applicable to diverse substrates and allow the routine and rapid fabrication of protein patterns embedded within a background that consists of quasi-three-dimensional microstructures of a cell-resistant Polymer. The ensemble of methods reported here utilizes three components to create topographically nonfouling Polymeric structures that present cell-adhesive protein patterns in the regions between the microstructures: the first component is an amphiphilic Comb Polymer that is comprised of a methyl methacrylate backbone and pendant oligo(ethylene glycol) moieties along the side chain, physically deposited films of which are protein- and cell-resistant. ne second component of the fabrication methodology involves the use of different variants of soft lithography, such as microcontact printing to create nonfouling topographical features of the Comb Polymer that demarcate cell-adhesive regions of the third component: a cell-adhesive extracellular protein or peptide. The ensemble of methods reported in this paper was used to fabricate quasi-three-dimensional patterns that present topographical and biochemical cues on a variety of substrates, and was shown to successfully maintain cellular patterns for up to two months in serum-containing medium. We believe that this, and other such methods under development that allow independent and systematic control of chemistry, topography and substrate compliance will provide versatile "test-beds" for fundamental studies in cell biology as well as allow the discovery of rational design principles for the development of biomaterials and tissue-engineering scaffolds.

  • Pretreatment of amphiphilic Comb Polymer surfaces dramatically affects protein adsorption.
    Biomacromolecules, 2005
    Co-Authors: Zhanping Zhang, Ashutosh Chilkoti, Douglas B. Hausner, Thomas P. Beebe
    Abstract:

    New applications in regenerative biotechnology require the ability to understand and control protein−surface interactions on micrometer and submicrometer length scales. Evidence presented here shows that micropatterned amphiphilic Comb Polymer films exhibit a pretreatment-dependent behavior with respect to protein adsorption for the proteins fibronectin, laminin, and for serum. A micropatterned surface, consisting of protein-reactive regions, separated by Comb Polymer, was created and tested for protein adsorption using the surface-sensitive imaging tool TOF−SIMS. Immersion of micropatterned surfaces in solutions of fibronectin or laminin resulted in uniform protein coverage on both the Comb Polymer and protein-reactive regions. However, preimmersion of similarly patterned surfaces in water for 2 h prior to protein incubation was found to dramatically improve the protein-resistant properties of the Comb Polymer regions. These results are consistent with poly(ethylene glycol) (PEG) side chain reorientation...

  • Fabrication of Biofunctionalized Quasi‐Three‐Dimensional Microstructures of a Nonfouling Comb Polymer Using Soft Lithography
    Advanced Functional Materials, 2005
    Co-Authors: Jinho Hyun, Zhanping Zhang, Thomas P. Beebe, Ashutosh Chilkoti
    Abstract:

    This paper describes a simple set of patterning methods that are applicable to diverse substrates and allow the routine and rapid fabrication of protein patterns embedded within a background that consists of quasi-three-dimensional microstructures of a cell-resistant Polymer. The ensemble of methods reported here utilizes three components to create topographically nonfouling Polymeric structures that present cell-adhesive protein patterns in the regions between the microstructures: the first component is an amphiphilic Comb Polymer that is comprised of a methyl methacrylate backbone and pendant oligo(ethylene glycol) moieties along the side chain, physically deposited films of which are protein- and cell-resistant. The second component of the fabrication methodology involves the use of different variants of soft lithography, such as microcontact printing to create nonfouling topographical features of the Comb Polymer that demarcate cell-adhesive regions of the third component: a cell-adhesive extracellular protein or peptide. The ensemble of methods reported in this paper was used to fabricate quasi-three-dimensional patterns that present topographical and biochemical cues on a variety of substrates, and was shown to successfully maintain cellular patterns for up to two months in serum-containing medium. We believe that this, and other such methods under development that allow independent and systematic control of chemistry, topography and substrate compliance will provide versatile “test-beds” for fundamental studies in cell biology as well as allow the discovery of rational design principles for the development of biomaterials and tissue-engineering scaffolds.

  • Micropatterns of a cell-adhesive peptide on an amphiphilic Comb Polymer film
    Langmuir, 2002
    Co-Authors: Jinho Hyun, Pallab Banerjee, Janet Cole, Kenneth E. Gonsalves, Ashutosh Chilkoti
    Abstract:

    We report in this paper a generic method to modify the surfaces of common Polymeric biomaterials that enables spatially resolved attachment and growth of mammalian cells in a biologically relevant milieu. We demonstrate that an amphiphilic Comb Polymer presenting short oligoethylene glycol side chains can be coated onto a number of different Polymeric biomaterials, namely polystyrene, poly(methyl methacrylate), and poly(ethylene terephthalate) from a methanol/water mixture. The Comb Polymer film is stable in water and presents reactive COOH groups at the oligoethylene glycol chain ends, thereby permitting the surface of the Comb Polymer to be patterned with a cell adhesive, arg-gly-asp peptide. The micropatterned surfaces spatially confine the attachment and growth of fibroblasts for ∼24 h in 10% serum to the patterned regions.

Linda G. Griffith - One of the best experts on this subject based on the ideXlab platform.

  • Nanoscale clustering of RGD peptides at surfaces using Comb Polymers. 1. Synthesis and characterization of Comb thin films.
    Biomacromolecules, 2001
    Co-Authors: Darrell J. Irvine, Anne M. Mayes, Linda G. Griffith
    Abstract:

    Theoretical and experimental studies were conducted to elucidate the structure and properties of amphiphilic Comb Polymer thin films presenting nanoscale clusters of Arg-Gly-Asp (RGD) peptides for control of cell adhesion on biomaterials. Combs comprised of a poly(methyl methacrylate) backbone and short poly(ethylene oxide) side chains were synthesized, and peptides were tethered to the side chain ends to create nanoscale peptide clusters. In thin films, Comb Polymers containing ≥30 wt % six to nine unit PEO side chains completely resisted adhesion of a model fibroblast cell line in the presence of 7.5% serum over 24 h. These same Polymers modified with RGD peptides elicited tunable cell adhesion when mixed with unmodified Combs in varying proportion. A self-consistent field lattice model of the interface between Comb Polymer films and water predicts an organization of the top molecular layer of Comb Polymer with the backbone oriented parallel to the interface in quasi-two-dimensional confinement and hydr...

  • Nanoscale clustering of RGD peptides at surfaces using Comb Polymers. 2. Surface segregation of Comb Polymers in polylactide.
    Biomacromolecules, 2001
    Co-Authors: Darrell J. Irvine, Anne M. Mayes, † And Anne-valerie G. Ruzette, Linda G. Griffith
    Abstract:

    Part 1 of these studies described poly(methyl methacrylate-r-polyoxyethylene methacrylate) P(MMA-rPOEM) Comb Polymers that present Arg-Gly-Asp (RGD) peptides at a surface in nanoscale clusters on a protein-resistant background for control of cell adhesion. Here in part 2, we examine surface segregation of these peptide-modified and unmodified Comb Polymers blended with polylactide (PLA) as a self-assembly approach suitable for surface modification of porous tissue engineering scaffolds. Multiple thermodynamic driving forces for surface enrichment of the Comb Polymer are exploited by annealing PLA/P(MMA-rPOEM) blends above the glass transition of the blend components but below the melting point of PLA, while in contact with water. Predictions of the interfacial composition profiles of annealed blends were made using a self-consistent field (SCF) lattice model. The calculations predict strong enrichment of the Comb in the top 50 A of blends, and organization of Comb molecules in quasi-2D conformations at the interface, similar to the apparent structure of pure Comb surfaces in contact with water described in part 1. Experimentally, PLA/Comb blend surfaces were characterized by contact angle measurements, XPS, quantification of ligand-cluster surface density and stability by AFM and fluorescent nanosphere labeling, and cell attachment assays. These data were consistent with SCF predictions, showing significant enrichment of the Comb at water-annealed surfaces and RGD cluster densities consistent with 2D conformations for Comb molecules in the surface layer. Bulk miscibility of the blends was verified by dynamic rheometry, small-angle neutron scattering, DSC and X-ray diffraction studies. Surface segregation of Combs provided tunable cell adhesion on PLA through surface-localized nanoclusters of RGD atop a cellresistant background.

Charles F. Zukoski - One of the best experts on this subject based on the ideXlab platform.

  • PAA/PEO Comb Polymer effects on rheological properties and interparticle forces in aqueous silica suspensions
    Journal of colloid and interface science, 2003
    Co-Authors: Catherine P. Whitby, Glen H Kirby, Jennifer A Lewis, Peter J. Scales, Franz Grieser, Thomas W. Healy, Charles F. Zukoski
    Abstract:

    The effects of a poly(acrylic acid) (PAA)-poly(ethylene) (PEO) Comb Polymer dispersant on the rheological properties and inter-particle forces in aqueous silica suspensions have been studied under varying pH conditions. The Comb Polymer was found to adsorb more strongly under acidic than basic conditions, indicating that the PAA backbone of the coPolymer preferentially adsorbs onto silica surfaces with the PEO "teeth" extending out from the surface into the solution. In the presence of low concentrations of coPolymer, the silica suspensions were stable due to electrostatic repulsions between the silica surfaces. At higher coPolymer concentrations and under neutral and basic conditions, where the coPolymer interacted only weakly with silica, the suspensions showed a transition from a dispersed to weakly flocculated state and attractive forces were measured between silica surfaces. Under acidic conditions, the silica dispersion also destabilized at intermediate coPolymer adsorbed density and then was re-stabilized at higher adsorbed coverage. The silica suspensions were stable at high coPolymer coverage due to steric repulsions between the particles. The destabilization at intermediate coverage is thought to be due to Polymer bridging between particles or possibly depletion forces.

  • paa peo Comb Polymer effects on rheological properties and interparticle forces in aqueous silica suspensions
    Journal of Colloid and Interface Science, 2003
    Co-Authors: Catherine P. Whitby, Glen H Kirby, Jennifer A Lewis, Peter J. Scales, Franz Grieser, Thomas W. Healy, Charles F. Zukoski
    Abstract:

    The effects of a poly(acrylic acid) (PAA)-poly(ethylene) (PEO) Comb Polymer dispersant on the rheological properties and inter-particle forces in aqueous silica suspensions have been studied under varying pH conditions. The Comb Polymer was found to adsorb more strongly under acidic than basic conditions, indicating that the PAA backbone of the coPolymer preferentially adsorbs onto silica surfaces with the PEO "teeth" extending out from the surface into the solution. In the presence of low concentrations of coPolymer, the silica suspensions were stable due to electrostatic repulsions between the silica surfaces. At higher coPolymer concentrations and under neutral and basic conditions, where the coPolymer interacted only weakly with silica, the suspensions showed a transition from a dispersed to weakly flocculated state and attractive forces were measured between silica surfaces. Under acidic conditions, the silica dispersion also destabilized at intermediate coPolymer adsorbed density and then was re-stabilized at higher adsorbed coverage. The silica suspensions were stable at high coPolymer coverage due to steric repulsions between the particles. The destabilization at intermediate coverage is thought to be due to Polymer bridging between particles or possibly depletion forces.