The Experts below are selected from a list of 321 Experts worldwide ranked by ideXlab platform

Atsushi Takahara - One of the best experts on this subject based on the ideXlab platform.

  • Cationic Polymer Brush/Giant Polysaccharide Sacran Assembly: Structure and Lubricity
    Langmuir : the ACS journal of surfaces and colloids, 2020
    Co-Authors: Kosuke Igata, Yuji Higaki, Norifumi L. Yamada, Tatsunori Sakamaki, Yoshihiro Inutsuka, Maiko K. Okajima, Tatsuo Kaneko, Atsushi Takahara
    Abstract:

    A highly effective aqueous lubrication strategy employing electrostatic assembly of a negatively charged ultrahigh molecular weight natural polysaccharide named "sacran" and a positively charged poly[2-(methacryloyloxy)Ethyltrimethylammonium chloride] (PMTAC) brush was investigated. The PMTAC brush was compressed through the adsorption of sacran to produce the layered structure of a PMTAC brush/sacran hybrid bottom layer and a poorly hydrated sacran top layer. The dynamic friction coefficients of the PMTAC brush were drastically reduced in salt-free sacran aqueous solutions, and the lubrication mode transition from the brush-lubrication regime to hydrodynamic lubrication was promoted. The electrostatic assembly was inhibited by the addition of NaCl into the lubricant solutions, leading to the loss of the lubrication effect. The hydrodynamic lubrication would be encouraged by the local viscosity enhancement at the friction boundary due to the poorly hydrated and highly viscous PMTAC brush/sacran hybrid film produced by the spontaneous electrostatic assembly.

  • Counteranion-Specific Hydration States of Cationic Polyelectrolyte Brushes
    Industrial & Engineering Chemistry Research, 2018
    Co-Authors: Yuji Higaki, Norifumi L. Yamada, Yoshihiro Inutsuka, Hitomi Ono, Yuka Ikemoto, Atsushi Takahara
    Abstract:

    While polyelectrolyte brushes have received extensive attention due to their particular surface properties, the ion-specific hydration states remain largely unknown. Here, we report the counteranion-specific hydration states of cationic poly[2-(methacryloyloxy)Ethyltrimethylammonium] (PMTA) brushes in salt-free water. The water droplet contact angle on the PMTA brushes depends on the counteranion species, and the order is consistent with the Hofmeister series. Weakly hydrated chaotropic counteranions are strongly bound to weakly hydrated quaternary ammonium (QA+) cations in the PMTA brush chains, which induces a reduction in the ζ-potential, dehydration, and collapse of the PMTA brushes. The PMTA brushes with strongly hydrated chloride counteranions produce a more diffuse tail and less swollen bound layer under salt-free deuterium oxide than brushes with weakly hydrated thiocyanate counteranions. Ion pairing disturbs the ordering of hydrated water in the PMTA brushes. Our work enhances the understanding o...

  • Counteranion-Specific Hydration States of Cationic Polyelectrolyte Brushes
    2018
    Co-Authors: Yuji Higaki, Norifumi L. Yamada, Yoshihiro Inutsuka, Hitomi Ono, Yuka Ikemoto, Atsushi Takahara
    Abstract:

    While polyelectrolyte brushes have received extensive attention due to their particular surface properties, the ion-specific hydration states remain largely unknown. Here, we report the counteranion-specific hydration states of cationic poly­[2-(methacryloyloxy)­Ethyltrimethylammonium] (PMTA) brushes in salt-free water. The water droplet contact angle on the PMTA brushes depends on the counteranion species, and the order is consistent with the Hofmeister series. Weakly hydrated chaotropic counteranions are strongly bound to weakly hydrated quaternary ammonium (QA+) cations in the PMTA brush chains, which induces a reduction in the ζ-potential, dehydration, and collapse of the PMTA brushes. The PMTA brushes with strongly hydrated chloride counteranions produce a more diffuse tail and less swollen bound layer under salt-free deuterium oxide than brushes with weakly hydrated thiocyanate counteranions. Ion pairing disturbs the ordering of hydrated water in the PMTA brushes. Our work enhances the understanding of the ion specificity in the hydration states of polyelectrolyte brushes and encourages the rational design of charged polymer materials

  • Aqueous lubrication of poly(etheretherketone) via surface-initiated polymerization of electrolyte monomers
    Polymer, 2017
    Co-Authors: Patcharida Chouwatat, Keiko Higaki, Yuji Higaki, Tomoyasu Hirai, Hung-jue Sue, Atsushi Takahara
    Abstract:

    Poly(etheretherketone) (PEEK) substrate surface was modified with charged cationic poly(2-(methacryloyloxy) Ethyltrimethylammonium chloride) (PMTAC) and anionic poly(3-sulfopropyl methacrylate potassium salt) (PSPMK) polymer brushes through surface-initiated radical polymerization triggered by UV light exposure of benzophenone groups in PEEK backbone as an initiator. After extensive UV light exposure, the PEEK surface was covered with grafted polyelectrolyte chains and exhibited swollen polyelectrolyte brushes with high roughness under water, indicating high graft density and wide molecular weight distributions of PMTAC and PSPMK brushes. The hydrated polyelectrolyte brushes on PEEK surface induce significant air bubble repellency in water. Thus, thickening of swollen polyelectrolyte brushes dramatically reduces the friction coefficient of PEEK surface under a wet condition.

  • Measurement of the electrostatic interaction between polyelectrolyte brush surfaces by optical tweezers.
    Langmuir : the ACS journal of surfaces and colloids, 2013
    Co-Authors: Daiki Murakami, Motoyasu Kobayashi, Ai Takenaka, Hiroshi Jinnai, Atsushi Takahara
    Abstract:

    We demonstrated an optical tweezers method to measure the electrostatic interaction between the strong polyelectrolyte brushes, poly(2-(methacryloyloxy)Ethyltrimethylammonium chloride) (PMTAC), grafted on silica particles in aqueous media. The weak electrostatic interaction was successfully detected with a resolution of less than 0.1 μN m–1. The apparent Debye length, including the charge distribution in the polymer brush and the surface potential, decreased as the salt concentration in the medium increased. The experimentally obtained surface charge density was much smaller than that estimated from the amount of polyelectrolyte on the surface. Furthermore, the dissociation of ionic groups was enhanced by decreasing the grafting density of the polyelectrolyte brush. The results suggest that the majority of chloride counterions was immobilized in the dense polyelectrolyte brush layer to neutralize the high charge density.

Jeong Ho Cho - One of the best experts on this subject based on the ideXlab platform.

  • Polyelectrolyte Interlayer for Ultra-Sensitive Organic Transistor Humidity Sensors
    ACS applied materials & interfaces, 2013
    Co-Authors: Yeong Don Park, Ho Sun Lim, Boseok Kang, Kilwon Cho, Moon Sung Kang, Jeong Ho Cho
    Abstract:

    We demonstrate low-voltage, flexible, transparent pentacene humidity sensors with ultrahigh sensitivity, good reliability, and fast response/recovery behavior. The excellent performances of these devices are derived from an inserted polyelectrolyte (poly[2-(methacryloyloxy)Ethyltrimethylammonium chloride-co-3-(trimethoxysilyl)propyl methacrylate] (poly(METAC-co-TSPM)) interlayer, which releases free Cl– ions in the electrolyte dielectric layer under humid conditions and boosts the electrical current in the transistor channel. This has led to extreme device sensitivity, such that electrical signal variations exceeding 7 orders of magnitude have been achieved in response to a 15% change in the relative humidity level. The new sensors exhibit a fast responsivity and a stable performance toward changes in humidity levels. Furthermore, the humidity sensors, mounted on flexible substrates, provided low voltage (

  • Polyelectrolyte Interlayer for Ultra-Sensitive Organic Transistor Humidity Sensors
    2013
    Co-Authors: Yeong Don Park, Ho Sun Lim, Boseok Kang, Kilwon Cho, Moon Sung Kang, Jeong Ho Cho
    Abstract:

    We demonstrate low-voltage, flexible, transparent pentacene humidity sensors with ultrahigh sensitivity, good reliability, and fast response/recovery behavior. The excellent performances of these devices are derived from an inserted polyelectrolyte (poly­[2-(methacryloyloxy)­Ethyltrimethylammonium chloride-co-3-(trimethoxysilyl)­propyl methacrylate] (poly­(METAC-co-TSPM)) interlayer, which releases free Cl– ions in the electrolyte dielectric layer under humid conditions and boosts the electrical current in the transistor channel. This has led to extreme device sensitivity, such that electrical signal variations exceeding 7 orders of magnitude have been achieved in response to a 15% change in the relative humidity level. The new sensors exhibit a fast responsivity and a stable performance toward changes in humidity levels. Furthermore, the humidity sensors, mounted on flexible substrates, provided low voltage (

  • Counterion-induced reversibly switchable transparency in smart windows.
    ACS nano, 2011
    Co-Authors: Chang-hwan Lee, Ho Sun Lim, Jooyong Kim, Jeong Ho Cho
    Abstract:

    Smart windows that can reversibly alternate between extreme optical characteristics via clicking counteranions of different hydration energies were developed on glass substrates through the facile spray-casting of poly[2-(methacryloyloxy)Ethyltrimethylammonium chloride-co-3-(trimethoxysilyl)propyl methacrylate]. The optical transmittance was either 90.9% or 0% over the whole spectral range when alternately immersed in solutions containing thiocyanate (SCN–) or bis(trifluoromethane)sulfonimide (TFSI–) ions, respectively. The extreme optical transitions were attributed to formation of microporous structures via the molecular aggregation of polyelectrolyte chains bearing TFSI– ions in methanol. Because the smart windows were either highly transparent toward or completely blocking of incident light upon direct counterion exchange, this kind of nanotechnology may provide a new platform for efficiently conserving on energy usage in the interior of buildings.

Simon Biggs - One of the best experts on this subject based on the ideXlab platform.

  • POLYELECTROLYTE ADSORPTION AT THE SOLID/LIQUID INTERFACE INTERACTION FORCES AND STABILITY
    Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1998
    Co-Authors: Kristin Elizabeth Bremmell, Graeme J Jameson, Simon Biggs
    Abstract:

    Abstract The forces between negatively charged surfaces in the presence of an adsorbing cationic copolymer of acrylamide and 2(methacryloyloxy)Ethyltrimethylammonium chloride have been investigated using an atomic force microscope. The results were compared with measurements from adsorption isotherm, electrophoretic mobility, stability, and light scattering experiments. The adsorbed amount of polyelectrolyte and adsorbed layer conformation at the solid/liquid interface were found to be strongly dependent on the polymer concentration from which initial adsorption takes place. At low polyelectrolyte concentrations unstable silica suspensions were observed from stability tests; light scattering experiments indicate a large aggregate size under equivalent conditions. The adsorbed amount was also seen to be low, well less than monolayer coverage, and force measurements indicated that the polymer was adsorbed in a flat conformation. At high polyelectrolyte concentrations, an increase in the adsorbed amount was observed which resulted in a higher surface coverage, a higher mobility and a stable suspension. Direct force measurements indicated the presence of an electrosteric barrier.

  • polyelectrolyte adsorption at the solid liquid interface interaction forces and stability
    Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1998
    Co-Authors: Kristin Elizabeth Bremmell, Graeme J Jameson, Simon Biggs
    Abstract:

    Abstract The forces between negatively charged surfaces in the presence of an adsorbing cationic copolymer of acrylamide and 2(methacryloyloxy)Ethyltrimethylammonium chloride have been investigated using an atomic force microscope. The results were compared with measurements from adsorption isotherm, electrophoretic mobility, stability, and light scattering experiments. The adsorbed amount of polyelectrolyte and adsorbed layer conformation at the solid/liquid interface were found to be strongly dependent on the polymer concentration from which initial adsorption takes place. At low polyelectrolyte concentrations unstable silica suspensions were observed from stability tests; light scattering experiments indicate a large aggregate size under equivalent conditions. The adsorbed amount was also seen to be low, well less than monolayer coverage, and force measurements indicated that the polymer was adsorbed in a flat conformation. At high polyelectrolyte concentrations, an increase in the adsorbed amount was observed which resulted in a higher surface coverage, a higher mobility and a stable suspension. Direct force measurements indicated the presence of an electrosteric barrier.

Kristin Elizabeth Bremmell - One of the best experts on this subject based on the ideXlab platform.

  • POLYELECTROLYTE ADSORPTION AT THE SOLID/LIQUID INTERFACE INTERACTION FORCES AND STABILITY
    Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1998
    Co-Authors: Kristin Elizabeth Bremmell, Graeme J Jameson, Simon Biggs
    Abstract:

    Abstract The forces between negatively charged surfaces in the presence of an adsorbing cationic copolymer of acrylamide and 2(methacryloyloxy)Ethyltrimethylammonium chloride have been investigated using an atomic force microscope. The results were compared with measurements from adsorption isotherm, electrophoretic mobility, stability, and light scattering experiments. The adsorbed amount of polyelectrolyte and adsorbed layer conformation at the solid/liquid interface were found to be strongly dependent on the polymer concentration from which initial adsorption takes place. At low polyelectrolyte concentrations unstable silica suspensions were observed from stability tests; light scattering experiments indicate a large aggregate size under equivalent conditions. The adsorbed amount was also seen to be low, well less than monolayer coverage, and force measurements indicated that the polymer was adsorbed in a flat conformation. At high polyelectrolyte concentrations, an increase in the adsorbed amount was observed which resulted in a higher surface coverage, a higher mobility and a stable suspension. Direct force measurements indicated the presence of an electrosteric barrier.

  • polyelectrolyte adsorption at the solid liquid interface interaction forces and stability
    Colloids and Surfaces A: Physicochemical and Engineering Aspects, 1998
    Co-Authors: Kristin Elizabeth Bremmell, Graeme J Jameson, Simon Biggs
    Abstract:

    Abstract The forces between negatively charged surfaces in the presence of an adsorbing cationic copolymer of acrylamide and 2(methacryloyloxy)Ethyltrimethylammonium chloride have been investigated using an atomic force microscope. The results were compared with measurements from adsorption isotherm, electrophoretic mobility, stability, and light scattering experiments. The adsorbed amount of polyelectrolyte and adsorbed layer conformation at the solid/liquid interface were found to be strongly dependent on the polymer concentration from which initial adsorption takes place. At low polyelectrolyte concentrations unstable silica suspensions were observed from stability tests; light scattering experiments indicate a large aggregate size under equivalent conditions. The adsorbed amount was also seen to be low, well less than monolayer coverage, and force measurements indicated that the polymer was adsorbed in a flat conformation. At high polyelectrolyte concentrations, an increase in the adsorbed amount was observed which resulted in a higher surface coverage, a higher mobility and a stable suspension. Direct force measurements indicated the presence of an electrosteric barrier.

Weichen Sheng - One of the best experts on this subject based on the ideXlab platform.

  • A facile method for the preparation of monodisperse hollow silica spheres with controlled shell thickness
    Journal of Polymer Science Part A: Polymer Chemistry, 2010
    Co-Authors: Shunsheng Cao, Xin Jin, Xinhua Yuan, Weichen Sheng
    Abstract:

    This article presents a facile, effective, mild synthesis process for well-defined hollow spheres by using cationic polystyrene (PS) submicro-particles as templates. In this approach, the cationic PS templates can be first prepared via emulsifier-free polymerization by using the cationic monomer 2-(methacryloyloxy) Ethyltrimethylammonium chloride as comonomer, then, the silica shells from the sol-gel process of tetraethoxysilane were coated on the surfaces of template particles via electrostatic interaction, finally the PS was dissolved in situ by modification of the reaction conditions in the same medium to form monodisperse hollow silica spheres with controlled shell thickness. Fourier transform-infrared spectroscopy, thermogravimetric analysis, Brunauer-Emmett-Teller, transmission electron microscopy, and scanning electron microscope measurements were used to characterize these hollow silica spheres.

  • The Preparation of Monodisperse Cationic Polystyrene and its Application to the Synthesis of Hollow Silica Spheres
    Australian Journal of Chemistry, 2010
    Co-Authors: Xin Jin, Shunsheng Cao, Xinhua Yuan, Weichen Sheng
    Abstract:

    The fabrication of hollow spheres with well defined size and morphology has been attracting much attention due to their unique structures and related physicochemical properties. Among the synthetic methods, the template-directed method is particularly interesting and extensively employed to fabricate hollow spheres due to templates available of essentially any size, shape, and chemistry. As a result, a new monodispersed cationic polystyrene (PS) template in this paper was fabricated by using 2-(methacryloyloxy) Ethyltrimethylammonium chloride as co-monomer via emulsifier-free polymerization. The template not only can easily be tuned to the size, but can combine the advantages of hard-templating and soft-templating methods. Subsequently, we used cationic PS particles as templates to prepare hollow silica spheres – the results indicated that cationic templates can attract the assembly of tetraethylorthosilicate hydrolyzate on their surface and that the dissolution of templates can be done in the system of silica encapsulation by modification of the reaction conditions.