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  • 1. Krivorotova, T.
    et al.
    Makuska, R.
    Naderi, Ali
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Dédinaité, Andra
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Synthesis and interfacial properties of novel cationic polyelectrolytes with brush-on-brush structure of poly(ethylene oxide) side chains2010In: European Polymer Journal, ISSN 0014-3057, E-ISSN 1873-1945, Vol. 46, no 2, p. 171-180Article in journal (Refereed)
    Abstract [en]

    Novel cationic polyelectrolytes with a brush-on-brush structure of poly(ethylene oxide) (PEO) side chains and a charge-containing polyacrylate backbone were synthesized. The PEO side chains were not directly attached to the backbone but via polymethacrylate spacers, thus locating the PEO chains a distance away from the charged units of the backbone. The cationic brush-on-brush polyelectrolytes with high density of PEO chains showed a strong affinity to silica surfaces, provided the backbone charge density was high enough. The adsorption of these polymers was studied by QCM-D giving very high sensed mass, 20 mg/m(2). It was shown by direct force measurements that protective surface layers were formed by the novel polyelectrolytes, generating strongly repulsive steric forces, which provided an effective barrier against flocculation. The adsorbed layer was sufficiently robust to withstand sliding experiments under a pressure of up to 35 MPa. The friction force in water was very low. and the lubrication was characterized by a friction coefficient in the range of 0.02-0.06.

  • 2.
    Naderi, Ali
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Polyelectrolytes: Bottle-Brush Architectures and Association with Surfactants2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis has the dual purpose of raising awareness of the importance of the mixing protocol on the end products of polyelectrolyte-oppositely charged surfactant systems, and to contribute to a better understanding of the properties of bottle-brush polyelectrolytes when adsorbed onto interfaces.

    In the first part of this thesis work, the effects of the mixing protocol and the mixing procedure on formed polyelectrolyte-oppositely charged surfactant aggregates were investigated. It was shown that the initial properties of the aggregates were highly dependent on the mixing parameters, and that the difference between the resulting aggregates persisted for long periods of time.

    The second part of the studies was devoted to the surface properties of a series of bottle-brush polyelectrolytes made of charged segments and segments bearing poly(ethylene oxide) side chains; particular attention was paid to the effect of side chain to charge density ratio of the polyelectrolytes. It was shown that the adsorbed mass of the polyelectrolytes, and the corresponding number of poly(ethylene oxide) bearing segments at the interface, went through a maximum as the charge density of the polyelectrolyte was increased. Also, it was found that bottle-brush polyelectrolyte layers were desorbed quite easily when subjected to salt solutions. This observation was rationalized by the unfavourable excluded volume interactions between the side chains and the entropic penalty of confining them at an interface, which weaken the strength of the binding of the polyelectrolytes to the interface. However, it was shown that the same side chains effectively protect the adsorbed layer against desorption when the layer is exposed to solutions containing an oppositely charged surfactant. Investigation of the lubrication properties of the bottle-brush polyelectrolytes in an asymmetric (mica-silica) system also related the observed favourable frictional properties to the protective nature of the side chains. The decisive factor for achieving very low coefficients of friction was found to be the concentration of the side chains in the gap between the surfaces. Interestingly, it was shown that a brush-like conformation of the bottle-brush polyelectrolyte at the interface has little effect on achieving favourable lubrication properties. However, a brush-like conformation is vital for the resilience of the adsorbed layer against the competitive adsorption of species with a higher surface affinity.

  • 3.
    Naderi, Ali
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Association between poly(vinylamine) and sodium dodecyl sulfate: Effects of mixing protocol, blending procedure, and salt concentration2005In: Journal of Dispersion Science and Technology, ISSN 0193-2691, E-ISSN 1532-2351, Vol. 26, no 3, p. 329-340Article in journal (Refereed)
    Abstract [en]

    The association between a weak cationic linear polyelectrolyte, poly(vinylamine), and the anionic surfactant sodium dodecyl sulfate (SDS) has been investigated in dilute solutions, containing 20 ppm of poly(vinylamine) and surfactant up to a concentration of 8 mM. We particularly focus on the importance of the order of addition of the components and of stirring after mixing. Two mixing protocols were used, denoted PTS and STP. In the PTS method the polyelectrolyte is added to the surfactant solution, and in the STP method the surfactant is added into the polyelectrolyte solution. The results obtained demonstrate the presence of long-lived trapped nonequilibrium states. In addition, we also address the effect of the blending procedure on association. We studied two blending methods, denoted Blending and Vigorous Blending. In the Blending method equal volumes of the polyelectrolyte and surfactant were added simultaneously to the sample tube, after which the ingredients were mixed together by turning the sample tube upside down a few times; in the Vigorous Blending method the mixing was provided by a magnetic stirrer. The results, obtained using turbidity, electrophoretic mobility, and light scattering measurements, demonstrate that Vigorous Blending facilitates flocculation at low SDS concentrations, close to the charge neutralization concentration of the system. This is interpreted as being due to additional surfactant incorporation in initially positively charged complexes during collision events. Vigorous mixing in excess surfactant produces stable dispersions consisting of small negatively charged complexes containing one polyelectrolyte and surfactant in excess of what is needed to neutralize the polyelectrolyte charges. The same results are obtained with the Blending protocol, which gives comparable particle size and polydispersity in excess surfactant and polyelectrolyte.

  • 4.
    Naderi, Ali
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Claesson, Per Martin
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Bergström, Lars Magnus
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Dedinaite, Andra
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Trapped non-equilibrium states in aqueous solutions of oppositelycharged polyelectrolytes and surfactants: effects of mixing protocoland salt concentration2005In: Colloids and Surfaces A: Physicochemical and Engineering Aspects, ISSN 0927-7757, E-ISSN 1873-4359, Vol. 253, no 1-3, p. 83-93Article in journal (Refereed)
    Abstract [en]

    The very slow equilibration time in oppositely charged systems makes it necessary to control not only the concentration of the species but also the details of the mixing process. This has been demonstrated for processes occurring at interfaces where order of addition effects can be of great importance. In this investigation we set out to study the bulk properties of aqueous mixtures of a highly charged cationic polyelectrolyte mixed with an anionic surfactant with the aim to learn if long-lived non-equilibrium states were formed also in this case, and thus if the details of the mixing procedure would affect the structure of the aggregates formed. For simplicity we chose two mixing protocols, denoted “PTS” and “STP”. In the PTS-method the polyelectrolyte is added to the surfactant solution whereas in the STP-method the surfactant is added into the polyelectrolyte solution. The properties of the mixtures in aqueous solutions, with different NaCl concentrations and as a function of time, were followed by conducting turbidity, electrophoretic mobility and dynamic light scattering measurements. The results demonstrate that the mixing protocol indeed has a great impact on the size of the aggregates initially formed and that this size difference persists for long times. Hence, trapped non-equilibrium states do play an important role also in the bulk solution. We found that in excess surfactant solutions the smaller aggregates formed by the STP-method are more resistant than the larger ones formed by the PTS-method to colloidal instability induced by electrolytes (NaCl). Based on our results we suggest that for producing small and stable polyelectrolyte–surfactant aggregates in systems with excess surfactant, the surfactant should be added last, while the opposite should be applied for systems with excess polyelectrolyte.

  • 5.
    Naderi, Ali
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Iruthayaraj, Joseph
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Pettersson, Torbjörn
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Makuška, Ričardas
    Department of Polymer Chemistry, Vilnius University.
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Effect of Polymer Architecture on the Adsorption Properties of a Nonionic Polymer2008In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 13, p. 6676-6682Article in journal (Refereed)
    Abstract [en]

    The adsorption of a linear- and bottle-brush poly(ethylene oxide (PEO))-based polymer, having comparable molecular weights, was studied by means of quartz crystal microbalance with dissipation monitoring ability (QCM-D) and AFM colloidal probe force measurements. The energy dissipation change monitored by QCM-D and the range of the steric forces obtained from force measurements demonstrated that linear PEO forms a more extended adsorption layer than the bottle-brush polymer, despite that the adsorbed mass is higher for the latter. Competitive adsorption studies revealed that linear PEO is readily displaced from the interface by the bottle-brush polymer. This was attributed to the higher surface affinity of the latter, which is governed by the number of contact points between the polymers and the interface, and the smaller loss of conformational entropy.

  • 6.
    Naderi, Ali
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Iruthayaraj, Joseph
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Vareikis, Aušvydas
    Department of Polymer Chemistry, Vilnius University.
    Makuška, Ričardas
    Department of Polymer Chemistry, Vilnius University.
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Surface Properties of Bottle-Brush Polyelectrolytes on Mica: Effects of Side Chain and Charge Densities2007In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 23, no 24, p. 12222-12232Article in journal (Refereed)
    Abstract [en]

    Surface properties of a series of cationic bottle-brush polyelectrolytes with 45-unit-long poly(ethylene oxide) side chains were investigated by phase modulated ellipsometry and surface force measurements. The evaluation of the adsorbed mass of polymer on mica by means of ellipsometry is complex due to the transparency of mica and its birefringence and low dielectric constant. We therefore employed a new method to overcome these difficulties. The charge and the poly(ethylene oxide) side chain density of the bottle-brush polymers were varied from zero charge density and one side chain per segment to one charge per segment and no side chains, thus spanning the realm from a neutral bottle-brush polymer, via a partly charged brush polyelectrolyte, to a linear fully charged polyelectrolyte. The adsorption properties depend crucially on the polymer architecture. A minimum charge density of the polymer is required to facilitate adsorption to the oppositely charged surface. The maximum adsorbed amount and the maximum side chain density at the surface are obtained for the polymer with 50% charged segments and the remaining 50% of the segments carrying poly(ethylene oxide) side chains. It is found that brushlike layers are formed when 25-50% of the segments carry poly(ethylene oxide) side chains. In this paper, we argue that the repulsion between the side chains results in an adsorbed layer that is non-homogeneous on the molecular level. As a result, not all side chains will contribute equally to the steric repulsion but some will be stretched along the surface rather than perpendicular to it. By comparison with linear polyelectrolytes, it will be shown that the presence of the side chains counteracts adsorption. This is due to the entropic penalty of confining the side chains to the surface region.

  • 7.
    Naderi, Ali
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Makuška, Ričardas
    Department of Polymer Chemistry, Vilnius University.
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Interactions between Bottle-Brush Polyelectrolyte Layers: Effects of Ionic Strength and Oppositely Charged Surfactant2008In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 323, no 1, p. 191-202Article in journal (Refereed)
    Abstract [en]

    Interactions between cationic bottle-brush polyelectrolyte layers adsorbed on mica across salt and oppositely charged surfactant solutions were investigated with the interferometric surface force apparatus, and the results were compared with what is known for similarly charged linear polyelectrolytes. Ellipsometric measurements demonstrated that the bottle-brush polyelectrolytes, which contain 45 units long poly(ethylene oxide) side chains, are more readily desorbed than linear equivalents when the ionic strength of the solution is increased. It is argued that this is due to the steric repulsion between the poly(ethylene oxide) side chains that reduces the surface affinity. The preadsorbed bottle-brush polyelectrolyte layers were also exposed to sodium dodecyl sulfate (SDS) solutions. It was found that the presence of SDS affected the force profiles less than observed for similarly charged linear polyelectrolytes. This observation was attributed to excluded volume constraints imposed by the poly(ethylene oxide) side chains that reduces the accessibility of the charged polyelectrolyte segments and counteracts formation of large aggregates within the layer.

  • 8.
    Naderi, Ali
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Olanya, Geoffrey
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Makuska, Ricardas
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface and Corrosion Science.
    Desorption of bottle-brush polyelectrolytes from silica by addition of linear polyelectrolytes studied by QCM-D and reflectometry2008In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 323, no 2, p. 223-228Article in journal (Refereed)
    Abstract [en]

    The possibility of exchanging adsorbed layers of PEO(45)MEMA:METAC-X brush polyelectrolytes (with two different charge densities, 10 and 75 mol%, denoted by X), with poly(MAPTAC), a highly charged linear polyelectrolyte, was investigated by quartz crystal microbalance with dissipation and reflectometry. The studies were conducted on a silica substrate at pH 10, conditions under which only electrostatic interactions are effective in the adsorption process. Based on the results, it was concluded that PEO(45)MEMA:METAC-10 forms an inhomogeneous layer at the interface through which poly(MAPTAC) chains can easily diffuse to reach the surface. On the other hand, the PEO(45)MEMA:METAC-75 layer was not affected when exposed to a poly(MAPTAC) solution. We argue that the observed effect for PEO(45)MEMA: METAC-75 is due to the formation of a homogeneous protective brush layer, in combination with the small difference in surface affinity between the bottle-brush polyelectrolyte and poly(MAPTAC), together with the difficulty of displacing highly charged polyelectrolyte chains once they are adsorbed on the oppositely charged surface. We also use the combination of QCM-D and reflectometry data to calculate the Water content and layer thickness of the adsorbed layers. (c) 2008 Elsevier Inc. All rights reserved.

  • 9.
    Pettersson, Torbjörn
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Naderi, Ali
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Makuška, Ričardas
    Department of Polymer Chemistry, Vilnius University.
    Claesson, Per M.
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Surface Chemistry.
    Lubrication Properties of Bottle-Brush Polyelectrolytes: An AFM Study on the Effect of Side Chain and Charge Density2008In: Langmuir, ISSN 0743-7463, E-ISSN 1520-5827, Vol. 24, no 7, p. 3336-3347Article in journal (Refereed)
    Abstract [en]

    The effect of side chain to charge ratio on the frictional properties of adsorbed layers formed by bottle-brush polyelectrolytes with poly(ethylene oxide) side chains has been investigated. The brush polyelectrolytes were preadsorbed from 0.1 mM NaNO3 solutions onto mica and silica surfaces; the interfacial friction was then measured in polyelectrolyte-free solutions via AFM (with the silica surface acting as the colloidal probe). It was concluded that the decisive factor for achieving favorable lubrication properties is the concentration of nonadsorbing poly(ethylene oxide) side chains in the interfacial region. However, contrary to what may be expected, the results showed that an ideal brush layer structure with the adsorbed polymers adopting comb-like conformation is not necessary for achieving a low coefficient of friction in the asymmetric mica-silica system. In fact, the lowest coefficient of friction (< 0.01) under applied pressures as high as 30 MPa was observed for a system with a side chain to charge ratio of 9: 1, incapable of forming brush-like layers.

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