| 1. |
- Bastardo Zambrano, Luis Alejandro, et al.
(författare)
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Soluble complexes in aqueous mixtures of low charge density comb polyelectrolyte and oppositely charged surfactant probed by scattering and NMR
- 2007
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 312, s. 21-33
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Tidskriftsartikel (refereegranskat)abstract
- A low charge density polyelectrolyte with a high graft density of 45 units long poly(ethylene oxide) side-chains has been synthesized. In this comb polymer, denoted PEO45 MEMA:METAC-2, 2 mol% of the repeating methacrylate units in the polymer backbone carry a permanent positive charge and the remaining 98 mol% a 45 unit long PEO side-chain. Here we describe the solution conformation of this polymer and its association with an anionic surfactant, sodium dodecylsulfate, SDS. It will be shown that the polymer can be viewed as a stiff rod with a cross-section radius of gyration of 29 Å. The cross section of the rod contracts with increasing temperature due to decreased solvency of the PEO side-chains. The anionic surfactant associates to a significant degree with PEO45 MEMA:METAC-2 to form soluble complexes at all stoichiometries. A cooperative association is observed as the free SDS concentration approaches 7 mM. At saturation the number of SDS molecules associated with the polymer amounts to 10 for each PEO side-chain. Two distinct populations of associated surfactants are observed, one is suggested to be molecularly distributed over the comb polymer and the other constitutes small micellar-like structures at the periphery of the aggregate. These conclusions are reached based on results from small-angle neutron scattering, static light scattering, NMR, and surface tension measurements.
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| 2. |
- Chernyy, Sergey, et al.
(författare)
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Superhydrophilic Polyelectrolyte Brush Layers with Imparted Anti-Icing Properties : Effect of Counter ions
- 2014
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Ingår i: ACS Applied Materials and Interfaces. - : American Chemical Society (ACS). - 1944-8244 .- 1944-8252. ; 6:9, s. 6487-6496
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Tidskriftsartikel (refereegranskat)abstract
- This work demonstrates the feasibility of superhydrophilic polyelectrolyte brush coatings for anti-icing applications. Five different types of ionic and nonionic polymer brush coatings of 25-100 nm thickness were formed on glass substrates using silane chemistry for surface premodification followed by polymerization via the SI-ATRP route. The cationic [2-(methacryloyloxy)ethyl]trimethylammonium chloride] and the anionic [poly(3-sulfopropyl methacrylate), poly(sodium methacrylate)] polyelectrolyte brushes were further exchanged with H+, Li+, Na+, K+, Ag+, Ca2+, La3+, C16N+, F-, Cl-, BF4-, SO42-, and C12SO3- ions. By consecutive measurements of the strength of ice adhesion toward ion-incorporated polymer brushes on glass it was found that Li+ ions reduce ice adhesion by 40% at 18 degrees C and 70% at 10 degrees C. Ag+ ions reduce ice adhesion by 80% at -10 degrees C relative to unmodified glass. In general, superhydrophilic polyelectrolyte brushes exhibit better anti-icing property at -10 degrees C compared to partially hydrophobic brushes such as poly(methyl methacrylate) and surfactant exchanged polyelectrolyte brushes. The data are interpreted using the concept of a quasi liquid layer (QLL) that is enhanced in the presence of highly hydrated ions at the interface. It is suggested that the ability of ions to coordinate water is directly related to the efficiency of a given anti-icing coating based on the polyelectrolyte brush concept.
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| 3. |
- Dédinaité, Andra, et al.
(författare)
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Interfacial properties of chitosan-PEO graft oligomers: Surface competition with unmodified chitosan oligomers
- 2006
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Ingår i: Progress in Colloid and Polymer Science. - Berlin/Heidelberg : Springer-Verlag. - 0340-255X .- 1437-8027. ; 132, s. 124-130
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Tidskriftsartikel (refereegranskat)abstract
- Oligomers of chitosan carrying 45 units long poly(ethylene oxide), PEO, chains grafted to the C-6 position of the sugar units were prepared using a novel synthesis route. The graft density was high, close to one poly(ethylene oxide) chain grafted to each sugar unit of the chitosan oligomer but a small fraction of unreacted chitosan remained in the sample. The molecular weight distribution of the sample was determined using GPC. The interfacial properties of the chitosan-PEO graft oligomers were evaluated using X-ray photoelectron spectroscopy and surface force measurements. It was found that the small fraction of unreacted chitosan was significantly enriched at the solid-solution interface on negatively charged muscovite mica surfaces. The interactions between chitosan-PEO oligomer coated surfaces were found to be dominated by the extended PEO chains, and at high coverage the measured forces were consistent with those expected for polymer brushes. Addition of salt up to 10 mM did not result in any significant desorption of preadsorbed oligomer layers.
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| 4. |
- Duner, Gunnar, et al.
(författare)
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Attractive double-layer forces and charge regulation upon interaction between electrografted amine layers and silica
- 2012
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 385:1, s. 225-234
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Tidskriftsartikel (refereegranskat)abstract
- Amine functionalities have been introduced on glassy carbon surfaces through electrografting of 4-(2-aminoethyl)benzenediazonium tetrafluoroborate. The grafted layers were characterized by ellipsometry and by nanomechanical mapping in air and aqueous solutions using the atomic force microscopy PeakForce QNM mode. The layer was found to be 2.5. nm thick with low roughness, comparable to that of the glassy carbon substrate. However, small semi-spherical features were observed in the topographical image, indicating a clustering of the grafted amine compound. The nanomechanical mapping also demonstrated some swelling of the layer in water and pointed toward an important contribution of electrostatic interactions for the tip-surface adhesion. The forces between an aminated glassy carbon surface and a μm-sized silica particle in aqueous solutions were measured at different ionic strength and pH-values. The results demonstrate that an attractive double-layer force predominates at large separations, and that the surface charge densities increase as the separation between the surfaces decreases. The degree of charge regulation on the aminated glassy carbon is significant. The relatively low surface charge density of the aminated glassy carbon is attributed to significant incorporation of counterions in the water-rich grafted layer.
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| 5. |
- Friis, Jakob Ege, et al.
(författare)
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Hydrophilic Polymer Brush Layers on Stainless Steel Using Multilayered ATRP Initiator Layer
- 2016
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Ingår i: ACS Applied Materials and Interfaces. - : AMER CHEMICAL SOC. - 1944-8244 .- 1944-8252. ; 8:44, s. 30616-30627
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Tidskriftsartikel (refereegranskat)abstract
- Thin polymer coatings (in tens of nanometers to a micron thick) are desired on industrial surfaces such as stainless steel. In this thickness range coatings are difficult to produce using conventional methods. In this context, surface-initiated controlled polymerization method can offer a promising tool to produce thin polymer coatings via bottom-up approach. Furthermore, the industrial surfaces are chemically heterogeneous and exhibit surface features in the form of grain boundaries and grain surfaces. Therefore, the thin coatings must be equally effective on both the grain surfaces and the grain boundary regions. This study illustrates a novel "periodic rejuvenation of surface initiation" process using surface-initiated ATRP technique to amplify the graft density of poly(oligoethylene glycol)methacrylate (POEGMA) brush layers on stainless steel 316L surface. The optimized conditions demonstrate a controlled, macroscopically homogeneous, and stable POEGMA brush layer covering both the grain surface and the grain boundary region. Various relevant parameters-surface cleaning methods, controllability of thickness, graft density, homogeneity and stability-were studied using techniques such as ellipsometer, X-ray photoelectron spectroscopy, scanning electron microscopy-energy-dispersive X-ray, surface zeta potential, and infrared reflection-adsorption spectroscopy.
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| 6. |
- Iruthayaraj, Joseph, et al.
(författare)
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Adsorption of Low charge Density Polyelectrolyte Containing Poly(ethylene oxide) Side chains on Silica : Effects of Ionic strength and pH
- 2005
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 38:14, s. 6152-6160
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Tidskriftsartikel (refereegranskat)abstract
- Adsorption characteristics of a random copolymer of poly(ethylene oxide) monomethyl ether methacrylate and methacryloxyethyl trimethylammonium chloride (PEOMENIA:METAC) on silica were studied using stagnation point adsorption reflectometry (SPAR), quartz crystal microbalance with dissipation (QCM-D), and contact angle techniques. The PEOMEMA:METAC copolymer used in this study is a low charge density polyelectrolyte, with 2% of the monomer units carrying permanent positive charges and 98% containing poly(ethylene oxide) side chains that are approximately 45 repeating units long. The surface excess was determined as a function of pH and concentration of indifferent electrolyte. It was found that the presence of a small amount of 1: 1 electrolyte decreases the adsorbed amount significantly. Further, increasing the pH at a constant ionic strength, 10 mM, results in decreasing surface excess. It is suggested that the adsorption is realized via a combination of non-Coulomb interactions between the poly(ethylene oxide), PEO, grafts and protonated silanol groups at the silica-solution interface and an electrostatic interaction between the charged segments and the oppositely charged surface. Increasing pH and/or salt concentration results in progressive charging of the silica surface with the consequent decrease in affinity between silica and PEO, explaining the decrease in the adsorbed amount of the polymer.
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| 7. |
- Iruthayaraj, Joseph, 1976-
(författare)
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Poly(Ethylene Oxide) Based Bottle-Brush Polymers and their Interaction with the Anionic Surfactant Sodium Dodecyl Sulphate : Solution and Interfacial Properties
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The aim of this thesis work is to study the physico-chemical properties of poly(ethylene oxide), PEO, based brush polymers both in solution and at solid/aqueous interfaces. The importance of studying the surface properties of brush polymers can be related to a broad spectrum of interfacial-related applications such as colloidal stability, lubrication, detergency, protein repellency to name a few. In many applications it is desirable to form brush-like structures through simple physisorption. In this context the surface properties of PEO based brush polymers differing in molecular architecture were studied, using ellipsometry and surface force apparatus (SFA), to gain some understanding regarding the effect of molecular architecture on the formation of brush structures. The molecular architecture was varied by varying the charge/PEO ratio along the backbone. This study demonstrates that the formation of a brush structure at solid/aqueous interface is due to interplay between the attraction of the backbone to the surface and the repulsions between the PEO side chains. An optimal balance between the two antagonistic factors is required if one aims to build a well-defined brush structure at the interface. In this study the brush-like structures are formed when 25-50% of the backbone segments carry poly(ethylene oxide) side chains. Scattering techniques such as light and neutron reveal that these brush polymers are stiff-rods up to a charge to PEO ratio of 75:25. These stiff PEO brush polymer easily replace the more flexible linear PEO at the silica/water interface, the reason being that the entropy loss on adsorption is smaller for the brush polymer due to its stiff nature. Polymer-surfactant systems play a ubiquitous role in many technical formulations. It is well known that linear PEO, which adopts random coil conformation in aqueous solution, interact strongly with the anionic surfactant, Sodium Dodecyl Sulphate (SDS). It is of interest to study the interaction between SDS and brush PEO owing to the fact that the PEO side chains have limited flexibility as compared to the linear PEO. The interaction between brush PEO and the anionic surfactant SDS in solution are studied using different techniques such as NMR, tensiometry, SANS and light scattering. The main finding of this study is that the interaction is weaker compared to the linear PEO-SDS interactions which poses an interesting question regarding the role of chain flexibility in polymer-surfactant interactions.
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| 8. |
- Iruthayaraj, Joseph, et al.
(författare)
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Viscoelastic properties of adsorbed bottle-brush polymer layers studied by quartz crystal microbalance : Dissipation measurements
- 2008
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Ingår i: The Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 112:38, s. 15028-15036
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Tidskriftsartikel (refereegranskat)abstract
- Adsorbed layers of a series of bottle-brush polyelectrolytes with 45 units long poly(ethylene oxide) [PEO], side chains have been investigated by the quartz crystal microbalance technique with dissipation monitoring. The data have been evaluated with three different models, the Sauerbrey model, the Johannsmann model, and the Voigt model. It is found that all three models predict the same trend in the variations of sensed mass and hydrodynamic layer thickness with polymer architecture, that is, with the backbone charge to side chain density ratio. However, the simple Sauerbrey model underestimates the sensed mass by a factor of 1.15-1.45 compared to the more accurate Voigt model. By following the evolution of the layer dissipation, elasticity, and viscosity with increasing surface coverage it was concluded that the layers formed by brush polymers with intermediate charge densities undergo a structural change as the coverage is increased. Initially, the polymers are anchored to the surface via the PEO side chains. However, as the adsorption proceeds a structural change that brings the backbone to the surface and forces the side chains to extend from it is observed. The layer elasticity and viscosity as a function of surface coverage go through a maximum in this transition region.
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| 9. |
- Naderi, Ali, et al.
(författare)
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Effect of Polymer Architecture on the Adsorption Properties of a Nonionic Polymer
- 2008
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 24:13, s. 6676-6682
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 10. |
- Naderi, Ali, et al.
(författare)
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Surface Properties of Bottle-Brush Polyelectrolytes on Mica : Effects of Side Chain and Charge Densities
- 2007
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 23:24, s. 12222-12232
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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