| 1. |
- Flodström, Katarina, et al.
(author)
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Formation of a new Ia(3)over-bard cubic meso-structured silica via triblock copolymer-assisted synthesis
- 2003
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In: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 125:15, s. 4402-4403
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Journal article (peer-reviewed)abstract
- A new mesoporous silica structure with cubic Iad symmetry has been synthesized. The structure has very large unit cell dimensions, up to 250 Å in the as-synthesized form and 222 Å after calcination, and the surface area is around 700 m2/g. The syntheses were done according to well-established synthesis conditions with the triblock copolymers Pluronics P103 or P123, except for the addition of NaI to the synthesis mixture. Small-angle X-ray scattering revealed that the sample has Iad symmetry. According to electron micrographs, the structure is similar to that of MCM-48, and we thus propose that the structure lies on the gyroid minimal surface.
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| 2. |
- Källrot, Niklas, et al.
(author)
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Dynamic study of single-chain adsorption and desorption
- 2007
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In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 40:13, s. 4669-4679
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Journal article (peer-reviewed)abstract
- The dynamics of adsorption and desorption of uncharged homopolymers have been investigated using a coarse-grained model comprised of a bead-spring chain and a planar surface. Brownian dynamics simulation has been used to examine the adsorption process for polymers released near the surface and with bulk properties as well as Monte Carlo simulations to explore equilibrium adsorption structures of the polymer. Systems with varying polymer contour length, polymer stiffness, and polymer-surface interaction potential have been considered. Investigations have been made on polymer extensions perpendicular and parallel to the surface and also characterized the adsorbed state in terms of loops, tails, and trains. After a diffusion of the polymer to the vicinity of the surface, three succeeding phases were identified: distortion, attachment, and relaxation phase. In the distortion phase, the polymer starts to experience the potential of the surface and becomes elongated perpendicular to the surface. In the attachment phase, the polymer makes direct contact with the surface and becomes contracted perpendicular to the surface and starts to spread on the surface. Finally, in the extended relaxation phase, the polymer continues to spread on the surface.
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| 3. |
- Källrot, Niklas, et al.
(author)
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Dynamics of competitive polymer adsorption onto planar surfaces in good solvent.
- 2010
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In: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 114:11, s. 3741-3753
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Journal article (peer-reviewed)abstract
- Adsorption of mixed polymer solutions in good solvent containing polymers of different chain length has been studied by applying simulation techniques on a coarse-grained bead-spring polymer model. Fully flexible polymers at varying bead-surface interaction strength and different combinations of flexible, semiflexible, and stiff polymers at a single bead-surface interaction strength have been examined. Monte Carlo simulation techniques have been employed to investigate static equilibrium properties and Brownian dynamic simulations to follow the dynamics of the adsorption process. The properties examined comprise the adsorbed number of polymers, adsorbed number of beads, bead density profiles, components of the polymer radius of gyration, tail, loop, and train configurations, and nematic bond order of adsorbed beads. The adsorption involves an initially independent adsorption of the two polymer types followed by competitive adsorption. The competitive adsorption is characterized by a maximum of the adsorbed amount and a desorption of the polymer with the smallest surface affinity and a continued, but reduced, growth of the adsorbed amount of the polymer with the largest surface affinity. The surface affinity difference between the two polymer types of different length increased with increasing bead-surface interaction. Furthermore, the surface affinity of a polymer initially decreased but then largely increased at increasing stiffness. As a consequence, a stiff short polymer was found to displace a 4-fold longer flexible polymer. The spatial extension of adsorbed polymers as characterized by the radius of gyration parallel and perpendicular to the surface of a polymer of a given flexibility was independent of the flexibility of the other polymer type. The fraction of beads in tails was increased and in trains reduced as the surface affinity of the dissimilar polymer type was raised. Finally, the adsorption layer of a stiff polymer possesses a nematic bond order. In mixed polymer systems, the nematic bond order of a given polymer type manifests a dependence on the flexibility of the other type.
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| 4. |
- Källrot, Niklas, et al.
(author)
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Dynamics of Polymer Adsorption from Bulk Solution onto Planar Surfaces
- 2009
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In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 42:10, s. 3641-3649
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Journal article (peer-reviewed)abstract
- Polymer adsorption of uncharged homopolymers onto planar surfaces has been investigated by employing a coarse-grained bcad-spring polymer model using simulation techniques. Polymer solutions of two different densities and polymers of two different Contour lengths have been examined. The dynamics of the adsorption process appearing in systems composed of a polymer Solution placed near attractive. but initially polymer-free, surfaces were determined by Brownian dynamics simulations and equilibrium properties of corresponding systems by Monte Carlo simulations. The properties of the systems have been analyzed by monitoring the number of adsorbed polymers, bead density profiles, time and frequency of polymer attachments, spatial extension of polymers perpendicular and parallel to the surface, and configurational characteristics. Initially, the polymers diffuse toward the Surfaces, and at shorter distances the attractive Surface potential starts to pull the polymers toward the surface, making them slightly stretched perpendicular to the Surface. Thereafter, the polymers collapse onto the surface with multiple anchoring, and a slower relaxation increasing the extension of the polymers parallel to the Surfaces appears. Finally, at even longer times, and connected to the slow relaxation of the number of adsorbed polymers, the extension of the polymer coils parallel to the Surface is reduced. and the perpendicular extension is increased, with associated changes of the number of beads residing in tails, loop, and trains. The adsorption process becomes faster at decreasing polymer length and at increasing polymer density.
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| 5. |
- Källrot, Niklas
(author)
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Dynamics of Polymer Adsorption onto Solid Surfaces in Good Solvent
- 2009
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Doctoral thesis (other academic/artistic)abstract
- Adsorption dynamics of various types of uncharged homopolymers onto solid surfaces in good solvent have been studied by using a coarse grained bead-spring model. Brownian dynamics simulation has been used to examine the adsorption process for polymers released near an adsorbing surface, and Monte Carlo simulations have been employed to explore equilibrium properties of adsorbed polymers. Two different types of approaches have been pursued: adsorption of single polymers and adsorption from polymer solutions. For single polymers of varying type, the entire adsorption process was examined and characteristic time dependent properties were extracted. Structural rearrangements of the polymers comprising time regimes of several orders of magnitude were identified. Regarding polymer solutions, polymers of varying length, flexibility, and surface attraction were examined for solutions of similar and dissimilar polymer types at different densities. Solutions containing flexible polymers revealed an extension perpendicular to the surface at long times as the surface pressure increases, reducing the adsorbed polymer segment fraction. Systems of rod-like polymers display an additional relaxation mode, prolonging the final stage of the adsorption process due to the formation of nematic structures of polymers on the surface. Finally, the competitive adsorption of mixed polymer systems is characterized by an initial adsorption of both polymer types, followed by a slow exchange at the surface as the preferentially adsorbing polymer type replaces the other one.
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| 6. |
- Källrot, Niklas, et al.
(author)
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Theoretical study of structure of catalytic copper site in nitrite reductase
- 2005
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In: International Journal of Quantum Chemistry. - : Wiley. - 0020-7608. ; 102:5, s. 520-541
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Journal article (peer-reviewed)abstract
- The catalytic copper site in nitrite reductase contains a Cu2+ ion bound to three histidine (His) ligands and a solvent molecule. Sites from various sources show a conspicuous variation in the structure. In some proteins, it is close to tetrahedral (even more so than are blue copper proteins), whereas in other proteins, it has a structure more similar to that expected for a type 2 copper site. We have studied this site with a number of theoretical methods, ranging from vacuum optimizations, combined quantum and molecular mechanics (QM/MM) optimization, quantum refinement (X-ray crystallography supplemented by quantum chemical calculations), and accurate energy calculations. We show that the difference in the structure arises from a movement of the solvent molecule and that this movement is determined by a compromise between its hydrogen bond interactions and the intrinsic preferences of the copper site. If the solvent molecule is deprotonated, the two structures have a similar energy, whereas if it is protonated, the more tetrahedral structure is energetically favorable. Neither of the structures involves a pi interaction as in the blue copper proteins; instead, both are strongly distorted tetragonal structures with sigma bonds to all four ligands. We have also examined the position of hydrogen atoms shared between second-sphere carboxylate groups and the first-sphere solvent molecule and one of the His ligands. In the oxidized state, the structure with the solvent deprotonate(d) but the His residue protonated seems to be most stable. (c) 2004 Wiley Periodicals, Inc.
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| 7. |
- Linse, Per, et al.
(author)
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Polymer Adsorption from Bulk Solution onto Planar Surfaces: Effect of Polymer Flexibility and Surface Attraction in Good Solvent
- 2010
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In: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 43:4, s. 2054-2068
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Journal article (peer-reviewed)abstract
- Adsorption of uncharged homopolymers of various flexibilities in good solvent onto planar surfaces Lit various polymer-surface interaction strengths have been investigated by employing a coarse-grained bead-spring polymer model using simulation techniques. The polymer flexibility ranged from fully flexible to rod-like polymers, and the adsorption strength varied from weak to strong adsorption. Equilibrium adsorption properties were determined by Monte Carlo simulations, and adsorption processes were investigated by Brownian dynamic simulations. In the latter case, file initial systems were composed of a polymer Solution and a surface separated by a slab of polymer-free solution. The equilibrium properties of the interfacial systems have been analyzed by monitoring bead and polymer density profiles, number of adsorbed beads and polymers, the components of the radius of gyration perpendicular and parallel to the surface as well as tail, loop, and train statistics. Flexible polymers adsorbed in two layers, and at ail increasing surface attraction file number of adsorbed beads and polymers increased and file adsorbed polymers become flatter, whereas rod-like polymers adsorbed ill a single and thin layer with a nematic-like order. At increasing polymer stiffness at fixed surface attraction strength, the number of adsorbed beads increased, whereas the number of adsorbed polymers. file polymer extension perpendicular to the surface, and the fraction of beads in tails all displayed nontrivial maxima Lit similar persistence length. The dynamic analysis showed that file initial adsorption was diffusion controlled, but soon became governed by the probability of a polymer to be captured by file surface attraction. Flexible polymers became flattened after attaching, but their Final relaxation mechanism involved an increased perpendicular extension with fewer adsorbed beads and longer tails driven by file Surface pressure originating from file surrounding adsorbed polymers. The stiff polymers displayed a much slower final relaxation to their equilibrium state; this relaxation predominately constituting a packing of the rocklike polymers in a 2-dimensional nematic order. Furthermore, we have defined an integration time denoting file adsorption time for adsorbed polymers to become fully integrated into the adsorbed layer. Integration times and residence times of integrated polymers became longer with increasing polymer stiffness and increasing bead-surface attraction.
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