| 1. |
- Dunér, Gunnar, et al.
(författare)
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Nanomechanical mapping of a high curvature polymer brush grafted from a rigid nanoparticle
- 2012
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 8:32, s. 8312-8320
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Tidskriftsartikel (refereegranskat)abstract
- Analysis of interaction forces when probing a silica core-polyelectrolyte brush shell nanoparticle, adsorbed on a silica substrate and bathed by aqueous electrolyte solution, with an ultrasharp atomic force microscopy (AFM) tip provides a spatially resolved map of heterogeneous mechanical properties across the nanoparticle. The deformation of the brush is mainly compressive when probed directly above the nanoparticle centre and mainly deflective when probed at a finite horizontal distance away from the centre. The brush is significantly stiffer against compression than against deflection, and ionization of the brush has a greater stiffening effect against compression than deflection. Whereas a height image of the core-shell nanoparticle was unremarkable, showing a monotonic decrease in height with increasing horizontal distance from the centre, brush deformation, energy dissipation and adhesion displayed local minima over the centre and maxima at a finite horizontal distance away from the centre, corresponding to a position near the rigid core nanoparticle edge. The different response to brush deformation depending on the angle of probing is relevant to the interactions of brush-decorated macroscopic surfaces with submicrometer roughness and to the interactions of brush-decorated nanoparticles with ultrafine structures in their environments.
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| 2. |
- Krivosheeva, Olga, et al.
(författare)
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Kinetic and Equilibrium Aspects of Adsorption and Desorption of Class II Hydrophobins HFBI and HFBII at Silicon Oxynitride/Water and Air/Water Interfaces
- 2013
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 29:8, s. 2683-2691
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Tidskriftsartikel (refereegranskat)abstract
- Hydrophobins are relatively small globular proteins produced by filamentous fungi. They display unusual high surface activity and are implied as mediators of attachment to surfaces, which has resulted in high scientific and technological interest. In this work we focus on kinetic and equilibrium aspects of adsorption and desorption properties of two representatives of class II hydrophobins, namely HFBI and HFBII, at a negatively charged hydrophilic solid/water interface and at the air/water interface. The layers formed at the air/liquid interface were examined in a Langmuir trough, whereas layers formed at the solid/liquid interface were studied using dual polarization interferometry (DPI) under different flow conditions. For comparison, another globular protein, lysozyme, was also investigated. It was found that both the adsorbed amount and the adsorption kinetics were different for HFBI and HFBII, and the adsorption behavior of both hydrophobins on the negatively charged surface displayed some unusual features. For instance, even though the adsorption rate for HFBI was slowed down with increasing adsorbed amount as expected from packing constraints at the interface, the adsorption kinetics curves for HFBII displayed a region indicating adsorption cooperativity. Further, it was found that hydrophobin layers formed under flow partly desorbed when the flow was stopped, and the desorption rate for HFBII was enhanced in the presence of hydrophobins in solution.
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| 3. |
- Lundin, Maria, et al.
(författare)
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Polymer Dynamics in Layer-by-Layer Assemblies of Chitosan and Heparin
- 2010
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:5, s. 3242-3251
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Tidskriftsartikel (refereegranskat)abstract
- The layer-by-layer deposition method has been used to build a multilayer thin film with two polysaccharides, chitosan CH (weak polycation) and heparin HEP (strong polyanion), on planar quartz surfaces. The film structure and dynamics in aqueous Solution were studied with fluorescence resonance energy transfer (FRET) and total internal reflection fluorescence (TIRF). Particular emphasis was placed on the effect of deposition conditions, i.e.. pH and salt concentration, on the out-of-plane (vertical) diffusion of fluorescence labeled chitosan in the chitosan/heparin (CH/HEP) film. FRET analysis showed that CH molecules diffused within the film with a diffusion coefficient that was not significantly sensitive to the deposition pH and Solution ionic strength. A pH-sensitive label bound to CH embedded within the CH/HEP Film wits sensitive to the charge of the outermost polymer layer even when buried under 14 alternate layers of CH and HER A consideration of the results obtained with both fluorescence techniques showed that the structure of the CH/HEP thin film wits highly interpenetrated without clear boundaries between each layer. These results are consistent with the hypothesis that the previously observed exponential-like film growth of CH and HEP in terms of, layer thickness and deposited amount versus deposition cycle can be attributed to out-of-plane diffusion of CH molecules in the multilayer.
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| 4. |
- Phenrat, Tanapon, et al.
(författare)
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Polymer-Modified Fe(0) Nanoparticles Target Entrapped NAPL in Two Dimensional Porous Media : Effect of Particle Concentration, NAPL Saturation, and Injection Strategy
- 2011
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 45:14, s. 6102-6109
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Tidskriftsartikel (refereegranskat)abstract
- Polymer-modified nanoscale zerovalent iron (NZVI) particles are delivered into porous media for in situ remediation of nonaqueous phase liquid (NAPL) source zones. A systematic and quantitative evaluation of NAPL targeting by polymer-modified NZVI in two-dimensional (2-D) porous media under field-relevant conditions has not been reported. This work evaluated the importance of NZVI particle concentration, NAPL saturation, and injection strategy on the ability of polymer-modified NZVI (MRNIP2) to target the NAPL/water interface in situ in a 2-D porous media model. Dodecane was used as a NAPL model compound for this first demonstration of source zone targeting in 2-D. A driving force for NAPL targeting, the surface activity of MRNIP2 at the NAPL/water interface was verified ex situ by its ability to emulsify NAPL in water. MRNIP2 at low particle concentration (0.5 g/L) did not accumulate in or near entrapped NAPL, however, MRNIP2 at moderate and high particle concentrations (3 and 15 g/L) did accumulate preferentially at entrapped NAPL, i.e., it was capable of in situ targeting. The amount of MRNIP2 that targets a NAPL source depends on NAPL saturation (S(n)), presumably because the saturation controls the available NAPL/water interfacial area and the flow field through the NAPL source. At effective S(n) close or equal to 100%, MRNIP2 bypassed NAPL and accumulated only at the periphery of the entrapped NAPL region. At lower S(n), flow also carries MRNIP2 to NAPL/water interfaces internal to the entrapped NAPL region. However, the mass of accumulated MRNIP2 per unit available NAPL/water interfacial area is relatively constant (similar to 0.8 g/m(2) for MRNIP2 = 3 g/L) from S(n) = 13 to similar to 100%, suggesting that NAPL targeting is mostly controlled by MRNIP2 sorption onto the NAPL/water interface.
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| 5. |
- Riley, John K., et al.
(författare)
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Ionic Surfactant Binding to pH-Responsive Polyelectrolyte Brush-Grafted Nanoparticles in Suspension and on Charged Surfaces
- 2015
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 31:51, s. 13680-13689
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Tidskriftsartikel (refereegranskat)abstract
- The interactions between silica nanoparticles grafted with a brush of cationic poly(2-(dimethylamino) ethyl methacrylate) (SiO2-g-PDMAEMA) and anionic surfactant sodium dodecyl sulfate (SDS) is investigated by dynamic light scattering, electrophoretic mobility, quartz crystal microbalance with dissipation, ellipsometry, and atomic force microscopy. SiO2-g-PDMAEMA exhibits pH-dependent charge and size properties which enable the SDS binding to be probed over a range of electrostatic conditions and brush conformations. SDS monomers bind irreversibly to SiO2-g-PDMAEMA at low surfactant concentrations (similar to 10(-4) M) while exhibiting a pH-dependent threshold above which cooperative, partially reversible SDS binding occurs. At pH 5, SDS binding induces collapse of the highly charged and swollen brush as observed in the bulk by DLS and on surfaces by QCM-D. Similar experiments at pH 9 suggest that SDS binds to the periphery of the weakly charged and deswollen brush and produces SiO2-g-PDMAEMA/SDS complexes with a net negative charge. SiO2-g-PDMAEMA brush collapse and charge neutralization is further confirmed by colloidal probe AFM measurements, where reduced electrosteric repulsions and bridging adhesion are attributed to effects of the bound SDS. Additionally, sequential adsorption schemes with SDS and SiO2-g-PDMAEMA are used to enhance deposition relative to SiO2-g-PDMAEMA direct adsorption on silica. This work shows that the polyelectrolyte brush configuration responds in a more dramatic fashion to SDS than to pH-induced changes in ionization, and this can be exploited to manipulate the structure of adsorbed layers and the corresponding forces of compression and friction between opposing surfaces.
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| 6. |
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| 7. |
- Saigal, Trishna, et al.
(författare)
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Poly(ethylene oxide) star polymer adsorption at the silica/aqueous interface and displacement by linear poly(ethylene oxide)
- 2013
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 29:12, s. 3999-4007
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Tidskriftsartikel (refereegranskat)abstract
- Multiarm star copolymers with approximately 460 poly(ethylene oxide) (PEO) arms that have a degree of polymerization N = 45 were synthesized via atom transfer radical polymerization (ATRP) of PEO-methacrylate macromonomers in the presence of divinyl benzene cross-linkers. These are an example of molecular or nanoparticulate brushes that are of interest as steric stabilizers or boundary lubrication agents when adsorbed from solution to a solid/aqueous interface. We use ellipsometry to measure adsorption isotherms at the silica/aqueous interface for PEO star polymers and linear PEO chains having molecular weights comparable either to the star polymer or to the individual arms. The compactness of the PEO star polymers (molecular weight 1.2 × 106) yields a saturation surface excess concentration that is approximately 3.5 times greater than that of the high molecular weight (1 × 106) linear PEO. Adsorption of low molecular weight (6000) linear PEO was below the detection limit. Competitive adsorption experiments were conducted with ellipsometry, complemented by independent quartz crystal microbalance with dissipation (QCM-D) measurements. Linear PEO (high molecular weight) displaced preadsorbed PEO star polymers over the course of approximately 1.5 h, to form a mixed adsorbed layer having not only a significantly lower overall polymer surface excess concentration, but also a significantly greater amount of hydrodynamically entrapped water. Challenging a preadsorbed linear PEO (high molecular weight) layer with PEO star polymers produced no measurable change in the overall polymer surface excess concentration, but changes in the QCM-D energy dissipation and resonance frequency suggested that the introduction of PEO star polymers caused a slight swelling of the layer with a correspondingly small increase in entrapped water content.
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