| 1. |
- Bergenholtz, Johan, 1964, et al.
(författare)
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Analysis of small-angle X-ray scattering data in the presence of significant instrumental smearing
- 2016
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Ingår i: Journal of Applied Crystallography. - 0021-8898 .- 1600-5767. ; 49, s. 47-54
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Tidskriftsartikel (refereegranskat)abstract
- A laboratory-scale small-angle X-ray scattering instrument with pinhole collimation has been used to assess smearing effects due to instrumental resolution. A new, numerically efficient method to smear ideal model intensities is developed and presented. It allows for directly using measured profiles of isotropic but otherwise arbitrary beams in smearing calculations. Samples of low-polydispersity polymer spheres have been used to show that scattering data can in this way be quantitatively modeled even when there is substantial distortion due to instrumental resolution.
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| 2. |
- Jonsson, Kristin, 1988, et al.
(författare)
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Semi-batch synthesis of colloidal spheres with fluorinated cores and varying grafts of poly(ethylene glycol)
- 2017
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Ingår i: Colloid and Polymer Science. - : Springer Science and Business Media LLC. - 0303-402X .- 1435-1536. ; 295:10, s. 1983-1991
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Tidskriftsartikel (refereegranskat)abstract
- Fluorinated spheres with grafted poly(ethyleneglycol) (PEG) have been synthesized using a semi-batch emulsion polymerization in which the initiator is fed slowly to the reaction. In this way, PEG-grafted colloidal spherescan be fabricated with varying PEG chain length, different cores and varying degrees of crosslinking. The resulting batches have been characterized using disc centrifuge photo-sedimentometry and small-angle X-ray scattering. The size distribution is shown to be a sensitive function of the molar ratio of the reactive PEG macromonomer to fluorinated monomer, and with some optimization latices of very low polydispersity can be obtained with this simple synthesis method. For short PEG grafts too high a molar ratio results in a build up of smaller size particles and a broadening of the size distribution, whereas for longer grafts the mean particle size increases with decreasing molar ratio.
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| 3. |
- Jonsson, Kristin, 1988, et al.
(författare)
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Stabilizing Colloidal Particles against Salting-out by Shortening Surface Grafts
- 2019
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 35:36
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Tidskriftsartikel (refereegranskat)abstract
- A dramatic improvement is reported in the stability of colloidalparticles when stabilizing surface grafts are systematically shortened from small polymers to single monomers. The colloidal dispersions consist of fluorinated latex particles, exhibiting a weak van der Waals attraction, with grafted steric layers of poly(ethylene glycol) (PEG) of different chain lengths. Using an effective salting-out electrolyte, Na2CO3, particle aggregates are detected above a threshold salt concentration that is independent of the particle concentration. The results are interpreted in terms of a sudden onset of nondispersibility of single particles, triggered by the solvent not completely wetting particle surfaces. By decreasing the PEG chain length, the threshold salt concentration is found to increase sharply. For grafts with just a single ethylene glycol group, dispersions remain stable up to exceedingly high concentrations of Na2CO3. However, on removal of the surface coverage altogether, the classical stability behavior of charge-stabilized dispersions is recovered. The behavior can be captured by a simple model that incorporates effective polymer−solvent interactions in the presence of an electrolyte.
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| 4. |
- Oskolkova, Malin Zackrisson, 1974, et al.
(författare)
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Concentration-dependent effective attractions between PEGylated nanoparticles
- 2015
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Ingår i: RSC Advances. - 2046-2069. ; 5:32, s. 25149-25155
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Tidskriftsartikel (refereegranskat)abstract
- Effective attractions between colloidal particles bearing a grafted poly(ethylene glycol) (PEG) layer in water have been studied and quantified by measurements of the collective diffusion coefficient and by quantitative analysis of small-angle neutron scatterin (SANS) data. Results for the collective diffusion coefficient in the dilute limit indicate that effective attractions develop gradually as carbonate anions are added to the dispersions. Analysis of SANS data within a square-well interaction model at a constant salt concentration allows for quantitative analysis of scattering patterns of samples prior to crossing into an aggregation regime, where particles form large clusters, reached either through increasing the temperature or the particle concentration. Aggregation is observed visually and is also evident in the scattering as a lowering of the intensity at intermediate wavevectors while leaving enhanced scattering in the forward direction, suggesting a nearby fluid–fluid phase transition. In addition, at low and moderate particle concentrations the attraction strength is shown to depend mainly on temperature but at high particle concentrations a much stronger temperature dependence is observed, which shows that the attraction acquires a dependence on particle concentration at sufficiently high concentrations. The concentration dependence is attributed to a decreased solvation of PEG chains due to an increased ratio of ethylene oxide segments to water.
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| 5. |
- Ulama, Jeanette
(författare)
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A Waterborne Colloidal Model System Consisting of Fluorinated Spheres Bearing Grafted PEG: Synthesis, Characterization and Properties
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Model systems have expanded our knowledge of numerous phenomena in Colloid Science, such as the appearance of glasses, order-disorder transitions involving crystals and attraction induced formation of gels. So far, the existing colloidal model systems have been limited mainly to nonaqueous media. Given that water is such an important solvent, an aqueous colloidal model system is called for. Here we present such an aqueous colloidal model system with core-shell particle morphology, where the interior is composed of spherical fluorinated cores and the exterior of a poly(ethylene glycol) (PEG) polymer graft. To synthesize these colloids, we have adopted a semi-batch emulsion polymerization, in which the initiator is slowly fed into the reaction mixture. Using this approach not only can monodisperse, low refractive index and sterically stabilized colloids be produced, but also various lengths of the PEG polymer could be successfully grafted onto the particles. Throughout this thesis, several different instrumental techniques have been used to gain an insight into the collective phenomena of these particles and how particle interactions contribute to the observed phase behavior. Although steric stabilization is very robust way of stabilizing colloidal particles against aggrega- tion, attractions between particles can nevertheless appear, e.g. through the addition of certain salts or addition of a non-solvent. The origin of these attractions is not fully understood. Our results show that colloidal stability increases with decreasing length of the steric stabilizer and that the polymer graft contracts as the solvent quality is worsened. The contraction is accompanied by moderately strong attractions even though the van der Waals force due to core-core interactions is essentially absent. It follows that the attractions are caused by purely polymer-mediated interactions.
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| 6. |
- Ulama, Jeanette, et al.
(författare)
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Monodisperse PEGylated Spheres: An Aqueous Colloidal Model System
- 2014
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 118:9, s. 2582-2588
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Tidskriftsartikel (refereegranskat)abstract
- Fluorinated core–shell spheres have been synthesized using a novel semibatch emulsion polymerization protocol employing slow feeding of the initiator. The synthesis results in aqueous dispersions of highly monodisperse spheres bearing a well-defined poly(ethylene glycol) graft (PEGylation). Measurements are consistent with the synthesis achieving a high grafting density that moreover consists of a single PEG layer with the polymer significantly elongated beyond its radius of gyration in bulk. The fluorination of the core of the particles confers a low index of refraction such that the particles can be refractive index matched in water through addition of relatively small amounts of a cosolvent, which enables the use of optical and laser-based methods for studies of concentrated systems. The systems exhibit an extreme stability in NaCl solutions, but attractions among particles can be introduced by addition of other salts, in which case aggregation is shown to be reversible. The PEGylated sphere dispersions are expected to be ideally suited as model systems for studies of the effect of PEG-mediated interactions on, for instance, structure, dynamics, phase behavior, and rheology.
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| 7. |
- Ulama, Jeanette, et al.
(författare)
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Polymer-Graft-Mediated Interactions between Colloidal Spheres
- 2016
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 32:12, s. 2882-2890
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Tidskriftsartikel (refereegranskat)abstract
- Aqueous dispersions of fluorinated colloidal spheres bearing grafted poly(ethylene glycol) (PEG) are studied as a function of salt and particle concentration with the aim of improving the understanding of interactions among polymer-grafted particles. These dispersions can sustain large concentrations of salt, but crystals nucleate in dilute dispersions when a sufficient Na2CO3 concentration is reached, which is attributed to the presence of attractions between particles. On further increasing the Na2CO3 concentration, the solvent is rapidly cleared of particles. Small-angle X-ray scattering and cryogenic transmission electron microscopy are employed in order to quantify the attractions. The former is used to extract a second virial coefficient, and the latter shows that the PEG-graft contracts as a function of increasing salt concentration. The contraction not only leads to a reduction in excluded volume but also is accompanied by attractions of moderate magnitude. In contrast, dispersion of the particles in ethanol, in which bulk PEG solutions crystallize, lead to fractal structures caused by strong attractions.
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| 8. |
- Zackrisson Oskolkova, Malin, et al.
(författare)
-
Concentration-dependent effective attractions between PEGylated nanoparticles
- 2015
-
Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 5:32, s. 25149-25155
-
Tidskriftsartikel (refereegranskat)abstract
- Effective attractions between colloidal particles bearing a grafted poly(ethylene glycol) (PEG) layer in water have been studied and quantified by measurements of the collective diffusion coefficient and by quantitative analysis of small-angle neutron scattering (SANS) data. Results for the collective diffusion coefficient in the dilute limit indicate that effective attractions develop gradually as carbonate anions are added to the dispersions. Analysis of SANS data within a square-well interaction model at a constant salt concentration allows for quantitative analysis of scattering patterns of samples prior to crossing into an aggregation regime, where particles form large clusters, reached either through increasing the temperature or the particle concentration. Aggregation is observed visually and is also evident in the scattering as a lowering of the intensity at intermediate wavevectors while leaving enhanced scattering in the forward direction, suggesting a nearby fluid-fluid phase transition. In addition, at low and moderate particle concentrations the attraction strength is shown to depend mainly on temperature but at high particle concentrations a much stronger temperature dependence is observed, which shows that the attraction acquires a dependence on particle concentration at sufficiently high concentrations. The concentration dependence is attributed to a decreased solvation of PEG chains due to an increased ratio of ethylene oxide segments to water.
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