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| 2. |
- Abrahamsson, Christoffer K., et al.
(författare)
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Magnetically induced structural anisotropy in binary colloidal gels and its effect on diffusion and pressure driven permeability
- 2014
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-683X .- 1744-6848. ; 10:24, s. 4403-4412
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Tidskriftsartikel (refereegranskat)abstract
- We report on the synthesis, microstructure and mass transport properties of a colloidal hydrogel self-assembled from a mixture of colloidal silica and nontronite clay plates at different particle concentrations. The gel-structure had uniaxial long-range anisotropy caused by alignment of the clay particles in a strong external magnetic field. After gelation the colloidal silica covered the clay particle network, fixing the orientation of the clay plates. Comparing gels with a clay concentration between 0 and 0.7 vol%, the magnetically oriented gels had a maximum water permeability and self-diffusion coefficient at 0.3 and 0.7 vol% clay, respectively. Hence the specific clay concentration resulting in the highest liquid flux was pressure dependent. This study gives new insight into the effect of anisotropy, particle concentration and bound water on mass transport properties in nano/microporous materials. Such findings merit consideration when designing porous composite materials for use in for example fuel cell, chromatography and membrane technology.
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| 3. |
- Abrahamsson, Christoffer, 1984, et al.
(författare)
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Magnetic orientation of nontronite clay in aqueous dispersions and its effect on water diffusion
- 2015
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 0021-9797 .- 1095-7103. ; 437, s. 205-210
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Tidskriftsartikel (refereegranskat)abstract
- The diffusion rate of water in dilute clay dispersions depends on particle concentration, size, shape, aggregation and water-particle interactions. As nontronite clay particles magnetically align parallel to the magnetic field, directional self-diffusion anisotropy can be created within such dispersion. Here we study water diffusion in exfoliated nontronite clay dispersions by diffusion NMR and time-dependant 1H-NMR-imaging profiles. The dispersion clay concentration was varied between 0.3 and 0.7 vol%. After magnetic alignment of the clay particles in these dispersions a maximum difference of 20% was measured between the parallel and perpendicular self-diffusion coefficients in the dispersion with 0.7 vol% clay. A method was developed to measure water diffusion within the dispersion in the absence of a magnetic field (random clay orientation) as this is not possible with standard diffusion NMR. However, no significant difference in self-diffusion coefficient between random and aligned dispersions could be observed.
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| 4. |
- Abrahamsson, Christoffer, 1984, et al.
(författare)
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Magnetically induced structural anisotropy in binary colloidal gels and its effect on diffusion and pressure driven permeability
- 2014
-
Ingår i: Soft Matter. - 1744-683X .- 1744-6848. ; 10:24, s. 4403-4412
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the synthesis, microstructure and mass transport properties of a colloidal hydrogel selfassembled from a mixture of colloidal silica and nontronite clay plates at different particle concentrations. The gel-structure had uniaxial long-range anisotropy caused by alignment of the clay particles in a strong external magnetic field. After gelation the colloidal silica covered the clay particle network, fixing the orientation of the clay plates. Comparing gels with a clay concentration between 0 and 0.7 vol%, the magnetically oriented gels had a maximum water permeability and self-diffusion coefficient at 0.3 and 0.7 vol% clay, respectively. Hence the specific clay concentration resulting in the highest liquid flux was pressure dependent. This study gives new insight into the effect of anisotropy, particle concentration and bound water on mass transport properties in nano/microporous materials. Such findings merit consideration when designing porous composite materials for use in for example fuel cell, chromatography and membrane technology.
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| 5. |
- Almgren, Mats, et al.
(författare)
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Nonideal Mixed Micelles of Fluorinated and Hydrogenous Surfactants in Aqueous Solution. NMR and SANS Studies of Anionic and Nonionic Systems
- 2010
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 26:8, s. 5355-5363
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Tidskriftsartikel (refereegranskat)abstract
- Contrast variation SANS and F-19 chemical shifts were measured for three mixed equimolar micelle systems: sodium perfluorooctanoate (SPED) and sodiumdecylsulfate (SDeS) in 200 mM NaCl, lithium perlluorononanate LiPFN) and lithium dodecylsulfate (Li DS) in 200 mM LiCl, and a nonionic system C8F17C2H4(OC2H4)(9) and C12H25(OC2H4)(8) in water, all at 25 C. The chemical shift measurements allow the calculation of the average fraction of nearest neighbors of each kind around the reporter group (the trifluoromethyl group). A preference for like neighbors were found in all systems, smallest in the SDeS/SPFO system and largest in the nonionic system, but in all cases substantially smaller than expected at critical conditions. From the SANS measurements the width of the micelle composition distribution was obtained. For the ionic systems similar values were obtained, showing a broadening compared to ideal mixtures, but not broad enough for demixing or clearly bimodal distributions. In the nonionic system the width was estimated as sigma = 0.18 and 0.22 using two different evaluation methods. These values suggest that the system is close to critical conditions. The lower value refers to a direct modeling of the system, assuming an ellipsoidal shape and a Gaussian composition distribution. The modeling showed the nonionic mixed micelles to be prolate ellipsoids with axial ratio 2.2 and an aggregation number larger than 100. whereas the two ionic systems fitted best to oblate shapes (axial ratios 0.8 and 0.65 for SDeS/SPFO and LiDS/LiPFN. respectively) and aggregation numbers of 60 for both.
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| 6. |
- Andersson Trojer, Markus, 1981, et al.
(författare)
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Charged microcapsules for controlled release of hydrophobic actives. Part III: The effect of polyelectrolyte brush- and multilayers on sustained release
- 2013
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 15:17, s. 6153-6165
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Tidskriftsartikel (refereegranskat)abstract
- Poly(methyl methacrylate) microspheres have been prepared by the internal phase separation method using either of the three conventional dispersants poly(vinyl alcohol) (PVA), poly(methacrylic acid) (PMAA), or the amphiphilic block copolymer poly(methyl methacrylate)-block-poly(sodium methacrylate). The block copolymer based microsphere, which has a polyelectrolyte brush on the surface, was surface modified with up to two poly(diallyldimethylammonium chloride)-poly(sodium methacrylate) bilayers. The microspheres were loaded with the hydrophobic dye 2-(4-(2-chloro-4-nitrophenylazo)-N-ethylphenylamino)ethanol (Disperse Red 13) and its release from aqueous dispersions of microspheres with the different surface compositions was measured by spectrophotometry. The burst fraction, burst rate and the diffusion constant were determined from a model combining burst and diffusive release. Out of the three dispersants, the block copolymer gave the slowest release of the dye, with respect to both burst release and diffusive release. A very pronounced further reduction of the diffusion constant was obtained by applying polyelectrolyte multilayers on top of the microspheres. However, the diffusion constant was very weakly dependent on further polyelectrolyte adsorption and one polyelectrolyte bilayer appeared to suffice.
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| 7. |
- Andersson Trojer, Markus, 1981, et al.
(författare)
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Encapsulation of actives for sustained release
- 2013
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 15:41, s. 17727-17741
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Forskningsöversikt (refereegranskat)abstract
- Encapsulation of actives in miniature reservoirs, called microcapsules, is used for protection and in particular controlled release of the active. Regarding controlled release applications, the most common function of the microcapsule is to sustain or extend the release of the active. A number of encapsulation methodologies are available including; internal phase separation, interfacial polymerization, formation of multiple emulsions, Layer-by-Layer adsorption of polyelectrolytes and soft templating techniques, all of which are reviewed in this Perspective. The choice of method depends on the nature of the active (hydrophilic/hydrophobic, size, physical state) and on the intended release rate and release profile. Ways to manipulate the release of the active by tailoring the physicochemical properties of the microcapsule are reviewed. Moreover, appropriate diffusion models are introduced to describe the release profile from a variety of microcapsule morphologies, including Fickian diffusion models and Brownian motion, and the meaning and the misuse of the term ``zero-order release'' are briefly discussed.
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| 8. |
- Andersson Trojer, Markus, 1981, et al.
(författare)
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Polymer Core-Polymer Shell Particle Formation Enabled by Ultralow Interfacial Tension Via Internal Phase Separation: Morphology Prediction Using the Van Oss Formalism
- 2018
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Ingår i: Colloid and Interface Science Communications. - : Elsevier BV. - 2215-0382. ; 25, s. 36-40
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Tidskriftsartikel (refereegranskat)abstract
- The internal phase separation technique is a versatile method for liquid core-polymer shell formation, yet limited to very hydrophobic core materials and actives. The use of polymeric cores instead circumvents this restriction due to the absent mixing entropy for binary polymer mixtures which allows the polymeric core (and the active) to approach the polarity of the shell. Polystyrene core-shell and janus particles were formulated using polymethylmethacrylate, poly(lactic acid), poly(lactic acid-co-glycolic acid), poly(epsilon-caprolactone) or cellulose triacetate as shell-forming polymers. The morphology and the partitioning was experimentally determined by selectively staining the core and the shell with beta-carotene and methylene blue respectively. In addition, the van Oss formalism was introduced to theoretically predict the thermodynamic equilibrium morphology. As elucidated using the theoretical predictions as well as experimental optical tensiometry, it was found that the driving force for core-shell morphology is, in contrast to liquid core-polymer shell particles, a low core-shell interfacial tension.
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| 9. |
- Andersson Trojer, Markus, et al.
(författare)
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Use of anchoring amphiphilic diblock copolymers for encapsulation of hydrophilic actives in polymeric microcapsules : methodology and encapsulation efficiency
- 2019
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Ingår i: Colloid and Polymer Science. - : Springer Science and Business Media LLC. - 0303-402X .- 1435-1536. ; 297:2, s. 307-313
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Tidskriftsartikel (refereegranskat)abstract
- Aqueous core-shell particles based on polystyrene, poly(methyl methacrylate) or polycaprolactone have been formulated using a facile double emulsion-based solvent evaporation method. The size distribution is narrow, and the morphology control is remarkable given the simple characteristics of the encapsulation method. The inner droplets are stabilized by oil-soluble poly(ethylene oxide)-based block copolymers which are anchored in the polymeric shell by using hydrophobic blocks of the same type as that of the shell-forming polymer. This facilitates the efficient encapsulation of dyes and hydrophilic biocides. [Figure not available: see fulltext.].
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| 10. |
- Andersson Trojer, Markus, 1981, et al.
(författare)
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Use of microcapsules as controlled release devices for coatings
- 2015
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Ingår i: Advances in Colloid and Interface Science. - : Elsevier BV. - 0001-8686. ; 222, s. 18-43
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Tidskriftsartikel (refereegranskat)abstract
- Biofouling of surfaces is a considerable problem in many industrial sectors and for the public community in general. The problem is usually approached by the use of functional coatings and most of such antifouling coatings rely on the effect of biocides. However, a substantial drawback is the poor control over the release of the biocide as well as its degradation in the paint. Encapsulation of the biocides in microcapsules is a promising approach that may overcome some of the problems associated with the more traditional ways of incorporating the antifouling agent into the formulation. In this review, we summarize more than a decade of microcapsule research from our lab as well as from other groups working on this topic. Focus will be on two coacervation-based encapsulation techniques; the internal phase separation method and the double emulsion method, which together enable the encapsulation of a broad spectrum of biocides with different physicochemical properties. The release of the biocide from core-shell particles and from encapsulated biocides in coatings is treated in detail. The release behaviour is interpreted in terms of the physicochemical properties of the core-shell particle and the coating matrix. In addition, special attention is given to the experimental release methodology and the implementation of proper diffusion models to describe the release. At the end of the review examples of antifouling properties of some coatings against common biofoulers are presented.
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