| 1. |
- Björkegren, Sanna, 1984, et al.
(författare)
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Surface activity and flocculation behavior of polyethylene glycol-functionalized silica nanoparticles
- 2015
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 452, s. 215-223
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Tidskriftsartikel (refereegranskat)abstract
- Colloidal silica nanoparticles have been functionalized with methyl polyethylene glycol silane (mPEG silane) and the PEGylated particles have been characterized with focus on exploring their surface chemical properties. The degree of surface functionalization was quantified using NMR diffusometry, and the measurements showed that the silane binds covalently to the silica surface. Samples with surface coverages ranging from 0.068 to 0.315 gmol silane/m(2) have been analyzed. The functionalized particles proved to be surface active and showed a significant reduction in surface charge and zeta potential with increasing degree of PEG functionalization. All samples showed colloidal stability at neutral pH and above within the range studied. At lower pH, the samples with low surface coverage displayed a reversible flocculation behavior, while samples with a high surface coverage and samples without functionalization remained stable. This suggests that steric stabilization is effective at low pH when the surface coverage is high enough; electrostatic stabilization is effective for samples without functionalization; and that inter-particle PEG-silica interactions cause flocculation of particles with too low degrees of PEG functionalization.
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| 2. |
- Björkegren, Sanna, 1984, et al.
(författare)
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Clouding observed for surface active, mPEG-grafted silica nanoparticles
- 2019
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Ingår i: RSC Advances. - : Royal Society of Chemistry (RSC). - 2046-2069. ; 9:23, s. 13297-13303
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Tidskriftsartikel (refereegranskat)abstract
- Temperature-dependent phase-separation, clouding, has been observed in suspensions of silica nanoparticles surface-functionalized with methyl-poly(ethylene glycol) silane. Interparticle interactions and conformational changes of the grafted poly(ethylene glycol) chains influence the observed cloud points, and can be controlled by electrolyte concentration and pH. These findings open new routes to tailoring properties of Pickering emulsions.
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| 3. |
- Björkegren, Sanna, 1984, et al.
(författare)
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Hydrophilic and hydrophobic modifications of colloidal silica particles for Pickering emulsions
- 2017
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Ingår i: Journal of Colloid and Interface Science. - : Elsevier BV. - 1095-7103 .- 0021-9797. ; 487, s. 250-257
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Tidskriftsartikel (refereegranskat)abstract
- Colloidal silica particles, functionalized with hydrophilic and hydrophobic groups, have been studied for utilization in particle-stabilized emulsions, so called Pickering emulsions. The amounts of attached groups have been characterized using NMR spectroscopy and elemental analysis. A range of particles were prepared, with sizes from around 13 to 70 nm in diameter. Hydrophilic functionalization of the silica sols was achieved by attaching methyl poly(ethylene glycol) (mPEG) silane to the silica particle surface. This provides a reduction of surface charge density, a pH dependent and controllable flocculation behavior and surface activity. The hydrophobic functionalization of the silica sols was accomplished by attaching organosilanes containing mainly propyl and methyl groups. The emulsification abilities were evaluated by preparing Pickering emulsions using particles, with varying degrees and combinations of surface functionalization, as stabilizers and comparing the obtained emulsion droplet size distributions. It was found that colloidal silica functionalized with hydrophobic groups produced emulsions with smaller droplets compared to using unmodified silica. The emulsification performance was further improved by the combination of both hydrophilic and hydrophobic groups. All particles having this heterogeneous modification were found to generate emulsions with high stability towards coalescence (from five weeks to 1.5 years).
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| 4. |
- Björkegren, Sanna, 1984, et al.
(författare)
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Phase Inversions Observed in Thermoresponsive Pickering Emulsions Stabilized by Surface Functionalized Colloidal Silica
- 2020
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 1520-5827 .- 0743-7463. ; 36:9, s. 2357-2367
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the emulsification performance of functionalized colloidal silica is explored with the aim to achieve phase inversion of particle-stabilized (Pickering) emulsion systems. An increased understanding of inversion conditions can facilitate surfactant-free emulsion fabrication and expand its use in industrial applications. Phase inversion was achieved by adjusting the temperature but without changing the composition of the emulsion formulation. Silica nanoparticles modified with hydrophobic propyl groups and hydrophilic methyl poly(ethylene)glycol (mPEG) groups are used as emulsifiers, enabling control of the wettability of the particles and exploration of phase inversion phenomena, the latter due to the thermoresponsiveness of the attached PEG chains. The phase inversion conditions as well as the reversibility of the emulsion systems were examined at varying electrolyte concentrations and pH values of the suspensions. Transitional phase inversions, from oil-in-water and water-in-oil and back, were observed in functionalized silica particle-stabilized butanol emulsions at distinct temperatures. The phase inversion temperature was affected by electrolyte concentration and pH conditions due to salting-out effects, PEG-silica interactions, and the effects of the particle surface charge. Investigations of phase inversion conditions, temperature, and hysteresis effects in Pickering emulsions can improve the theoretical understanding of these phenomena and facilitate the implementation of low-energy emulsion preparation.
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