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- 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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| 2. |
- Andersson, Helena, 1966
(författare)
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Spira frågar Jörgen Lundälv
- 2009
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Ingår i: SPIRA - från Svenska kyrkan i Umeå. ; :6, s. 4-
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Annan publikation (övrigt vetenskapligt/konstnärligt)
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| 3. |
- Andersson, Helena, 1966
(författare)
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Crosslinking of Polymers. Molecular Structure and Properties of Sol and Network
- 2004
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Crosslinking is a well-known procedure for improving a variety of features of polymers, particularly the dimension stability at elevated temperatures. Crosslinking implies the formation of a network, the gel, but there is always a certain portion of the material, the sol, that remains non-crosslinked within the network. Both fractions contribute to the properties of the crosslinked polymer, and the relative importance of the respective fraction depends on the type of polymer and the field of application. In this thesis, the significance of the molecular structure and property of a sol was illustrated by investigating the ability of crosslinked silicone elastomers to contaminate nearby structures, while analyses of the molecular structure of crosslinked polyethylene elucidated the behaviour of the network. The silicone study showed that the non-crosslinked fraction of a cured silicone elastomer consists mainly of non-volatile, low molecular weight siloxanes with a potential capacity of causing silicone contamination through migration. Gel-content determinations together with molecular weight determinations of the sol clearly showed that the most effective way to minimise migration is to remove the low molecular weight fraction prior to crosslinking. Thermal analyses demonstrated the pronounced temperature sensitivity of the crosslinking process, something which must be considered, as a too low temperature could lead to unnecessary low gel-contents, whereas an elevated temperature can be used as a tool to increase the final curing level. Analyses of crosslinked polyethylene demonstrated an extensive impact of the molecular weight on the gel-content formed upon crosslinking. Bimodal polyethylene, which always contains a substantial amount of low molecular weight chains, can thereby be prevented from developing high gel-contents upon crosslinking. A polymer network is to a large extent affected by the presence of long chain branches on the polymer chain. The amount and length of the branches influence the network performance mainly by affecting disentanglement of the branches. Coil volume and intramolecular crosslinking are other factors that are governed by the presence of long chain branches.
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