| 1. |
- Modig, Gustaf, et al.
(författare)
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Homogenization-induced degradation of hydrophobically modified starch determined by asymmetrical flow field-flow fractionation and multi-angle light scattering
- 2006
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Ingår i: Food Hydrocolloids. - : Elsevier BV. - 0268-005X. ; 20:7, s. 1087-1095
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Tidskriftsartikel (refereegranskat)abstract
- High-pressure homogenization of modified starches is a type of treatment used within the food and pharmaceutical industry for the production of emulsions. Such intense mechanical treatment may, however, influence the size and size distribution of the starch polymer, which may affect the properties of the emulsions. In this work, asymmetrical flow field-flow fractionation (AsFIFFF) connected on-line to a multi-angle light scattering detector (MALS) was used to study the influence of high-pressure homogenization upon molar mass and root-mean-square (r.m.s.) radius of three different octenyl succinate anhydride (OSA) starch samples originating from potato. The homogenization at constant pressure resulted in a significant decrease of both molar mass and r.m.s. radius. The magnitude of the change in molar mass and r.m.s. radius could be correlated to the initial size of the OSA starch and the energy dissipation rate of the homogenization treatment.
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| 2. |
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| 3. |
- Nilsson, Lars, et al.
(författare)
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Competitive adsorption of a polydisperse polymer during emulsification: Experiments and modeling
- 2007
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 23:5, s. 2346-2351
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we study the selective adsorption of a high molar mass polymer, OSA-starch, at the cyclohexane/water interface during emulsification. This was made possible through the use of AsFlFFF-MALS-RI which enables us to characterize the size and molar mass of polydisperse ultrahigh molar mass polymers. The results show that the high molar mass components in the molar mass distribution of the polymer were selectively adsorbed. The selective adsorption is most likely due to convective mass transport in the turbulent flow fields, during formation of the emulsion, which favors transport to the interface of the high molar mass polymers in the sample. The rapid adsorption that occurs during emulsification is likely to give rise to nonequilibrium effects and jamming at the interface. Furthermore, we describe the adsorption process and illustrate its selective nature through a turbulent flow collision model.
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| 4. |
- Nilsson, Lars, et al.
(författare)
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Mechanical degradation and changes in conformation of hydrophobically modified starch
- 2006
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1526-4602 .- 1525-7797. ; 7:9, s. 2671-2679
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we study the mechanical degradation and changes in conformation of a branched ultrahigh molar mass biomacromolecule, hydrophobically modified starch, as caused by high-pressure homogenization. The characterization was performed with asymmetrical flow field-flow fractionation (AsFlFFF) with multiangle light scattering (MALS) and refractive index detection. The starch which had been chemically modified with octenyl succinate anhydride (OSA) proved to be very large and polydisperse. Upon high-pressure homogenization, the molar mass and rms radius (r(rms)) decreased, and the extent of these changes was related to the turbulent flow conditions during homogenization. The treatment also induced an increase and scaling with size in the apparent density of the macromolecules. To further study the changes in conformation, it was necessary to calculate the hydrodynamic radii (r(h)). This can be determined numerically from the elution times in the analysis and the flow conditions in the AsFlFFF channel. The results showed that the treatment can cause a dramatic decrease in the quotient between r(rms) and r(h), suggesting major conformational changes. These results together could be interpreted as degradation and "crumpling" of the macromolecule, which would give a decrease in rrms and an increase in apparent density, together with a "fraying" of more outer parts of the macromolecule, which could give rise to the increase in r(h).
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| 5. |
- Rojas, Carola, et al.
(författare)
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Macromolecular geometries determined with field-flow fractionation and their impact on the overlap concentration.
- 2008
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Ingår i: Biomacromolecules. - : American Chemical Society (ACS). - 1526-4602 .- 1525-7797. ; 9:6, s. 1684-1690
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Tidskriftsartikel (refereegranskat)abstract
- In this paper we aim to understand the size/conformation relationship in waxy barley starch, a polydisperse and ultrahigh molar mass biomacromolecule. Characterizations are performed with asymmetrical flow field-flow fractionation (AsFlFFF). Furthermore, we study the effect of homogenization on the molar mass, rms radius (r rms) and hydrodynamic radius (r h). For the untreated sample, the macromolecules are elongated objects with low apparent density. As a result of homogenization, molar mass, and r rms decrease, while r h remains unaffected. The process also induces an increase, and scaling with size, of apparent density as well as changes in conformation, represented qualitatively by r rms/ r h. Finally, results from AsFlFFF are compared with viscosimetry and discussed in terms of concentration and close-packing in relation to macromolecular shape and conformation. Hence, the results show that AsFlFFF and our novel methodology enable the determination of several physical properties with high relevance for the solution behavior of polydisperse macromolecules.
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| 6. |
- Tornberg, Anna-Karin, et al.
(författare)
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A new type of boundary treatment for wave propagation
- 2006
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Ingår i: BIT Numerical Mathematics. - : Springer Science and Business Media LLC. - 0006-3835 .- 1572-9125. ; 46, s. S145-S170
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Tidskriftsartikel (refereegranskat)abstract
- Numerical approximation of wave propagation can be done very efficiently on uniform grids. The Yee scheme is a good example. A serious problem with uniform grids is the approximation of boundary conditions at a boundary not aligned with the grid. In this paper, boundary conditions are introduced by modifying appropriate material coefficients at a few grid points close to the embedded boundary. This procedure is applied to the Yee scheme and the resulting method is proven to be L2-stable in one space dimension. Depending on the boundary approximation technique it is of first or second order accuracy even if the boundary is located at an arbitrary point relative to the grid. This boundary treatment is applied also to a higher order discretization resulting in a third order accurate method. All algorithms have the same staggered grid structure in the interior as well as across the boundaries for efficiency. A numerical example with the extension to two space dimensions is included.
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