| 1. |
- Ahlström, Peter, et al.
(author)
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Water absorption in polymers
- 2010
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Conference paper (other academic/artistic)abstract
- In this work two different examples of water absorbtion in polymers are studied by Monte Carlo simulations. Both of them are of large technical and commercial impotance. The first example is the water absorption in polyethylene cables where the water absorption plays a crucial role in the degradation of the cable insulation and thus should be as low as possible. The second example is bio-based superabsorbents made from denatured protein where water absorption capability is the prime desired property. Methods Gibbs Ensemble Monte Carlo simulations [1] were used to study the hydration of polymers. All simulations are performed with two boxes, one of which is filled with water at the start of the simulation, whereas the other contains polymer molecules and possible ions. The polymer molecules are not allowed to swap boxes whereas the water molecules are allowed to do so thus constituting an osmotic Gibbs ensemble [2]. For the polyethylene a connectivity-altering algorithm was used whereas the protein molecules were simulated using a side-chain regrowth model in addition to traditional Monte Carlo moves. For the polyethylene, the TraPPE [3] force field was used and the protein molecules, the Amber force field [4] was used. Water was modelled using simple point charge models [5]. Electrostatic interactions are treated using Ewald summation methods. The protein molecules were of different amino acid compositions and in different conformations, e.g., β-turns and random coils obtained using the amorphous cell method[6]. Studies were made with different degrees of charging on, e.g., lysine side chains mimicking different ionization states. Results The studies of polyethylene revealed the importance of ions left from the polymerisation catalyst for the absorbtion of water and the concomitant degradation of polyethylene cable insulation. Also the absorption properties of the protein molecules is strongly related to the presence of charged groups and fully charged protein molecules absorb large amounts of water. However, neither native nor denatured protein molecules show superabsorbing properties (i.e. absorbing hundreds of times their own mass) as they show in experimental studies and the reasons for this discrepancy will be discussed. References 1. A.Z. Panagiotopoulos, Mol. Phys. 61, 813 (1987). 2. E. Johansson, K. Bolton, D.N. Theodorou, P. Ahlström, J. Chem. Phys., 126, 224902 (2007). 3. M.G. Martin, and J.I. Siepmann, J. Phys. Chem. B, 103, 4508-4517 (1999). 4. W.D. Cornell, P. Cieplak, C.I. Bayly, I.R. Gould, K.M. Merz Jr, D.M. Ferguson, D.C. Spellmeyer, T. Fox, J.W. Caldwell, P.A. Kollman (1995). J. Am. Chem. Soc. 117, 5179–5197. 5. H. J. C. Berendsen, J. P. M. Postma and W. F. van Gunsteren, in Intermolecular Forces, B. Pullman, ed. (Reidel, Dordrecht, 1981) p. 331; H. J. C. Berendsen, J. R. Grigera and T. P. Straatsma, J. Phys. Chem. 91, 6269 (1987). 6. D.N. Theodorou, U.W. Suter, Macromolecules, 18, 1467 (1985).
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| 2. |
- Andersson, Johanna, 1984, et al.
(author)
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Dynamics of capillary transport in semi-solid channels
- 2017
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In: Soft Matter. - 1744-683X .- 1744-6848. ; 13, s. 2562-2570
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Journal article (peer-reviewed)abstract
- © The Royal Society of Chemistry. Capillary action has been described by Lucas and Washburn and extensively studied experimentally in hard materials, but few studies have examined capillary action in soft materials such as hydrogels. In tissue engineering, cells or dispersions must be often distributed within a hydrogel via microporous paths. Capillary action is one way to disperse such substances. Here, we examine the dynamics of capillary action in a model system of straight capillaries in two hydrogels. The channels had a circular cross-section in the micrometer size range (180-630 μm). The distance travelled over time was recorded and compared with the predictions of Lucas and Washburn. Besides water, we used a sucrose solution and a hydroxyethyl cellulose solution, both with viscosities slightly higher than that of water. The results showed that the distance travelled is proportional to the square root of time, , and that larger capillaries and lower viscosities result, as expected, in faster speeds. However, the absolute experimental values display large discrepancies from the predictions. We demonstrate that several possible reasons for these discrepancies can be ruled out and we describe a novel hypothesis for the cause of the retarded meniscus movement.
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| 3. |
- Antonsson, Jakob, et al.
(author)
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Modeling Colloidal Particle Aggregation Using Cluster Aggregation with Multiple Particle Interactions
- 2024
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In: Journal of Physical Chemistry B. - 1520-6106 .- 1520-5207. ; 128:18, s. 4513-4524
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Journal article (peer-reviewed)abstract
- In this study, we investigate the aggregation dynamics of colloidal silica by generating simulated structures and comparing them to experimental data gathered through scanning transmission electron microscopy (STEM). More specifically, diffusion-limited cluster aggregation and reaction-limited cluster aggregation models with different functions for the probability of particles sticking upon contact were used. Aside from using a constant sticking probability, the sticking probability was allowed to depend on the masses of the colliding clusters and on the number of particles close to the collision between clusters. The different models of the sticking probability were evaluated based on the goodness-of-fit of spatial summary statistics. Furthermore, the models were compared to the experimental data by calculating the structures’ fractal dimension and mass transport properties from simulations of flow and diffusion. The sticking probability, depending on the interaction with multiple particles close to the collision site, led to structures most similar to the STEM data.
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| 6. |
- Asadzadeh, Mohammad, 1952, et al.
(author)
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Spherical Harmonics and a Semidiscrete Finite Element Approximation for the Transport Equation
- 2012
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In: Transport Theory and Statistical Physics. - : Informa UK Limited. - 0041-1450 .- 1532-2424. ; 41:1-2, s. 53-70
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Journal article (peer-reviewed)abstract
- This work is the first part in a series of two articles, where the objective is to construct, analyze, and implement realistic particle transport models relevant in applications in radiation cancer therapy. Here we use spherical harmonics and derive an energy-dependent model problem for the transport equation. Then we show stability and derive optimal convergence rates for semidiscrete (discretization in energy) finite element approximations of this model problem. The fully discrete problem that also considers the study of finite element discretizations in radial and spatial domains as well is the subject of a forthcoming article.
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| 7. |
- Bezabih, M., et al.
(author)
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ENVIRONMENTAL CHANGE AND THE CONTRIBUTION OF BIODIVERSITY TO ECOSYSTEM ADAPTATION
- 2010
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In: Natural Resource Modeling. - : Wiley. - 0890-8575 .- 1939-7445. ; 23:2, s. 253-284
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Journal article (peer-reviewed)abstract
- P>This paper develops a measure of the contribution of biodiversity in enhancing ecosystem performance that is subject to environmental fluctuation. The analysis draws from an ecological model that relates high phenotypic variance with lower short-term productivity (due to the presence of suboptimal species) and higher long-term productivity (due to better ability to respond to environmental fluctuations). This feature, which is a notable extension to existing economic-ecological models of biodiversity, enables assessment of the interactions between diversity and a range of environmental fluctuations to highlight that biodiversity could be rendered economically disadvantageous when environmental fluctuation is insufficient. The resulting economic-ecological model generates discounted present value of harvests for an ecosystem with diverse set of species. This value is compared with the harvest value of a similar economic-ecological model with no diversity and that of an ecosystem where the dynamics of phenotypes in response to environmental fluctuations is disregarded. The results show that diversity positively contributes to the performance of ecosystems subject to sufficiently large environmental fluctuation. In addition, neglecting an ecosystem's increasing ability to adapt to match environmental conditions is also shown to be more costly than having no diversity in an otherwise identical ecosystem.
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| 8. |
- Bylund Melin, Charlotta, et al.
(author)
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Monitoring Dynamic Moisture Gradients in Wood using Inserted Relative Humidity and Temperature Sensors
- 2016
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In: e-Preservation Science. - 1854-3928. ; 13, s. 7-14
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Journal article (peer-reviewed)abstract
- To be able to combine the preservation of wooden objects of cultural significance with energy efficiency measures it is important to develop our knowledge of the relation between the rate of change of relative humidity and temperature, moisture content gradients and the resulting dimensional change of wood. The work presented here introduces and evaluates a method for monitoring dynamic moisture content gradients, mainly for research applications. Relative humidity and temperature were measured by miniature sensors, placed in drilled holes at different depths in wood samples to monitor the moisture transport. The data was used to calculate moisture content and the results could hence be compared with the results from a commercial resistance moisture meter, monitored at the same depths. The results of the two methods did not coincide. A Fickian model for moisture diffusion was chosen to verify the monitored results. It showed poor fit with the commercial resistance method and a reasonably good fit with the new method using relative humidity and temperature sensors. We concluded that the new method provides reliable and consistent data suitable for monitoring moisture content at different depths under unsteady state conditions, while the data generated by the resistance method in our set-up was inconsistent with the model and with our understanding of the moisture transport process.
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| 9. |
- Bylund Melin, Charlotta, et al.
(author)
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Monitoring Dynamic Moisture Gradients in Wood using Inserted Relative Humidity and Temperature Sensors
- 2016
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In: e-Preservation Science. - 1581-9280. ; 13, s. 7-14
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Journal article (peer-reviewed)abstract
- To be able to combine the preservation of wooden objects of culturalsignificance with energy efficiency measures it is important to developour knowledge of the relation between the rate of change of relativehumidity and temperature, moisture content gradients and the resultingdimensional change of wood. The work presented here introduces andevaluates a method for monitoring dynamic moisture content gradients,mainly for research applications. Relative humidity and temperaturewere measured by miniature sensors, placed in drilled holes at differentdepths in wood samples to monitor the moisture transport. The data wasused to calculate moisture content and the results could hence be comparedwith the results from a commercial resistance moisture meter,monitored at the same depths. The results of the two methods did notcoincide. A Fickian model for moisture diffusion was chosen to verify themonitored results. It showed poor fit with the commercial resistancemethod and a reasonably good fit with the new method using relativehumidity and temperature sensors. We concluded that the new methodprovides reliable and consistent data suitable for monitoring moisturecontent at different depths under unsteady state conditions, while thedata generated by the resistance method in our set-up was inconsistentwith the model and with our understanding of the moisture transportprocess.
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