| 1. |
- Nordin, Matias, 1981, et al.
(författare)
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Estimation of mass thickness response of embedded aggregated silica nanospheres from high angle annular dark-field scanning transmission electron micrographs
- 2014
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Ingår i: Journal of Microscopy. - : Wiley. - 0022-2720 .- 1365-2818. ; 253:2, s. 166-170
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we investigate the functional behaviour of the intensity in high-angle annular dark field scanning transmission electron micrograph images. The model material is a silica particle (20 nm) gel at 5 wt%. By assuming that the intensity response is monotonically increasing with increasing mass thickness of silica, an estimate of the functional form is calculated using a maximum likelihood approach. We conclude that a linear functional form of the intensity provides a fair estimate but that a power function is significantly better for estimating the amount of silica in the z-direction. The work adds to the development of quantifying material properties from electron micrographs, especially in the field of tomography methods and three-dimensional quantitative structural characterization from a scanning transmission electron micrograph. It also provides means for direct three-dimensional quantitative structural characterization from a scanning transmission electron micrograph.
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| 2. |
- Hamngren Blomqvist, Charlotte, 1984, et al.
(författare)
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Pore size effects on convective flow and diffusion through nanoporous silica gels
- 2015
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757 .- 1873-4359. ; 484, s. 288-296
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Tidskriftsartikel (refereegranskat)abstract
- Material structure has great impact on mass transport properties, a relationship that needs to be understood on several length scales. Describing and controlling the properties of flow through soft materials are both challenges concerning the industrial use of gel structures. This paper reports on how the porous structure in nanoporous materials affects the water transport through them. We used three different silica gels with large differences in the pore sizes but of equal silica concentration. Particle morphology and gel structure were studied using high-resolution transmission electron microscopy and image analysis to estimate the pore size distribution and intrinsic surface area of each gel. The mass transport was studied using a flow measurement setup and nuclear magnetic resonance diffusometry. The average pore size ranged from approximately 500. nm down to approximately 40. nm. An acknowledged limit for convective flow to occur is in the pore size range between 100 and 200. nm. The results verified the existence of a non-linear relationship between pore size and liquid flow at length scales below 500. nm, experimentally. A factor of 4.3 in flow speed separated the coarser gel from the other two, which presented almost identical flow speed data despite a factor 3 in pore size difference. In the setup, the mass transport in the gel with the largest pores was flow dominated, while the mass transport in the finer gels was diffusion dominated. Besides providing new insights into mass transport as a function of pore sizes, we conclude that three-dimensional analysis of the structures is needed for a comprehensive understanding of the correlation between structure and mass transport properties.
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| 3. |
- Häbel, Henrike, 1987, et al.
(författare)
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From static micrographs to particle aggregation dynamics in three dimensions
- 2016
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Ingår i: Journal of Microscopy. - : Wiley. - 1365-2818 .- 0022-2720. ; 262:1, s. 102-111
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Tidskriftsartikel (refereegranskat)abstract
- Studies on colloidal aggregation have brought forth theories on stability of colloidal gels and models for aggregation dynamics. Still, a complete link between developed frameworks and obtained laboratory observations has to be found. In this work, aggregates of silica nanoparticles (20 nm) are studied using diffusion limited cluster aggregation (DLCA) and reaction limited cluster aggregation (RLCA) models. These processes are driven by the probability of particles to aggregate upon collision. This probability of aggregation is one in the DLCA and close to zero in the RLCA process. We show how to study the probability of aggregation from static micrographs on the example of a silica nanoparticle gel at 9 wt%. The analysis includes common summary functions from spatial statistics, namely the empty space function and Ripley's K-function, as well as two newly developed summary functions for cluster analysis based on graph theory. One of the new cluster analysis functions is related to the clustering coefficient in communication networks and the other to the size of a cluster. All four topological summary statistics are used to quantitatively compare in plots and in a least-square approach experimental data to cluster aggregation simulations with decreasing probabilities of aggregation. We study scanning transmission electron micrographs and utilize the intensity - mass thickness relation present in such images to create comparable micrographs from three-dimensional simulations. Finally, a characterization of colloidal silica aggregates and simulated structures is obtained, which allows for an evaluation of the cluster aggregation process for different aggregation scenarios. As a result, we find that the RLCA process fits the experimental data better than the DLCA process.
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| 4. |
- Antonsson, Jakob, et al.
(författare)
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Modeling Colloidal Particle Aggregation Using Cluster Aggregation with Multiple Particle Interactions
- 2024
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Ingår i: Journal of Physical Chemistry B. - 1520-6106 .- 1520-5207. ; 128:18, s. 4513-4524
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Tidskriftsartikel (refereegranskat)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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| 5. |
- Hamngren Blomqvist, Charlotte, 1984, et al.
(författare)
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A Single-Cell Study of a Highly Effective Hog1 Inhibitor for in Situ Yeast Cell Manipulation
- 2014
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Ingår i: Micromachines. - : MDPI AG. - 2072-666X. ; 5:1, s. 81-96
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Tidskriftsartikel (refereegranskat)abstract
- We present a single cell study of a highly effective Hog1 inhibitor. For this application, we used sequential treatment of a Saccharomyces cerevisiae cell array, with the Hog1 inhibitor and osmotic stress. For this purpose, a four-inlet microfluidic chamber with controlled introduction of two different cell strains within the same experimental setting and a subsequent rapid switching between treatments was designed. Multiple cell strains within the same experiment is a unique feature which is necessary for determining the expected absent cellular response. The nuclear translocation of the cytosolic MAPK, Hog1, was monitored by fluorescence imaging of Hog1-GFP on a single-cell level. An optical tweezers setup was used for controlled cell capture and array formation. Nuclear Hog1-GFP localization was impaired for treated cells, providing evidence of a congenial microfluidic setup, where the control cells within the experiments validated its appropriateness. The chamber enables multiple treatments with incubation times in the order of seconds and the possibility to remove either of the treatments during measurement. This flexibility and the possibility to use internal control cells ensures it a valuable scientific tool for unraveling the HOG pathway, similar signal transduction pathways and other biological mechanisms where temporal resolution and real time imaging is a prerequisite.
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| 6. |
- Hamngren Blomqvist, Charlotte, 1984, et al.
(författare)
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Design and evaluation of a microfluidic system for inhibition studies of yeast cell signaling
- 2012
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Ingår i: Proceedings of SPIE. - : SPIE. - 0277-786X .- 1996-756X. - 9780819491756 ; , s. 84582K-
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Konferensbidrag (refereegranskat)abstract
- In cell signaling, different perturbations lead to different responses and using traditional biological techniques that result in averaged data may obscure important cell-to-cell variations. The aim of this study was to develop and evaluate a four-inlet microfluidic system that enables single-cell analysis by investigating the effect on Hog1 localization post a selective Hog1 inhibitor treatment during osmotic stress. Optical tweezers was used to position yeast cells in an array of desired size and density inside the microfluidic system. By changing the flow rates through the inlet channels, controlled and rapid introduction of two different perturbations over the cell array was enabled. The placement of the cells was determined by diffusion rates flow simulations. The system was evaluated by monitoring the subcellular localization of a fluorescently tagged kinase of the yeast "High Osmolarity Glycerol" (HOG) pathway, Hog1-GFP. By sequential treatment of the yeast cells with a selective Hog1 kinase inhibitor and sorbitol, the subcellular localization of Hog1-GFP was analysed on a single-cell level. The results showed impaired Hog1-GFP nuclear localization, providing evidence of a congenial design. The setup made it possible to remove and add an agent within 2 seconds, which is valuable for investigating the dynamic signal transduction pathways and cannot be done using traditional methods. We are confident that the features of the four-inlet microfluidic system will be a valuable tool and hence contribute significantly to unravel the mechanisms of the HOG pathway and similar dynamic signal transduction pathways.
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| 7. |
- Hamngren Blomqvist, Charlotte, 1984, et al.
(författare)
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Interconnectivity imaged in three dimensions : Nano-particulate silica-hydrogel structure revealed using electron tomography
- 2017
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Ingår i: Micron. - : Elsevier BV. - 0968-4328 .- 1878-4291. ; 100, s. 91-105
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Tidskriftsartikel (refereegranskat)abstract
- We have used Electron Tomography (ET) to reveal the detailed three-dimensional structure of particulate hydrogels, a material category common in e.g. controlled release, food science, battery and biomedical applications. A full understanding of the transport properties of these gels requires knowledge about the pore structure and in particular the interconnectivity in three dimensions, since the transport takes the path of lowest resistance. The image series for ET were recorded using High-Angle Annular Dark Field Scanning Transmission Electron Microscopy (HAADF-STEM). We have studied three different particulate silica hydrogels based on primary particles with sizes ranging from 3.6 nm to 22 nm and with pore-size averages from 18 nm to 310 nm. Here, we highlight the nanostructure of the particle network and the interpenetrating pore network in two and three dimensions. The interconnectivity and distribution of width of the porous channels were obtained from the three-dimensional tomography studies while they cannot unambiguously be obtained from the two-dimensional data. Using ET, we compared the interconnectivity and accessible pore volume fraction as a function of pore size, based on direct images on the nanoscale of three different hydrogels. From this comparison, it was clear that the finest of the gels differentiated from the other two. Despite the almost identical flow properties of the two finer gels, they showed large differences concerning the accessible pore volume fraction for probes corresponding to their (two-dimensional) mean pore size. Using 2D pore size data, the finest gel provided an accessible pore volume fraction of over 90%, but for the other two gels the equivalent was only 10–20%. However, all the gels provided an accessible pore volume fraction of 30–40% when taking the third dimension into account.
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| 8. |
- Hamngren Blomqvist, Charlotte, 1984
(författare)
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Nano-particulate Silica Hydrogels Imaged in 2D and 3D using TEM: Effects of local pore structure on mass transport and applications in aggregation dynamics
- 2016
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Porous materials are frequently used in everyday applications including food science, pharmaceuticals, fuel cell membranes, batteries and solar cells. A key aspect in these porous materials is how their micro- and nano-structure affect the internal transport of for example water, particles or charges. The transport is a three-dimensional process. Therefore, structure information in three dimensions is especially important when analysing and further improving as well as developing new types of porous materials. We used Electron Tomography (ET) to directly reveal and quantify the three-dimensional structure of one type of soft porous material on the nano-scale.Three different nanoscale Particulate Silica Hydrogel (PSH) samples were synthesised and examined regarding the relationship of material nanostructure to both mass transport and particle aggregation dynamics. The PSH samples had equal percentage of silica, but had particle sizes ranging from 3.6 nm to 22 nm, and different aggregation parameters which rendered structural differences between the samples.The samples were imaged in two dimensions using Scanning Transmission Electron Microscopy (STEM) and in three dimensions using ET. The two-dimensional STEM micrographs were examined using stereological and geometrical image analysis. The water transport properties of the PSHs were studied by direct measurements, Nuclear Magnetic Resonance (NMR) diffusometry and by in situ Lattice-Boltzmann Modelling (LBM).In both two and three dimensions, we determined the local structure of the different PSHs. We quantified the characteristics of the PSHs concerning primary particle shape in two dimensions and geometrical pore size distribution in two and three dimensions. Here, we highlight both the nanostructure of the particle network and the connectivity of the pore network, seeing indications that the finer two gels had more narrow pore throats than the coarser gel. The pore size distribution had a minimal impact on water permeability below a pore size of 120 nm. Despite the almost identical flow properties of the two finer gels, they showed large differences concerning the accessible pore volume fraction in relation to their mean pore size. The LBM simulations showed higher values than the experiments for the permeability of the gels. Hence, a comparative study of simulated PSH sections was performed, from which it was clear that the simulation templates needed to be thicker in order to provide values more coherent to the experimental data.We have proposed and demonstrated an approach for estimating the three-dimensional structure from two-dimensional STEM micrographs, using the intensity profile as a structure parameter in the third dimension. From the 2D data, we concluded that the Reaction Limited Cluster Aggregation process (RLCA) explains the structure of the particle network in the hydrogels better than the Diffusion Limited Cluster Aggregation process (DLCA) does. However, there is not a perfect match. Our preliminary results show that the acquired three-dimensional data agrees significantly better to the RLCA model compared to the two-dimensional data.Here, the liquid flow properties of PSHs and the relation between liquid flow and nanoscale structure, including the interconnectivity of the pore network, is addressed. Thus, contributing to the field of mass transport in nanoscale porous materials. We also predict ET to be applied more frequently in the field of particulate hydrogels, including e.g. controlled release, battery and biomedical applications.
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| 9. |
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| 10. |
- Häbel, Henrike, 1987, et al.
(författare)
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Colloidal particle aggregation in three dimensions
- 2019
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Ingår i: Journal of Microscopy. - : Wiley. - 0022-2720 .- 1365-2818. ; 275:3, s. 149-158
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Tidskriftsartikel (refereegranskat)abstract
- Colloidal systems are of importance not only for everyday products, but also for the development of new advanced materials. In many applications, it is crucial to understand and control colloidal interaction. In this paper, we study colloidal particle aggregation of silica nanoparticles, where the data are given in a three-dimensional micrograph obtained by high-angle annular dark field scanning transmission electron microscopy tomography. We investigate whether dynamic models for particle aggregation, namely the diffusion limited cluster aggregation and the reaction limited cluster aggregation models, can be used to construct structures present in the scanning transmission electron microscopy data. We compare the experimentally obtained silica aggregate to the simulated postaggregated structures obtained by the dynamic models. In addition, we fit static Gibbs point process models, which are commonly used models for point patterns with interactions, to the silica data. We were able to simulate structures similar to the silica structures by using Gibbs point process models. By fitting Gibbs models to the simulated cluster aggregation patterns, we saw that a smaller probability of aggregation would be needed to construct structures similar to the observed silica particle structure.
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