| 1. |
- Agzenai, Y, et al.
(författare)
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In Situ X-ray Polymerization: From Swollen Lamellae to Polymer-Surfactant Complexes
- 2014
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Ingår i: The Journal of Physical Chemistry Part B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 118:4, s. 1159-1167
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Tidskriftsartikel (refereegranskat)abstract
- The influence of the monomer diallyldimethylammonium chloride (D) on the lamellar liquid crystal formed by the anionic surfactant aerosol OT (AOT) and water is investigated, determining the lamellar spacings by SAXS and the quadrupolar splittings by deuterium NMR, as a function of the D or AOT concentrations. The cationic monomer D induces a destabilization of the AOT lamellar structure such that, at a critical concentration higher than 5 wt %, macroscopic phase separation takes place. When the monomer, which is dissolved in the AOT lamellae, is polymerized in situ by X-ray initiation, a new collapsed lamellar phase appears, corresponding to the complexation of the surfactant with the resulting polymer. A theoretical model is employed to analyze the variation of the interactions between the AOT bilayers and the stability of the lamellar structure.
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| 2. |
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| 3. |
- Akesson, Anna, et al.
(författare)
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The effect of PAMAM G6 dendrimers on the structure of lipid vesicles
- 2010
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 12:38, s. 12267-12272
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Tidskriftsartikel (refereegranskat)abstract
- Dendrimers are polymers with unique properties that make them promising in a variety of applications such as potential drug and gene delivery systems. PAMAM dendrimers, in particular, have been widely investigated and are efficiently translocated into the cell. The mechanism of translocation, however, is still unknown. Recently it was proposed that PAMAM dendrimers are able to open holes in lipid bilayers by stealing lipid from the bilayer and forming "dendrisomes''. The present work intends to contribute in the clarification of this question: why are dendrimers able to translocate into the cell? We create simple models for cell membranes by using small lipid vesicles that present a single lipid phase at physiologically relevant conditions. We then follow the effect that dendrimers have on the structure of the vesicles by using a combination of various techniques: dynamic light scattering, cryo-TEM and small angle X-ray scattering. We discuss our results with respect to the previous findings and reflect on their possible implications for real translocation in living cells.
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| 4. |
- Alfredsson, Viveka
(författare)
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Cryo-TEM studies of DNA and DNA-lipid structures
- 2005
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Ingår i: Current Opinion in Colloid & Interface Science. - : Elsevier BV. - 1359-0294. ; 10:5-6, s. 269-273
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Forskningsöversikt (refereegranskat)abstract
- Studies published between 2001 and 2005 that utilise cryogenic transmission electron microscopy as a tool for investigating solutions containing DNA with or without amphiphiles present are reviewed. DNA or oligonucleotides form complexes with amphiphilic molecules such as lipids, so-called lipoplexes, and the structures and morphologies are excellent objects to study by cryogenic transmission electron microscopy. Recent studies show that this technique is in effective tool for identification of a range of structures such as unilamellar or multilamellar vesicles or dispersed liquid crystalline phases. (c) 2005 Elsevier Ltd. All rights reserved.
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| 5. |
- Alfredsson, Viveka, et al.
(författare)
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Formation mechanism of mesoporous silica formed with triblock copolymers; effect of salt addition
- 2005
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Ingår i: Studies in Surface Science and Catalysis. - 0167-2991. ; 158, s. 97-104
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Tidskriftsartikel (refereegranskat)abstract
- SBA-15 was synthesised with Pluronic P104 ((EO)(27)-(PO)(61)-(EO)(27))) its Structure promoter at 45 degrees C, with and without NaCl (1.0 M) added to the Synthesis Mixture. TEOS (tetraethyl orthosilicate) was used as silica source. The formation process was studied by in-situ SAXS/SAXD using synchrotron light. Addition of salt affects the micellar size, initial cell-parameter of the 2-D hexagonal phase (p6mm) as well as the kinetics of the aggregation of the polymer-silica composite. The effects caused by the salt are explained by a general ionic effect. The salt makes the aqueous Solution more polar and hence a worse solvent for the polymer. The ethylene oxide chains of the polymer will be more solvophobic. This leads to a larger aggregation number ofthe micelles as well as to a stronger interaction between them.
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| 6. |
- Alfredsson, Viveka, et al.
(författare)
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In-situ studies of the formation mechanism of SBA-15
- 2005
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Ingår i: Nanoporous Materials IV, 156. - 0444517480 ; 156, s. 69-74
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Konferensbidrag (refereegranskat)abstract
- The formation process of SBA-15 has been investigated by time resolved TEM, in-situ SAXS/SAXD and in-situ NMR. The synthesis was done at 35 degrees in acidic solution with tetramethylorthosilicate as the silica source and Pluronic P123 as the structure directing amphiphile. The initially formed silica-polymer composite consists of flocs of spherical micelles in a silica matrix. The micelles then coalesce forming rods that eventually pack into the ordered array of which SBA-15 consists.
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| 7. |
- Alfredsson, Viveka, et al.
(författare)
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Morphologies and Structure of Brain Lipid Membrane Dispersions
- 2021
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Ingår i: Frontiers in Cell and Developmental Biology. - : Frontiers Media SA. - 2296-634X. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- This study aims to explore the variety of previously unknown morphologies that brain lipids form in aqueous solutions. We study how these structures are dependent on cholesterol content, salt solution composition, and temperature. For this purpose, dispersions of porcine sphingomyelin with varying amounts of cholesterol as well as dispersions of porcine brain lipid extracts were investigated. We used cryo-TEM to investigate the dispersions at high-salt solution content together with small-angle (SAXD) and wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC) for dispersions in the corresponding salt solution at high lipid content. Sphingomyelin forms multilamellar vesicles in large excess of aqueous salt solution. These vesicles appear as double rippled bilayers in the images and as split Bragg peaks in SAXD together with a very distinct lamellar phase pattern. These features disappear with increasing temperature, and addition of cholesterol as the WAXD data shows that the peak corresponding to the chain crystallinity disappears. The dispersions of sphingomyelin at high cholesterol content form large vesicular type of structures with smooth bilayers. The repeat distance of the lamellar phase depends on temperature, salt solution composition, and slightly with cholesterol content. The brain lipid extracts form large multilamellar vesicles often attached to assemblies of higher electron density. We think that this is probably an example of supra self-assembly with a multiple-layered vesicle surrounding an interior cubic microphase. This is challenging to resolve. DSC shows the presence of different kinds of water bound to the lipid aggregates as a function of the lipid content. Comparison with the effect of lithium, sodium, and calcium salts on the structural parameters of the sphingomyelin and the morphologies of brain lipid extract morphologies demonstrate that lithium has remarkable effects also at low content.
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| 8. |
- Alfredsson, Viveka, et al.
(författare)
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The Dynamic Association Processes Leading from a Silica Precursor to a Mesoporous SBA-15 Material.
- 2015
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Ingår i: Accounts of Chemical Research. - : American Chemical Society (ACS). - 1520-4898 .- 0001-4842. ; 48:7, s. 1891-1900
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Forskningsöversikt (refereegranskat)abstract
- During the last two decades, the synthesis of silica with an ordered mesoporous structure has been thoroughly explored. The basis of the synthesis is to let silica monomers polymerize in the presence of an amphiphilic template component. In the first studies, cationic surfactants were used as structure inducer. Later it was shown that pluronic copolymers also could have the role. One advantage with the pluronics copolymers is that they allow for a wider variation in the radius of pores in the resulting silica material. Another advantage lies in the higher stability resulting from the thicker walls between the pores. Mesoporous silica has a very high area to volume ratio, and the ordered structure ensures surface homogeneity. There are a number of applications of this type of material. It can be used as support for catalysts, as templates to produces other mesoporous inorganic materials, or in controlled release applications. The synthesis of mesoporous silica is, from a practical point of view, simple, but there are significant possibilities to vary synthesis conditions with a concomitant effect on the properties of the resulting material. It is clear that the structural properties on the nanometer scale are determined by the self-assembly properties of the amphiphile, and this knowledge has been used to optimize pore geometry and pore size. To have a practical functional material it is desirable to also control the structure on a micrometer scale and larger. In practice, one has largely taken an empirical approach in optimizing reaction conditions, paying less attention to underlying chemical and physicochemical mechanisms that lead from starting conditions to the final product. In this Account, we present our systematic studies of the processes involved not only in the formation of the mesoporous structure as such, but also of the formation of structures on the micrometer scale. The main point is to show how the ongoing silica polymerization triggers a sequence of structural changes through the action of colloidal interactions. Our approach is to use a multitude of experimental methods to characterize the time evolution of the same highly reproducible synthesis process. It is the silica polymerization reactions that set the time scale, and the block copolymer self-assembly responds to the progress of the polymerization through a basically hydrophobic interaction between silica and ethylene oxide units. The progression of the silica polymerization leads to an increased hydrophobicity triggering an aggregation process resulting in the formation of silica-copolymer composite particles of increasing size. The particle growth occurs in a stepwise way caused by intricate shifts between colloidal stability and instability. By tuning reaction conditions one can have an end product of hexagonal prism composite particles with single crystal 2D hexagonal order.
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| 9. |
- Ambrosi, M, et al.
(författare)
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Nanotubes from a vitamin C-based bolaamphiphile
- 2006
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 128:22, s. 7209-7214
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Tidskriftsartikel (refereegranskat)abstract
- A bolaform surfactant, 1,12-diascorbyl dodecanedioate (BOLA12), with ascorbic acid units as the polar headgroups was synthesized for the first time. Once dispersed in water above 0.5% w/w, BOLA12 forms hollow nanotubes as revealed by cryo-TEM experiments. These nanostructures transform into clear micellar solutions on heating. X-ray diffraction and SAXS experiments were performed both on the pure solid and on its aqueous dispersions. The critical aggregation concentration and the phase behavior were determined by conductivity and DSC experiments. The latter technique provided also the amount of strongly bound, solvating water molecules that surround the polar headgroups. BOLA12 shows the same reducing properties of ascorbic acid, as indicated by the antioxidant activity evaluated with the DPPH method. This feature was used for the reduction of Pd(II) ions on the surface of the nanoassemblies, which lead to the formation of large bundles homogeneously coated with palladium as observed in SEM micrographs.
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| 10. |
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| 11. |
- Andersson, M, et al.
(författare)
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Macroscopic alignment of silver nanoparticles in reverse hexagonal liquid crystalline templates
- 2002
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Ingår i: Nano Letters. - : American Chemical Society (ACS). - 1530-6992 .- 1530-6984. ; 2:12, s. 1403-1407
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Tidskriftsartikel (refereegranskat)abstract
- A flexible method of preparing and macroscopically aligning nanoparticles of crystalline silver into millimeter long fibers is presented. The approach utilizes the dual functionality of a reverse hexagonal liquid crystalline template containing a built-in reducing agent facing the aqueous domain. The method is advantageous in that its slow kinetics allows for a thorough introduction of a silver salt into the liquid crystal before the reduction takes place, allowing for an efficient loading of he template and a retained mesoscopic ordering as evidenced by SAXS. It was confirmed by H-1 NMR that the oxyethylene groups of the amphiphilic polymer reduce the silver ions while being oxidized to aldehydes. The silver nanoparticles are uniform in size and in the same size range as the diameter of the aqueous domain of the liquid crystal (3 nm), further supporting that the silver particles form inside the liquid crystal. TEM images confirm the macroscopic alignment of silver nanoparticles into fibrils and the packing of fibrils into millimeter long fibers. The diameter of the fibrils and fibers ranges from 30 nm to several hundreds of micrometers. Electron diffraction analysis of a collection of silver nanoparticles confirms their crystallinity as three diffraction rings could be indexed to the face centered cubic structure of silver. A key to the successful macroscopic alignment of the nanoparticles is that the particles are formed inside the liquid crystal, thus minimizing the need for their diffusion i to and inside the liquid crystal.
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| 12. |
- Andersson, Martin, 1974, et al.
(författare)
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Vesicle and bilayer formation of diphytanoylphosphatidylcholine (DPhPC) and diphytanoylphosphatidylethanolamine (DPhPE) mixtures and their bilayers' electrical stability
- 2011
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Ingår i: Colloids and Surfaces B: Biointerfaces. - : Elsevier BV. - 0927-7765 .- 1873-4367. ; 82:2, s. 550-561
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Tidskriftsartikel (refereegranskat)abstract
- Lipid bilayers are of interest in applications where a cell membrane mimicking environment is desired. The performance of the lipid bilayer is largely dependent on the physical and chemical properties of the component lipids. Lipid bilayers consisting of phytanoyl lipids have proven to be appropriate choices since they exhibit high mechanical and chemical stability. In addition, such bilayers have high electrical resistances. Two different phytanoyl lipids, 1,2-diphytanoyl-sn-glycero-3-phosphocholine (DPhPC) and 1,2-diphytanoyl-sn-glycero-3-phosphoethanolamine(DPhPE), and various combinations of the two have been investigated with respect to their behavior in aqueous solutions, their interactions with solid surfaces, and their electrical stability. Dynamic light scattering, nuclear magnetic resonance diffusion, and cryogenic transmission electron microscopy measurements showed that pure DPhPC as well as mixtures of DPhPC and DPhPE consisting of greater than 50% (mol%) DPhPC formed unilamellar vesicles. If the total lipid concentration was greater than 0.15 g/l, then the vesicles formed solid-supported bilayers on plasma-treated gold and silica surfaces by the process of spontaneous vesicle adsorption and rupture, as determined by quartz crystal microbalance with dissipation monitoring and atomic force microscopy. The solid-supported bilayers exhibited a high degree of viscoelasticity, probably an effect of relatively high amounts of imbibed water or incomplete vesicle fusion. Lipid compositions consisting of greater than 50% DPhPE formed small flower-like vesicular structures along with discrete liquid crystalline structures, as evidenced by cryogenic transmission electron microscopy. Furthermore, electrophysiology measurements were performed on bilayers using the tip-dip methodology and the bilayers' capacity to retain its electrical resistance towards an applied potential across the bilayer was evaluated as a function of lipid composition. It was shown that the lipid ratio significantly affected the bilayer's electrical stability, with pure DPhPE having the highest stability followed by 3DPhPC:7DPhPE and 7DPhPC:3DPhPE in decreasing order. The bilayer consisting of 5DPhPC:5DPhPE had the lowest stability towards the applied electrical potential.
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| 13. |
- Burrows, Hugh D., et al.
(författare)
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Solubilization of poly{1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl} in Water by Non-Ionic Amphiphiles
- 2009
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 25:10, s. 5545-5556
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Tidskriftsartikel (refereegranskat)abstract
- In the presence of the nonionic alkyloxyethylene surfactant n-dodecylpentaoxyethylene glycol ether (C12E5), the anionic conjugated polyelectrolyte (CPE) poly{1,4-phenylene-[9,9-bis(4-phenoxy-butylsulfonate)]fluorene-2,7-diyl} (PBS-PFP) dissolves in water, leading to a blue shift in fluorescence and dramatic increases in fluorescence quantum yields above the surfactant critical micelle concentration (cmc). No significant changes were seen with a poly(ethylene oxide) of similar size to the surfactant headgroup, confirming that specific surfactant-polyelectrolyte interactions are important. From UV-visible and fluorescence spectroscopy, dynamic light scattering (DLS), small-angle X-ray scattering (SAXS), cryogenic transmission electron microscopy (cryo-TEM), and electrical conductivity, together with our published NMR and small-angle neutron scattering (SANS) results, we provide a coherent model for this behavior in terms of breakup of PBS-PFP clusters through polymer-surfactant association leading to cylindrical aggregates containing isolated polymer chains. This is supported by molecular dynamics simulations, which indicate stable polymer-surfactant structures and also provide indications of the tendency of C12E5 to break up polymer clusters to form these mixed polymer-surfactant aggregates. Radial electron density profiles of the cylindrical cross section obtained from SAXS results reveal the internal structure of such inhomogeneous species. DLS and cryo-TEM results show that at higher surfactant concentrations the micelles start to grow, possibly partially due to formation of long, threadlike species. Other alkyloxyethylene surfactants, together with poly(propylene glycol) and hydrophobically modified poly(ethylene glycol), also solubilize this polymer in water, and it is suggested that this results from a balance between electrostatic (or ion-dipole), hydrophilic, and hydrophobic interactions. There is a small, but significant, dependence of the emission maximum on the local environment.
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| 14. |
- Cárdenas, Marité, et al.
(författare)
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Solubilization of sphingomyelin vesicles by addition of a bile salt.
- 2008
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Ingår i: Chemistry and Physics of Lipids. - : Elsevier BV. - 0009-3084 .- 1873-2941. ; 151:Sep 25, s. 10-17
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Tidskriftsartikel (refereegranskat)abstract
- The interactions of the bile salt sodium taurocholate (TC) in 50mM Trizma-HCl buffer and 150mM NaCl (pH 9) at 37 degrees C with membranes composed of sphingomyelin (SM) were studied by dynamic light scattering, cryogenic transmission electron microscopy (cryo-TEM) and turbidity measurements. Small unilamellar SM vesicles were prepared by extrusion. Below the CMC of TC, taurocholate addition leads to vesicle growth due to incorporation of the taurocholate molecules into the vesicle bilayer. At around half the CMC of the bile salt, the SM vesicles are transformed into SM/TC mixed worm-like micelles, which are visualized by cryo-TEM for the first time. Further increase in the taurocholate concentration leads to the rupture of these structures into small spherical micelles. Interestingly, large non-spherical micelles were also identified for pure taurocholate solutions. Similar threadlike structures have been reported earlier for the bile salt sodium taurodeoxycholate [Rich, A., Blow, D., 1958. Nature 182, 1777; Blow, D.M., Rich, A., 1960. J. Am. Chem. Soc. 82, 3566-3571; Galantini, L., Giglio, E., La Mesa, C., Viorel-Pavel, N., Punzo, F., 2002. Langmuir 18, 2812] and for mixtures of taurocholate and phosphatidylcholate [Ulmius, J., Lindblom, G., Wennerström, H., Johansson, L.B.-A., Fontel, K., Söderman, O., Ardvisson, G., 1982. Biochemistry 21, 1553; Hjelm, R.P., Thiyagarajan, P., Alkan-Onyuksel, H., 1992. J. Phys. Chem. 96, 8653] as determined by various scattering methods.
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| 15. |
- Carnerup, Anna, et al.
(författare)
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Condensation of DNA using poly(amido amine) dendrimers: effect of salt concentration on aggregate morphology
- 2011
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Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 7:2, s. 760-768
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Tidskriftsartikel (refereegranskat)abstract
- The condensation of DNA and poly(amido amine) dendrimers of generation 1, 2, 4, 6, and 8 has been studied as a function of salt concentration in order to reveal the forces that control the aggregate size and morphology. For the lower generation dendrimers (1, 2, and 4) a dramatic increase in aggregate size occurs as a result of an increase in salt concentration. Toroidal aggregates having an outer diameter of up to several hundreds of nm are observed. For the higher generation 6 dendrimers, the size of the condensed DNA aggregates does not change, however, an alteration in morphology is seen at high salt concentration, as more rod-like aggregates are observed. The size and morphology of generation 8 dendrimers are seemingly insensitive to salt concentration. It is believed that the effective neutralisation of the dendrimer and DNA charge in the aggregate is the reason for the observed effects. It is further shown that the 2D hexagonal lattice spacing observed in toroids is close to constant irrespective of the size of the cation responsible for the DNA condensation.
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| 16. |
- Carnerup, Anna, et al.
(författare)
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Watching DNA condensation induced by poly(amido amine) dendrimers with time-resolved cryo-TEM.
- 2009
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 25:21, s. 12466-12470
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Tidskriftsartikel (refereegranskat)abstract
- The condensation of DNA by poly(amido amine) dendrimers of generation 1, 2, and 4 has been followed by time-resolved cryogenic transmission electron microscopy (cryo-TEM). The recorded images show that significant morphological rearrangement occurs for DNA condensed with the lower generation dendrimers leading to the formation of toroidal aggregates. Higher charge density dendrimers, on the other hand, give rise to globular aggregates, where no transient morphologies are observed. We suggest that the dendrimers in this case are kinetically trapped as soon as they bind to the DNA strand.
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| 17. |
- Castro, Maria, et al.
(författare)
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Zeolite Beta Formation from Clear Sols : Silicate Speciation, Particle Formation and Crystallization Monitored by Complementary Analysis Methods
- 2016
-
Ingår i: Chemistry - A European Journal. - : Wiley. - 0947-6539. ; 22:43, s. 15307-15319
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Tidskriftsartikel (refereegranskat)abstract
- The formation of silicate nanoaggregates (NAs) at the very early stages of precursor sols and zeolite beta crystallization from silicate nanoparticles (NPs) are investigated in detail using a combination of different analysis methods, including liquid-state 29Si, 27Al, 14N, and 1H NMR spectroscopy, mass spectrometry (MS), small-angle X-ray scattering (SAXS), X-ray diffraction (XRD), and transmission electron microscopy at cryogenic temperatures (cryo-TEM). Prior to hydrothermal treatment, silicate NAs are observed if the Si/OH ratio in the reaction mixture is greater than 1. Condensation of oligomers within the NAs then generates NPs. Aluminum doped into the synthesis mixtures is located exclusively in the NPs, and is found exclusively in a state that is fourfold connected to silicate, favoring their condensation and aggregation. These results are in agreement with general trends observed for other systems. Silicate NAs are essential intermediates for zeolite formation and are generated by the aggregation of hydrated oligomers, aluminate, and templating cations. Subsequent further intra-nanoaggregate silicate condensation results in the formation of NPs. 1H and 14N liquid NMR as well as diffusion ordered spectroscopy (DOSY) experiments provide evidence for weakly restricted rotational and translational mobility of the organic template within NAs as a consequence of specific silicate–template interactions. NAs thus appear as key species in clear sols, and their presence in the precursor sol favors silicate condensation and further crystallization, promoted either by increasing the Si/OH ratio or by heating.
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| 18. |
- Diaz, Isabel, et al.
(författare)
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Transmission electron microscopy in formation and growth of ordered mesoporous materials
- 2006
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Ingår i: Current Opinion in Colloid & Interface Science. - : Elsevier BV. - 1359-0294. ; 11:5, s. 302-307
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Forskningsöversikt (refereegranskat)abstract
- In the boundary of materials and colloidal science, TEM became a very powerful technique used to image the interfaces and early stages of mesoporous materials formation, to obtain symmetry information about the porous network at the meso-scale, furthermore to obtain images of final structures and transformations that could not be observed otherwise. The aim of the present contribution is to give insights that may contribute to a better understanding of TEM applied to the study of ordered mesoporous materials from three points of view: i) mechanism ii) formation from zeolite precursors; iii) structure of intermediate mesophases. (c) 2006 Elsevier Ltd. All rights reserved.
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| 19. |
- Du, Guanqun, et al.
(författare)
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Condensed Supramolecular Helices : The Twisted Sisters of DNA
- 2022
-
Ingår i: Angewandte Chemie (International edition). - : Wiley. - 1521-3773. ; 61:4
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Tidskriftsartikel (refereegranskat)abstract
- Condensation of DNA helices into hexagonally packed bundles and toroids represents an intriguing example of functional organization of biological macromolecules at the nanoscale. The condensation models are based on the unique polyelectrolyte features of DNA, however here we could reproduce a DNA-like condensation with supramolecular helices of small chiral molecules, thereby demonstrating that it is a more general phenomenon. We show that the bile salt sodium deoxycholate can form supramolecular helices upon interaction with oppositely charged polyelectrolytes of homopolymer or block copolymers. At higher order, a controlled hexagonal packing of the helices into DNA-like bundles and toroids could be accomplished. The results disclose unknown similarities between covalent and supramolecular non-covalent helical polyelectrolytes, which inspire visionary ideas of constructing supramolecular versions of biological macromolecules. As drug nanocarriers the polymer-bile salt superstructures would get advantage of a complex chirality at molecular and supramolecular levels, whose effect on the nanocarrier assisted drug efficiency is a still unexplored fascinating issue.
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| 20. |
- Du, Guanqun, et al.
(författare)
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Effect of temperature on the association behavior in aqueous mixtures of an oppositely charged amphiphilic block copolymer and bile salt
- 2020
-
Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 206
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Tidskriftsartikel (refereegranskat)abstract
- The association in aqueous mixtures of a thermoresponsive cationic diblock copolymer composed of poly(N-isopropylacrylamide) (PNIPAM) and poly(3-acrylamidopropyl)-trimethylammonium-chloride (PAMPTMA(+)) and the oppositely charged bile salt sodium deoxycholate (NaDC) is investigated at different compositions by light and X-ray scattering, calorimetry, and electrophoretic mobility measurements. Clouding reveals aggregation upon heating. The addition of NaDC to the copolymer solution lowers the temperature of the transition and increases its cooperativity. At high temperature and low NaDC fractions, mixed aggregates with a dehydrated PNIPAM-rich interior and a PAMPTMA(+)-rich shell partially neutralized by DC– anions are formed. At high NaDC fractions, the aggregates present internal regularly spaced segregated nanoregions of dehydrated PNIPAM and PAMPTMA(+)/DC– (microphase separation). The results suggest that the mixed aggregates have appealing composition-controlled thermoresponse. The system phase separates at body temperature and the highest NaDC fractions investigated, meaning in conditions accomplished when the use of the polymer as a bile salt sequestrant is hypothesized.
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| 21. |
- Elding, Lars Ivar, et al.
(författare)
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Sofi K.C. Elmroth : 1962-2022
- 2022
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Ingår i: Kungliga Fysiografiska Sällskapet i Lund. Årsbok 2021-2022. - 1402-1277. ; 2021-2022, s. 98-100
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Bokkapitel (populärvet., debatt m.m.)
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| 22. |
- Falk, Yana Znamenskaya, et al.
(författare)
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Langmuir - Blodgett monolayers of SBA-15 particles with different morphologies
- 2018
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier. - 1387-1811 .- 1873-3093. ; 256, s. 32-38
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Tidskriftsartikel (refereegranskat)abstract
- This study presents an optimized protocol for the deposition of mesoporous SBA-15 particles with platelet-like and rod-like morphologies on different types of supporting substrates using LangmuirBlodgett methodology, resulting in the formation of monolayers with porosity orientation controlled by the type, i. e. the morphology, of particles used over large areas. The morphology of the SBA-15 particles and specifically their aspect ratio are essential for the orientation of the particles and, hence, the orientation of the intrinsic porosity. Deposition on a surface, establishes a layer of SBA-15 platelets with pores oriented perpendicular to the substrate, or a layer of SBA-15 rods with pores oriented parallel to the substrate. In both cases, the oriented SBA-15 particles can be deposited onto areas that are larger than square centimeter using Langmuir-Blodgett technique. SEM characterization demonstrates formation of uniform close-packed layer of oriented mesoporous SBA-15 silica particles. Additionally, the particles coverage of the surface is independent and unaffected by the type of supporting substrate, which allows convenient experimental performance without requiring surface or particle modifications. In conclusion, Langmuir Blodgett is a convenient technique for deposition of mesoporous SBA-15 particles with different morphology types in order to obtain a close-packed layer. The methodology is suitable to create large area sensors, used in; for instance, bio-sensing applications. (C) 2017 Elsevier Inc. All rights reserved.
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| 23. |
- Flodström, Katarina, et al.
(författare)
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Formation of a new Ia(3)over-bard cubic meso-structured silica via triblock copolymer-assisted synthesis
- 2003
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 125:15, s. 4402-4403
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Tidskriftsartikel (refereegranskat)abstract
- A new mesoporous silica structure with cubic Iad symmetry has been synthesized. The structure has very large unit cell dimensions, up to 250 Å in the as-synthesized form and 222 Å after calcination, and the surface area is around 700 m2/g. The syntheses were done according to well-established synthesis conditions with the triblock copolymers Pluronics P103 or P123, except for the addition of NaI to the synthesis mixture. Small-angle X-ray scattering revealed that the sample has Iad symmetry. According to electron micrographs, the structure is similar to that of MCM-48, and we thus propose that the structure lies on the gyroid minimal surface.
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| 24. |
- Flodström, Katarina, et al.
(författare)
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In situ synchrotron small-angle X-ray scattering/X-ray diffraction study of the formation of SBA-15 mesoporous silica
- 2004
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:12, s. 4885-4891
-
Tidskriftsartikel (refereegranskat)abstract
- The initial stages of the formation of SBA-15 have been studied by in situ SAXS/XRD using synchrotron radiation. Modeling of both the diffuse scattering and the X-ray diffraction patterns obtained at different stages of the reaction results in a detailed description of the different reaction steps. The first step in the formation is the liquid-liquid phase separation of spherical P123-silicate hybrid micelles after which nucleation and growth of the 2D hexagonal phase occurs. Two-dimensional electron density maps calculated on the basis of the intensities of the Bragg reflections suggest that changes in the degree of intermicellar condensation are responsible for the time-dependent observations. The silica source (alkoxysilanes) may be partially unhydrolyzed long after formation of the hexagonal structure, since the kinetics of the mesophase evolution is notably slower when TEOS is used as the silica precursor as compared to TMOS. The results obtained for SBA-15 are compared with other published data on the formation of SBA-15 and of the smaller pore MCM-41 materials.
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| 25. |
- Flodström, Katarina, et al.
(författare)
-
Influence of the block length of triblock copolymers on th formation of mesoporous silica
- 2003
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Ingår i: Microporous and Mesoporous Materials. - 1387-1811. ; 59:2-3, s. 167-176
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of different block lengths of Pluronic surfactants, (EO)(x)-(PO)(y)-(EO)(x), in the formation of mesoporous silica has been investigated. The syntheses were performed in micellar solution of the surfactant under acidic conditions. The materials were characterized by SAXS, TEM and nitrogen adsorption measurements. The EO-block length of the polymers determines the mesostructure of the silica. For the hexagonal material (SBA-15) the wall thickness is largely dependent on the length of the EO-blocks, while the PO-block length has a great effect on the pore diameter. Furthermore, the PO-block length influences the templating ability, as longer PO-blocks result in more highly ordered domai s and well defined particles. The synthesis temperature also influences these parameters. (C) 2003 Elsevier Science Inc. All rights reserved.
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| 26. |
- Flodström, Katarina, et al.
(författare)
-
Mechanism of mesoporous silica formation. A time-resolved NMR and TEM study of silica-block copolymer aggregation
- 2004
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:3, s. 680-688
-
Tidskriftsartikel (refereegranskat)abstract
- The dynamics of the synthesis of a mesoporous silica material SBA-15 is followed using time-resolved in situ H-1 NMR and transmission electron microscopy (TEM). Block copolymer-silica particles of two-dimensional hexagonal symmetry evolve from an initially micellar solution. The synthesis was carried out with the block copolymer Pluronic P123 (EO20-PO70-EO20) at 35 degreesC and using tetramethyl orthosilicate as the silica precursor. By using TEM, we can image different stages during the evolution of the synthesis. Floes of spherical micelles held together by the polymerizing silica are observed prior to precipitation. With time, the structure of these floes evolves and the transition from spherical to cylindrical hexagonally packed micelles can be monitored. The signal from the methyl protons of the PO part was recorded with H-1 NMR. One observes a continuous increase in the signal width but with distinct changes in the spectral characteristics occurring in narrow time intervals. The spectral changes can be attributed to structural changes of the self-assembled aggregates. The H-1 NMR and TEM studies reveal the same mechanism of formation. It is concluded that the aggregation is caused by a micelle-micelle attraction induced by oligomeric/polymeric silica that adsorbs to the EO palisade layer of the micelles and has the ability to bridge to another micelle. This adsorption also favors the formation of cylindrical aggregates relative to spherical micelles. The sequence of NMR and TEM observations can then be interpreted as the following sequence of events: (i) silicate adsorption on globular micelles possibly accompanied with some aggregate growth, (ii) the association of these globular micelles into floes, (iii) the precipitation of these floes, and (iv) micelle-micelle coalescence generating (semi)infinite cylinders that form the two-dimensional hexagonal packing.
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| 27. |
- Flodström, Katarina, et al.
(författare)
-
Time-resolved in situ studies of the formation of cubic mesoporous silica formed with triblock copolymers
- 2004
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:23, s. 10311-10316
-
Tidskriftsartikel (refereegranskat)abstract
- The mechanism of formation of two different cubic mesoporous silica materials formed with Pluronic triblock copolymers is investigated with in situ time-resolved small-angle synchrotron X-ray scattering, in situ time-resolved H-1 nuclear magnetic resonance, and time-resolved transmission electron microscopy. The materials studied are the micellar cubic (Im (3) over barm) SBA-16 formed with Pluronic F108 and the bicontinuous cubic (Ia (3) over bard) silica material formed with Pluronic P103 and NaI. The formation mechanisms of the two cubic structures are shown to be dissimilar. For the Im (3) over barm material, in the early stages of the synthesis, floes of unordered micelles are observed, but areas where the micelles have started to order are also present. With time, there is an increase in order; however, there is a coexistence of unordered micelles and ordered material all through this study. The bicontinuous cubic silica is formed via a different path. The system is phase-separated already before the addition of the silica source, which implies that a concentrated phase is present, acting as the structure director of the Ia (3) over bard structure. The results are compared with earlier reports on the formation of the hexagonal SBA-15 material.
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| 28. |
- Friman, Rauno, et al.
(författare)
-
Oppositely charged surfactant-polyelectrolyte systems as model systems for mesoscopically ordered surfactant-silicates
- 2006
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Ingår i: Colloids and Surfaces A: Physicochemical and Engineering Aspects. - : Elsevier BV. - 0927-7757. ; 291:1-3, s. 148-154
-
Tidskriftsartikel (refereegranskat)abstract
- Due to the strongly kinetic nature of the chemical events leading to the formation of mesoscopically ordered inorganic-surfactant composite materials, detailed studies on the interdependency between the degree of inorganic condensation and the co-operative self-assembly is difficult to perform. We have therefore undertaken a study where organic polyelectrolytes are used as models for the inorganic oligomeric/polymeric species and studied the phase behavior of negatively charged polyacrylate positively charged surfactant complexes in aqueous solution as a function of polyelectrolyte molar mass. Dodecyltrimethyl ammonium chloride was used as the surfactant. The toluene solubilization capacity of the complexes were also determined, and a clear dependency on the (poly)electrolyte molar mass was found. The results can be used to explain many of the observed features observed for evolving silicate-surfactant under kinetic control. It is suggested that electrostatic screening effects dominate at low degrees of silicate condensation, while the stabilizing effect of the polyelectrolyte becomes increasingly dominant upon further silicate condensation. (c) 2006 Elsevier B.V. All rights reserved.
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| 29. |
- Han, Lu, et al.
(författare)
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Silica-Based Nanoporous Materials
- 2014
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Ingår i: Zeitschrift für Anorganische und Allgemeines Chemie. - : Wiley. - 0044-2313 .- 1521-3749. ; 640:3-4, s. 521-536
-
Forskningsöversikt (refereegranskat)abstract
- Ordered nanoporous structures are among the most fascinating and industrially important materials currently in use. The archetypal zeolite material has now been joined by an eclectic array of new structures that exhibit porosity over a wide range of length scales and with order/disorder expressed in a multitude of ways. This raises the bar in terms of characterization and extends a real challenge to the scientific community to fully understand the properties and potential future applications of such materials. In this review we discuss the importance of modern microscopy tools combined with diffraction in this endeavour and show how the details of even the most complex quasi-crystalline nanoporous architectures can be elucidated. We show by using the appropriate spherical aberration (C-s) corrections in scanning transmission electron microscopy it is possible to decipher all the individual silicon and aluminum atoms in a zeolite structure. Automated routines for using large electron diffraction datasets for crystal structure determination of nanocrystals is described making the need for large single crystal synthesis less-and-less important. The power of complementary combinations of surface tools such as atomic force microscopy and high-resolution scanning electron microscopy is discussed to elucidate crystal growth mechanisms. For mesoporous materials synthesized from self-organized organic mesophases electron microscopy reveals the details of the complex hierarchy of porosity so crucial for the functional performance of the structure.
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| 30. |
- Han, Lu, 1983-
(författare)
-
Synthesis and Characterization of Functionalized Silica Mesoporous Crystals : Cationic Surfactant and Co-structure Directing Agent System
- 2010
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This dissertation has been focused on the synthesis and characterization of novel functionalized silica mesoporous crystals by using cationic surfactant and co–structure directing agents (CSDA), the central concept of the synthesis method is to build proper organic/inorganic interactions by introducing CSDA into the synthesis system. By using cationic surfactant as template and anionic CSDA, carboxylic group functionalized mesoporous silicas were successfully synthesized. Well ordered 2D p6mm, cubic Fm-3m, mixture of CCP (Fm-3m) and HCP (P63/mmc), and cubic Fd-3m with uniform carboxylic group distribution have been obtained. Besides, we have investigated the Fm-3m/Fd-3m type intergrowth and new type defects observed in the Fd-3m structure using transmission electron microscopy (TEM) and proposed a “polyhedron packing” model. New amphoteric, inorganic amino acid with highly ordered mesopores were synthesized. Uniform distribution of acid and base organic groups on the mesopore surfaces were formed by interactions between the counter charged surfactant head groups and ionic parts of CSDAs. It has been demonstrated that organic (–NH2 and –COOH) pairs incorporated in the mesopore walls behave as natural amino acids, collectively exhibiting an isoelectric point of ~6.0. Moreover, we have demonstrated that the inorganic amino acid is an efficient catalyst for the reaction between aldehydes and carbon nucleophiles.
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| 31. |
- Hu, Jianfeng, 1979-
(författare)
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Grain growth by Ordered Coalescence of crystallites in Ceramics : Grain Growth Mechanisms, Microstructure Evolution and Sintering
- 2013
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Grain growth and densification process play the two most crucial roles on the microstructure evolution and the achieved performances during sintering of ceramics. In this thesis, the grain growth of SrTiO3, BaTiO3-SrTiO3 solid solutions and Si3N4 ceramics during spark plasma sintering (SPS) were investigated by electron microscopy.SrTiO3 ceramics starting from nanopowders were fabricated by SPS. A novel grain growth mechanism was discovered and named as ordered coalescence (OC) of nanocrystals. This mechanism involved nanocrystals as building blocks and is distinguished from atomic layer epitaxial growth (AEG) in classical sintering theory. The results also revealed that the dominant grain growth mechanism can be changed by varying heating rates. Low rate (10°C/min) gives AEG, whereas high rates (≥ 50°C/min) yields three-dimensional coalescence of nanocrystals, i.e. OC.BaTiO3-SrTiO3 sintered bodies were made by SPS of BaTiO3 and SrTiO3 nanopowders mixtures. A novel Sr1-xBaxTiO3 “solid solution” with mosaic-like single crystal structure was manufactured by OC of the precursor crystallites. This reveals a new path for preparation of solid solution grains or composites. Si3N4 ceramics were prepared from α- or β-Si3N4 nanopowders at the same SPS conditions. The anisotropic OC of precipitated β-Si3N4 crystallites gives elongated β-Si3N4 grains at 1650°C using α-Si3N4 nanopowder. In contrast, AEG leads to the equi-axed β-Si3N4 grains using β-Si3N4 nanopowder. The metastable α- to β-Si3N4 phase transformation and OC accelerates anisotropic grain growth.Grain motions contribute to the densification process during pressureless sintered 3Y-ZrO2 (>87%TD) or SPS of SrTiO3 (>92%TD) ceramics. This extends the sintering range for active grain re-arrangement over that predicted by classical theory.In this thesis a new grain growth mechanism (OC) is proved by using SPS and nanopowders. By OC the microstructural evolution can be manipulated.
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| 32. |
- Kipkemboi, P, et al.
(författare)
-
Phase behaviour and structure of amphiphilic poly(ethylene oxide)-poly(propylene oxide) triblock copolymers ((EO)(4)(PO)(59)(EO)(4) and (EO)(17)(PO)(59)(EO)(17)) in ternary mixtures with water and xylene
- 2003
-
Ingår i: Canadian Journal of Chemistry. - 0008-4042. ; 81:8, s. 897-908
-
Tidskriftsartikel (refereegranskat)abstract
- The isothermal ternary phase behaviour and structure of amphiphilic copolymer-water-xylene systems was investigated for two poly(ethylene oxide)-poly(propylene oxide) (PEO-PPO) triblo k copolymers, (EO)(4)(PO)(59)(EO)(4) and (EO)(17)(PO)(59)(EO)(17), at 25degreesC. The phase boundaries were identified using H-2 NMR and inspection under polarized light. The microstructure and structural length scales in the lyotropic liquid crystalline phases were determined and characterized by small-angle X-ray scattering. The amounts and relative proportions of the selective solvents can modulate the resulting microstructures, although the phase sequence observed depends on the relative PEO-PPO block ratio. A variety of lyotropic liquid crystalline (LLC) phases are thermodynamically stable in the system with copolymer (EO)(17)(PO)(59)(EO)(17), both of the normal ("oil-in-water") and of the reverse ("water-in-oil") morphology. The high hydrophobic content of copolymer (EO)(4)(PO)(59)(EO)(4), however, favours reverse LLC structures with low interfacial curvature. No normal LLC phases are formed by this system.
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| 33. |
- Kipkemboi, Pius, et al.
(författare)
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Triblock copolymers as templates in mesoporous silica formation : Structural dependence on polymer chain length and synthesis temperature
- 2001
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 17:17, s. 5398-5402
-
Tidskriftsartikel (refereegranskat)abstract
- Mesoporous silica can be formed with amphiphilic molecules acting as structure-directing templates in dilute systems. The templating properties of five related triblock copolymers, (EO)x-(PO)y-(EO)x (Pluronic L101, P103, P104, P105, and F108), have been investigated regarding the length of the EO blocks as well as the temperature of the synthesis. It was found that the number of EO units is essential in determining which silica mesophase is obtained. Lamellar structure is obtained with short EO chains (4 units); hexagonal structure, with medium length EO chains (17-37 units); and cubic structure, with long EO chains (132 units). The hydrophobicity of the (EO)x-(PO)y-(EO)x polymer is strongly affected by the temperature. This is to some extent reflected in the silica mesostructure formed; a multilamellar vesicle morphology can be obtained at elevated synthesis temperatures. Also, the temperature has an influence on particle size.
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| 34. |
- Kjellman, Tomas, et al.
(författare)
-
Direct Observation of Plugs and Intrawall Pores in SBA-15 Using Low Voltage High Resolution Scanning Electron Microscopy and the Influence of Solvent Properties on Plug-Formation
- 2013
-
Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 25:20, s. 4105-4112
-
Tidskriftsartikel (refereegranskat)abstract
- Through the use of low voltage high resolution scanning electron microscopy (LV-HRSEM) we have studied the fine details of the intricate pore structure of SBA-15. Intrawall pores and deviations from the ideal and uniform cylindrical pores are clearly observed, and we report for the first time the direct observation of plugs in the pores. N-2-sorption measurements confirm their existence. LV-HRSEM provides an opportunity to quantify the frequency of occurrence of plugs within the pore structure. The rate of mesophase formation, followed with in situ small angle X-ray scattering (SAXS) under different solvent conditions, is shown to have a significant influence on the development of plugs and how frequently they occur. We suggest a mechanism explaining the existence of the plugs, providing means for a better understanding and control over material properties.
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| 35. |
- Kjellman, Tomas, et al.
(författare)
-
Independent Fine-Tuning of the Intrawall Porosity and Primary Mesoporosity of SBA-15
- 2013
-
Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 25:9, s. 1989-1997
-
Tidskriftsartikel (refereegranskat)abstract
- We present a study in which the intrawall porosity and primary mesoporosity. of SBA-15 are independently controlled by modifying the strength of the molecular interaction that governs the formation of the material. The interactions are targeted at specific times during the process of formation, which results in selective tuning of the porosity, while other characteristics of the SBA-15 material are retained. We show that the intrawall porosity can be considerably reduced by addition of NaI, but not NaCl, and that the shape of the primary mesopores can be influenced by a decrease in temperature, while while the two-dimensional hexagonal structure and the particle morphology and size remain unchanged. The timing of the "tuning event" is imperative. We show that a decrease in intrawall porosity by addition of NaI is generic to Pluronic-based mesoporous silica syntheses. This work demonstrates that the material characteristic of mesoporous silica is not necessarily restricted by the initial synthesis conditions as the material properties can be tuned by "actions" taken upon the ongoing synthesis. The triblock copolymer Pluronic P104 was used as a structure director and tetramethyl orthosilicate as a silica source. The materials have been characterized primarily with nitrogen sorption and small angle X-ray diffraction.
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| 36. |
- Kjellman, Tomas, et al.
(författare)
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Influence of microporosity in SBA-15 on the release properties of anticancer drug dasatinib
- 2014
-
Ingår i: Journal of materials chemistry. B. - : Royal Society of Chemistry (RSC). - 2050-750X .- 2050-7518. ; 2:32, s. 5265-5271
-
Tidskriftsartikel (refereegranskat)abstract
- The release of the hydrophobic cancer drug dasatinib from two mesoporous silica materials as drug delivery vehicles has been studied. One material is a reference 2D-hexagonal SBA-15 with the typical bimodal pore system with ordered primary mesopores and disordered intrawatI pores. The other material is a modified version of the same material where the intrawall porosity in the micropore regime has been selectively removed. Material characterization shows that, with the exception of the difference in intrawall porosity, the materials have identical properties. The drug dasatinib, a tyrosine kinase inhibitor, has been loaded, to the same extent, into the pores of both materials. The two materials give rise to very different release profiles of the drug. The presence of micropores leads to desired release properties: a high initial release of the drug, which is maintained over time. The lack of micropores also leads to a high initial release but followed by a rapid drop in the concentration of released drug, a consequence of its low solubility and hence crystallisation. We suggest that the presence of micropores in the carrier material, and the resultant kinetic release profile, leads to a stabilization of dasatinib in solution and to a sustained supersaturated level of the released drug. Our findings suggest that by controlling the mesoporous host with small variation in the textural properties, the kinetic release and crystallization behaviour of a drug can be altered. It is thus potentially possible to influence the drug post-release and thereby its bioavailability.
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| 37. |
- Kjellman, Tomas, et al.
(författare)
-
Orientation specific deposition of mesoporous particles
- 2014
-
Ingår i: APL Materials. - : AIP Publishing. - 2166-532X. ; 2:11
-
Tidskriftsartikel (refereegranskat)abstract
- We present a protocol for a facile orientation specific deposition of plate-like mesoporous SBA-15 silica particles onto a surface (mesopores oriented normal to surface). A drop of an aqueous dispersion of particles is placed on the surface and water vaporizes under controlled relative humidity. Three requirements are essential for uniform coverage: particle dispersion should not contain aggregates, a weak attraction between particles and surface is needed, and evaporation rate should be low. Aggregates are removed by stirring/sonication. Weak attraction is realized by introducing cationic groups to the surface. Insight into the mechanisms of the so-called coffee stain effect is also provided. (C) 2014 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution 3.0 Unported License.
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| 38. |
- Kjellman, Tomas, et al.
(författare)
-
The use of in situ and ex situ techniques for the study of the formation mechanism of mesoporous silica formed with non-ionic triblock copolymers.
- 2013
-
Ingår i: Chemical Society Reviews. - : Royal Society of Chemistry (RSC). - 0306-0012. ; 42:9, s. 3777-3791
-
Forskningsöversikt (refereegranskat)abstract
- Since the discovery of the mesoporous silica material templated by ionic surfactants and the subsequent development of materials templated by non-ionic surfactants and polymers, for example SBA-15, there has been a continuous research effort towards understanding their formation. In situ methodologies, such as Small Angle X-ray Scattering (SAXS), Small Angle Neutron Scattering (SANS), spectroscopic techniques like NMR and EPR, and ex situ methodologies such as electron microscopy techniques (SEM, TEM and cryo-TEM) are powerful and important tools in the investigation of the mechanism by which these materials form. The need for a fundamental understanding of the systems is of academic concern and of great importance when developing materials for applications. In this tutorial review we aim to give the reader a comprehensive overview on the development of the field over the years and an introduction to the experimental in situ and ex situ techniques that have been used.
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| 39. |
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| 40. |
- Kocherbitov, Vitaly, et al.
(författare)
-
Assessment of Porosities of SBA-15 and MCM-41 Using Water Sorption Calorimetry
- 2011
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 27:7, s. 3889-3897
-
Tidskriftsartikel (refereegranskat)abstract
- Water sorption calorimetry has been used for characterization of 2D hexagonally ordered mesoporous silica SBA-15. Experimental data on water sorption isotherm, the enthalpy, and the entropy of hydration of SBA-15 are presented. The results were compared with previously published results on MCM-41 obtained using the same technique. The water sorption isotherm of SBA-15 consists of four regimes, while the sorption isotherm of MCM-41 consists only of three. The extra regime in the water sorption isotherm for SBA-15 arises from filling of intrawall pores, that are present in SBA-15 but absent in MCM-41. The water sorption isotherms of the two types of mesoporous silica were analyzed using the Barrett−Joyner−Halenda approach. For the BJH analysis, t-curves of silica with different degrees of hydroxylation were proposed. Comparison of water and nitrogen t-curves shows that, independent of hydroxylation of silica surface, the adsorbed film of water is much thinner than the adsorbed film of nitrogen at similar relative pressures. This fact decreases the uncertainty of the assessment of porosity with water sorption originated from variations in surface properties. The pore size distribution of SBA-15 calculated with BJH treatment of water sorption data is in good agreement with nitrogen NLDFT results on the same material.
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| 41. |
- Kocherbitov, Vitaly, et al.
(författare)
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Hydration of MCM-41 Studied by Sorption Calorimetry
- 2007
-
Ingår i: J. Phys. Chem. C. - : American Chemical Society (ACS). ; :2007, 111 (35)
-
Tidskriftsartikel (refereegranskat)abstract
- Hydration of mesoporous silica MCM-41 was studied using the method of sorption calorimetry. By combining water sorption and nitrogen sorption experiments, we calculated the density of silanol groups on the MCM-41 surface as 1.6 nm-2. Comparison of capillary condensation regimes of water and nitrogen showed that the apparent density of water confined in MCM-41 pores is ca. 0.88 g/cm3. The pore diameter calculated using a combination of X-ray and sorption data is 39 Å. Calculations based on application of the Kelvin-Cohan equation on the water sorption data are in reasonable agreement with this value. The sorption calorimetric results show that the capillary condensation of water in the pores is driven by enthalpy; the entropic effect is negative. A mechanism of hydration that involves formation of small unfilled cavities adjacent to pore walls can be used to explain the observed enthalpy end entropy effects. Comparison of sorption and desorption data indicates the presence of air trapped in pores when hydration is performed by mixing MCM-41 with liquid water. The heat effect of pre-capillary condensation adsorption of water on hydroxylated MCM-41 is much more exothermic compared to the original calcined material.
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| 42. |
- Lazzara, Giuseppe, et al.
(författare)
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Temperature-responsive inclusion complex of cationic PNIPAAM diblock copolymer and gamma-cyclodextrin
- 2012
-
Ingår i: Soft Matter. - : Royal Society of Chemistry (RSC). - 1744-6848 .- 1744-683X. ; 8:18, s. 5043-5054
-
Tidskriftsartikel (refereegranskat)abstract
- Aqueous mixtures of gamma-cyclodextrin (gamma-CD) and the thermosensitive cationic diblock copolymer poly(N-isopropylacrylamide)-b-poly(3-acrylamidopropyl)trimethylammonium chloride (PNIPAAM(24)-b-PAMPTAM(+)(9)) or the PNIPAAM homopolymer PNIPAAM(47) have been investigated using various experimental methods. Solid g-CD-polymer inclusion complexes (pseudopolyrotaxanes) form at ambient temperatures in fairly concentrated CD solutions. The NMR measurements showed that the stoichiometry of the inclusion complexes is close to two NIPAAM units per CD molecule. The cationic block of the copolymer is not incorporated into the CD cavity. Synchrotron radiation X-ray diffraction spectra of the solid inclusion complexes indicate a compact columnar structure of CD molecules threaded onto the PNIPAAM chains. In water, square-shaped cyclodextrin aggregates were found to co-exist with single cyclodextrin molecules. In mixed solutions of gamma-CD and PNIPAAM(24)-b-PAMPTAM(+)(9) these aggregates disintegrate with time as inclusion complexes are formed and the kinetics was studied using time-resolved static and dynamic light scattering and cryo-TEM. Steady-state fluorescence spectroscopy measurements reveal that the CD molecules dethread from the PNIPAAM chains upon increasing the temperature to 40 degrees C, which is above the lower critical solution temperature of PNIPAAM.
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| 43. |
- Lin, Ruiyu, et al.
(författare)
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Kinetic Influence of Siliceous Reactions on Structure Formation of Mesoporous Silica Formed via the Co-Structure Directing Agent Route
- 2016
-
Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 120:7, s. 3814-3821
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the mechanism responsible for the formation of mesoporous silica formed with the so-called costructure directing agent (CSDA) route. The synthesis relies on the interaction between silica source (tetraethylorthosilicate), cationic surfactant (C18H37N+(CH3)2(CH2)3N+(CH3)3Br2), and CSDA (carboxyethylsilanetriol), which results in a material functionalized with carboxylic groups. Depending on the concentration of HCl in the synthesis, the structure is defined by Fm3¯m (at high pH) and by Fd3¯m (at low pH), with a gradual transition in the intermediate pH range. Here, we aim at finding the origin for the structural change triggered by pH and investigate the effects of the hydrolysis of the silica source on the overall kinetics of the synthesis. A fast process results in Fm3¯m, regardless of pH, and a slow process results in Fd3¯m. The hydrolysis step is the important structural control parameter. We studied the cross-linking of silica and CSDA using 29Si NMR. The cross-linking is similar for the two structures, and possibly the Fd3¯m structure contains slightly more CSDA. 13C PT ssNMR was used to investigate the surfactant mobility/rigidity during the synthesis. The rigidity of the Fm3¯m is established much faster than that of the Fd3¯m.
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| 44. |
- Linton, Peter, et al.
(författare)
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Controlling particle morphology and size in the synthesis of mesoporous SBA-15 materials
- 2010
-
Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 12:15, s. 3852-3858
-
Tidskriftsartikel (refereegranskat)abstract
- Plate-like particles of SBA-15 form from smaller units (primary particles) that aggregate in an oriented manner. In this report we influence this aggregation by adding salt to the ongoing synthesis, generating well-ordered hexagonal p6m structure (SBA-15), with varying particle diameters. The additions, with either NaCl or NaI, were made at a time corresponding to the onset of oriented aggregation. Both salts promote the aggregation and particles with diameters of up to 5 mm were obtained. The thickness, about 0.4 mu m, of the particles was retained, in accordance with the proposed growth mechanism. The aggregation characteristic was dependent on the salt used and the concentration of the salt. Both the cation and the anion were found to influence the aggregation. Having salt present already at the start of the synthesis gave a different product. The particle formation process depends on an interplay between attractive and repulsive forces between aggregates. We interpret the observed effect of salt addition to a medium which already has a very high ionic strength (1.6 M HCl) as due to ion binding to the combined polyethylene oxide-silica brush at the particles surface.
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| 45. |
- Linton, Peter, et al.
(författare)
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Evolution of structure and composition during the synthesis of mesoporous silica SBA-15 studied by small-angle neutron scattering
- 2011
-
Ingår i: Solid State Sciences. - : Elsevier BV. - 1293-2558 .- 1873-3085. ; 13:4, s. 793-799
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Tidskriftsartikel (refereegranskat)abstract
- In-situ time-resolved small-angle neutron scattering (SANS) has been applied for the study of the formation of mesoporous silica SBA-15. The advantage of neutron scattering, compared to X-ray scattering, is the possibility to contrast match i.e. highlight certain parts of the sample. Three different solvents with different scattering contrasts were used for each synthesis. Three different silica sources (tetramethyl orthosilicate, tetraethyl orthosilicate and tetrapropyl orthosilicate) were used and in three cases salts (sodium chloride or sodium bromide) were added prior to addition of the silica source. Hence, the effect of the silica sources and of the salts, on the formation of SBA-15 was investigated. The main focus was on the evolution of the ordered hexagonal structure i.e. investigation of the (10) Bragg peak. In synchrotron SAXS measurements the intensity of the (10) Bragg peak continuously increases during the measurement. However, in the SANS measurements the (10) Bragg peak area decreases with time. The decrease of the (10) peak is highly dependent on the solvent, a larger fraction of D2O in the solvent results in a bigger reduction. The decrease is also more pronounced when salt is present in the synthesis. The reduction of intensity reflects the chemistry in the wall and is explained by the compositional change in the wall during the maturation of the hexagonal order.
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| 46. |
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| 47. |
- Linton, Peter, et al.
(författare)
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In Situ Observation of the Genesis of Mesoporous Silica SBA-15 : Dynamics on Length Scales from 1 nm to 1 mu m
- 2009
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 25:8, s. 4685-4691
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Tidskriftsartikel (refereegranskat)abstract
- We report on the mechanism of growth of mesoporous silica (SBA-15, plane group p6m). In situ studies of the formation using ultrasmall angle X-ray scattering (USAXS) and small-angle X-ray scattering (SAXS) covering length scales from 5 to 10000 A, complemented with UV-vis and transmission electron microscopy (TEM), provide unique data on particle growth coupled with information regarding the progression of the mesostructure formation and the micellar evolution.
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| 48. |
- Linton, Peter, et al.
(författare)
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Morphology of SBA-15-directed by association processes and surface energies.
- 2009
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Ingår i: Physical chemistry chemical physics : PCCP. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 11:46, s. 10973-10982
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Tidskriftsartikel (refereegranskat)abstract
- We present a model that explains the morphology of mesoporous SBA-15 particles based on the relative surface energies of the defining faces. We also describe how the formation process influences the morphology and hence the surface energies. The model is compared to experimental observations, made primarily with scanning and transmission electron microscopy. Some materials were also examined in more detail with scanning transmission electron microscopy tomography. Materials were synthesized as a function of synthesis temperature, silica source and content of sodium chloride. The model describes the observed change in aspect ratio of the particles with respect to temperature. Silica source and addition of sodium chloride also affect the morphology. Under certain conditions the particle morphology is the result of an aggregation step that has an orientational character. Under the lower synthesis temperatures this association leads to flake-like particles whereas at higher temperatures rods of particles associated end-to-tail will result. At intermediate temperatures the aggregation is non-specific. The presented model could be used as a means for controlling particle morphology and size.
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| 49. |
- Lundberg, Dan, et al.
(författare)
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Interactions between Cationic Lipid Bilayers and Model Chromatin
- 2010
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 26:15, s. 12488-12492
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Tidskriftsartikel (refereegranskat)abstract
- Complexes formed in mixtures of cationic liposomes of varying charge density and nucleosome core particles (NCPs) or nucleosome arrays have been characterized. Under most of the conditions studied, the lipids and NCPs or arrays formed lamellar structures similar to those obtained with the liposomes and pure DNA. Thus, the dissociation of DNA from the NCP or nucleosome array and the formation of a DNA-lipid complex is thermodynamically favored, which can likely be ascribed mainly to the gain in entropy on release of the small counterions. Only at very low liposome charge densities are there indications that the NCPs/arrays do not dissociate upon interaction with the lipid bilayers. The reported results can serve as a valuable reference point in investigations of biologically more relevant systems.
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| 50. |
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