| 1. |
- 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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| 2. |
- 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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| 3. |
- 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
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:12, s. 4885-4891
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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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| 4. |
- Flodström, Katarina, et al.
(författare)
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Time-resolved in situ studies of the formation of cubic mesoporous silica formed with triblock copolymers
- 2004
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:23, s. 10311-10316
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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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| 5. |
- Friman, Rauno, et al.
(författare)
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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
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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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| 6. |
- Kjellman, Tomas, et al.
(författare)
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Independent Fine-Tuning of the Intrawall Porosity and Primary Mesoporosity of SBA-15
- 2013
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Ingår i: Chemistry of Materials. - : American Chemical Society (ACS). - 0897-4756 .- 1520-5002. ; 25:9, s. 1989-1997
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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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| 7. |
- Kvist Christensen, Karen, et al.
(författare)
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Chlorhexidine for prevention of neonatal colonization with group B streptococci. I. In vitro effect of chlorhexidine on group B streptococci
- 1983
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Ingår i: European Journal of Obstetrics, Gynecology, and Reproductive Biology. - : Elsevier BV. - 0301-2115. ; 16:3, s. 157-165
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Tidskriftsartikel (refereegranskat)abstract
- Forty-three strains of group B streptococci (GBS) of types Ia, Ib, II and III were tested for susceptibility to chlorhexidine in concentrations ranging from 256 to 0.25 mg/l using the agar and tube dilution methods. The strains showed minimum inhibitory concentration (MIC) values ranging from 0.5 to 1 mg/l. Serum added to the test medium (50%) increased the MIC values to 4-8 mg/l, while amniotic fluid (50%) had almost no effect, increasing the values to 1-2 mg/l. The minimum bactericidal concentration (MBC) ranged from 1 to 5 mg/l. The killing kinetics were related to the concentration of chlorhexidine and the length of exposure. For example, at a concentration of 63 mg/l, 7 h were required for a bactericidal effect in broth, as compared to 1 h at 500 mg/l chlorhexidine. 200 mg/l chlordexidine had no effect on the adherence of two GBS strains to vaginal epithelial cells, and no effect on the phagocytosis of GBS with mouse peritoneal macrophages.
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| 8. |
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| 9. |
- Lidegran, Marika, et al.
(författare)
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Cranial CT for diagnosis of intracranial complications in adult and pediatric patients during ECMO : Clinical benefits in diagnosis and treatment
- 2007
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Ingår i: Academic Radiology. - Netherlands : Elsevier BV. - 1076-6332 .- 1878-4046. ; 14:1, s. 62-71
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Tidskriftsartikel (refereegranskat)abstract
- RATIONALE AND OBJECTIVES: To evaluate the clinical utility of cranial computed tomography (CT) in pediatric and adult patients during ongoing extracorporeal membrane oxygenation (ECMO) treatment from acute respiratory failure and to assess the frequency of intracranial hemorrhage (ICH) and infarction during the treatment. MATERIALS AND METHODS: The medical records of 123 consecutive patients, 54 children (ages 3 months-17 years) and 69 adults (ages 18-62 years), treated with ECMO over a 10-year period were searched for cranial CT performed during ECMO. Indications for CT, CT findings, impact on clinical management, and patient outcome were noted. In addition, all CT scans were reviewed for the frequency of ICH or infarction. RESULTS: Seventy-eight patients had cranial CT while on ECMO. ICH or cerebral infarction were detected in 45 (37%) of the 123 patients. Eighteen patients (15%) had focal hemorrhage, 11 (9%) focal infarction, and 16 (13%) general brain edema. In 16 of the 45 patients, the CT findings were decisive to withdraw the ECMO treatment. Five patients were weaned from ECMO, and in four patients the findings motivated cranial surgery during ECMO. In the remaining 20 patients with less extended intracranial pathology, the ECMO treatment was continued with high survival. CONCLUSION: Cranial CT has an important role during ECMO treatment to reveal or exclude severe intracranial complications where ECMO treatment should be discontinued. Less severe complications have a favorable prognosis with continued treatment. Our study suggests an underreporting of intracranial complications in adults and pediatric patients on ECMO because of low utilization of neuroimaging.
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| 10. |
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