| 1. |
- Kadi, M., et al.
(författare)
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Mixed micelles of fluorocarbon and hydrocarbon surfactants. A small angle neutron scattering study
- 2004
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:10, s. 3933-3939
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Tidskriftsartikel (refereegranskat)abstract
- Mixtures of the partly fluorinated cationic surfactant HFDePC (N-(1, 1,2,2-tetrahydroperfluorodecanyl)pyridinium chloride and deuterated headgroup) with C(16)TAC, hexadecyl-trimethylammonium chloride, have been investigated using small angle neutron scattering with contrast matching. Earlier results from this system suggested that a demixing occurred, into two coexisting populations of micelles, hydrocarbon-rich and fluorocarbon-rich, respectively. The present results could be explained by one type of mixed micelles with an inhomogeneous distribution of fluorinated and hydrogenated surfactants within the micelles although a demixing cannot be definitely excluded.
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| 2. |
- Kadi, M., et al.
(författare)
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Demixing of fluorinated and hydrogenated surfactants into distinct aggregates and into distinct regions within aggregates. A combined NMR, fluorescence quenching, and cryo-TEM study
- 2002
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 18:24, s. 9243-9249
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Tidskriftsartikel (refereegranskat)abstract
- The formation of two different kinds of micelles in the cationic surfactant mixture of HFDePC and CTAC as well as the increased mixing with increasing temperature has been investigated. A critical temperature of demixing was appreciated to 42 degreesC. NMR self-diffusion measurements reveal to us a coexistence of larger fluorocarbon-rich and smaller hydrocarbon-rich micelles, which is also observed using cryo-TEM. We also suggest, from F-19 line width data, that the two surfactant species constituting the demixed micelles are I'microphase-separated. The existence of such aggregates has earlier only been speculated upon. From time-resolved fluorescence quenching measurements, we have estimated the fraction of fluorocarbon surfactant in the hydrocarbon-rich micelles to larger than 0.1.
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| 3. |
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| 4. |
- Valstar, A., et al.
(författare)
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Heat-set bovine serum albumin-sodium dodecyl sulfate gels studied by fluorescence probe methods, NMR, and light scattering
- 2001
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Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 17:11, s. 3208-3215
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Tidskriftsartikel (refereegranskat)abstract
- In this work, concentrated protein-surfactant solutions and their corresponding heat-set gels; were studied by fluorescence probe methods, NMR, and light scattering. Bovine serum albumin (BSA) was used as the protein, and sodium dodecyl sulfate (SDS) as the surfactant. Heating concentrated BSA solutions gives turbid gels. Heat-setBSA-SDS gels are transparent. From fluorescence measurements it was concluded that SDS forms micelle-like clusters on BSA, both in solution and in the corresponding heat-set gel. Aggregation numbers were found to be similar in solution and gel. Also, I-1/I-3 values in solution and gel were similar. H-2 NMR relaxation measurements of specifically deuterated SDS at the ct-carbon position next to the headgroup were performed, and the longitudinal relaxation rates R-1 were found to be the same in solution and gel. High values for the transverse relaxation rate R-2 (indicating slow motions of SDS bound to large aggregates) were obtained, and the largest R-2 value was found for the gel. Dynamic light scattering on BSA-SDS gels was used to obtain the correlation length xi, which defines a mean distance between two points of entanglements. The decrease of xi with increasing [SDS]/[BSA] molar ratio was explained by the size of the BSA-SDS complex and the possibility that micelle-like structures might form cross-links between different BSA molecules. With static light scattering the extent of inhomogeneities in BSA and BSA-SDS gels was found to decrease with increasing SDS concentration. Also, the gel region in the ternary phase diagram BSA-SDS-3.1 mM NaN3 at room temperature and constant pressure (1 atm) was determined.
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| 5. |
- Almgren, Karin M., et al.
(författare)
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Characterization of interfacial stress transfer ability by dynamic mechanical analysis of cellulose fiber based composite materials
- 2010
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Ingår i: Composite interfaces (Print). - 0927-6440 .- 1568-5543. ; 17:9, s. 845-861
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Tidskriftsartikel (refereegranskat)abstract
- The stress transfer ability at the fiber-matrix interface of wood fiber composites is known to affect the mechanical properties of the composite. The evaluation of interface properties at the level of individual fibers is however difficult due to the small dimensions and variability of the fibers. The dynamical mechanical properties of composite and constituents, in this case wood fibers and polylactide matrix, was here used together with micromechanical modeling to quantify the stress transfer efficiency at the fiber-matrix interface. To illustrate the methodology, a parameter quantifying the degree of imperfection at the interface was identified by inverse modeling using a micromechanical viscoelastic general self-consistent model with an imperfect interface together with laminate analogy on the composite level. The effect of moisture was assessed by comparison with experimental data from dynamic mechanical analysis in dry and moist state. For the wood fiber reinforced polylactide, the model shows that moisture absorption led to softening and mechanical dissipation in the hydrophilic wood fibers and biothermoplastic matrix, rather than loss of interfacial stress transfer ability.
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| 6. |
- Almgren, Karin M., et al.
(författare)
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Contribution of wood fiber hygroexpansion to moisture induced thickness swelling of composite plates
- 2010
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Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 31:5, s. 762-771
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Tidskriftsartikel (refereegranskat)abstract
- One of the main drawbacks of wood fiber-based composite materials is their propensity to swell due to moisture uptake. Because the wood fibers are usually the main contributor to hygroexpansion, it is of interest to quantify the hygroexpansion coefficient of wood fibers, to compare and rank different types of fibers. This investigation outlines an inverse method to estimate the transverse hygroexpansion coefficient of wood fibers based on measurements of moisture induced thickness swelling of composite plates. The model is based on composite micromechanics and laminate theory. Thickness swelling has been measured on polylactide matrix composites with either bleached reference fibers or crosslinked fibers. The crosslinking modification reduced the transverse hygroexpansion of the composites and the transverse coefficient of hygroexpansion of the fibers was reduced from 0.28 strain per relative humidity for reference fibers to 0.12 for cross-linked fibers
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| 7. |
- Almgren, Karin M., et al.
(författare)
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Effects of Moisture on Dynamic Mechanical Properties of Wood Fiber Composites Studied by Dynamic FT-IR Spectroscopy
- 2008
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Ingår i: Journal of reinforced plastics and composites (Print). - : SAGE Publications. - 0731-6844 .- 1530-7964. ; 27:16-17, s. 1709-1721
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Tidskriftsartikel (refereegranskat)abstract
- Wood fiber reinforced polylactide is a biodegradable composite where both fibers and matrix are from renewable resources. In the development of such new materials, information on mechanical behavior on the macroscopic and the molecular level is useful. In this study, dynamic Fourier transform infrared (FT-IR) spectroscopy is used to measure losses at the molecular level during cyclic tensile loading for bonds that are characteristic of the cellulosic fibers and the polylactid matrix. This molecular behavior is compared with measured macroscopic hysteresis losses for different moisture levels. The results show that moisture ingress will transfer the load from the fibers to the matrix, and that a more efficient fiber-matrix interface would diminish mechanical losses. Although the dynamic FT-IR spectroscopy method is still qualitative, this investigation shows that it can provide information on the stress transfer of the constituents in wood fiber reinforced plastics.
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| 8. |
- Almgren, Karin M., et al.
(författare)
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Moisture uptake and hygroexpansion of wood fiber composite materials with polylactide and polypropylene matrix materials
- 2009
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Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 30:12, s. 1809-1816
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Tidskriftsartikel (refereegranskat)abstract
- Effects of butantetracarboxylic acid (BTCA) modification, choice of matrix, and fiber volume fraction on hygroexpansion of wood fiber composites have been investigated. Untreated reference wood fibers and BTCA-modified fibers were used as reinforcement in composites with matrices composed of polylactic acid (PLA), polypropylene (PP), or a mixture thereof. The crosslinking BTCA modification reduced the out-of-plane hygroexpansion of PLA and PLA/PP composites, under water-immersed and humid conditions, whereas the swelling increased when PP was used as matrix material. This is explained by difficulties for the BTCA-modified fibers to adhere to the PP matrix. Fiber volume fraction was the most important parameter as regards out-of-plane hygroexpansion, with a high-fiber fraction leading to large hygroexpansion. Fiber-matrix wettability during processing and consolidation also showed to have a large impact on the dimensional stability and moisture uptake. POLYM. COMPOS., 30:1809-1816, 2009.
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| 9. |
- Almgren, Karin M., 1980-
(författare)
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Wood-fibre composites : Stress transfer and hygroexpansion
- 2010
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Wood fibres is a type of natural fibres suitable for composite applications. The abundance of wood in Swedish forests makes wood-fibre composites a new and interesting application for the Swedish pulp and paper industry. For large scale production of composites reinforced by wood fibres to be realized, the mechanical properties of the materials have to be optimized. Furthermore, the negative effects of moisture, such as softening, creep and degradation, have to be limited. A better understanding of how design parameters such as choice of fibres and matrix material, fibre modifications and fibre orientation distribution affect the properties of the resulting composite material would help the development of wood-fibre composites. In this thesis, focus has been on the fibre-matrix interface, wood-fibre hygroexpansion and resulting mechanical properties of the composite. The importance of an efficient fibre-matrix interface for composite properties is well known, but the determination of interface properties in wood-fibre composites is difficult due to the miniscule dimensions of the fibres. This is a problem also when hygroexpansion of wood fibres is investigated. Instead of tedious single-fibre tests, more straightforward, macroscopic approaches are suggested. Halpin-Tsai’s micromechanical models and laminate analogy were used to attain efficient interface characteristics of a wood-fibre composite. When Halpin-Tsai’s model was replaced by Hashin’s concentric cylinder assembly model, a value of an interface parameter could be derived from dynamic mechanical analysis. A micromechanical model developed by Hashin was used also to identify the coefficient of hygroexpansion of wood fibres. Measurements of thickness swelling of wood-fibre composites were performed. Back-calculation through laminate analogy and the micromechanical model made it possible to estimate the wood-fibre coefficient of hygroexpansion. Through these back-calculation procedures, information of fibre and interface properties can be gained for ranking of e.g. fibre types and modifications. Dynamic FT-IR (Fourier Transform Infrared) spectroscopy was investigated as a tool for interface characterization at the molecular level. The effects of relative humidity in the test chamber on the IR spectra were studied. The elastic response of the matrix material increased relative to the motion of the reinforcing cellulose backbone. This could be understood as a stress transfer from fibres to matrix when moisture was introduced to the system, e.g. as a consequence of reduced interface efficiency in the moist environment. The method is still qualitative and further development is potentially very useful to measure stress redistribution on the molecular level.
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| 10. |
- Kharlamova, N., et al.
(författare)
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False Positive Results in SARS-CoV-2 Serological Tests for Samples From Patients With Chronic Inflammatory Diseases
- 2021
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Ingår i: Frontiers in Immunology. - : Frontiers Media SA. - 1664-3224. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Patients with chronic inflammatory diseases are often treated with immunosuppressants and therefore are of particular concern during the SARS-CoV-2 pandemic. Serological tests will improve our understanding of the infection and immunity in this population, unless they tests give false positive results. The aim of this study was to evaluate the specificity of SARS-Cov-2 serological assays using samples from patients with chronic inflammatory diseases collected prior to April 2019, thus defined as negative. Samples from patients with multiple sclerosis (MS, n=10), rheumatoid arthritis (RA, n=47) with or without rheumatoid factor (RF) and/or anti-cyclic citrullinated peptide antibodies (anti-CCP2) and systemic lupus erythematosus (SLE, n=10) with or without RF, were analyzed for SARS-CoV-2 antibodies using 17 commercially available lateral flow assays (LFA), two ELISA kits and one in-house developed IgG multiplex bead-based assay. Six LFA and the in-house validated IgG assay correctly produced negative results for all samples. However, the majority of assays (n=13), gave false positive signal for samples from patients with RA and SLE. This was most notable in samples from RF positive RA patients. No false positive samples were detected in any assay using samples from patients with MS. Poor specificity of commercial serological assays could possibly be, at least partly, due to interfering antibodies in samples from patients with chronic inflammatory diseases. For these patients, the risk of false positivity should be considered when interpreting results of the SARS-CoV-2 serological assays.
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