| 1. |
- Kadi, M., et al.
(författare)
-
Mixed micelles of fluorocarbon and hydrocarbon surfactants. A small angle neutron scattering study
- 2004
-
Ingår i: Langmuir. - : American Chemical Society (ACS). - 0743-7463 .- 1520-5827. ; 20:10, s. 3933-3939
-
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.
|
|
| 2. |
- Swansson Vethamuthu, M, et al.
(författare)
-
The hexagonal phase and cylindrical micelles in the system alkyltrimethylammonium bromide-sodium desoxycholate-water as studied by x-ray diffraction and fluorescence quenching
- 1996
-
Ingår i: Journal of Colloid and Interface Science. - 0021-9797 .- 1095-7103. ; 178, s. 538-548
-
Tidskriftsartikel (refereegranskat)abstract
- The hexagonal (E) liquid-crystaline phase in mixtures of sodium desoxycholate (NaDOC) with the catiorwic surfactant cetyltrimethylammonium bromide (CTAB) in water has been investigated by small-angle X-ray diffraction and optical polarizing microscopy. Large proportions of the dihydroxy bile salt can be incorporated in the E phase of the detergent and lead to a decreasing average radius from 22 Å for pure CTAB to 19.5 Å at 46 mole% of NaDOC. The introduction of the bile salt in the cylinders thus increases the curvature, whereas the same bile salt induces a transition to rod-like micelles when added to spherical CTAB micelles at low surfactant concentration. The mixed E phase was identified and characterized as a hexagonal mesophase by optical polarizing microscopy. The diffusion-limited fluorescence quenching of excited state pyrene by dimethylbenzophenone was investigated in the cylindrical mixed micelles of the micellar (Ll) phase in the same system. The decay curves were evaluated using a model of excited state deactivation in infinitely long rod-like micelles without exchange of quenchers (Almgren, M., Alsins, J., Mukhtar, E., and van Stam, J., J. Phys. Chem. 92, 4479 (1988)) and gave as results the relative diffusion coefficient of the excUed probe and quencher. The addition of DOC- up to an equimolar concentration decreased the diffusion coefficient substantially, indicating an increased rigidity of the micelle.
|
|
| 3. |
|
|
| 4. |
- Almgren, Karin M., et al.
(författare)
-
Characterization of interfacial stress transfer ability by dynamic mechanical analysis of cellulose fiber based composite materials
- 2010
-
Ingår i: Composite interfaces (Print). - 0927-6440 .- 1568-5543. ; 17:9, s. 845-861
-
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.
|
|
| 5. |
- Almgren, Karin M., et al.
(författare)
-
Effects of Moisture on Dynamic Mechanical Properties of Wood Fiber Composites Studied by Dynamic FT-IR Spectroscopy
- 2008
-
Ingår i: Journal of reinforced plastics and composites (Print). - : SAGE Publications. - 0731-6844 .- 1530-7964. ; 27:16-17, s. 1709-1721
-
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.
|
|
| 6. |
- Almgren, Karin M., et al.
(författare)
-
Moisture uptake and hygroexpansion of wood fiber composite materials with polylactide and polypropylene matrix materials
- 2009
-
Ingår i: Polymer Composites. - : Wiley. - 0272-8397 .- 1548-0569. ; 30:12, s. 1809-1816
-
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.
|
|
| 7. |
- Isaksson, M., et al.
(författare)
-
Determination of the retention of 47Ca by whole-body counting
- 2000
-
Ingår i: Applied Radiation and Isotopes. - 0969-8043 .- 1872-9800. ; 52:6, s. 1441-1450
-
Tidskriftsartikel (refereegranskat)abstract
- Retention of intravenously or orally administered 47Ca in the human body are described by a two-parameter function. It is then sufficient to make only a few whole-body measurements to determine the retention function, avoiding faeces sampling and stool markers. Seven days after intake the non-absorbed calcium was excreted and the model agreed with the measured relative retention. Absorption of calcium could then, in some cases (e.g. comparative studies), be described by relative retention at the 7th day after intake. Copyright (C) 2000 Elsevier Science Ltd.
|
|
| 8. |
- Landström, K, et al.
(författare)
-
A fluorescence method for quantitative measurements of specific protein at powder surfaces
- 1999
-
Ingår i: Colloids and Surfaces B. - 0927-7765 .- 1873-4367. ; 12, s. 429-440
-
Tidskriftsartikel (refereegranskat)abstract
- A new method using fluorescence labeled proteins was developed to determine the quantitative amount of specific protein at the powder surface. The method is based on steady-state fluorescence measurements of pyrene labeled proteins with oxygen gas phase quenching at the powder surface. The surface load of protein was measured for spray-dried dextran powders containing bovine serum albumin (BSA). The results show a patchwise surface load of about 1.3 mg/m2 at a concentration of 0.33 % (dry weight) BSA in the powder. The patchwise surface load stays constant with increased BSA concentration in the powder.
|
|
| 9. |
- Mays, H, et al.
(författare)
-
Spontaneous formation of reverse vesicles with soybean phosphatidyl ethanolamine in mixture with triglyceride and some water
- 1999
-
Ingår i: Langmuir. - 0743-7463 .- 1520-5827. ; 15, s. 8072-8079
-
Tidskriftsartikel (refereegranskat)abstract
- Mixing the phospholipid soybean phosphatidyl ethanolamine (PE) with the triglyceride triolein and a trace amount of water leads to a spontaneous formation of isotropic aggregates. Evidence for the existence of such aggregates in pseudo-three-component systems is presented here for the first time. Dynamic light scattering and cryogenic temperature transmission electron microscopy reveal polydisperse spherical particles with radii in the range of 250-840 nm and a mean radius of the order 600 nm. From the results of both depolarized light scattering and time-resolved electro-optical birefringence (Kerr effect) the presence of aggregates with an optical anisotropy (rodlike or wormlike reverse micelles as well as particles with lamellar structure) can be excluded. The remaining possibilities are reverse vesicles and a dispersed cubic bicontinuous phase, where our results favor reverse vesicles. A necessary condition for the formation of reverse vesicles is a saturation of the PE-triolein mixture with water; at lower water content the particles are significantly smaller.
|
|
