Biomedical subjects

M Nydén

Publications and source records attributed to M Nydén.

4 recordsLinked to original sources

PubMed2005

Water mobility in heterogeneous emulsions determined by a new combination of confocal laser scanning microscopy, image analysis, nuclear magnetic resonance diffusometry, and finite element method simulation.

Nuclear magnetic resonance (NMR) diffusometry and confocal laser scanning microscopy (CLSM) were combined in a quantitative way in finite element calculations of water propagation in CLSM images obtained from a very heterogeneous emulsion. The propagators calculated on the basis of microstructure were Fourier transformed and subsequently compared with the echo decays obtained by the NMR diffusometry method. The results showed very good agreement between microstructure based calculations and experiments, indicating that the short gradient pulse approximation in the NMR diffusometry experiment holds for a certain q range. Furthermore, the CLSM was able to achieve a relevant two-dimensional microstructure although some discrepancy at low q values was noted. This effect is attributed to the inherent three-dimensional connectivity between the water domains in this type of structures, making the calculations slightly underestimate the water diffusion at longer distances.

Computer Simulation↗

PubMed2003

Power laws in polymer solution dynamics.

The dynamical screening length xi(h) in semidilute to highly concentrated polymer solutions of poly(methyl methacrylate) in propylene carbonate has been examined using photon correlation spectroscopy and pulsed field gradient nuclear magnetic resonance. A crossover between different concentration dependent regimes, xi(h) approximately phi(-alpha), where alpha is found to be approximately 0.5, approximately 1, and approximately 2, is observed when the local viscosity is taken into account. Here phi is the volume fraction of polymer in the solution. Well-defined crossovers between alpha=0.5 and alpha=1 corresponding to a transition from a marginal solvent to a theta solvent behavior have been predicted to occur due to the reduction of excluded-volume effects between the spatially correlated polymer segments with increasing polymer volume fraction. However, a clear experimental validation of the crossover has never been presented before. The third regime (alpha approximately 2) is observed in the highly concentrated region where the static screening length is comparable to the persistence length of the polymer. The observation indicates that the rigid rod model previously used to describe concentrated solutions is an oversimplification valid only in the very high concentration limit. The obtained results at high concentrations are discussed in the frame of a simple physical model where segments at the persistence length scale are treated as flexible rodlike segments.

Journal Article↗

PubMed2000

Interactions between a lipase and charged surfactants--a comparison between bulk and interfaces.

The interaction between a charged surfactant and a lipase has been investigated by several methods. Interactions in aqueous bulk phase was studied by NMR and by microcalorimetry. Surface tension and neutron reflectivity were used for studies at the air-water interface. Interactions at the interface between a hydrophobic solid surface and water was investigated by ellipsometry. The results obtained are as follows. The cationic surfactant, tetradecyltrimethylammonium bromide (iodide in the NMR experiments), showed strong interaction at the air-water and the hydrophobic solid-water interfaces but no clear indication of an interaction in bulk phase was seen. The anionic surfactant showed no interaction with the lipase neither at the interfaces, nor in bulk. The difference in behavior of the system cationic surfactant-lipase in bulk and at the interfaces may be due to the change in enzyme conformation that is known to occur at interfaces between water and an apolar phase.

Calorimetry↗

PubMed1998

An NMR Self-Diffusion Investigation of Aggregation Phenomena in Solutions of Ethyl(hydroxyethyl)cellulose.

Water solutions of ethyl(hydroxyethyl)cellulose have been investigated with the PFG NMR technique and by means of 1H NMR relaxation measurements. The echo decays in PFG experiments have been recorded for EHEC with concentrations ranging from the dilute (c < c) to the semidilute (c > c). In addition, the temperature dependence of the echo decay was investigated. It is shown that the echo decays deviate substantially from Gaussian diffusion behavior. We discuss this in terms of polydispersity, aggregation, and scaling effects. It is argued that the observed deviations are too large to be caused by polydispersity effects alone. We base this conclusion on the observation that the molar mass scaling of the polymer diffusion coefficient goes roughly as M-4. We focus on using a log-normal distribution of diffusion coefficients in the evaluation procedure of the PFG data. It is found that by comparing the diffusion coefficients extracted from this type of procedure with "Dmean" as extracted from a "stretched exponential" approach, there is a difference in the evaluated diffusion constant by up to 1 order of magnitude. The difference depends on the degree of deviation from linear behavior in the echo decay when represented in a logarithmic plot vs the relevant experimental parameter.

Journal Article↗