Biomedical subjects

Harald Morgner

Publications and source records attributed to Harald Morgner.

5 recordsLinked to original sources

PubMed2006

Chemical potential of a nonionic surfactant in solution.

The chemical potential of a surfactant in solution can be calculated from the Gibbs adsorption equation when the surface excess of the surfactant and the surface tension of the solution as a function of surfactant concentration are known. We have investigated a solution of the nonionic surfactant 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC) in the polar solvent 3-hydroxypropionitrile at concentrations below and above the critical micelle concentration (cmc). Neutral impact collision ion scattering spectroscopy was applied for the direct measurement of the surface excess of POPC as a function of concentration. The Gibbs adsorption equation was applied in conjunction with surface tension measurements to evaluate the chemical potential and the activity coefficients of POPC, respectively. We find that the solution shows ideal behavior up to the cmc and that the chemical potential remains constant at concentrations larger than the cmc.

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PubMed2006

Increased layer interdiffusion in polyelectrolyte films upon annealing in water and aqueous salt solutions.

As-deposited films of multilayered polyelectrolytes are considered to be non-equilibrium structures. Due to the strong attraction between oppositely charged polyions, polyelectrolyte interdiffusion is thought to be suppressed during the adsorption process. Equilibration is promoted by a decrease of the electrostatic attraction between polyion pairs. We have used neutral impact collision ion scattering spectroscopy to investigate the influence of polyelectrolyte multilayer annealing in water and aqueous 1 M NaCl solutions at different temperatures (20 and 70 degrees C) on the increase in interpenetration of a single polyelectrolyte layer throughout the whole film. The multilayers were composed of poly(4-vinylpyridinium) and poly(4-styrenesulfonate). Contrast between neighboring layers was established by labelling the layer in question with the heavy atom ruthenium. It is found that both temperature and salt increase layer interpenetration, whereas salt has a stronger influence than temperature. From numerical simulations polyelectrolyte diffusion coefficients were evaluated for the different annealing conditions. The influence of temperature and salt on the equilibration of the film is interpreted in terms of increased screening of polyion charges and binding of small counterions to polyion monomeric units.

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PubMed2006

Binary liquid mixtures. The relation between surface tension and surface composition as studied by MIES (metastable induced electron spectroscopy).

For a binary liquid mixture, we define the surface fraction of a component as the fraction of the surface which is covered by this species. The perfectly surface-sensitive electron spectroscopy MIES (metastable induced electron spectroscopy) allows to derive this quantity in a very direct manner from experiment with no model assumption needed. We find for several binary mixtures that the surface tension depends linearly on the surface fraction with striking accuracy. Even more surprising is the fact that for a system which deviates from this simple linear behavior the surface tension turns out to be a piecewise linear function of the surface fraction. Tentatively, we introduce as possible explanation the concept of phase separation within the surface layer. Further, we show that the surface molar fraction, i.e., the molar fraction within the top surface layer, deviates significantly from a linear or a piecewise linear relation to the surface tension.

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PubMed2005

Angle resolved ion scattering spectroscopy reveals the local topography around atoms in a liquid surface.

Neutral impact collision ion scattering spectroscopy under normal incidence is known to yield the concentration depth profiles of all elements except hydrogen at the surface of liquids and other amorphous material. In the evaluation of the data one tactically has to assume that the top surface layer and the adjacent layers are laterally homogeneous. In the present paper we establish that the angular resolved mode of this spectroscopy is able to test with high accuracy whether the lateral homogeneity is valid and-if this is not the case-in which way the top layer is structured. In particular, it is possible to map out the local environment of selected atoms. We expect that this so far inaccessible information on the local topography at liquid surfaces will have an impact on the understanding of reactions at the gas/liquid interface.

Algorithms↗

PubMed2005

Internal structure of polyelectrolyte multilayers probed via neutral impact collision ion scattering spectroscopy.

Layering in polyelectrolyte multilayer films has been studied by neutral impact collision ion scattering spectroscopy. The method affords a direct look at vertical ordering within these films at the nanometer scale. By labeling certain polyelectrolyte layers with heavy atom (Ru) probes, sufficient contrast has been obtained to visualize and quantify the distribution of these labeled polyelectrolytes throughout the film. The results indicate that the materials under investigation here produce linear film growth with very limited layer interpenetration. The interdigitation length between neighboring layers within the film is measured as 3.9 nm, which is approximately 1.4 times the thickness of an individual polycation/polyanion pair and is slightly less than the measured air/film roughness (4.7 nm). Detailed analysis shows that under the conditions used and at the depths probed in this study, the observed layer thickness is not significantly broadened by either instrumental or stochastic factors.

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