Biomedical subjects

Peter Bräuer

Publications and source records attributed to Peter Bräuer.

6 recordsLinked to original sources

PubMed2006

Simultaneous adsorption at the liquid/solid and liquid/gas interfaces.

Physical adsorption from binary or higher-order liquid mixtures on solids is often accompanied by adsorption phenomena at the liquid/gas interface. As long as the adsorption effects are comparable, both interfaces have to be included in the respective thermodynamic equations. A purely phenomenological thermodynamic description in terms of excess quantities is given of the simultaneous adsorption from multicomponent liquid mixtures at the liquid/solid and liquid/gas interfaces. In order to illustrate the thermodynamic procedure, the individual and simultaneous adsorption excess isotherms of three binary liquid mixtures at the liquid/Teflon and liquid/vapor interfaces are calculated from experimental surface-tension and contact-angle data taken from the literature. Special attention is focused on the estimation of error in calculated adsorption isotherms. A line of approach is given to find the confidence limits of adsorption isotherms that cover the entire mole fraction scale. The isotherms as well as their confidence limits are presented and discussed.

Journal Article↗

PubMed2006

Two-component desorption from anisotropic pore networks.

Dynamic Monte Carlo simulations are performed to explore molecular desorption of a two-component mixture from a mode adsorbent of adsorbate-related anisotropy. The intrinsic dynamics of the adsorbent-adsorbate host-guest system is described by assuming a situation typical of a "molecular-traffic-control" system, where the hopping rates of the two components in two directions, perpendicular to each other, are identical, while for each component, perpendicular to that direction of preferential propagation, the hopping rates are reduced. The resulting desorption patterns are discussed in terms of the jump probabilities and are shown to approach the corresponding analytical solutions in the limiting cases of isotropic and unidirectional diffusions.

Journal Article↗

PubMed2004

Prediction of multicomponent liquid adsorption using excess quantities. II. Calculations for the liquid/solid interface.

The utilization of excess quantities as the basis for a thermodynamic approach can simplify the prediction of multicomponent liquid adsorption from binary data. A new method for predicting liquid adsorption on solids is suggested, which is different from the existing equations with respect to the theoretical background and formulation. The applicability of the new model is tested with three ternary adsorption systems. The predicted surface excesses are discussed and compared with experimental ones and with those of other prediction models in the literature. The accordance between measured and predicted ternary data is convincing.

Journal Article↗

PubMed2004

Prediction of multicomponent liquid adsorption using excess quantities I. Statistical thermodynamic derivation of the basic equation of excess formalism.

The utilization of excess quantities as the basis of a thermodynamic approach can simplify the prediction of multicomponent liquid adsorption from binary data. From statistical thermodynamics, the fundamental equation is derived for the prediction of ternary or higher order data from adsorption data for the constituent binary mixtures. An additive expression is obtained for the double Gibbs free excess energies, valid for adsorption on liquid mixture/air interfaces as well as liquid mixture/solid interfaces.

Journal Article↗

PubMed2002

Calculation and prediction of adsorption excesses on the ternary liquid mixture/air interface from surface tension measurements.

The surface tensions of the n-propanol/ethylene glycol/water ternary mixture and its binary mixtures are measured at 293 K and described by mathematical functions. The experimental data and their descriptions are shown in the three-dimensional space by means of coordinate transformation. A thermodynamic model to calculate and predict ternary adsorption excess data on the ternary liquid mixture/air interface from surface tensions is presented. The calculated adsorption excess data in the ternary triangle are discussed.

Journal Article↗

PubMed2002

High-resolution DOSY NMR with spins in different chemical surroundings: influence of particle exchange.

The effect of chemical exchange in the diffusion-ordered (DOSY) spectra of a two-site system in the slow-exchange limit with respect to the chemical shift is studied. The problem is addressed both theoretically and experimentally. The relationship between diffusion time (t) and mean lifetimes (tau) is studied by the simulation of the magnetization attenuations as a function of the gradient strength, under PFG conditions. The influence of the difference in populations and diffusion coefficients of the two sites is also considered. In analogy to the limiting cases of fast- and slow-exchange with respect to the chemical shift, limiting cases with respect to the diffusion dimension are defined. The slow-exchange limit in diffusion corresponds to the relation of t and tau that allows us to observe the two spins in exchange associated with the individual diffusion coefficients of the two sites when no exchange is present. The fast-exchange limit in diffusion is reached when the relation of t and tau is such that the two spins present the same apparent diffusion coefficient. By using a model system consisting of water/t-butanol it is shown that by recording several DOSY experiments with increasing diffusion times it is possible to estimate the value of the exchange rate.

Journal Article↗