Martin Schimpf - Academia.edu (original) (raw)

Papers by Martin Schimpf

Field-flow fractionation (FFF) is a family of instrumental techniques that separates and characte... more Field-flow fractionation (FFF) is a family of instrumental techniques that separates and characterizes macromolecules, colloids, and particles (macromaterials) on an analytical scale (Colfen and Antonietti, 2000; Schimpf et al., 2000). As illustrated in Fig. 1, the FFF channel has a ribbon-shaped geometry, typically with length 30-50 cm, breadth 1-3 cm, and thickness 0.005-0.025cm. Because of the high aspect ratio between breadth and thickness, liquid that is pumped through the channel flows in a laminar fashion, with a velocity profile that varies across the thin (x) dimension. A field is applied external to the channel in order to force analyte into the slower flow streams near one wall. The resulting velocity of the analyte through the channel depends on its interactions with the field, and therefore, on physicochemical properties that govern that interaction. Those physicochemical properties vary with the nature of the applied field, but always include the size of the analyte, because size determines the ability of analyte to reach the faster moving flow streams away from the accumulation wall

Physical chemistry chemical physics/PCCP. Physical chemistry chemical physics, 2024

$Research paper thumbnail of Asymmetrical flow field-flow fractionation as a method to study the behavior of humic acids in solution$

Journal of Microcolumn Separations, 1997

Asymmetrical flow field-flow fractionation AsFlFFF is used to measure the size distributions of h... more Asymmetrical flow field-flow fractionation AsFlFFF is used to measure the size distributions of humic acids in solution. Shifts in the size distribution are used to study the behavior of these amphiphilic macromolecules in solution with changes in pH, ionic strength, and humic acid concentration. Humic acid concentrations are increased by on-channel focusing of the injected samples. As the concentration is increased, the humic acids aggregate, but the effect varies with solution conditions. As the concentration of calcium chloride is increased, size distributions broaden and become multimodal. The decrease in size is consistent with reports that divalent cations induce conformational changes by the formation of intramolecular bridges between carboxylate moieties; multimodality indicates intermolecular interactions as well. Lowering the pH also promotes intermolecular interactions, with severe aggregation occurring below pH 4. The work demonstrates the utility of AsFlFFF in studies of the hydrodynamic behavior of amphiphilic macromolecules.

CRC Press eBooks, Jun 6, 2005

Physical Chemistry Chemical Physics

We present a self-consistent model rooted in nonequilibrium thermodynamics for defining concentra... more We present a self-consistent model rooted in nonequilibrium thermodynamics for defining concentration gradients in the electron/hole pairs and electric-field gradients in an intrinsic semiconductor created upon exposure to a temperature gradient.

Encyclopedia of Chromatography, Third Edition (Print Version), 2009

Encyclopedia of Chromatography, Second Edition, 2005

Physical Chemistry Chemical Physics, Nov 7, 2022

Comptes Rendus Mécanique, 2011

A thermodynamic theory is developed for the thermophoresis of dilute suspensions of charged collo... more A thermodynamic theory is developed for the thermophoresis of dilute suspensions of charged colloid particles in electrolyte solutions. The calculation of relevant thermodynamic parameters using statistical mechanics is carried out in the Debye-Hueckel approximation. The main experimental features observed for such systems are explained.

The Journal of Physical Chemistry C, 2016

We use methods of physicochemical hydrodynamics to study the working principles of a thermophoret... more We use methods of physicochemical hydrodynamics to study the working principles of a thermophoretic microgear in which an axially symmetric temperature gradient causes rotational movement of a heated rotor in the shape of a pinion confined in a cylindrical cavity filled with liquid. Calculations indicate that the rotation of the microgear arises from differences in the physicochemical properties along the edges of the teeth. The angular velocity of the gear under load decreases linearly with the load torque. The resulting characteristics of the thermophoretic gear are compared with that of a thermoosmotic engine having comparable parameters. Optimal geometrical parameters of both systems are discussed. It is shown that performance of the two devices is similar.

The Journal of Physical Chemistry B