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Johannes Nowak, Caroline Barhold, Christian Kessler, Stefan Odenbach
Gelation of a Nanocomposite-Hydrogel system and its dependency on mechanical loads

Appl. Rheol. 27:5 (2017) 52850 (6 pages)

Hydrogels are cross-linked polymer networks which are water-insoluble. They are suitable for several technical and biomedical applications due to the ability of some gels to swell and deswell as reaction to external stimuli. Such gels are synthesized and shift from a fluid-like liquid with solved components towards the final polymeric network with gel-like properties. Monitoring and characterizing this process is fundamental on the one hand to understand the chemical and physical behavior and on the other hand to adopt the application and production of such gels. Therefore, this investigation focuses on the characterization of the gelation of a nanocomposite hydrogel system based on PNIPAm with and without mechanical loads applied, using rheology. Measurements are conducted featuring rotational and oscillating rheometry and the results found are compared and evaluated. Furthermore the impact of a strong pre-shear, preventing the gelation, prior to the actual gelation, is investigated. The results found show a strong influence of the applied load as well as of an applied pre-shear on the gelation and furthermore on the mechanical properties of the final hydrogels. Therefore those parameters be taken into account for future investigations as well as for the large scale productions of hydrogels.

Cite this publication as follows:
Nowak J, Barhold C, Kessler C, Odenbach S: Gelation of a Nanocomposite-Hydrogel system and its dependency on mechanical loads, Appl. Rheol. 27 (2017) 52850.

Johannes Nowak, Christoph Nowak, Stefan Odenbach
Consequences of sheep blood used as diluting agent for the magnetoviscous effect in biocompatible ferrofluids

Appl. Rheol. 25:5 (2015) 53250 (8 pages)

Magnetic nanoparticles suspended in suitable carrier liquids can be adopted for use in biomedicine. For this to be achieved, the biocompatibility of these ferrofluids needs to be ascertained. In cancer treatment, potential applications currently under investigation include, e.g. drug targeting by using magnetic fields and the destruction of diseased cells by applying alternating magnetic fields, which cause heating of magnetic nanoparticles. To enable the use of ferrofluids in the actual biomedical context, detailed knowledge of the flow characteristics is essential to ensure safe treatment. From ferrofluids used in the engineering context, a rise of viscosity when a magnetic field is applied - the magnetoviscous effect - is well known. This effect, which leads to an increased viscosity and profound alteration of a fluid's rheological behaviour, has also been demonstrated for biocompatible ferrofluids used in the aforementioned applications. In biomedical applications, ferrofluids will be diluted in the blood stream. Therefore, the interaction between whole blood and the ferrofluid has to be investigated. This is the focus of the current experimental study, which makes use of two different ferrofluids diluted in sheep blood to gain a deeper understanding of the fluid mixtures primarily regarding the relative change in viscosity if an external magnetic field is applied. The results demonstrate a strong interaction between blood cells and structures formed by the magnetic nanoparticles and show a high deviation of results compared to ferrofluids diluted in water. These findings have to be taken into account for future research and applications of similar biocompatible fluids to guarantee safe and effective use in living organisms.

Cite this publication as follows:
Nowak J, Nowak C, Odenbach S: Consequences of sheep blood used as diluting agent for the magnetoviscous effect in biocompatible ferrofluids, Appl. Rheol. 25 (2015) 53250.

Dmitry Borin, Piotr Nikrityuk, Stefan Odenbach
On the magnetic field influence on the viscosity of liquid GaInSn with suspended solid particles

Appl. Rheol. 19:6 (2009) 61995 (7 pages)

Experimental and numerical studies have been undertaken to check the influence of a magnetic field on the viscosity of liquid GaInSn with suspended solid particles.The rheological investigations show a significant change of the slope of the measured flow curves between the situation B = 0 and 0.02 T. By means of numerical simulations of the flow in the presence of Lorentz forces it could be shown that the influence of magnetohydrodynamic damping of the flow reduces the measured changes but does not annihilate them. As conclusion a 15 % change of viscosity of the melt in a magnetic field with B = 0.02 T could be fixed.

Cite this publication as follows:
Borin D, Nikrityuk P, Odenbach S: On the magnetic field influence on the viscosity of liquid GaInSn with suspended solid particles, Appl. Rheol. 19 (2009) 61995.

Hamid Shahnazian, Stefan Odenbach
New driving unit for the direct measurement of yield stress with a stress controlled rheometer

Appl. Rheol. 18:5 (2008) 54974 (7 pages)

Investigations of rheological properties of ferrofluids have shown strong changes of the viscosity in magnetic fluids with an applied magnetic field. The change of the viscosity . the magnetoviscous effect . can theoretically be described with chain and structure formation under the influence of a magnetic field. Moreover, the formation of these structures leads to the appearance of viscoelastic effects or other non-Newtonian features like yield stress in ferrofluids with an applied magnetic field. With a shear rate controlled rheometer . as it as been used in former experiments . the yield stress could not be investigated directly. Therefore the results concerning a field dependent yield stress based on an extrapolation of shear controlled measurements. For the direct investigations of the yield stress, a dedicated stress controlled rheometer is required, allowing direct investigations of the magnitude and field dependence of this effect. In this work the design of the stress controlled rheometer with its main parameters has been described in detail. The rheological investigations with differently composed fluids show that the stress controlled rheometer enables direct measurements of even small yield stresses in ferrofluids as well as large effects like they are found in magnetorheological fluids (MRF).

Cite this publication as follows:
Shahnazian H, Odenbach S: New driving unit for the direct measurement of yield stress with a stress controlled rheometer, Appl. Rheol. 18 (2008) 54974.

Stefan Odenbach
3rd German Ferrofluid workshop

Appl. Rheol. 10:6 (2000) 315-316

Cite this publication as follows:
Odenbach S: 3rd German Ferrofluid workshop, Appl. Rheol. 10 (2000) 315.

S. Odenbach
Magnetoviscous effects in ferrofluids

Appl. Rheol. 10:4 (2000) 178-184

Cite this publication as follows:
Odenbach S: Magnetoviscous effects in ferrofluids, Appl. Rheol. 10 (2000) 178.


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