Deformationsgesteuertes Scherrheometer
Zusammenfassung der Projektergebnisse
• The main topic of one project is the characterization of emulsions via nonlinear measurements. Fourier Transform Rheology was used to investigate materials with different length scale heterogeneities. It could be shown that simulations via constitutive models in combination with nonlinear oscillatory measurements are able to quantify emulsion properties like volume average radius and interfacial tension. The simulation parameters were varied to investigate a wide range of emulsion properties including the radii, excitation frequencies, the matrix viscosities, viscosity ratio and interfacial tension. At low strain amplitudes the master curve has a constant value called the nonlinear mechanical master number, which is related to both the emulsion properties and the rheological parameters. For polydisperse emulsions a nonlinear mechanical master curve was established as a universal correlation between the ratio of the higher harmonics, the capillary number and the viscosity ratio. • The diblock copolymers poly(styrene-b-4vinylpyridine) and poly(styrene-b-2vinylpyridine) were investigated using large amplitude oscillatory shear (LAOS). By applying LAOS to the sample at an arbitrary temperature between the glass-transition temperature (Tg) and the order-disorder transition temperature (TODT), the macroscopically isotropic sample with an anisotropic microstructure aligns macroscopically. Consequently, the sample becomes macroscopically anisotropic. From rheological measurements, both Tg and TODT were identified by a drastic drop in the mechanical moduli obtained during a heating ramp on the ARES-G2. A newly developed rheo-dielectric combined method also measured the dielectric conductivity of samples at various temperatures. It was performed before, during and after LAOS by applying an electric field of an ALFA-Analyzer in ac-mode, that was combined with the ARES-G2. It covers a frequency range that is about 12 orders of magnitude (3x10-5 to 1x107 Hz), which makes this a very sensitive method to investigate the kinetics of alignment of diblock copolymers over a wide range of temperatures. • In the other project we developed a new synthesis method for polystyrene with monodisperse comb architectures containing controlled branching degrees and branch lengths. The samples were examined to determine the effect of branching on the (non-) linear rheological properties of polymer melts. In the non-linear regime, two different rheological measurements, extensional and large amplitude oscillatory shear (LAOS) in combination with Fourier Transformation (FT-Rheology), were used. The results of the correlation between the molecular structure and rheological properties of polymer combs helped us to develop a model for optimizing the processing conditions of polymers like branched polyolefins (e.g. LDPE). • In a further project, the ARES-G2 was used for characterizing the effect of various parameters (molecular weight (Mw), molecular weight distribution (MWD), long-chain branching (LCB), addition of particles in the polymer matrix) on the properties of polymeric materials. The aim was to establish the structure-property relationships for different polymeric materials. The experiments were performed on the following systems: polystyrene, polyethylene, poly(ɛ-caprolactone) solution, scaffolds of poly(ɛ-caprolactone), and polymer composites containing carbon nanotubes.
Projektbezogene Publikationen (Auswahl)
- Mechanische Eigenschaften mit Obertonanalyse: FT-Rheologie. Nachrichten aus der Chemie 57 422-425 (2009)
M. Wilhelm
- New developments for the mechanical characterization of materials. Korea-Australia Rheology Journal 22 317-330 (2010)
N. Dingenouts, M. Wilhelm
- A Review on Nonlinear Oscillatory Shear tests: Analysis and Application of Large Amplitude Oscillatory shear (LAOS). Prog. Polym. Sci. 36 1697-1753 (2011)
K. Hyun, C.O. Klein, M. Wilhelm, K.S. Cho, J.G. Nam, K.H. Ahn, S.J. Lee, R.H. Ewoldt, G.H. McKinley
- Fourier Transform Rheology as a universal non-linear mechanical characterization of droplet size and interfacial tension of dilute monodisperse emulsions. J. Colloid Interface Sci. 360 818-825 (2011)
K. Reinheimer, M. Grosso, M. Wilhelm
- Fourier Transform Rheology as a universal non-linear mechanical characterization of droplet size and interfacial tension of dilute monodisperse emulsions. J. Colloid Interface Sci. 360 818-825 (2011)
K. Reinheimer, M. Grosso, M. Wilhelm
- Acyclic Triene Metathesis Polymerization of Plukenetia conophora oil: branched polymers by direct polymerization of renewable resources. Macromol. Chem. Phys. 213 87-96 (2012)
C.O. Akintayo, H. Mutlu, M. Kempf, M. Wilhelm, M.A.R. Meier
- Fourier Transform Rheology as a noninvasive morphological characterization technique for the emulsion volume average radius and its distribution. J. Colloid Interface Sci. 380 201-212 (2012)
K. Reinheimer, M. Grosso, F. Hetzel, J. Kübel, M. Wilhelm
- Optimizing the sensitivity of FT-Rheology to quantify and differentiate for the first time the nonlinear mechanical response of dispersed beer foams of light and dark beer. Z. Phys. Chem. 226 547-567 (2012)
K. Reinheimer, J. Kübel, M. Wilhelm
- April-Science: Charakterisierung von hellen und dunklen Bierschäumen durch mechanische Obertonanlyse, FT-Rheologie. Bunsenmagazin 15 52-55 (2013)
K. Reinheimer, M. Wilhelm
- Synthesis and Linear and Nonlinear Melt Rheology of Well-Defined Comb Architectures of PS and PpMS with a Low and Controlled Degree of Long-Chain Branching. Macromolecules (2013)
M. Kempf, D. Ahriwal, M. Cziep, M. Wilhelm
(Siehe online unter https://doi.org/10.1021/ma302033g)
