Forschungsgebiet 3: Methodenentwicklung in der Rheologie

Mechanical and rheological properties are commonly used to set processing conditions or design polymer applications. These material properties originate in the molecular structure of the polymer. Neither this structure, nor its connection to the resulting material properties is usually known in detail. Therefore, the correlation between mechanical properties and the molecular structure is a major issue in our research (fig.1)

Fig.1: Interaction of research strand  synthesis  with research strand rheology.
Model polymers with defined molecular weight and topology are synthesized via anionic polymerisation.  With these fully customizable model systems, the correlation between the molecular structure and the mechanical properties of the final material can be examined.
Fourier Transformation Rheology (FT-Rheology), extends the standard method of oscillating rheology into the non-linear regime and was developed in our group. Recently, we introduced a new non-linearity parameter Q. Examples of its use can be found in literature [Cziep et al., 2016]. The parameter Q is extremely sensitive to the topology of polymers, one can distinguish e.g. linear and star polymers. It also reflects strongly the influence of long-chain branching even for extremely low concentrations of branching points. This is an important ability because the influence of long-chain branches on the processing properties are drastically, but the detection and quantification is complicated via alternative methods. Also other material classes’ benefits from our developments in non-linear rheology, e.g. filled rubbers and emulsions.

Another topic are Flow instabilities in polymer melts and the method of capillary rheology: We developed new dies for capillary rheology that can measure pressure fluctuation inside the die allowing to determine the onset of flow instabilities an important problem in production limiting the throughput in industrial production. Actual research here are dies that can measure normal forces, this will help to understand flow instabilities better.

 

Examples of research topics in this strand:

  • FT-Rheology
  • Flow instabilities of polymers
  • Pressure fluctuations in dies in capillary rheology or in extrusion
  • Normal forces in capillary rheology

 

Review/basic articles about FT-Rheology
Please see also the full list of publications  
The Intrinsic Mechanical Nonlinearity 3Q0(ω) of Linear Homopolymer Melts M.A. Cziep, M. Abbasi, M. Wilhelm; Novel Trends in Rheology VII, AIP Conference Proceedings 1843 0400002 (2017) ISBN 978-0-7354-1513-3; DOI: 10.1063/1.4982991 
A Review on Nonlinear Oscillatory Shear tests: Analysis and Application of Large Amplitude Oscillatory shear (LAOS) 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; Prog. Polym. Sci. 36 1697-1753 (2011); DOI 10.1016/j.progpolymsci.2011.02.002
Establishing a New Nonlinear Coefficient Q from FT-Rheology, first investigations on entangled linear and branched Polymer melts K. Hyun, M. Wilhelm;
Macromolecules 42 411-422 (2009); DOI 10.1021/ma8017266
Fourier-Transform Rheology M. Wilhelm; Feature Artikel; Macromol. Mater. Eng. 287 83-105 (2002)

 

Selected related articles connected to research strand 3: Method development in rheology
Please see also the full list of publications  
Fatigue life prediction via the time-dependent evolution of linear and nonlinear mechanical parameters determined via Fourier transform of the stress V. Hirschberg; M. Wilhelm; D. Rodrigue; Journal of Applied Polymer Science 135, 46634 (2018); DOI 10.1002/app.46634
High sensitivity measurements of normal force under large amplitude oscillatory shear I. F. C. Naue; R. Kádár; M. Wilhelm; Rheologica Acta 57, 757–770 (2018); DOI 10.1007/s00397-018-1111-y
First normal stress difference and in-situ spectral dynamics in a high sensitivity extrusion die for capillary rheometry via the ’hole effect’ R. Kádár, I.F.C. Naue, M. Wilhelm; Polymer 104, 193-203 (2016); DOI 10.1016/j.polymer.2016.07.061
Fourier–Transform rheology of unvulcanized, carbon black filled styrene butadiene rubber L. Schwab, N. Hojdis, J. Lacayo-Pineda, M. Wilhelm; Macromol. Mat. Eng. 301 457-468 (2016); DOI: 10.1002/mame.201500356
A New High Sensitivity System to Detect Instabilities During the Extrusion of Polymer Melts I.F.C. Naue, R. Kádár, M. Wilhelm; Macromol. Mater. Eng. 300 1141–1152 (2015); DOI: 10.1002/mame.201500148
Correlation between polyethylene topology and melt flow instabilities by determining in-situ pressure fluctuations and applying advanced data analysis H. Palza, S. Filipe, I.F.C. Naue, M. Wilhelm; Polymer 51 522-534 (2010); DOI 10.1016/j.polymer.2009.11.050