Advanced combined rheometer setups to in-situ correlate molecular dynamics and molecular structure formation with mechanical properties: Rheo-NMR, Rheo-IR, Rheo-dielectric and Rheo-SAXS

Molecular understanding of mechanical properties over a broad length and time scale is crucial to develop advanced materials. Our research aims to design and built unique combined rheometer setups that can monitor in-situ molecular observables, such as molecular dynamics or chemical functional groups that are directly correlated to the macroscopic mechanical responses. These combined experimental setups overcome the experimental challenges associated with offline measurements and facilitate the understanding of structure-mechanical property relationships. Specifically, the following combinations will be presented in detail: Rheo-NMR, Rheo-dielectric, Rheo-IR and Rheo-SAXS.

Over the last 20 years, we developed a unique combination of rheology and low-field time domain ¹H NMR by implementing a compact 25 MHz Halbach NMR magnet into a high end rheometer. This Rheo-NMR device can quantify segmental motion of polymer chains via transverse relaxation times (T₂) while simultaneously performing advanced rheological protocols. Examples in polymer crystallisation, rubber crosslinking and the investigation of the kinetics of polymer synthesis will be displayed for this unique Rheo-NMR set-up.

To correlated molecular dynamics and mechanical properties broadband dielectrics spectroscopy (BDS) was combined with a rheometer, Rheo-BDS. By using anionic polymerization of isoprene derivatives 32 decades in dynamic range could be covered by rheology and 34 decades in dielectric spectroscopy.

Covalent bond formation during polymerization is directly related to changing mechanical properties. To do so ATR-IR spectroscopy was in-situ correlated to mechanical characterization via a Rheo-IR set-up to investigate e.g. hydrogel formation of polyacrylic acid. In the later stage of the chemical reaction a very high scaling exponent of 10 was determined for G’ as a function of chemical bond formation for the second half of the chemical reaction. Currently this set-up is further extended with respect to IR spectroscopic sensitivity, time resolution and available temperature range.