Quiescent and flow-induced crystallization of polyolefins studied by a novel low-field RheoNMR combination

Combining NMR and rheology has received great attention in the past, as it allows studying the interdependence of macroscopic and molecular properties of soft matter, e.g. polymers, liquid crystals or colloids. Flow profiles (e.g. steady or oscillatory shear) both in the linear and non-linear regime can be applied to monitor and also to modify the (time) evolution of sample properties. Most RheoNMR designs have been realized for high-field NMR spectrometers using only simple shear cells. Here we present a low-field RheoNMR set-up based on a portable 30 MHz NMR unit that was integrated into a commercial strain-controlled rheometer. This unique combination can be employed to simultaneously conduct a full rheological characterization while monitoring molecular dynamics in-situ via ¹H TD-NMR. Possible applications include the measurement of quantitative composition in crystallizing soft matter (fats, polymers, etc.) and multiphase systems during the application of shear protocols. To display the possibilities of this new technique, studies on the quiescent and flow-induced crystallization of polyolefins are presented. A short time steady-shear protocol was applied to study flow-induced crystallization as a function of different temperatures and flow conditions.