Mechanically stable high-sensitivity Rheo-NMR spectroscopy for real-time monitoring of shear-induced phase...

Rheo-NMR is a powerful technique to bridge the gap between macroscopic rheology and microscopic molecular dynamics. Although we previously developed an air-driven, high-sensitivity Rheo-NMR system compatible with cryogenic probes to study dilute biological samples, this system suffered from limited torque and mechanical instabilities due to the mechanical separation of the inner and outer tubes. In this study, we constructed a novel motor-driven Rheo-NMR device that retains compatibility with high-sensitivity cryogenic probes while overcoming the mechanical and operational limitations of earlier designs. A unified assembly was engineered to ensure precise coaxial alignment and vertical positioning between the inner and outer tubes of the sample cell, effectively eliminating mechanical instability while maintaining high spectral quality. The system utilizes a high-torque brushless motor, extending the operational rotational frequency range to 0.017-67 Hz (1-4000 rpm), thereby enabling the investigation of highly viscous fluids. To demonstrate the system's performance, we monitored the phase transition from heavy cream to butter under continuous shear in real time. Using a time-interleaved NMR protocol, we successfully synchronized the observation of lipid solidification, the sequestration of water droplets within the lipid matrix, and the desorption of milk fat globule membrane proteins. These findings highlight the potential of the motor-driven Rheo-NMR system as a robust tool for the rational design of next-generation soft materials and the characterization of complex systems under practical industrial shear-flow conditions.