Hyphenated low‐field NMR techniques: combining NMR with NIR, GPC/SEC and rheometry

Abstract

Hyphenated low-field NMR techniques are promising characterization methods for online process analytics and comprehensive offline studies of soft materials. By combining different analytical methods with low-field NMR, information on chemical and physical properties can be correlated with molecular dynamics and complementary chemical information. In this review, we present three hyphenated low-field NMR techniques: a combination of near-infrared spectroscopy and time-domain NMR (TD-NMR) relaxometry, online (1) H-NMR spectroscopy measured directly after size exclusion chromatographic (SEC, also known as GPC) separation and a combination of rheometry and TD-NMR relaxometry for highly viscous materials. Case studies are reviewed that underline the possibilities and challenges of the different hyphenated low-field NMR methods. Copyright © 2015 John Wiley & Sons, Ltd.

Rheo‐NMR in food science—Recent opportunities

“…However, torque and NMR data could be acquired successively (much in the spirit of the work cited above) using the same shear geometry, yielding NMR relaxation data, or 1D velocity profiles across the sheared material in addition to the separately measured shear stress. Later developments lifted this limitation, now providing low field Rheo‐NMR accessories that can be fitted to commercial rheometers, providing simultaneously the capabilities of high end rheometry coupled with NMR relaxometry …”

“…Later developments lifted this limitation, now providing low field Rheo-NMR accessories that can be fitted to commercial rheometers, providing simultaneously the capabilities of high end rheometry coupled with NMR relaxometry. [39][40][41][42] Although Rheo-NMR was initially developed and mainly used with superconducting high field NMR systems, [2,43,44] only a few attempts have been reported to record rheological behavior simultaneously with NMR data. A notable exception was the acquisition of 2 H spectra while measuring torque in the meantime, [45] thus correlating shear-induced molecular alignment of side-chain liquid-crystalline polymers with their shear dependent viscosity.…”

Polymer Crystallization Studied by Hyphenated Rheology Techniques: Rheo‐NMR, Rheo‐SAXS, and Rheo‐Microscopy

“…[57][58][59][60][61][62] Techniques that characterize molecular dynamics and consequently probe local molecular conformations were also combined with rheology. These set-ups are based on dielectric spectroscopy [63][64][65][66][67] and NMR relaxometry, [68][69][70][71] and can be used to investigate the origins of macroscopic flow behavior in soft matter. Further hyphenated rheology techniques that do not belong to any of the three main categories listed above are based on calorimetry, [72][73][74][75] dilatometry, [76][77][78] or electrical conductivity.…”

Medium Resolution 1H‐NMR at 62 MHz as a New Chemically Sensitive Online Detector for Size‐Exclusion Chromatography (SEC–NMR)

“…In many cases, “information‐rich detectors” are thus helpful as they can distinguish between chemically different chemical species eluting simultaneously or identify unknown species solely from the measured data . Such detectors are not commonly found in SEC setups with the exception of the UV‐vis detector, which depends on the presence of a suitable chromophore in the analyte …”

“…[2] Such detectors are not commonly found in SEC setups with the exception of the UV-vis detector, which depends on the presence of a suitable chromophore in the analyte. [3] block copolymers, [10] PI with different microstructures, [11] and PS-PMMA block copolymers. [17] Despite these and other successful studies, the usage of SEC-HF-NMR lags behind the other mentioned information-rich detectors, which is most likely due to operational requirements and the high costs and complexity of HF-NMR instruments especially when compared with those of a typical SEC setup.…”