Fast Field Cycling Relaxometry (FFCR) is a low field NMR technique used to determine the longitudinal relaxation time (T1) over a range of B0-fields spanning about six decades, from about 10-6 Tesla up to ~ 1 Tesla, or 3 Tesla, without varying the frequency of the spectrometer.1,2 The main information that can be extracted from NMR dispersion (NMRD) curves, T1 or R1=1/ T1 versus the Larmor frequency ω (ω=γB0, γ is the gyromagnetic ratio), is that concerning molecular motions characterized by temperature-activated frequencies and described by means of the spectral density J(ω).
The data obtained may be correlated directly to the physical/chemical proprieties of complex materials. The use of radio frequency allows the easy penetration of most materials, thus permitting, the exploration of slow dynamics which are often difficult to study in heterogeneous materials (including liquids, solids and gels) by other spectroscopic methods.
The benefit of exploring the range of low Larmor frequencies is to detect typical relaxation features associated with molecular processes characterized by very long correlation times, such as molecular surface dynamics and collective effects. The FFCR technique shows greatest potential where the characteristics of a sample depend intimately on the molecular dynamics and / or the state of aggregation.
Herein we show developments in the FFCR method. We show in practice how relaxation experiments can be applied for qualitative structural diagnostics in solutions, quantitative structural determinations, recognitions of weak intermolecular interactions and studies of molecular mobility. The findings that have been established more recently are noteworthy for their potential industrial use in quality assessment and off-line process monitoring.
FFCR is a technique which has remained as a research tool and practically unexploited in industry, and thus an important challenge is the transfer of this important technique towards more industrial applications.