Dynamic NMR microscopy

Y. Xia, P.T. Callaghan 1991, (Study of shear thinning in high polymer solution using dynamic NMR microscopy), Macro. Mol. 24 (17), 4777 1786. 

Hyperpolarized 129Xe NMR Spectroscopy, MRI and Dynamic NMR Microscopy for the In Situ Monitoring of Gas Dynamics in Opaque Media Including Combustion Processes... 

Fig. 5.3.4 (A) Stimulated echo dynamic NMR microscopy pulse sequence. The first field gradient pulse (g,) of duration 8 serves to encode spatial positions of spins and the second field gradient pulse has a refocusing effect.

Figure 5.3.5 displays dynamic NMR microscopy of xenon gas phase Poiseuille flow with an average velocity of 25 mm s-1 and self-diffusion coefficient of 4.5 mm2 s-1 at 130 kPa xenon gas pressure with numerical simulation (A) and experimental flow profiles (B-D) of xenon gas. 

Flow Velocity, Rheometry. - Papers relating to the flow of hyperpolar-ized He or Xe gas are picked up in Sections 2 and 6 as well. Poiseuille flow in Xe gas phase was studied by dynamic NMR microscopy. The flow profile images are different for a short observation time than for a longer... 

The power law exponent, n, is unity for a Newtonian fluid and less than unity for a shear-thinning fluid. One of the central questions of polymer physics concerns the molecular basis for the constitutive equations. Because NMR is so sensitive to molecular dynamical parameters, the simultaneous mapping of velocity profiles and molecular properties such as the polymer self-diffusion coefficient by means of the dynamic NMR microscopy technique offers an effective test of much molecular models. 

Figure 9.10(a) compares velocity profiles obtained in a dynamic NMR microscopy experiment performed at 30°C using 1.6 x 10 Da poly (ethylene oxide) (PEO) dissolved in water at a range of concentrations between 0.5% and 4.5% (w/v) where the solution is forced through a Teflon capillary with internal diameter 700 jum [17, 18]. A transition from Newtonian to non-Newtonian behaviour is observed as the concentration increases, an effect that is consistent with a measured value of (p of around 0.5%. Pressure heads of up to 21 atm were used to drive the polymer solution from the header tank reservoir through the capillary. A power law fit to the high concentration velocity profiles yields an exponent of 0.4, similar to that found in laser Doppler anemometry experiments using polyethylene melts [127]. 

Figure 9.10 (a) Normalised velocity profiles for different concentration solutions of polyfethylene oxide) in water obtained using dynamic NMR microscopy. The concentrations increase in equal steps from 0.5% (w/v) ( ) to 4.5% (w/v) ( ). (b) The polymer self-diffusion profile for the highest concentration solution in units of 10 m s" Note that this was obtained in a separate experiment so that the capillary wall does not fall at precisely the same pixel as in (a), (c) Water solvent velocity and (d) diffusion maps for the 4.5% (w/v) poly(ethylene oxide) solution. (From Y. Xia and P.T. Callaghan [18] and reproduced by permission of the American Chemical Society.)... 

---