Pulsed field gradient echo formation

From such a background, the structure and dynamics of the main chain and side chains of LC polymers have been sophisticatedly characterized by solid-state NMR and pulse field-gradient spin-echo (PFGSE) NMR to understand an important role for formation of the thermotropic liquid crystals [21-25], Details of these works will be introduced. 

In this article, we have discussed the use of ionic liquids as solvent for the seE-assembly of surfactants. In ionic liquids, the formation of the same types of amphiphile self-assembly phases as aqueous systems (micelles, vesicles and microemulsions) was evidenced. These aggregates were characterized by surface tension measurements, differential scanning calorimetry, scattering experiments (DLS and SANS), pulse field gradient spin-echo NMR, electrical conductivity measurements, electron microscopy. 

In this section, we provide an outline of the theoretical and practical aspects of diffusometry NMR experiments that are the core of chrom-NMR. This issue has been reviewed at large38,39 and thus only the key and most relevant aspects will be mentioned below. The displacement of a given molecular tracer is followed by a classical Stejskal-Tanner experiment. In this, pulses of magnetic field gradients are used to label the initial position of the tracer, and to follow its displacement along the direction of the gradient, Az. Indeed, in a spin-echo experiment, any displacement corresponds to a reduction of the efficiency of the echo formation. 

We now consider the simple case of a spin echo in which two rectangular linear gradient pulses are applied as shown in Fig. 1. In this pulsed gradient spin-echo (PGSE) experiment, the time t used in Eq. (41) will refer to the position of the spin-echo formation. In analyzing this experiment, we will assume the weak inhomogeneous field limit and the uniform... 

Fig. 9.1.5 [Akol] Timing of rf and gradient signals for the PRESS method. Transverse magnetization of a volume element is selected by formation of a double Hahn echo with selective pulses in the presence of orthogonal field gradients.

Point resolved spectroscopy (PRESS) and stimulated-echo acquisition mode (STEAM) use three selective RE pulses in combination with linear field gradients to yield localization of the VOI in a single shot. Thus, the localization provided by these techniques is not degraded by subject motion or system instability. Generally, the use of three RF pulses leads to the formation of five coherent pathways for echo formation. Both PRESS and STEAM are designed to yield a particular echo that is localized to the VOI the other echoes are suppressed by the use of spoiler gradients and phase cycling of the RF pulses. The... 

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