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3. Evolution of a lamellar domain structure for an equilibrating lyotropic liquid crystal

Author

Callaghan, Paul T., Hubbard, Penny L., and McGrath, Kathryn M.

Subjects
Magnetic resonance -- Structure, Magnetic resonance -- Analysis, Scanning microscopy -- Structure, Scanning microscopy -- Analysis, Chemicals, plastics and rubber industries
Abstract

A demonstration that the morphology of the lamellar phase varies significantly across that range and that the rate of equilibrium depends strongly on concentration with, paradoxically, the faster equilibrium at higher surfactant concentrations is conducted by magnetic resonance (NMR) and scanning electron microscopy (SEM). Results reveal that the 25-wt percent sample exhibits a defect-rich local structure, characteristic of superposed L3 character.

Published
2006

4. How two pairs of gradient pulses give access to new information about molecular dynamics

Author

Callaghan, Paul T., Victoria University of Wellington, and Universität Leipzig

Subjects
diffusion, transport, ddc:530
Abstract

Pulsed Gradient Nuclear Magnetic Resonance provides direct insight regarding the translational motion of spin-bearing molecules. These methods gain a second dimension when the simple gradient pulse pair is enhanced by a second pair. Where the motion encoding of the two pairs is opposite, flow effects are removed from the echo attenuation, making it possible to measure diffusion in the presence of shear flow, or to measure the stochastic part of dispersive flow, and in particular the velocity auto-correlation function. Where the gradient pulse pairs are stepped in independent dimensions, two-dimensional experiments become possible. One class (Fourier-Fourier) is the Velocity Exchange (VEXSY) experiment in which flow velocities may be correlated at different times. Another class (inverse Laplace-inverse Laplace) is the diffusion correlation (DDCOSY) or diffusion exchange (DEXSY) experiment. This approach has proven of particular value in ascertaining local anisotropies in globally isotropic systems, as well as in the model-free measurement of exchange effects.

Published
2005

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