Evolution of a Lamellar Domain Structure for an Equilibrating Lyotropic Liquid Crystal

Abstract

Aerosol OT/water exhibits a lamellar phase over a wide range of concentrations. We show, by magnetic resonance (NMR) and scanning electron microscopy (SEM), that the morphology of the lamellar phase varies significantly across that range and that the rate of equilibration depends strongly on concentration (25, 33, and 50 wt %) with, paradoxically, the faster equilibration at higher surfactant concentrations. We find that the 25 wt % sample exhibits a defect-rich local structure, characteristic of a superposed L(3) character. Further into the lamellar region, at 33 wt %, this defect-rich structure persists heterogeneously, while, at 50 wt %, the lamellar phase domains are highly ordered. The NMR methods used here included (2)H spectroscopy and the two-dimensional NMR method, diffusion-diffusion exchange spectroscopy (DEXSY). The latter was used to obtain quantitative information on the domain sizes and defects within the polydomain lamellar mesophase. Comparison of the NMR with the SEM results suggests that, at 25 wt % AOT, bilayer defects play an important role in influencing the (2)H NMR and DEXSY NMR results.

Microanisotropy imaging: quantification of microscopic diffusion anisotropy and orientational order parameter by diffusion MRI with magic-angle spinning of the q-vector

“…Here we implement a numerically optimized version of the q-MAS pulse sequence [37] on a high-performance microimaging system, limited to specimens with maximum 10 mm diameter, and on a standard whole-body clinical scanner. The efficiency of the q-MAS sequence is demonstrated using two materials with pronounced water diffusion anisotropy: lyotropic liquid crystals [24,25,27,34,[38][39][40] and pureed asparagus [41][42][43][44]. For contrast, a yeast cells suspension is used, exhibiting two isotropic diffusion components [34,[45][46][47].…”

Compartment shape anisotropy (CSA) revealed by double pulsed field gradient MR

“…A spin echo version of such a pulse sequence is illustrated in Figure 1. Variants of this double-PFG sequence have been considered for and employed in a host of different applications [9, 10, 11, 12, 13, 14, 15, 16]. …”

Microscopic anisotropy revealed by NMR double pulsed field gradient experiments with arbitrary timing parameters

“…This approach has been applied to plant tissue, 13 as well as various phases of liquid crystals. [14][15][16] The double-PFG experiments have received increasing attention recently due to the realization that such experiments are sensitive to restricted diffusion even at diffusion wavelengths that are long compared to the pore dimensions. Note that by diffusion wavelength we mean the quantity ⌳ = ͑␥␦G͒ −1 , where ␥ denotes the gyromagnetic ratio of the spins and G is the gradient magnitude.…”