Freeze-fracture transmission electron microscopy

The final evidence for the formation of an Abrikosov flux lattice of screw dislocations in liquid crystals was achieved by Zasadzinski et al. [39] via the visualization of the screw dislocations of (R)- and (S-)l-methylheptyl 4 -(4-n-tetradecyloxyphenylpropioloyloxy)-biphenyl-4-carboxylates using freeze-fracture transmission electron microscopy. Freeze-fracture transmission microscopy (TEM) is an essential tool for visualizing the TGBA phase at sufficient resolution in order to resolve the molecular organization. 

A polyethyleneoxide-Z)-polydimethylsiloxane-polyethyleneoxide surfactant, (EO)i5-(DMS)i5-(EO)i5, was studied with freeze-fracture transmission electron microscopy and pulsed-field gradient nuclear magnetic resonance speetroseopy, in order to establish the effeet of glyeerol on the permeability of vesiele membranes. Small vesicles with diameters of less than 25 run and multilamellar vesicles with diameters larger than 250 nm were observed in pure water, which were modified when water was gradually replaced with glycerol [47]. 

It will be appreciated that visualization of the structure of liquid crystalline materials is a particularly difficult task as the phase being studied has liquid-like character. The technique of freeze fracture transmission electron microscopy allows examination of most systems however, lyotropic materials which contain greater than 85% water still prove to be difficult. The technique involves the fast freezing of the material and then examination of the fracture surface. Despite the obvious attraction of this method it appears to be still in its infancy. Studies of cholesteric, smectic " phases have been reported and show that it is possible to identify stacks of well-ordered materials which are often bananashaped but do conform to the concepts that have been developed above. 

It was proposed that the monomer/dopant salts form micelles which then serve as the soft-template for the formation of tubular structures. For the dopant-free or simplified method in which only aniline and ammonium persulfate are mixed, the initial formation of spherical micelles was observed by freeze-fracture transmission electron microscopy from which tubular structures were obtained. ... 

Dynamic light scattering (DLS) along with freeze-fracture transmission electron microscopy (FF-TEM) measurements revealed that the sizes of single microemnl-sion droplets vary with temperatme [19,20]. The role of the organic solvent was also investigated for this system changing cyclohexane by benzene, tolnene, or p-xylene [21-26]. 

P.K. Vinson, J.G. Sheehan, W.G. Miller, L.E. Scriven, and H.T. Davis 1991 Viewing microemulsions with freeze-fracture transmission electron microscopy, J. Phys. Chem. 95, 2546-2550. 

In this study we have investigated the structural and interaction parameters of ternary water/octane/CiaEs system by means of SAXS. Phase behavior of this system was studied by Kahlweit et al. [9]. This system shows interesting phase behavior (Fig. 1). One can study the structures of low-temperature microemulsion (LTM) phase, middle-temperature lamellar (MTL) phase and high-temperature microemulsion (HTM) phase by changing temperature only, provided that the sample contains approximately more than 12 wt% of surfactant at equal volume fraction of water and oil. Bodet et al. have clarified the structural evolution of this system by means of pulsed-field gradient spin-echo NMR, quasi-elastic light scattering and freeze-fracture transmission electron microscopy [10]. Local structure of the bilayer and monolayer of the same system was also studied by Strey et al. [11]. Recently, we have studied the mechanism of the phase transition [12]. 

We started from a micellar solution of 100 mM TDMAO and 25 mM SHNC and added 100 mM MF. With time we observed the formation of a lamellar L phase, a vesicular Lv phase, and a vesicular precipitate. This precipitate dissolved to form a vesicular phase, an L phase, and finally again a micellar phase. The hydrolysis of the MF and the resulting phase transitions were observed by measurements of pH, conductivity, turbidity, and by means of freeze-fracture transmission electron microscopy. The microstructures of the phases obtained were compared with the microstructures of the corresponding phases when increasing amounts of HCO2H were mixed with solutions of 100 mM TDMAO and 25 mM SHNC. 

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