Freeze fracture-etching

The structure of this type of L2 phase has been analyzed by electron microscopy and by X-ray diffraction [6]. The results indicate that flexible disk-shaped water micelles occur, separated by lipid bilayers. The X-ray data are in agreement with electron micrographs of freeze-etched freeze-fractured samples. An analysis of the X-ray scattering results at a weight ratio of monoglyceride to water of 8 2 gave these results ... 

FIGURE 19.3 Low voltage scanning electron micrograph of permanganic etched freeze fracture surface of UHMWPE. 

Knoll G 1995 Time resolved analysis of rapid events Rapid Freezing, Freeze-fracture and Deep Etching ed N Sievers and D Shotton (New York Wiley-Lyss) p 105... 

For freeze-fracture, a drop of the formulation containing 30% glycerol was deposited on a thin copper planchet and rapidly frozen in liquid propane. Fracturing and shadowing using Pt-C were performed in a Balzers BAF 310 freeze-etch unit. Other samples were simply deposited on a freshly cleaved mica plate and air-dried before shadowing as above. Replicas were examined with a Philips 410 electron microscope. 

Figures 9a-c represent transmission electron micrographs of different lyotropic liquid crystals after freeze fracture without etching. The layer structure of the lamellar mesophase including confocal domains, hexagonal arrangement of rodlike micelles within the hexagonal mesophase, as well as close-packed spherical micelles within the cubic liquid crystal can be clearly seen.

Severs N.J. and Shotton D.M., eds.. Rapid Freezing, Freeze Fracture and Deep Etching, Wiley-Liss, New York, 1995. 

Figure 18-2 (A) Schematic diagram of mitochondrial structure. (B) Model showing organization of particles in mitochondrial membranes revealed by freeze-fracture electron microscopy. The characteristic structural features seen in the four half-membrane faces (EF and PF) that arise as a result of fracturing of the outer and inner membranes are shown. The four smooth membrane surfaces (ES and PS) are revealed by etching. From Packer.8...

Various electron microscopy techniques have been used to study the structures of whippable emulsions such as normal and cryo-scanning electron microscopy or transmission electron microscopy using various preparation methods such as freeze fracturing, freeze etching, etc. The literature is quite extensive, and only a few important papers will be discussed in this chapter. 

The most thorough study of the formation of artificial casein micelles is that of Schmidt and co-workers (1977 1979 Schmidt and Koops, 1977 Schmidt and Both, 1982 Schmidt and Poll, 1989), who not only studied the properties of the casein aggregates but also attempted to relate them to the solution conditions under which they were formed. In the precipitation of calcium phosphate from solution, the means by which solutions are mixed together is of crucial importance Schmidt et al. (1977) described a method in which four solutions were pumped simultaneously into a reaction vessel while keeping the pH constant. As a result of careful, slow mixing, the reproducibility of the size distributions of particles, measured by electron microscopy on freeze-fractured and freeze-etched specimens, was very good. In the first series of experiments, the objective was to produce milk like concentrations of the most important ions while... 

Fig. 12. Electron micrographs of bovine casein micelles obtained by different techniques, (a) Freeze fractured and etched (L. K. Creamer and D. M. Hall, unpublished). (b) Fixed and rotary shadowed (Kalab et al., 1982). (c) Unstained, embedded thin section [reproduced from Knoop et al. (1979), by permission of the publishers, Cambridge University Press), (d). Unstained, unfixed, hydrated sample (van Bruggen et al., 1986).

The surface layer of the fat globule may act as a catalytic impurity (e.g., when it contains mono-glycerides or di-glycerides with long-chain fatty acid residues) however, there is still some uncertainty as to whether this process actually occurs (see Walstra, 1995). Although concentric layers of apparently crystalline fat have been observed in electron micrographs of freeze-etched or freeze-fractured milk or cream samples (Buchheim, 1970 Henson et al., 1971), these observations could not be confirmed by other microscopy techniques. Noda and Yamamoto (1994) reported that it is thermodynamically more favorable for fat crystals to be located at the oil/water interface, rather than in the interior of the droplet, which may explain the presence of fat crystals at the membrane. 

Although freeze-fracture TEM provides direct visualization of ME structures, it is not currently in wide use probably due to the experimental difficulties associated with the technique. The points to consider when preparing conventional TEM replicas are the physical and chemical sample properties, freezing, cleaving, etching, replication, cleaning, and mounting steps of the procedure. 

Comparison of the molecular length of CAB (ca. 38 A) and the characteristic lengths calculated from SAS data (vide ante) indicate that molecular pairs are involved in the columns of the solid state while, in gels, association of swollen columns might be involved. Micrographs of freeze-fractured and etched CAB gels (Fig. 17) show a 3-D network of fibrous bundles. The dimensions of the rectangular cross sections of the nontwisted fibers in dodecane, 209 x 104 A. and the twisted ones in 1-octanol, 263 x 82 A [481, correspond approximately to the cross-sectional areas determined by SANS in which a circular cross section model was employed. 

Immediate etching after freeze fracture provides sublimation of non-permanent constituents (commonly ice), with the effect that level differences in the sample surface appear more pronounced. 

Fig. 18. Freeze-fracture electron micrography of thylakoid membrane. (A) A portion of the chioroplast thylakoids (B top) a schematic view of the stacked region of thylakoids frozen in freon at liquid-nitrogen temperature ("freeze etch") and (B bottom) after fracture along the thick dashed line by the impact of a microtome knife [freeze fracture] (C) an electron micrograph of a replica of the EF and PF faces such as those shown in (B) bottom (D) distribution of the four photosynthetic complexes in the various fracture faces. (A) kindly furnished by Dr. Andrew Staehelin Source for (B) and (C) Miller (1978) The photosynthetic membrane. SciAm241 107.

Usui and Haino-Fukushima, 1991) and freeze fracture deep-etch replicas of VEs (Mozingo et al., 1995) show VEs have a complex, fibrous ultrastructure. The VE is a tough, elastic envelope 0.6 pm in thickness that remains intact following homogenization of eggs (Lewis et al., 1982). After isolation, the VEs are stable for several years if stored at 4°C in EDTA, Tris and azide at pH 8 (Lewis et al., 1982). 

Figure 21.26 SEM micrographs of freeze-fractured surface of PP/epoxy/CB (60/40/10, etched). (From Reference 60 with permission from Wiley Interscience.)...

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