Freeze-fracture direct imaging

Three different techniques, namely FFEM [20, 22], Cryo-Direct Imaging (Cryo-DI) [104] and freeze-fracture direct imaging (FFDI) [105], can be used to visualise the structure of micro emulsions. In FFEM the samples are prepared in a protected fashion in a sandwich. They are then rapidly frozen, fractured, shadowed with metal, and replicated with a thin carbon film. The replica of the fractured surface, the morphology of which is controlled by the sample s microstructure, is then studied by a TEM. In contrast to FFEM, in Cryo-DI thin films of the sample are rapidly frozen but immediately, without replication, trans-... 

Figure 1.19 Micrographs of microemulsion droplets of the o/w-type in the system II2O- n-octane-CnEs prepared near the emulsification failure boundary at ya = 0.022, wb = 0.040 and T = 26.1 °C. (a) Freeze-fracture direct imaging (FFDI) picture showing dark spherical oil droplets of a mean diameter = 24 9 nm in front of a grey aqueous background. Note that each oil droplet contains a bright domain of elliptic shape which is interpreted as voids, (b) The freeze-fracture electron microscopy (FFEM) picture supports the FFDI result. Each fracture across droplets which contain bubbles shows a rough fractured surface. (From Ref. [26], reprinted with permission of Elsevier.)...

Belkoura, L., Stubenrauch, C. and Strey, R. (2004) Freeze fracture direct imaging A hybrid method in preparing specimen for Cryo-TEM. Langmuir, 20, 4391—4399. 

Finally, a novel technique is freeze-fracture direct imaging, where sensitive samples such as microemulsions can be studied without the need for a replica. This technique does not have a blotting step (as per cryo-TEM) that can damage micioemulsion structures (Belkoura et al, 2004 Gradzielski, 2008). 

Belkoura, L, StubenrauchC and Strey R. 2004. Freeze fracture direct imaging A new freeze fracture method for specimen preparation in cryo-transmission electron microscopy. Langmuir 4391-4399. 

The evolution of the solution microstructures during the formation of the hexagonal mesoporous material SBA-15 was studied by direct imaging and freeze-fracture replication cryo-TEM.[72] A continuous transformation from spherical micelles, into threadlike micelles, which become longer and stiffer, followed by the formation of bundles with dimensions similar to those found in the final material, was observed. The direct imaging... 

There are two variations of theTEM technique for fluid samples (1) the cryo-TEM analyses in which samples are directly visualized after fast-freeze and freeze-fracture in the cold microscope and (2) the FFTEM technique in which a replica of the specimen is imaged under room temperature conditions. 

D. Danino and Y. Tahnon, Direct-Imaging and Freeze-Fracture Cryo-Transmission Electron Microscopy of Molecular Gels, ChaptCT 9 in Molecular Gels, Materials with... 

Figure 13-3. Freeze-fracture images showing cellulose-synthesizing terminal complexes (TCs) of Metandrocarpa uedai. (a) Linear shaped TCs consist of two kinds of membrane particles, and they are located on the P-fracture face of the epidermal cell membrane facing the timic. In the case of M. uedai, TCs are grouped in almost the same direction on the epidermal cell membrane. (Figure 3a from Kimura, S. and Itoh, T. 2004. Cellulose-synthesizing terminal complexes in the asddians. Cellulose 11 377-383. Reproduced with kind permission of Springer Sdence and Business Media).

Microemulsion structure can be observed by electron microscopy (EM). Jahn and Strey (4) were the first to publish reliable electron microscopy images of microemulsions. Their systematic study involved both droplet and bicontinuous structures, using the so-called freeze-fracture technique where a replica of the sample is made which is then monitored by the electron microscope. Another technique, Cryo transmission electron microscopy (Cryo-TEM), is probably less suitable for microemulsions with larger oil contents. In this technique, a thin slice of the sample is directly monitored... 

An alternative method is the freeze-etching technique [24, 25], which consists of producing platinum shadowed replicas of fractures created in rapidly frozen biological systems or lyotropic liquid crystals. The fracture orientation is somewhat haphazard, but occurs preferentially within the paraffinic level of the bilayers. These methods offer the possibility of viewing bilayers directly and preparing stereoviews. Beautiful pictures of liquid crystalline DNA, both cholesteric and hexagonal, have been obtained, but individual molecules are not easily resolved. However, the director distribution can be deduced from the images [26],... 

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