Microtomes ultrathin sectioning

The interior of bulk samples can be revealed by fracture, freeze fracture, or (cryo-/ultra)microtoming. These techniques are well established in electron microscopy and require substantial training to ensure that the knives used do not introduce scratches and other artefacts. Unlike in SEM or TEM analysis, however, it is very well possible to analyze the trimmed specimen instead of the very thin sections removed (cryofacing). This loosens the constraint of ultrathin sections in many applications. Care has to be taken that the sample to be imaged is not significantly thicker or thinner than the calibration grating used for scanner calibration (see Sect. 2.2.5)... 

The most successful method is the preparation of ultrathin sections by microtoming. Cryosec-tioning is required for the samples that may be deformed during sectioning at room temperature. 

Ultramicrotomy is an obvious example of a preparation method developed by biologists and now in general use by polymer microsco-pists. In the early 1950s Porter and Blum [62], Sjostrand [63] and Haanstra [57] were constructing microtomes to provide sections, about 0.1 /im thick (or less), for TEM study. Today, ultramicrotomes are available from companies such as LKB and Reichert that permit ultrathin sections of polymers to be obtained on a routine basis. 

Portions of the stained specimens were embedded in an epoxy resin, trimmed to a truncated pyramid shape, and microtomed on a Porter Blum MT-2 ultramicrotome using a diamond knife. Ultrathin sectioning at room temperature to a thickness of 60-80 nm (600-800 A) yielded satisfactory results. Transmission electron micrographs were taken employing a Philips 300 electron microscope. 

A small rectangular block (10x5x3 mm) is excised from the specimen containing the feature of interest and immersed in molten sulfur at 125°C for 24 hours. At the end of this period, the speci-ment is obtained in the form of a hard ebonite-like solid suitable for ultrathin sectioning in the usual manner. In this study, the rubbers were sectioned in the usual manner with a Reichert OMU-2 ultra-microtome and subsequently examined using transmission electron microscopy. 

Transmission electron microscopy (TEM) was performed using a high-resolution transmission electron microscope (JEOL 2010). Ultrathin sections about 100 nm thick were cut with a Power TEOMEX microtome equipped with a diamond knife and placed on a 200-mesh copper grid. 

Generally, microtomy refers to the preparation of thin slices of material by sectioning for observation in an optical microscope by transmitted light. Microtomed sections are cut with steel or glass knives to about 1 to 40/tm thickness. Ultramicrotomy methods involve the preparation of ultrathin sections of material for observation in an electron microscope. Ultramicrotome sections are cut with glass or diamond knives to a thickness ca. 30-100 nm. If imaging is to be done via many techniques, the TEM preparation method can be utilized to prepare thin sections for OM, TEM, and AFM, and the flat block face is used for SEM and/or SPM. 

Today, the most common methods of observing multiphase polymers are by phase contrast OM of thin sections, TEM of stained ultrathin sections, SEM of etched or fractured surfaces, and SPM of microtomed or etched surfaces. Osmium and ruthenium tetroxide are the most commonly used stains for observation of the dispersed phases in multiphase blends, whereas other stains have more limited application. Detailed fine structure of polymers is also made... 

Ceynowa performed a TEM study of microtomed Nafion 124 membranes. To increase the electron density contrast, H+ form membranes were converted to the Pb + form using 1.0 M Pb(N03)2 for 60 h. Then, the sample was dehydrated using ethanol solutions, rehydrated in 1,2-epoxypropane, and embedded into epoxy resin. Ultrathin sections were cut to 60-80 nm size. TEM images of the film indicate ion cluster of 3-6 nm in diameter uniformly distributed in the polymer matrix. ... 

Ultrathin (ca. 100 mn) sections of the polymer, which had been pressed into a sheet, were cut on a Reica Ultracut Microtome equipped with a diamond knife at a low temperature and were then stained with RUO4. TEM observations were made with a Hitachi H-7000 transmission electron microscope at an acceleration voltage of 75 kV and at a magnification of 5,000. 

As discussed in Section 2.23.1.2, one of the advantages of AFM over electron miaoscopy is that it enables 3D imaging of untreated samples in a physically relevant environment. Given the surface nature of the technique, initial AFM studies of phase separation processes in polymer mixtures have been primarily focused on thin or ultrathin films. " " The confinement in a film and component segregation to the interfaces have been shown to have a profound effect in both spinodal decomposition, and nucleation and growth processes of the phase separation. The spectrum of AFM applications has been extended to bulk phase separation of polymer mixtures using conventional and oblique microtoming of polymer blend films. 

---