Formvar, solution preparation

The hydrophilic SiO substrate)static water contact angle 0=3O°) was prepared by vapor-deposited SiO onto a Formvar substrate[4], with which an electron microscope grid(200-mesh) was covered. The relatively hydrophobic siliconized substrate(0=9O°) was also prepared by surface siliconized treatment a collodion-covered electron microscope grid was dipped into an aqueous solution of silane coupling agent. 

The procedure for preparing holey carbon films (carbon film containing small holes of 100 nm diam.) is somewhat more complex. In this case the microscope slide is initially dipped into a 0.25% solution of formvar in ethylene dichloride and then held over a source of water vapor for sufficient time for an array of droplets to collect on the formvar surface. Excess formvar is drained off the slide and allowed to dry. During this stage the water droplets evaporate leaving behind a wide size range of bubbles in the formvar film. Carbon is evaporated onto this surface following the procedure described above so that the eventual result is the formation of a holey carbon film. 

Plastic films can be formed from a number of polymers two of the most common are collodion (nitrocellulose) and polyvinyl formal (Formvar). A number of other plastic materials can be used for thin films, some with specific advantages (101). Plastic films are usually prepared either by spreading a drop of solution of the plastic (in an appropriate solvent) onto a clean water surface, or by stripping off a film that has been coated onto a clean, flat surface (such as a glass slide) onto the surface of clean water. 

Extensive documentation on the preparation of holey film substrates for cryo-TEM sample preparation is available in the literature. Holey films or nets have been produced [10,25-27] from a glycerol-water mixture in a solution of a mixture of formvar and triafol in dichloromethane spread on mica. After floating the thin film off the mica support, the films were treated with ethyl acetate to transform pseudoholes into holes or nets. 

Slides must be coated with a thin plastic film [e.g., Formvar, 1% (w/v) in chloroform]. It can also be easily prepared from polystyrene labware (e.g.. Falcon petri dishes) by dissolving 0.75% (w/v) crumbled material in chloroform. Slides are dipped in the solution and air dried. The interesting area is scaled with a scalpel or a glass cutter. Small drops of 1% (v/v) hydrofluoric acid are put on the edges (hydrofluoric acid is toxic and corrosive wear gloves and full-face protection). A thin layer of the glass is etched underneath the plastic film by the acid and the film is lifted. Drops of water are added until the film comes off... 

Plastic, carbon and metal films (Section 4.7) are used as specimen supports on TEM grids. There are two plastic support materials in use collodion, 0.5% solution of nitrocellulose in amyl acetate and formvar, 0.25% polyvinyl formal in ethylene dichloride. These polymers are available as powders, solutions or prepared films on TEM grids. Formvar films, especially holey ones, are used as substrates for the formation of holey carbon films. Today, collodion is not used too often, as it is not as stable in the electron beam as formvar or carbon films. 

Shaffer et al [365] have continued to modify staining techniques for TEM of latex particles. Recent work on structured latex particles prepared by seeded emulsion polymerization focused on the effects of changes in polymerization variables, such as batch versus semicontinuous, core-shell ratio, shell thickness and shell composition. In this system the core was poly(n-butyl acrylate) and the shell was poly(benzyl methacrylate-styrene). A few drops of the latex was combined with a few drops of a 2% uranyl acetate solution which serves as a negative stain. A drop of that mixture was deposited on a stainless steel formvar-coated grid. After drying it was stained in ruthenium tetroxide vapor to differentiate the rubbery core, which is not... 

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