Trough technology

Amphiphilic materials spread at the air/water interface have been the subject of intensive study over a long period of time. The type of apparatus usually used for this purpose has much in common with the apparatus needed to form Langmuir-Blodgett films and, indeed, it is usually possible to adapt the same apparatus for both purposes. In this section the problems which must be overcome if these processes are to be carried out are discussed and the most effective solutions to these problems described. 

Teflon (polytetrafluoroethylene) does not leach out plasticisers and can be purchased in substantial blocks, sheets and rods of various thicknesses. The preferred method is to machine a trough from a solid block of this material. This is a practicable procedure if a good milling machine is available but one is limited to a rather shallow trough. This does not matter if it is to be used for the study of monolayers at the air/water interface only but is a severe limitation if it is to be used to make LB films. Attempts have been made to use a metal trough and coat it using a Teflon aerosol. Such attempts have not proved very successful. 

The amphiphilic material to be studied is dissolved at a known concentration in a volatile solvent which is not miscible with water and a known quantity is spread at the water surface using a micropipette. In order to study the physical properties of the film thus formed, one needs to be able to confine the film to a definite area and to be able to vary this area at will. It might appear that it would be equally possible to maintain a constant area and vary the amount of material which is spread. For the majority of materials this latter procedure is not satisfactory as equilibrium is not arrived at in a reasonable period of time and this method would not allow one to take the material through successive cycles of compression and expansion. We thus turn to a discussion of the various ways in which a film can be confined and its area varied in a systematic manner. Leaving aside methods which are really only of historical interest, for which reference should be made to the book by 

Gaines [14], there are two basic methods of confining and compressing films at the air/water interface. 

The edges of the trough are machined flat and are maintained in a horizontal position. They are either made of a hydrophobic material such as Teflon or are covered with a hydrophobic material such as wax. Only the former procedure is normally now used. The trough is filled to a point where it almost overflows. If a Teflon barrier is arranged so that it lies flat on, and makes contact with, both sides of the trough it will, under these circumstances, act as a barrier to the film which is spread between it and one end of the trough. 

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Power Tower — Similar in principle to parabolic-trough technology, the mirrors are placed in a circular pattern. At the center of the circle is a tower, at the top of which is a receiver filled with water, air, liquid metal or molten salt that moves to a power block and is used to power a steam turbine. 

Parabolic-trough technology offers the lowest-cost, near-term option for large-scale solar power. 

See http //www.eren.doe.gov/power/pdfs/solar trough.pdf and H. Price and D. Kearney. A Pathway for Sustained Commercial Development and Deployment of Parabolic-Trough Technology, NICH Report No. TP-550-24748 (1999), found at http //www.nrel.gov/docs/fy99osti/24748.pdf Hull, J.R., IEEE Spectrum 34(7) 20-25, (1997). 

Expansion of microreactor capabilities trough improved thermalrrmnagement and catalystdeposition, in Ehrfeld.W. (Ed.), Microreaction Technology 3rd International Conference on Microreaction Technology, Proc. ofIMRET3, pp.l97-... 

Thin-fdm was prepared from a slurry of catalyst powder which was prepared from 10 mg catalyst in 5 ml of 2-propanol. The catalyst slurry was sonicated for 30 min. and allowed to sit stagnant overnight. Before preparing the films, the slurry was sonicated for 15 min., 20 drops (0.1 ml) were added onto a ZnSe trough plate internal reflection element (022-2010-45, Pike Technologies). The solvent was allowed to evaporate, the procedure was repeated a total of five times. After drying in air at room temperature, the catalyst thin-film was ready for 2-propanol dehydrogenation studies. 

Because of the sequential nature of atomic layer deposition, it is a slow method for preparing thin films. The sequential nature, however, also produces a film of uniform thickness, referred to as a conformal film. This is important when the surface being coated is not atomically flat, but rather, has troughs and islands to be coated. Some of the most important technological materials, such as silicon and germanium, have not shown themselves to be amenable to the atomic layer deposition technique. This points to the need for continued research in the field of precursor synthesis. 

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