Film excessive

Phenol is treated with concentrated H2S04 at elevated temperatures leading to phenolsulfonic acid in paraform, a brown crystalline material. The phenolsul-fonic acid and a solution of formaldehyde in water is treated at elevated temperatures for several hours. The solution is cast into a film. Excess monomers are removed by washing the film in water. 

A certain degree of variation in thickness is unavoidable. When caused by the tubular film die, these variations always occur at the same position. A local film excess usually appears as a line. This can be countered if the die head, the haul-off and wind-up gear, or, with a vertical extruder, the extruder barrel is rotated or moved from side to side at regular intervals (Fig. 3-25). 

The cobalt drier containing 6 to 12% metal cobalt is the most powerful drier used by the coatings industry. It acts as an oxidation catalyst, and it is known as a top drier, diying the top of the film. Excessive amounts of cobalt drier will create stresses and strains in the paint film that can result in wrinkling. Though purple in color, cobalt has low tinting strength and will not discolor a paint. 

Fig. II-4. (a) A cylindrical soap film (b) manner of a collapse of a cylindrical soap film of excessive length.

A quite different means for the experimental determination of surface excess quantities is ellipsometry. The technique is discussed in Section IV-3D, and it is sufficient to note here that the method allows the calculation of the thickness of an adsorbed film from the ellipticity produced in light reflected from the film covered surface. If this thickness, t, is known, F may be calculated from the relationship F = t/V, where V is the molecular volume. This last may be estimated either from molecular models or from the bulk liquid density. 

Fig. IV-22. Excess free energy of mixing of condensed films of octadecanol-docosyl sulfate at 25°C, at various film pressures. Top curve t = 5 dyn/cm bottom curve ir = 50 dyn/cm intermediate curves at 5-dyn/cm intervals. The curves are uncorrected for the mixing term at low film pressure. (From Ref. 246.)...

In contrast to tire preparation of LB films, tliat of SAMs is fairly simple and no special equipment is required. The inorganic substrate is simply immersed into a dilute solution of tire surface active material in an organic solvent (typically in tire mM range) and removed after an extended period ( 24 h). Subsequently, tire sample is rinsed extensively witli tire solvent to remove any excess material (wet chemical preparation). 

In general there are two factors capable of bringing about the reduction in chemical potential of the adsorbate, which is responsible for capillary condensation the proximity of the solid surface on the one hand (adsorption effect) and the curvature of the liquid meniscus on the other (Kelvin effect). From considerations advanced in Chapter 1 the adsorption effect should be limited to a distance of a few molecular diameters from the surface of the solid. Only at distances in excess of this would the film acquire the completely liquid-like properties which would enable its angle of contact with the bulk liquid to become zero thinner films would differ in structure from the bulk liquid and should therefore display a finite angle of contact with it. 

The ethylene glycol liberated by reaction (5.L) is removed by lowering the pressure or purging with an inert gas. Because the ethylene glycol produced by reaction (5.L) is removed, proper stoichiometry is assured by proceeding via the intermediate, bis(2-hydroxyethyl) terephthalate otherwise the excess glycol used initially would have a deleterious effect on the degree of polymerization. Poly(ethylene terephthalate) is more familiar by some of its trade names Mylar as a film and Dacron, Kodel, or Terylene as fibers it is also known by the acronym PET. 

Phenolic Resins. Phenohc resins (qv) are formed by the reaction of phenol [108-95-2] C H O, and formaldehyde [50-00-0] CH2O. If basic conditions and an excess of formaldehyde are used, the result is a resole phenohc resin, which will cure by itself Hberating water. If an acid catalyst and an excess of phenol are used, the result is a novolac phenohc resin, which is not self-curing. Novolac phenohc resins are typically formulated to contain a curing agent which is most often a material known as hexamethylenetetraamine [100-97-0] C H22N4. Phenohc resin adhesives are found in film or solution... 

Because of its small size and portabiHty, the hot-wire anemometer is ideally suited to measure gas velocities either continuously or on a troubleshooting basis in systems where excess pressure drop cannot be tolerated. Furnaces, smokestacks, electrostatic precipitators, and air ducts are typical areas of appHcation. Its fast response to velocity or temperature fluctuations in the surrounding gas makes it particularly useful in studying the turbulence characteristics and rapidity of mixing in gas streams. The constant current mode of operation has a wide frequency response and relatively lower noise level, provided a sufficiently small wire can be used. Where a more mgged wire is required, the constant temperature mode is employed because of its insensitivity to sensor heat capacity. In Hquids, hot-film sensors are employed instead of wires. The sensor consists of a thin metallic film mounted on the surface of a thermally and electrically insulated probe. 

Extended x-ray absorption fine stmcture measurements (EXAFS) have been performed to iavestigate the short-range stmcture of TbFe films (46). It is observed that there is an excess number of Fe—Fe and Tb—Tb pairs ia the plane of the amorphous film and an excess number of Tb—Fe pairs perpendicular to film. The iacrease of K with the substrate temperature for samples prepared by evaporation is explained by a rearrangement of local absorbed atom configurations duting the growth of the film (surface-iaduced textuting) (47). 

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