Uniformity contact angle

The mercury intrusion technique requires large pressures if the pore radius becomes smaller than 100 A. Since Eq. 1 is based on a cylindrical pore, the complex structure is approximated by an idealized structure in which each of the pores has a constant diameter. In addition a uniform contact angle is assumed. The intrusion technique should not be applied to composite electrodes without special precautions for the latter reason. 

Perhaps the best discussions of the experimental aspects of the capillary rise method are still those given by Richards and Carver [20] and Harkins and Brown [21]. For the most accurate work, it is necessary that the liquid wet the wall of the capillary so that there be no uncertainty as to the contact angle. Because of its transparency and because it is wet by most liquids, a glass capillary is most commonly used. The glass must be very clean, and even so it is wise to use a receding meniscus. The capillary must be accurately vertical, of accurately known and uniform radius, and should not deviate from circularity in cross section by more than a few percent. 

In the pendular state, shown in Figure la, particles ate held together by discrete lens-shaped rings at the points of contact or near-contact. For two uniformly sized spherical particles, the adhesive force in the pendular state for a wetting Hquid (contact angle zero degree) can be calculated (19,23) and substituted for H. in equation 1 to yield the foUowing, where y is the Hquid surface tension in N/m. 

In a similar procedure, the atomizer test, which depends on the behavior of an advancing rather than a receding contact angle, a fine mist of water is apphed to the metal surface and the spreading of water is observed. On a clean surface, water spreads to a uniform film. With oleic acid as the test soil, the atomizer test can detect the presence of 10 mg of soil per cm, less than a monomolecular layer (115). For steel that is to be electroplated, the copper dip test is often employed. Steel is dipped into a cupric salt solution and the eveimess of the resulting metallic copper deposit is noted. 

To inspect for contaminants, a water break test is frequently employed. Water, being a polar molecule, will wet a high-energy surface (contact angle near 180 ), such as a clean metal oxide, but will bead-up on a low-energy surface characteristic of most organic materials. If the water flows uniformly over the entire surface, the surface can be assumed to clean, but if it beads-up or does not wet an area, that area probably has an organic contaminant that will require the part be re-processed. 

Eadie, in Ref 69, reports on a considerable amount of work done on the ability of beeswax and paraffin wax to remain coated on HMX surfaces when immersed in liq TNT. Thru measurements of contact angles, a technique used earlier on RDX/wax systems reported on by Rubin in Ref 23, it was determined that the TNT preferentially wets the HMX and the wax is stripped away. He concludes that the most important property of a desensitizing wax is that it should be readily dispersed uniformly thruout the TNT phase. He also suggests that a better desensitizer for investigation for use would be a wax or substituted hydrocarbon having a low interfacial tension with TNT. The smaller the wax droplet size the more efficiently it will be distributed and the more effectively it should desensitize. Williamson (Ref 64) in his examination of the microstructures of PETN/TNT/wax fusion-casts detected that wax is dispersed thru the cast as isolated descrete globules which he refers to as blebs or irregular or streak-like areas, surrounded by TNT (see also Ref 54)... 

Polymeric surface treatments are applied in similar fashion, namely spin-coating from a low-concentration solution of the polymer in organic solvent, e.g. 0.1% (w/w) polymer in toluene. Spin conditions can vary widely but, as reported by 3M [30a], 500 rpm for 20 s then 2000 rpm for 40 s provides 100 A thick dry polymer films on smooth dielectrics with good surface quality and contact-angle uniformity. Spun layers are typically air-dried for several hours, or dried at an elevated temperature of 110-130 °C for 30 min in an oven or 5 min on a hot plate. These materials are typically not rinsed after they are baked, because the homopolymer version would redissolve, removing almost all of the polymer. In a recent report from Fris-bie s group, in collaboration with 3M, device oxides were intentionally roughened... 

In this regard, Washburn [147,150] supposed that for cylindrical pores of equivalent radius, r, wetted with a liquid of contact angle, 8 [149] (see Figure 4.66), a liquid/gas interface enclosed inside a pore will at equilibrium take on the shape of the uniform average curvature. That is, in a uniform cylindrical pore of radius r or in a parallel-sided slit of width r, the mean curvature, 1/r, is equal to [148]... 

The term ysv is the interfacial tension of the solid material in equilibrium with a fluid vapor yLV is the surface tension of the fluid material in equilibrium with its vapor and ySL is the interfacial tension between the solid and liquid materials. Complete, spontaneous wetting occurs when 9 = 0° or when the material spreads uniformly over a substrate to form a thin sheet. A contact angle of 0° occurs with pure water droplet on a clean, glass shde. Therefore, for complete spontaneous wetting, cos 9 > 1.0 or when... 

Test methods used to determine the uniformity of substrates are numerous and vary with the type of material. They are generally the same tests used to characterize the material or to determine its fundamental physical properties. Tests that are commonly employed are hardness, tensile strength, modulus, and surface characteristics such as roughness or contact angle with a standard liquid. Often a test similar to the nonvolatile test mentioned above is used to determine if there are any compounds in the substrate that are capable of out-gassing on exposure to elevated temperatures. Moisture content of certain hydroscopic polymers, such as nylon and polycarbonate, is also known to affect adhesion. 

Many different techniques have been developed for the measurement of contact angles 17.8). Of these, the three most useful methods are the Wilhelnty technique, the technique of capillary rise at a vertical plate, and the drop shape methods. These techniques require the solid surface to be flat and smooth. Direct measurement of contact angles on fibers (of uniform thickness) can also be performed using the Wilhelmy technique. For nonflat surfaces or particles, indirect methods such as capillary penetration into columns of powders, sedi-... 

It is by rearranging this equation and assuming 9 to be zero that we obtain Eq. (4). For practical purposes, plates that are about 2 cm wide satisfy the theoretical requirement of infinite width. For such a plate (assumed to have a uniform surface), the line of contact is straight in the central part of the plate for all liquids of moderate surface tension, including water. If we assume g. A(0, and )/ V to be known, the task of determining a contact angle is reduced to the measurement of a length (the capillary rise h), which can be determined optically, e g., with a cathetometer. 

If the liquid meniscus is always brought to the same position in the tube,i the error due to non-uniformity of bore is avoided. The use of the above formulae assumes a zero contact angle this was verified by an optical method by Richards and Carver, i who gave some interesting photographs of the shapes of menisci. 

There are three major complications in contact angle studies of proteins and other water sensitive polymers. First, no simple or safe method of guaranteeing the cleanliness or uniformity of specimen surfaces is available the initial purity of the sample must be relied upon as the primary criterion of surface uniformity. Second, there is a strong effect from adsorbed water molecules which remain on the surface and... 

Contact Angle Measurements. The angle of contact of 93° for poly(L-norleucine) has been reported previously. Problems of preparing uniform adherent films of poly(L-methionine) and hysteresis effects combined to make measurements of 0 very imprecise it is estimated at 55° 10°. No measurements at all were possible with poly(L-leucine) for similar reasons. 

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