Repellency

The contact angle has a significant effect on repellency. The work of adhesion, Wa, required to remove the droplets, ignoring viscoelastic effects is  

As the contact angle increases, the work of adhesion decreases. This is the basis for repellency. 

Another macroscopic feature that arises from surface tension is the rate, u, at which a liquid will spread on a solid surface (again, ignoring any viscoelastic 

The surface tensions of materials prepared with are some of the lowest attainable with the reagents commonly available, which is why many carpet and textile repellents are based on the chemistry of perfluoroalkyl chains. For example, a nylon-6,6 carpet would be wetted by oily soils, which, according to Eq. (4), would be difficult to remove. The presence of a FA coating on die fiber lowers its surface tension and repels the oil contaminant. In general, a liquid dial has a high surface tension will not wet a solid with low surface tension (e.g., water on PTFE). The converse is also true. A low-surface-tension liquid will wet a high surface tension solid (e.g., hexadecane on nylon-6,6). 

29 AVmolecule.2 Similar studies using hydrocarbon fatty acid monolayers provided molecular areas of about 20 AVmoleculc.  

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It has been used as a bird repellant and is the parent compound of the anthraquinone vat dyes in which the dyeing is carried out by immersion in the reduced vat solution followed by air oxidation to the original insoluble compound. 

Complementary to the matter of wetting is that of water repellency. Here, the desired goal is to make 6 as large as possible. For example, in steam condensers, heat conductivity is improved if the condensed water does not wet the surfaces, but runs down in drops. 

Fig. Xm-3. Effect of contact angle in determining water repellency of fabrics.

Apparently a negative AP with Q < 90° can be found for particular pore geometries [53]. A different type of water repellency is desired to prevent the deterioration of blacktop roads consisting of crushed rock coated with bituminous materials. Here the problem is that water tends to spread into the stone-oil interface, detaching the aggregate from its binder [54]. No entirely satisfactory solution has been found, although various detergent-type additives have been found to help. Much more study of the problem is needed. 

J. L. Moilliet, ed.. Waterproofing and Water Repellency, Elsevier, New York, 1963. 

There are interactions between the adsorbates themselves, which greatly affect the structure of the adsorbates [32]. If surface difhision is sufficiently facile during or following the adsorption step, attractive interactions can induce the adsorbates to fomi islands in which the local adsorbate concentration is quite high. Other adsorbates may repel each other at low coverages fomiing structures in which the distance between adsorbates... 

Figure Bl.7.1. Schematic diagram of an electron ionization ion source source block (1) filament (2) trap electrode (3) repeller electrode (4) acceleration region (5) focusing lens (6).

Note that negative Acoj (red detuning) produces a force attracting the atom to the intensity maximum while positive (blue detuning) repels the atom away from the intensity maximum. The spontaneous force or cooling force can also be written in tenns of the saturation parameter and the spontaneous emission rate. 

If < 1, then binding is anticooperative, for example when an electrically charged particle adsorbs at an initially neutral surface the accumulated charge repels subsequent arrivals and makes their incorjDoration more difficult [58]. 

The phase-change nale, also known as the Ben phase [101], the geometric phase effect [102,103] or the molecular Aharonov-Bohm effect [104-106], was used by several authors to verify that two near-by surfaces actually cross, and are not repelled apart. This point is of particular relevance for states of the same symmetry. The total electronic wave function and the total nuclear wave function of both the upper and the lower states change their phases upon being bansported in a closed loop around a point of conical intersection. Any one of them may be used in the search for degeneracies. 

Fig. 1. Motion of a material point on the body over time (left, short time interval right, long interval). The rigid body swings repeatedly toward the plane where it is repelled by the strong short-range force.

This represents an attractive (Coulombic) potential coupled with a repulsive soft wall, relative to a plane situated just below the rigid body. The rigid body is repeated drawn toward the plane, then repelled sharply from the wall. 

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