Wettability

Adhesion and printing operations on a plastic surface depend on the substrate s wettability, which indicates the ability of a liquid to spread on the surface. Wettability is a function of surface tension, and ASTM D2578 describes a standard procedure for measuring the wettability of a surface by determining the surface tension required for a liquid to wet the film surface. 

The end result of the surface chemistry of the reinforcement, the adsorbed material, topographical features, and epoxy composition is in the formation of the polymerized epoxy on the reinforcement surface. In order for this to happen, the fluid epoxy mixture must be brought into contact with the reinforcement surface, wetting must take place and energy added to aid the polymerization. The wetting of the reinforcement by the epoxy is a necessary criterion for optimum mechanical properties. 

A polymer should be readily wet with water for applications such as contact lenses and for the preparation of hydrogels for a variety of biomedical applications. Increased wettabilit) is reflected by reduced values of the contact angle of the polymer with water. Another application is silicone surface modification of wool for self-cleaning.  

Much study of adhesion has focused on developing improved adhesives and composites for aerospace applications [391,392]. Surface analysis techniques such as SEM and XPS are commonly employed to analyze fracture surfaces, and contact angle measurements have also 

Two more examples of the application of microscopy techniques to adhesive structural studies are fiber finishes and adhesive labels. Glass fibers are usually pretreated with a polymer coating which protects the fibers during 

Sticky tapes and labels are obvious uses of adhesives that cover a wide range of everyday applications. A relatively new type of adhesive has apparently been used in the manufacture of Post-it (trademark, 3M) products, small slips of paper with a reusable adhesive strip at one edge. SEM images show the adhesive partly coating the paper fibers (Fig. 5.83) [396]. Rounded domains of about 5-50 /xm form a contact on the applied surface (Fig. 5.83A). Regions between these rounded domains have a fine particulate structure which does not adhere, permitting the label to be removed easily. In order to image the adhesive nature of these materials, two adhesive strips were attached and then peeled back and exanuned in the SEM. (The adhesive strip and a piece of paper peel away from each other too 

All adhesives are polymers, and they are used in many ways, for example in composites, automotive tire cords, ply yood, tapes and labels. A particularly demanding application is the cementing of metal joints in military aircraft with polymers such as epoxy resins. The interfaces in such materials must be characterized to determine the strength of the adhesive bond and the relation of such properties as peel strength with 

Finally, sticky tapes and labels are obvious uses of adhesives that cover a wide range of everyday applications. A relatively new type of adhesive has apparently been used in the manufacture of Post-it (trademark, 3M) products, small slips of paper with a reusable adhesive strip at one edge. 

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In oil bearing formations, the presence of polar chemical functions of asphaltenes probably makes the rock wettable to hydrocarbons and limits their production. It also happens that during production, asphaltenes precipitate, blocking the tubing. The asphaltenes are partly responsible for the high viscosity and specific gravity of heavy crudes, leading to transport problems. 

The capillary effect is apparent whenever two non-miscible fluids are in contact, and is a result of the interaction of attractive forces between molecules in the two liquids (surface tension effects), and between the fluids and the solid surface (wettability effects). 

It is believed that the majority of clastic reservoir rocks are water wet, but the subject of wettability is a contentious one. 

Fig. X-10. The wettability spectrum for selected low-energy surfaces. (From Ref. 155.)...

Discuss the paradox in the wettability of a fractal surface (Eq. X-33). A true fractal surface is infinite in extent and a liquid of a finite contact angle will trap air at some length scale. How will this influence the contact angle measured for a fractal surface ... 

Diamond behaves somewhat differently in that n is low in air, about 0.1. It is dependent, however, on which crystal face is involved, and rises severalfold in vacuum (after heating) [1,2,25]. The behavior of sapphire is similar [24]. Diamond surfaces, incidentally, can have an oxide layer. Naturally occurring ones may be hydrophilic or hydrophobic, depending on whether they are found in formations exposed to air and water. The relation between surface wettability and friction seems not to have been studied. 

Contact Angle, Wettability and Adhesion , Adv. Chem. Series No. 43, Amer. Chem. Soc. (1964). 

W. A. Zisman, in F. M. Fowkes, ed.. Contact single, Wettability andA.dhesions (Adv. Chem. Ser. No. 43), American Chemical Society, Washington,... 

Fig. 21. Performance cut diameter prediction for typical sieve plate operation on wettable particulates at foam densities F solid line, F = 0.4 g/cm, dashed...

Lithium fluoride is an essential component of the fluorine cell electrolyte 1% LiF in the KF 2HF electrolyte improves the wettability of the carbon anodes and lowers the tendency of the cells to depolarize (18). Thermoluminescent radiation dosimeters used in personnel and environmental monitoring and in radiation therapy contain lithium fluoride powder, extmded ribbons, or rods (19). 

Sulfur and its compounds are among the oldest and most widely used pesticides. Elemental sulfur is especially effective as a dust for the control of mites attacking citms, cotton, and field crops and as a protectant against chiggers, Trombicula spp., attacking humans. Sulfur also is a valuable fungicidal diluent for other dust insecticides and is used in wettable form as a spray mixture. Time sulfur has been a standard dormant spray for the control of the San Jose Quadraspidiotuspemiciosus and for other scales and various plant diseases. Time sulfur is a water-soluble mixture of calcium pentasulfide,... 

Rya.nia., The root and stem of the plant yania speciosa family Flacourtiaceae, native to South America, contain from 0.16—0.2% of iasecticidal components, the most important of which is the alkaloid ryanodine [15662-33-9] C25H250 N (8) (mp 219—220°C). This compound is effective as both a contact and a stomach poison. Ryanodine is soluble ia water, methyl alcohol, and most organic solvents but not ia petroleum oils. It is more stable to the action of air and light than pyrethmm or rotenone and has considerable residual action. Ryania has an oral LD q to the rat of 750 mg/kg. The material has shown considerable promise ia the control of the European com borer and codling moth and is used as a wettable powder of ground stems or as a methanohc extract. Ryanodine uncouples the ATP—ADP actomyosia cycle of striated muscle. 

Wettable powders are prepared by blending the toxicant in high concentration, usually from 15 ndash 95%, with a dust carrier such as attapulgite which wets and suspends properly in water. One to two percent of a surface-active agent usually is added to improve the wetting and suspensibiUty of the powder. Sprays of wettable powders are used widely in agriculture because of their relative safety to plants. 

Pesticide Dispersants. Modified ligaosulfates are used ia the formulatioa of pesticides, la wettable powders, suspeasioa coaceatrates, and water dispersible granules, they act as dispersants and prevent sedimentation. They also act as biaders ia the productioa of granular pesticides. Typical usage levels ia these types of products range from 2—10%. 

All lnaphthalenesulfonic Acids. The aLkyLnaphthalenesulfonic acids can be made by sulfonation of aLkyLnaphthalenes, eg, with sulfuric acid at 160°C, or by alkylation of naphthalenesulfonic acids with alcohols or olefins. These products, as the acids or their sodium salts, are commercially important as textile auxiUaries, surfactants (qv), wetting agents, dispersants (qv), and emulsifying aids, eg, for dyes (qv), wettable powder pesticides, tars, clays (qv), and hydrotropes. 

Poljraer surfaces can be easily modified with microwave or radio-frequency-energized glow discharge techniques. The polymer surface cross-links or oxidizes, depending on the nature of the plasma atmosphere. Oxidizing (oxygen) and nonoxidizing (helium) plasmas can have a wide variety of effects on polymer surface wettability characteristics (92). 

Plasma processing technologies ate used for surface treatments and coatings for plastics, elastomers, glasses, metals, ceramics, etc. Such treatments provide better wear characteristics, thermal stability, color, controlled electrical properties, lubricity, abrasion resistance, barrier properties, adhesion promotion, wettability, blood compatibility, and controlled light transmissivity. 

E. G. Shafrin and W. A. Zisman, Contact A.ngle, Wettability, andHdhesion, Advances in Chemisty Series No. 43, American Chemical Society, Washington, D.C., 1964, p. 145. 

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