Wetting, Adsorption, and Cleaning Processes

When a liquid comes into contact with a solid, there are a few processes of interest to analyze. These are 

One finds that the wetting characteristics of any solid surface play an important role in all kinds of systems. The next most important step is the process of adsorption of substances on solid surfaces. These phenomena are the crucial steps for all kinds of cleaning processes. Typical systems involved are washing, coatings, adhesion, lubrication, oil recovery, etc. 

The liquid-solid or liquidj-solid-liquidz system is both a contact angle (Young s equation) and capillary phenomena (Laplace equation). These two parameters are 

In the following, we will consider some significant phenomena where these parameters are of importance. 

In everyday life, one finds various systems where a liquid comes in contact with the surface of a solid (rain drops on solid surfaces, paint, ink on paper, washing and cleaning, oil reservoirs, etc.). The contact angle studies of liquid-solid systems showed that wetting is dependent on different parameters. It is found that when a liquid comes in contact with a solid, there are a few specific surface-related processes, which one needs to analyze. These processes are 

Cleaning processes garment industry, etc. (car or aeroplane washing) 

These systems may be as follows washing, coatings, adhesion, lubrication, oil recovery, etc. 

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Surfactants have very special qualities that make them invaluable to the petroleum industry. The relevance of various interfacial phenomena, such as adsorbed surfactant films, self-assembly, contact angle, wetting, foams and emulsions, in nearly every process in the industry has been discussed. In addition, this chapter summarized the importance of the adsorption and aggregation behaviour of surfactants with regard to drilling, enhanced oil recovery, antifoaming, corrosion inhibition, oil spill clean-up, oil/water separation and fluidization of highly viscous materials. 

The economic evaluation above is only of the adsorption process which removes solvent vapor from emitted air. Byproducts of the adsorption process are solvent-laden water, dean air, and recovered wet solvent. In the above economic analysis a modest debit of 0.75/gallon is made for the necessary off-site treatment of the dirty steam condensate, and no financial credit Is given for the value of clean air. 

Surfactants are widely used to control wetting, capillary penetration, and evaporation. Adsorption of surfactants accelerates mass transfer processes, such as impregnation of hydrophobic porous bodies by aqueous solutions, cleaning of greasy oiled surfaces, and crude oil recovery. Surface modification of adsorbents, membranes, and catalysts by surfactants is often used to control their properties. 

The first step, just after wetting, is to attack the oily—greasy component. Surfactants made available by adsorption will directly cope with the oily part of the soil, whereas solid parts will be liquefied by surfactant penetration [59]. Although cleaning per se is not the purpose of this chapter, it is worthwhile to highlight similarities between the wetting of a solid surface coated with oily soil and the flotation process. 

Superhydrophobic materials have surfaces that are extremely difficult to wet, with water contact angles in excess of 150° or even greater, see Fig. 20.6 shows that surfaces with ultrahydrophobicity have aroused much interest with their potential applications in self-cleaning coatings, microfluidics, and biocompatible materials and so on. Many physical-chemical processes, such as adsorption, lubrication, adhesion, dispersion, friction, etc., are closely related to the wettability of materials surfaces [52, 53]. Examples of hydrophobic molecules include alkanes, oils, fats, wax, and greasy and organic substances with C, N, O, or F as the key constituent element. 

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