Wetting a powder

The liquid will spread on the surface if the spreading coefficient is positive, i.e. the liquid will wet the solid. 

The work of cohesion is defined as the work necessary to separate unit area of one phase 

The energy of immersion is defined as the surface energy loss per unit area of surface on immersion. 

The ease of displacement of air from the surface of the powder is enhanced if is increased. This is frequently accomplished by the use of surfactants to reduce the contact angle 6 to zero if possible. 

The addition of surfactant usually causes a reduction in and, if absorbed, a reduction in Both effects lead to better wetting. The change in is negligible in most cases so the dominating factor is the surface tension of the liquid phase. 

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According to the above equation, the time t that is required to wet a powder is proportional to the viscosity of the surrounding medium, the depth of the pores, and the transported volume. The wetting time, on the other hand, is inversely proportional to the wetting tension — the driving force that promotes wetting — and to the cube of the radius of the pores in the agglomerates. 

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