Page 140 - Adsorption by Powders and Porous Solids
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ADSORPTION BY POWDERS AND POROUS S0unS
Solid I Liquid Adhesion
I Spreading I SolidlSolld Adhesion
Figure 5.4. Interfaces lost or fonned during immersional, adhesional and spreading wetting and during
solid-solid adhesion.
At this stage, it may be noted (Jaycock and Parfitt, 1981) that the above types of
wetting do not all have the same contact angle requirement (0 < 90') for spontaneous
occurrence. Thus:
(a) adhesional wetting requires 0 < 180°, which is of course the most general case;
(b) immersional wetting requires 6J < 90' (otherwise external work must be applied);
(c) spreading and condensational wetting require 6J = 0.
Wettability of a solid surface: definition and assessment
The concept of wettability of a solid by a liquid is directly related to the wetting
processes. This concept is specially useful in the fields of detergency, lubrication or
enhanced oil recovery. In the context of the oil industry. proposals were made by
Briant and Cuiec (1972) for the experimental assessment of wettability, which was
defined in terms of the thermodynamic affinity of a solid surface for a liquid.
According to this approach wettability is equated to the work exchanged by the
immersion system with its surroundings when the process of immersional wetting of
