Wetting Agents for Hydrophobic Pigments

The most effective wetting agent gives a zero contact angle at the lowest concentration. For 6 = 0° or cos6 = 1, Tiv must be as small as possible, and this 

It should be noted that a reduction of y v uot always accompanied by a simultaneous reduction of yg. and hence it is necessary to obtain information on both interfacial tensions this, in turn, means that measurement of the contact angle is essential in the selection of wetting agents. Measurements of ygL and y y should be carried out under dynamic conditions (i.e., within very short times). In the absence of such measurements, the sinking time (as described above) could be applied as a guide for wetting agent selection. 

The above molecule has a low cmc of 0.7 gdm , at and above which water surface tension is reduced to 25 mN in less than 15 s. 

An alternative anionic wetting agent is sodium dodecylbenzene sulphonate (NaDBS) with a branched alkyl chain. 

NaDBS has a higher cmc (1 gdm ) than Aerosol OT, and it is also less effective in lowering the surface tension of water, reaching a value of 30 mN m at and above the cmc. It is, therefore, less effective as Aerosol OT for powder wetting. 

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