You ask about wetting agent (surfactant). Surfactant is short for surface active agent which (surprisingly) means an agent which is active at surfaces. The important characteristic of surfactants is that they contain both a water soluble (insoluble in oil) group and an oil soluble (insoluble in water) group.
Take a shampoo as an example. The most common surfactant used in shampoos is sodium lauryl ether (2-3 mole) sulphate. The ether is an alcohol ethoxylated with between 2 and 3 moles ethylene oxide. The layryl ether is then sulphated. The oil soluble part is the lauryl C₁₂ which may be petroleum derived or it may be deruved from fatty acids such as coconut fatty acid. The water-souble part is the sulphate group.

In detergent/cleaning applications the oil-soluble part acts at the oil/water surface where it dissolves in the oily impurities you want to remove. The water/soluble part then helps to lift them into the water solution. In a shampoo the surfactant helps to remove natural oils and greases from the hair.

There is a lot more to formulating shampoos. Other surfactants, especially amphoteric surfactants, are used to reduce eye irritation. If you want to know more about this, WHICH I AM SURE YOU DO NOT, you could refer to my book "Amphoteric Surfactants" in the Marcel Dekker Surfactant Science Series

Backtracking for a moment, there are 4 types of surfatant: anionic, cationic, nonionic and amphoteric surfactants. In anionic surfactants the water soluble group is anionic (mostly sulphate, sulphonate or carboxylate -COONa), in cationic surfactants the water soluble group is (wait for it) ... cationic. In nonionic surfactants the water soluble group is an ethylene oxide chain or sometimes an ester group.  Amphoteric surfactants contain both anionic and surfactants.

Getting back to your question, most surfaces in nature are negatively charged so it follows that most surfactants are anionics.  The negative charge in anionics is used to repel the negative surface charge to provide detergency. Cationics are used to convert negative surfaces to oily surfaces, for example in corrosion inhibitors.

Chances are you will need an anionic surfactant to improve wetting but you wll have to check that it does not interact with other chemicals in your system. If you need such an anionic then 'washing up liquid' is the easily obtainable source. For specific surfaces such as plastics you need a wetting agent (surfactant) compatible with the plastic surface.

I hope this has been helpful, but I am here if you need any clarification.

Catastrophe