What will the use of cationic surfactants do in pool water?

[anthonypool89]

Hi,

I am going to try a product that is designed to remove white water mold and pink slime in pool water that is said to contain cationic surfactants. From some quick research, I find that cation has to do with a positively charged ion that is attracted to the cathode in electrolysis. And I also find that surfactants are compounds that lower the interfacial tension between two liquids or between a liquid and a solid. They apparently play a big role in detergents and softeners, etc. Another use is as a biocide. I'm trying to put together how a product that contains (among other proprietary ingredients not revealed in SDS info) cationic surfactants will take care of mold and slime in the water. Any ideas?

 

[JoyfulNoise]

A cationic surfactant is simply an organic molecule, typically a polymer, that has a functional group on it with a positive (+) charge. The functional groups are typically a quaternary ammonium group that has a positive charge on the nitrogen atom. The molecule itself has both hydrophilic and and hydrophobic characteristics and so it is able to breakup adherent films into smaller particulates and hold them in solution as a suspension. Because particles suspended in water (whether dirt or algae) tend to develop a negative surface charge, the cationic end group is good at attracting itself to the negatively charged particles and making them agglomerate into larger sizes.

So the cationic surfactant will act to remove adhered films and make them soluble in water (surfactant part) as well as act like like a clarifier attracting the particles together so that the filter can capture them (cationic clarifier).

NOTE - You should NEVER add an cationic polymer to water that has any kind of metal sequestrant in it because metal sequestrants are typically anionic in nature (negatively charged) and you will create a cloudy mess.

 

[JoyfulNoise]

To the question of it being a biocide - some cationic surfactants will bind to the surface proteins of living biological entities and cause some of the surface transport proteins (cellular pores, sodium/potassium ion channels, etc) to be forced open. This will then lyse the cells and cause cell death. This is the main mode of action of biguanides (Baquacil sanitizer). For planktonic (free-floating) algae, the cationic surfactants usually cause them to agglomerate into larger clusters where the filter will capture them and give more time for the sanitizer to work to kill them or for the pool owner to backwash them out of the system.

 

[anthonypool89]

Stain control was added to the pool last season, but I haven't added anything like "pool magnet" for many years. Since that time, the water has been drained and fresh fill added in 2014. So I should be ok in terms of there being no metal sequestrate in the water. Thanks for the detailed explanation. You must have a pretty formidable knowledge of chemistry. Besides barely passing High School chemistry, I was a music major in both undergrad and grad school and so much of what you said is a bit over my head but I'll certainly take your word for all of it!

You got me curious so I looked up some more. I had to start with polymers - which I find means "many monomers". Then I had to figure out what a functional group is. Am I correct that if a monomer contains two functional groups then it is by definition considered difunctional? Ergo, the difunctionality allows the monomers to form the long polymer chains? On a much simpler level, isn't a product with cationic surfactants - (since you said the negative and positive aspects allows for agglomeration into larger particles) - basically working like a flocculent?

Won't the larger clusters result in shorter filter cycles / increased backwashing? I always heard that DE filters and biguanide, in general, are not the best combination.