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For many years I've used a Rainbow vacuum, which uses a reservoir of water as the filter. While I'm quite pleased with it, I've found that when trying to vacuum cement dust or wood ash not all of the particles are captured in the water. I believe a remedy to this would be to lower the surface tension of the water. Yes, I can always be sure to use hot water, but I'd like to go further. Obviously I can't use a suds-producing detergent because the vacuum produces lots of turbulence in the reservoir.

What commonly available chemicals could I use that would give me the greatest reduction of surface tension? So far I've tried to research trisodium phosphate, sodium carbonate, and a product called Haemo-Sol which is a non-ionic surfactant... but I can't find surface tension numbers for any of these much less the concentration to use.

The manufacturer suggests adding a tablespoon of vinegar, which I think is rather lame.

Can anyone make a good guess or point me in the right direction?

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  • $\begingroup$ Reduction of surface tension is a most interesting science however currently friccohesity has superseded the surface tension experimental approach.The trimethylsulfoxonium iodide (TMSOI), methyltrioctylammonium chloride (MTOAC) have largely reduced the surface tension which was measured with survismeter. Pl consult the following paper- Int. J. of Thermodynamics ISSN 1301-9724, Vol. 11 (No. 4), pp. 181-186, December 2008. 'Solvodynamics of Benzene and Water Phases by DTAB, MTOAC,TMSOI and Orcinol Studied with Interfacial Tension, Surface Tension and Viscosity Measured with Survismeter' $\endgroup$ – mansingh Nov 8 '17 at 17:34
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Your goal is to reduce the surface tension of the water so that it does not support the formation of large bubbles or inhibit the whetting of the dirt particles.

When the bubbles are small, the dust inside will be more likely to make contact with the liquid surface of the bubble within the lifetime of the bubble. Also, when it does make contact, it will be much more likely to irreversibly adhere to the water if you have reduced the surface tension.

The word "surfactant" is a blend of "surface active agent"$^1$, and this is what you need to interfere with the surface tension of your water. I believe that you may have written off detergents too hastily. I think the best solution will be to add a small amount of laundry detergent, or possibly non-foaming carpet cleaner. Each of these products are designed to foam to a lesser degree than, say, dishwashing detergent or most hand soaps.

I suspect that you will have to experiment a bit, but that something on the order of a single cc per liter may be sufficient to increase the effectiveness of dust removal without causing excessive suds. Your goal should be to see how much detergent you can add without adversely affecting your vacuum, and decide whether this has resulted in a decreased throughput of dust particles.

As to your title question, "How do I lower the surface tension of water without using a detergent?", what I'm really saying is 1) that most anything that does what you want could probably be deemed a detergent and 2) that a detergent is likely the most practical solution to your problem.

1) Surfactants and Interfacial Phenomena, Fourth Edition, Rosen and Kunjappu, John Wiley and Sons, Inc., 2012

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Vinegar does reduce the surface tension quite a bit. If you put a tablespoon or two of vinegar in a bowl and then run water into it, the bubbles that form on the surface persist much longer than they do if there's no vinegar present.

I suggest reconsidering your rejection of the vinegar recommendation.


Beyond that, airhuff's right -- you're searching for something that will preferentially accumulate at the air-water interface. Air is far less polar that water, which means that you need a chemical that has both polar and nonpolar characteristics. No small inorganic solutes possess appreciable nonpolar regions, and once you tack on a nonpolar tail of any substantial length, you're back under the umbrella of detergents/surfactants.

The foaming potential is absolutely a function of concentration, as airhuff says, so it's a matter of finding the right number of drops per gallon to achieve the balance of properties you're seeking.

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Amway makes a product called L.O.C. It is somewhat of a detergent, However, it has been sold as a product that "makes water, wetter". It has been added (as I have been told) to chemicals in crop dusters. It allows the chemicals to spread over the leaves, giving greater surface area of coverage because of loss of surface tension.

Product: L.O.C.™ Multi-Purpose Cleaner (click "Ingredients") and MSDS

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Ethanol, ionic liquids, dyes, protein, reduce surface tension of water, however these chemicals increase viscosity so it is better to deal with friccohesity. The surface tension and viscosity determinations need density data measurements but friccohesity does not. The deepest mechanistic changes are accurately resolved by friccohesity. Acetic acid, sodium acetate and others reduce the surface tension of water.

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