Getting particles to sink and stay in solution

Question

I'm working on a project that involves finding moving particles in a solution (in my case, a syringe, or vial). The goal is to identify particles as small as 125um(micrometers), but the problem I face when I spin the container to get the particle moving, is that the particle gets stuck on the sidewall of the container, or on the top of the solution. Being that these are very small particles, I'm assuming my problem is surface tension related. The solution i'm working with is distilled water. I want to add a surfactant to reduce the surface tension, but I'm not sure what to use because I can't have bubbles forming due to the surfactant, and I need to retain the color of the solution. An idea I had was maybe some p80? Any other ideas? Also, do you think spraying the particles with a hydrophobic spray would help with anything?

Answer 1

Here are some things to try.

First, there are non-foaming surfactants available. They are commonly used in commercial floor-scrubbing machine solutions, where the presence of foam in the pump system would upset the pumping action. Many are hydrolyzable silicones.

Second, you could try agitating the test solution with ultrasonics, as in miniature jewelry-cleaning tanks for use in the home.

Third, there are surfactants which are used to prevent particles of dirt from settling out of solution & redepositing themselves once they have been dislodged from things like dishes, floors, and car bodies. These are called dispersion agents.