Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Charged Droplets and Dust
Name: Mike C.
Status: other
Age: 40s
Location: N/A
Country: N/A
Date: 10/27/2003


Question:
My question is, we have water being passed thought fine nozzles at pressure, the water droplets are less than 50mu, we then blow the water droplets into the air to make a fog, very similar to a snow making machine, I was trying to make a correlation between positive and negative charges, to say that the water droplets are charged and therefore the negative dust particles would be attracted to them, is there a science behind that theory?


Replies:
There is a lot of science surrounding the behavior of small droplets (solid or liquid). As the diameter of a particle decreases below about 0.1-0.2 microns (100-200 nanometers) two properties that are usually negligible become dominant and one property that dominates the behavior of matter becomes increasingly negligible. The surface charge and the surface tension become increasingly important, and gravity becomes decreasingly important. As a result some strange things happen. Dust "clouds" become stabilized because the particles repel one another and Brownian motion (explained by Albert Einstein) keeps them in motion. This makes these small particles able to pass through cell membranes and / or be deposited permanently in the lower lungs and pass directly into other cellular tissue. In addition the surface energy increases as approximately 1/R where R is the particle diameter. So even liquid particles can "bounce" together but not coalesce. If you wish to enter this fascinating world of small particles search the terms: colloids, colloid chemistry, or colloid physics and you can find information at any level of sophistication you wish.

Vince Calder


Mike,

Indeed, if one can produce water droplets with a charge opposite to the charge borne by dust particles in the air, there would be a mutual attraction between them. Although water molecules are electrically neutral, they do have a dipole that results in the oxygen atom bearing a slight negative charge -- the region near the hydrogen atoms bears a corresponding positive charge of equal magnitude. When water molecules coalesce into a droplet. the droplet is likewise electrically neutral.

How does your spray technology impart a net (+) or (-) charge to the droplets? How do you determine the polarity of the charge on the droplets and dust particles? In other words, how do you know they are of opposite charge? These questions must be addressed before one could posit facts supporting your hypothesis, " ...trying to make a correlation between positive and negative charges, to say that the water droplets are charged and therefore the negative dust particles would be attracted to them."

Regards,
ProfHoff 737



Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (help@newton.dep.anl.gov), or at Argonne's Educational Programs

NEWTON AND ASK A SCIENTIST
Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory