Predict the qualitative dielectrophoretic behavior (positive or negative DEP at
ID: 702182 • Letter: P
Question
Predict the qualitative dielectrophoretic behavior (positive or negative DEP at low and at high frequency) of the following particles: a) Air bubble in mineral (hydrocarbon) oil. b) Water droplet in hydrocarbon oil. c) Latex particle in water (note: have in mind that the surface charge and the counterion atmosphere lead to significant surface conductivity) d Air bubble in water stabilized by ionic surfactant (similar arguments for a large surface ionic conductance and polarization as above apply) e) Metallic sphere in mineral oil f) Metallic sphere in water g Live cell in isotonic solution.Explanation / Answer
Dielectophoresis is a phenomenon in which a force is extended on a dielectric particle when it is subjected to a non-uniform electric field. This force does not require a particle to be charged. All particles exhibit dielectrophoretic activity in the presence of electric fields. However, the strength of the force depends strongly on the medium and particles electric properties, on the shape and size, as well as on the frequency of the electric field.
If the particle moves in the direction of increasing electric field, the behaviour is reffered to as positive DEP(sometime pDEP), if acting to move the particle away from high field regions, it is known as negative DEP(or nDEP).
a) nDEP- Since air is neutrally charged, it will show negative DEP at both low and high Frequency.
b) nDEP at low Frequency since Hydrocarbons show neutral behaviour as they have low dielectric strength and pDEP at very high frequency due to the presence of greater field.
c) pDEP: At low and high frequency due to the presence of ionic particles.
d) pDEP at low and high frequnecy for similar reason as of c)