A variety of forces influence the movement of particles through the nanopore:
- Convection
- Electrophoresis
- Electroosmosis
- Dielectrophoresis
- Drag within confined nano/micropores
Convection
Convection is the fluid flow caused by the pressure difference across the nanopore. There is always a static pressure head due to gravitational force on the fluid. An additional pressure or vacuum can be applied using the VPM.
Electrophoresis
Electrophoresis is one of the three electro-kinetic forces that influence particle movement. It relates to the movement of charged nanoparticles through an electrolyte solution towards an oppositely-charged electrode. It is proportional to particle charge (ζ-potential) and the applied voltage.
Electroosmosis
The second electro-kinetic force is electro-osmosis. Electro-osmosis relates to the fluid flow caused by the charge on the surface of the nanopore. It is proportional to the nanopore surface charge (ζ-potential) and the applied voltage.
Dieelectrophoresis
Dielectrophoresis is caused by the force on a dielectric particle in an electric field gradient. Dieelectrophoresis is commonly significantly smaller than electrophoresis and can be neglected in most cases.
Hydrodynamic Drag
Drag on particles will have no effect on TRPS size and concentration measurements. However it may have an impact on zeta potential measurements of polydisperse samples.
Chief Scientist Emma summarises these forces in this short video: