Sedimentation potential
Sedimentation potential occurs when dispersed particles move under the influence of either gravity or centrifugation or electricity in a medium.
While the particle moves, the ions in the electric double layer lag behind due to the liquid flow.
Particles influenced by an external force generate tangential motion of a fluid with respect to an adjacent charged surface.
As a charged particle moves through a gravitational force or centrifugation, an electric potential is induced.
While the particle moves, ions in the electric double layer lag behind creating a net dipole moment behind due to liquid flow.
Sedimentation potential has the opposite effect compared to electrophoresis where an electric field is applied to the system.
The following relation provides a measure of the sedimentation potential due to the settling of charged spheres.
In 1954, Booth proved that this idea held true for Pyrex glass powder settling in a KCl solution.
Smoluchowski's sedimentation potential is defined where ε0 is the permitivity of free space, D the dimensionless dielectric constant, ξ the zeta potential, g the acceleration due to gravity, Φ the particle volume fraction, ρ the particle density, ρo the medium density, λ the specific volume conductivity, and η the viscosity.
To account for different geometries of the electrode, the column is typically rotated 180 degrees while measuring the potential.
[9] An improved design cell was developed to determine sedimentation potential, specific conductivity, volume fraction of the solids as well as pH.
A flip switch is utilized to avoid polarization of the resistance electrodes and buildup of charge by alternating the current.
Some applications of SFFF include characterization of particle size of latex materials for adhesives, coatings and paints, colloidal silica for binders, coatings and compounding agents, titanium oxide pigments for paints, paper and textiles, emulsion for soft drinks, and biological materials like viruses and liposomes.
[11] Some main aspects of SFFF include: it provides high-resolution possibilities for size distribution measurements with high precision, the resolution is dependent on experimental conditions, the typical analysis time is 1 to 2 hours, and it is a non-destructive technique which offers the possibility of collecting fraction.
Some of the assumptions to develop the theoretical equations include that there is no interaction between individual particles and equilibrium can occur anywhere in separation channels.
Following "Fundamentals of Interface and Colloid Science" by Lyklema (1995), the complete family of electrokinetic phenomena includes:
