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Electrokinetic Lab

 

The potential on the surface of a solid in contact with a polar medium is governed according to Lyklema by the dissociation of surface groups, the preferential adsorption of cations or anions, the adsorption of polyelectrolytes, the isomorphic substitution of cations and anions, and lastly the accumulation or depletion of electrons. In case of most nonmetallic surfaces, particularly organic polymers in contact with aqueous electrolytes, surfactants or polyelectrolyte solutions, the first three of the above mechanisms predominate.

Generally, descriptions of the charge distribution at the interface are based on the model developed by Gouy and Chapman and completed by Stern and Grahame (GCSG-model).

The electric double layer can generally be regarded as consisting of two regions: a fixed layer and a diffuse layer. Between these two parts lies a "surface of shear" or "slipping plane". Externally used electrical or mechanical forces cause a relative movement between the fixed part and the diffuse part. The potential at this surface is called the electrokinetic or zeta (ζ) potential.

It is possible to distinguish between dissociation and adsorption processes according to Jacobasch. Also we can recognize reaction processes on the surface during measurements.

Streaming potential / streaming current

Electrokinetic Set-Up (Zetascience)

technical specifications:
- streaming potential
- streaming current
- max. pressure: 1000 mbar
- pH range: 2 to 12
- electrodes: Ag/ AgCl

sample requirements:
- fibres
- plates / foils from 10x20 mm, ø 26 mm

SurPASS (ANTON PAAR GmbH/Graz/A)

technical specifications:
- streaming potential: - 2000 to +2000 mV
- streaming current: -200 to +200 µA
- max. pressure: 1000 mbar
- pH range: 2 to 12
- electrodes: Ag/ AgCl

sample requirements:
- fibres
- powders > 25 µm
- plates / foils from 10x20 mm

EKA (ANTON PAAR GmbH/Graz/A)

technical specifications:
- streaming potential: -2000 to +2000 mV
- max. pressure: 1000 mbar
- pH range: 2 to 12
- electrodes: Ag/ AgCl, Pt, Pd

sample requirements:
- fibres
- membranes from 2 µm pore size
- powders > 25 µm
- plates / foils from 10x20 mm, ø 26 mm
- contact lenses

Electrophoresis

Zetasizer nano ZS
(MALVERN Instruments Ltd./Malvern/GB)

technical  specifications:
- Laser: 633 nm He-Ne-Laser
- measurement technique: M3 - PALS (Phase Analysis Light Scattering)

sample requirements:
- suspensions
- size range: 5 nm to 10 µm
- minimum sample volume: 1 mL, for pH-dependence 50 mL
- solid concentration: < 10 vol%

Zetasizer 3000
(MALVERN Instruments Ltd./Malvern/GB)

technical specifications:
- 633 nm He-Ne-laser

sample requirements:
- suspensions
- size range: 10 nm to 30 µm
- min. volume: 10 mL, for pH-dependence 50mL
- solid concentration: < 1 vol%

Acoustophoresis

DT 1200
(Dispersion Technology, Inc./Bedford Hills/USA)

technical specifications:
- measurement technique: colloidal vibration current

sample requirements:
- suspensions
- size range: < 100 µm
- solid concentration: 0,1 to 50 vol%