ZETA POTENTIAL ANALYSIS
The main focus of zeta potential analysis of macroscopic solid surfaces is to gain information on the surface charge. This charge is established on the surface of a solid material when it gets in contact with water. The zeta potential provides information on surface functionality, the specific interaction of dissolved compounds with the solid surface, and liquid-on-solid surface adsorption processes. [1]
Furthermore, the zeta potential measurements are not only a useful experimental technique to determine the nature of functional groups (polar acidic or basic, non-polar) and the amount of dissociating groups, but also to estimate the hydrophilicity and hydrophobicity of solid surfaces. [2]
The zeta potential is thus important for understanding the behaviour of solid materials in many technical processes where aqueous systems play a role, e.g. membranes for water treatment, biomaterials in contact with blood or wet processing of semiconductor wafers. Knowledge of the zeta potential of a material helps you optimize specific surface modification processes for a material to perform at its best when applied. [1]
APPLICATIONS
The SurPASS electrokinetic analyzer enables the investigation of electrokinetic effects at the solid/liquid interface for solids of almost any size and shape. For measuring different types of solid samples there are four different measuring cells available:
- Cylindrical Cell (a.)
- Clamping Cell (b.)
- Adjustable Gap Cell (c.)
- Adjustable Gap Cell for Discs (d.)
SurPASS electrokinetic analyzer with available measuring cells (Anton Paar GmbH, Austria)
The SurPASS
Cylindrical Cell is designed for the zeta potential determination of fibre and powder samples, such as:
- Natural and technical fibres
- Hair
- Textile fabrics
- Filter disks
- Hollow fibres
- Powder samples with > 25 μm particle size
- Granular samples
The SurPASS
Clamping Cell has been developed for the zeta potential determination of solids with a flat surface with size min. 55 mm × 25 mm and max. thickness 30 mm, such as:
- Polymer foils and thin films
- Metal plates
- Ceramic tiles
- Semiconductor wafers
- Hard disks
The SurPASS
Adjustable Gap Cell accommodates small planar samples with a rectangular size of 20 mm × 10 mm and max. thickness 1 mm, such as:
- Polymer membranes
- Filters
- Textile fabrics
- Leather
- Solid minerals and rocks
The SurPASS
Adjustable Gap Cell for Disks is suitable for QCM-D sensors with diameter of 14 mm. [3, 4]
ZETA POTENTIAL AND ITS DEPENDENCES
The zeta potential depends on both, the solid sample itself but also the properties of the liquid phase used for the measurement. The pH dependence of zeta potential is among the most extensively studied dependences of zeta potential. It gives valuable information on the composition of the outermost surface, i.e. the presence of acidic or basic functional groups. The pH value at which the zeta potential is 0 mV is known as the isoelectric point and is used as an indicator for the chemistry of a surface.[1]
Schematic representation of zeta potential versus pH plots for polymer/electrolyte interfaces. (a)
dissociable basic functional groups,
dissociable acidic and basic functional groups (amphoteric behaviour),
dissociable acidic functional groups. (b)
non-polar surface without dissociable functional groups [5]
References:
[1] Anton Paar GmbH,
http://wiki.anton-paar.com/zeta-potential
[2] Grundke et al., Characterization of fillers and fibres by wetting and electrokinetic measurements, Colloids and Surfaces, 58 ( 1991) 47-59.
[3] Anton Paar GmbH, Instruction Manual: SurPASS Electrokinetic Analyzer, Graz, 2007.
[4] Anton Paar GmbH, Brochure: SurPASS Electrokinetic Analyzer for Solid Samples.
[5] Grundke K., Chapter: Characterization of Polymer Surfaces by Wetting and Electrokinetic Measurements – Contact Angle, Interfacial Tension, Zeta Potential, In: M. Stamm (ed.), Polymer Surfaces and Interfaces, 2008.