The ZPA 20 can be used to measure surface charge properties (the zeta potential) of solid macroscopic samples by measuring the streaming potential or streaming current produced when shearing an electrolyte along a sample's surface. Measurements of zeta potential over changes in pH, ionic strength or adsorbent concentrations typically provides characteristic information that reflect the surface chemistry, charging- and swelling behaviour, and adsorption processes on a material surface. Dynamic measurements are possible and effectively turns the ZPA into a charge-based surface sensitive instrument complementary to mass-based techniques such as SPR or QCMD, enabling adsorption studies of molecular species or the effects of chemical treatments to the sample's surface chemistry in real-time.

This instrument features a bi-directional oscillating piston which gives the ZPA a high degree of control over the flow of electrolyte in both directions, fast measurement times and information about the quality of measurement. The flow cell tower is made of transparent PMMA, allowing the user to observe the sample during ongoing measurements. In the ZPA's default configuration an electrolyte volume between 220-250 ml is required, but this can be reduced to 20 ml with some in-house modifications that make it more suitable for dynamic measurements (contact the tool responsible if you have questions). 

Virtually any type of sample material can be studied as long as it remains on/as a substrate in water and can be fitted within one of the following two available flow cells:

- The gap cell - Can measure two opposing identical planar samples of dimensions 20x10 mm (these dimensions are critical!). Maximum 2+2 mm sample thickness. Sample/substrate needs to strongly adhere to the provided double sided tape or directly to the PEEK component by other means that doesn't damage the PEEK, or bonded to a substrate that can be taped. Recommended pressure range and gap height during measurement is 700-1300 mbar and 100-130 µm respectively.

- The permeable (fiber) cell - Can measure fiber bundles, textiles, granules, powders and other types of permeable samples where the electrolyte can be flowed through the sample. The sample must be able to fill the cylindrical compartment in X-Y direction fully and not pass through or around the filter membranes. The amount of sample and an adjustable compression torquewrench is used to dial in the required pressure range for a measurement. Recommended pressure range during measurement is 700-1300 mbar. If you wish to measure powders, you MUST contact the tool responsible before testing yourself, as the instrument can easily be damaged if the powder is unsuitable or mounted incorrectly!!!