Rapid Particle Charge Titrations and Size Distribution

In many applications, particle charge and particle size characterise the behaviour of a dispersion. The Stabino® - NANO-flex® System is derived from the StabiSizer® - analysis instrument. It provides higher flexibility and is applicable to colloids with particle sizes between sub-nm and 100 µm. Measurements at concentrations up to 40% are possible.

Method

The “heart” of the Stabino® is a cylindrical PTFE chamber with an oscillating piston, both carrying only very little anionic charge at the surface (Figure 1).

The cylinder contains 1 mL and 10 mL sample respectively. The addition of titrands is controlled via two incorporated precision titration pumps delivering titrand solution from one or the other reservoir.  A fraction of the particles in the cell is immobilised at the surface of the wall. Therefore, with the piston movement Dv, the mobile cloud of the double layer of the immobilised particles is pushed up and down. That oscillating ion cloud produces an alternating voltage SP = streaming potential at the two electrodes. It is proportional to the zeta potential of the particles.

The Particle Interface Potential, like the streaming potential measured in Stabino®, represents the degree of electrostatic repulsion between particles and reacts to pH, conductivity and the poly-electrolyte surrounding, respectively. Any or all of these parameters can cause a material system to shift. The titration result is characteristic for the sample in a certain chemical environment. A charge titration with the Stabino® specifies which parameters require special attention.

Close to reality Multi-Parameter Particle Charge Mapping (3D - Plot)

The intuitive tablet PC controlled automatic titration of the Stabino® opens the way to particle charge finger-printing of colloids and dispersions. The isoelectric point is reached quickly, gathering information on charge density and stable zones, whilst pH, conductivity and temperature are measured simultaneously.

Applications

The sensitivity of the streaming potential depends on surface area. This criteria may be used to follow changes in surface area, as it happens in milling processes. Secondly, the smaller the particles are, the more sensitive the method is.