Surface charge measurement

An apparatus for determining a zeta potential of a planar surface of a sample, comprising:

• a sample holder having an opposed pair of electrodes and configured to hold the sample in position in a measurement volume between the electrodes such that the planar surface of the sample is aligned orthogonal to the electrode surfaces;
• a measurement chamber for containing a liquid electrolyte and having an open end configured to receive the sample holder to position the electrodes in a preset orientation;
• a laser light source positioned and configured to direct a laser beam through the measurement chamber such that, when the sample holder is received in the measurement chamber, the laser beam is directed through the measurement volume between the electrodes and parallel to the planar surface of the sample;
• and
• a detector positioned and configured to detect scattered light from the measurement volume,
• wherein the apparatus is configured to allow for detection of the scattered light by the detector received from detection points over a range of distances from the planar surface of the sample;
• wherein the sample holder includes an actuation mechanism supported by a static section, the actuation mechanism configured to adjust a position of the planar surface of the sample, relative to the static section, in a direction normal to the planar surface of the sample, to allow the detector to receive light from detection points over a range of distances from the planar surface of the sample.