User:HypoTheSiS/sandbox

Scanning Droplet Adhesion Microscopy (SDAM) is a wetting characterization technique for lateral mapping of wetting properties of surfaces in terms of droplet adhesion force. The approach is in contrast to wetting characterization by measurement of the droplet-surface contact angle.

Technical overview
SDAM is a scanning method where a microdroplet suspended from a force sensor is utilized to measure the droplet-surface interaction (adhesion) upon contact with a sample surface. Measurements are carried out point-by-point on a mobile sample stage. At every measurement point, a vertical stage is used to lift the sample into contact with the droplet, and subsequently retract it until the droplet-surface contact is broken. Force measurement is carried out in a continous manner, yielding a force curve where the adhesion forces can be inferred.

In relation to other methodologies
Wetting characterization of surfaces is predominantly via optical side-view measurement of droplet-surface contact angle, referred as contact angle goniometry or optical tensiometry. SDAM is, by contrast, a force tensiometry technique where the droplet-surface adhesion force is measured instead. Droplet adhesion measurements provide an alternative approach for wetting characterization since the adhesion forces have been shown to correlate with advancing and receding contact angles. In SDAM, precise force measurements are coupled with small dimensions of the measurement droplet and high lateral positioning accuracy to enable systematic wetting mapping of arbitrary surface.

Limitations
On surfaces that are highly wetting to the liquid to be tested, the applicability of the droplet adhesion measurements is limited due to the cohesive breakage of the droplet upon retraction from the contact. In this case, a residual droplet remains on the surface, and the maximal retraction force cannot be measured. For water, this tends to take place for surfaces that are termed hydrophilic (≤ 90° water contact angle).