Method and device for detecting substances on surfaces

A method of determining the presence of substances on a surface, the method comprising:

• ballistically dispensing one or more pulses of liquid to deposit a liquid drop on a surface;
• after a first time interval, detect via the sensor a geometric characteristic of the liquid drop that is related to a contact angle of the liquid drop to the surface corresponding to the first time interval;
• after a second time interval, detect via the imaging detector the geometric characteristic of the liquid drop that is related to a second contact angle of the liquid drop to the surface corresponding to the second time interval;
• compare the first and second contact angle;
• and
• determine a substance on the surface that is capable of interacting with the liquid through dissolution or some other interaction in response to a change between the first and second contact angles.

A method of determining the presence of substances on a surface, the method comprising:

• depositing a liquid drop on a surface with one of the liquid drop and the surface having kinetic energy parallel to the plane of the surface;
• detecting an initial position of the liquid drop on the surface;
• detecting a stopping position of the liquid drop on the surface;
• determining an amount of displacement of the liquid drop parallel to the plane of the surface in response to a change in the surface energy of the substrate, a change in the surface tension of the liquid or both;
• wherein the amount of displacement is based on the initial position and the stopping position;
• comparing the amount of displacement to a threshold amount that is preset based upon characteristics of a known clean surface;
• and
• determining the surface to be contaminated with a film in response to the comparison to the threshold amount.