Abstract: A method and testing apparatus determine receding contact angles of liquids on surfaces by depositing a liquid in a manner whereby the volume of the drop is increased through stepwise addition of smaller drops. Each increment of volume growth causes the perimeter of the drop to advance across the surface. The incremental volume elements impart sufficient energy to the growing drop such that the drop perimeter expands beyond its equilibrium diameter for that volume. The drop perimeter tends to contract between volume additions as the excess energy is dissipated. The method and testing apparatus determine the receding contact angle between the incremental volume additions.

Abstract: A testing device determines the presence of substances on a surface using a sensor positioned at a known vantage point to the surface. A liquid dispenser deposits a liquid drop on the surface. A data generator after a first time interval for allowing the liquid drop to stabilize on the surface detects, via the sensor, a geometric characteristic of the liquid drop that is related to a first equilibrium contact angle of the liquid drop to the surface. The data generator after a second time interval detects via the sensor the geometric characteristic of the liquid drop that is related to a second equilibrium contact angle. The data generator compares the first and second contact angle and determines a contamination on the surface that is soluble in the liquid drop in response to a change between the first and second contact angles.

Abstract: A method and testing apparatus determine receding contact angles of liquids on surfaces by depositing a liquid in a manner whereby the volume of the drop is increased through stepwise addition of smaller drops. Each increment of volume growth causes the perimeter of the drop to advance across the surface. The incremental volume elements impart sufficient energy to the growing drop such that the drop perimeter expands beyond its equilibrium diameter for that volume. The drop perimeter tends to contract between volume additions as the excess energy is dissipated. The method and testing apparatus determine the receding contact angle between the incremental volume additions.

Abstract: A testing device determines the presence of substances on a surface using a sensor positioned at a known vantage point to the surface. A liquid dispenser deposits a liquid drop on the surface. A data generator after a first time interval for allowing the liquid drop to stabilize on the surface detects, via the sensor, a geometric characteristic of the liquid drop that is related to a first equilibrium contact angle of the liquid drop to the surface. The data generator after a second time interval detects via the sensor the geometric characteristic of the liquid drop that is related to a second equilibrium contact angle. The data generator compares the first and second contact angle and determines a contamination on the surface that is soluble in the liquid drop in response to a change between the first and second contact angles.