While static and dynamic measurements of contact angle and surface/interfacial tension of liquid/fluid systems can be done directly, there is no direct measuring method for surface free energy (SFE) of solid surfaces, whose values (and their components of different chemical natures) can be only estimated indirectly, for example, based on measured contact angles of different liquids (of knowing surface tension properties) on them.

Besides the BASIC part that services as the framework of the application, MD consists currently three different modules:

CAD: contact angle determination (based on sessile drop method)
IFT: surface/interfacial determination of liquid/fluid systems (based on Pendant/Sessile drop methods)
SFE: surface free energy computation of a solid surface based on measured contact angles.

The MD Software developed for Windows NT/2000/XP offers by various expansion steps:

Gradient Thresholds for Edge Detection:

Edge Detection (image segmentation) is a key operation for the image processing application. In MD edge detection is based on gradient threshold method in combination with precise sub-pixel routines. This value gives the minimum gradient value any "edge" must have so that it will be recognized as an edge by MD. An edge is a transition zone from white/bright gray to black/dark gray (or vice versa), whose maximum gradient (i.e. first derivative of gray value vs. location) is compared to this threshold value. Only if this maximum gradient is large than the threshold value given here, it will be recognized as an edge.

Gray Level:

To make the edged detection more robust, MD uses the second parameter: gray level of an object. For a 8-bit gray image, each pixel may have a gray value between 0 to 255. This value is called pixel's gray level. The larger the gray level a pixel has, the brighter it appears. A gray level of 0 means total black, and a value of 255 total white.

The parameters under "Gray Level" tell MD that pixels on the drop side must have gray levels under (<) the specified value here, i.e. must be darker than the given value, whereas pixels of it's background (i.e. environment) must have gray levels higher than (>) the value specified here.

VIDEO Computation

Video recording is a very useful and powerful tool in studying dynamic, sometimes static as well, phenomena, both for contact angle measurements and for interfacial tension determinations. In a number of cases, precise measurements will become impossible without it's usage.

MD makes recording and late computation of a video clip straightforward and with a fun. After a stored video clip (avi-file) has been opened, you may want to check it by playing or browsing (you may use the page-up, page-down buttons, or your mouse wheel to browse through frames), reset time ZERO for the clip if necessary.

There are two arts to perform a video computation, and both automatically or manually

Surface/Interfacial Tension Determination (IFT)

With the current MD software surface tension and interfacial tension of a liquid/fluid system can be determined by using the Pendant Drop (or Rising Bubble) method and/or Sessile Drop method (or Captive Bubble) method.

The Laplace-Young equation that describes the shape of interface of a liquid droplet (or gaseous bubble) at its hydrostatic equilibrium between surface tension/interfacial tension and gravitational forces lays the foundation for these methods (assuming that all other external forces are absent). One of the pre-requisites for the methods used here is the assumption of axis-symmetry of a liquid droplet or a gaseous bubble. It is therefore critical for the available accuracy of methods to set up your measuring device properly to ensure that a resulting droplet or gaseous bubble that is being measured is approaching axis-symmetry.

Surface Free Energy (SFE) Determination

While static and dynamic measurements of contact angle and surface/interfacial tension of liquid/fluid systems can be done directly, there is no direct measuring method for surface free energy (SFE) of solid surfaces, whose values (and their components of different chemical natures) can be only estimated or computed indirectly, for example, from contact angles measured using one or more (different) liquids (of knowing surface tension properties).

For theories, models and some of common computational methods, please refer to
"The Measurement of surface energy of polymer by means of contact angles of liquids on solid surfaces - A short overview of frequently used methods" by Finn Knut Hansen, Department of Chemistry, University of Oslo.