Tensiometer

So far we have been wrinkling with water as our base liquid, which is what the film floats on, and with water as the liquid for the drops. Now we will be wrinkling with solutions of different surface tensions, which will be water but with differing amounts of surfactant. Remember surfactants decrease the surface tension. The normal surface tension of water is 72 mN/m (milliNewton per meter). We will determine the surface tension using a device, the Tensiometer, which measures the surface tension of a liquid based on a drop of the liquid.
First, we need to learn how to set up the Tensiometer. This instrument has a precise set up regimen. After turning the instrument on, a microsyringe is filled with the solution to be analyzed. Then the syringe is inserted into the syringe holder, just to the right of the thermometer. A cuvette has one ml of water added to it, then it is covered with parafilm. A hole is cut into the parafilm so that the tip of the syringe can be inserted into the covered cuvette; all this is done to prevent evaporation of water from the surface of the drop being analyzed during the measuring period and it reduces any disturbance from the air hitting the drop. It is critical that the syringe is precisely perpendicular to the water surface, and that the drop is as large as possible without falling off the tip of the syringe.


As is true of every instrument we have encountered in the lab, the Tensiometer is computer driven. The software, SCA20, is initiated and the parameters for the system and for the ambient conditions are entered into the computer. Once the program is set, the computer directs the volumes to be dispensed from the syringe to create the drop to be analyzed.
The data is recorded for at least 30 minutes since it takes some time for the drop to become stable, so the first ten to fifteen minutes of readings are discarded. The readings then become stable and are displayed alphanumerically as well as graphically.
At the end of the day, we attended a seminar presented by two professors from Tsinghua University in Beijing, considered China's M.I.T., which has a total enrollment of 30,000 students. Dr. Quingling Feng presented her work on :The Fabrication and Characterization of Scaffolds for Tissue Engineering", which explained the use of biomimetic composites to encourage bone growth. The biomimetric composites are based on studies of natural bone; nanohydroxyapatite/collagen can be molded on PLLA to create a bone scaffold very similar in structure to naural bone. In some work, chitin was used instead of hydroxyapatite in conjuncton with the collagen, and more crosslinking between molecules (therefore higher compression strength) was found. A combination of the two polymers was used to repair fractures in goat tibia, and the healing time was decreased. The material has received approval for trials in humans in China. The second presentation was by Professor Guosheng Gai, whose field of expertise is the behavior of fine powders. His current research investigates the construction of composite particles and modification of their shape. He controls the microstructure within the material to affect particle shape. He has been able to create conductie plastics through particle coating. This was hard for me to follow.