Friday July 27, 2007

Efren and I arrived by 9 to set up the 0.12% solution for three tensiometer readings. The first result is 40, the second run gave us 44, and the third run gave us 42.

Jiangshui then suggested that we determine the surface tension of a 3% sample. This seems to be quite a jump in concentration, but he wants us to see that there is a limit to the effect of surfactant concentration on the surface tension of water. We will investigate both .30% and 3%.

At 10 am we attend the dissertation defense of Edwin P. Chan, a member of Dr. Alfred Crosby's group. This is Dr. Chan's fourth year; upon receipt of his degree today, he will do postdoctoral work at M.I.T.. His dissertation, "Adhesion of Patterned Polymer Interfaces", was inspired by nature; specifically the ability of beetles, bugs, and geckos to climb up walls.

He examined research that indicated that as the mass of the organism increases, the number of setae per area increases while the diameter of each seta decreases. In addition, the shape of the setae vary in nature, some are nearly round (bugs) while others are nearly triangular (gecko). Edwin compares adhesion using a single smooth surface to a surface with a patterned series of posts, then he varies the size, number, and shape of the posts to see the effects of these changes on adhesion. After this work was concluded, he determined that the establishment of these patterns was both labor intensive and expensive, so he sought another means to establish a pattern of adhesion posts. He then investigated wrinkling. He was able to establish a relationship between wrinkling pattern, pattern orientation, and the area being subjected to the stress that causes wrinkling. This provides a quick, inexpensive, and simple way to affect adhesion. This was an extremely interesting presentation, and Dr. Chan's knowledge and ability to explain precisely what he had done, what it meant, and the mathematical and scientific principles behind it on multiple levels was so impressive. I did not feel lost at any time, even though all of the math he presented was most assuredly way over my head. He could rapidly go from gecko feet to Young's modulus and back again, explaining why wrinkling would increase adhesion.

We returned to the lab to set up another reading for the 0.12% solution, then went to lunch. The usual Friday fare was followed by a 4th year PhD candidate's explanation of her work. Liz is a graduate of Carnegie-Mellon with a degree in Chemistry.

She is working on nanoparticles for drug delivery systems, concentrating on the use of gold and PEG (polyethylene glycol) nanoparticles, which are amphiphilic and aggregate at an oil/water or nonpolar/polar liquid interface. We then returned to the lab to complete our work with the tensiometer.