Tensiometer and Dissertation Defense

We arrived early 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. A. Crosby's group. This is Mr. 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. 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. After about an hour, it was not Mr. Chan anymore, it was Dr. Chan, he had been awarded his PhD. Congratulations!!
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.

Final entry for RET experience.

Some link and info:

Sabra's experience

Dave's experience

Lauren, Mary and Renee's experience

Thanks Go Out To:

Dr. Thomas P. Russell
Dr. Narayanan Menon
Dr. Greg Dabkowski
Jiangshui Huang
MRSEC
NSF
PSE staff and students
UMass - Amherst
Bill Brewer
Joe Alvarado

More Tensiometer!!

Just because I use exclamation points does not mean its a bad thing, its actually very interesting. Today was all tensiometer since we need to get data for each surfactant concentration and several readings for each. The 0.03% solution results from yesterday are 59, 60, and 61. We are satisfied that this surface tension is around 60. We then empty the 0.03% solution from the syringe, and rinse the syringe three times using the 0.06% solution. We then set up the tensiometer to take three readings on this solution, and the surface tension of the 0.06% solution was determined to be 50, 51.5, and 51, so the average surface tension is 51 for 0.06% surfactant solution. We will continue with the remaining solutions tomorrow.

AFM, Tensiometer and Dr. Menon

Today we were shown how the Atomic Force Microscope (AFM)works. This is one of the things I have enjoyed most being here, just seeing and sometimes using all the different devices I have ready about. We will not use this instrument, but Ji Xu explained the principles of its operation and how to use it. He was very helpful and did not mind all the questions I asked. :-)

The AFM is not optical; it has a tip (visible only using an optical microscope) that vibrates vertically in response to an oscillating voltage, so that in effect it gently taps, very gently, the surface of the sample at a constant amplitude as it moves along its surface. The constant amplitude of the tapping allows the tip to move up and down with the variations of the topography of the sample. The tip is attached to a cantilever which is just barely visible to the naked eye; this is attached to a black matrix that is large enough to be manipulated into position on the instrument. Prior to analyzing the sample, the AFM must be calibrated for that specific sample. First, the tip size is selected; the smaller the tip, the higher the possible magnification. Resolution is determined by the number of oscillations, or vibrations, of the tip on the sample surface, and magnification is again affected by the amplitude of the oscillation of the tip.

A laser beam shines down onto the cantilever and, as the tip moves across the topography of the sample, the beam is reflected at different angles. The reflected laser is collected by receptors that are analyzed and interpreted by the computer to create images. Ji Xu has hexagons that self-assembled as his polymer annealed. A close up of one of the hexagons is seen below, from the AFM, the other picture shows the sample in an optical microscope, the hexagons are the tiny dots to the left of the large drop.


After lunch, we then set up the Tensiometer to measure the surface tension of the 0.03% solution again.

At 2 pm we went with Jaingshui to meet with Dr. Menon of the physics department in Hasbrouck. The first discussion focused on our progress with wrinkling, use of the reflectometer, and data analysis with ImageJ and Origin software. We then discussed problems that we could encounter using the surfactant. The surfactant is amphipathic, and the polar tails actually stick up from the surface of the water, making the environment at the surface of the drop different from the drop's internal environment. The same is true in a bowl of water/surfactant solution: the hydrophobic tails of the surfactant stick up while the hydrophilic heads are oriented toward the water. In the rest of the water, the hydrophobic tails of the surfactant are attracted to one another and form mycellae. The mycellae eventually form spheres (head to head/tail to tail attraction). If the spheres are broken apart (agitation, heat) they may reassemble as cylinders. If the concentration of the surfactant continues to increase, and the cylinders are broken apart, then lamellae may form. The formation of these various structures is dictated by the general rule that material tries to form the geometrical shape with the smallest surface area relative to its concentration.

Jiangshui then discussed the next focus of his research with Menon. Jaingshui will be working to create experimental evidence to support the mathematical explanation for wrinkling patterns when a force, using a tip, is applied to the surface of the film.