The first step in our procedure is to select and cut which surface we wish to analyze. We have at our disposal large circular wafers of silica and titania. We pick one wafer and then place it face down on a piece of paper in order to determine where to cut. The dimensions we use are 1 inch 𝘹 1.5 inches. Then a scriber tool is used to trace and cut the size needed from the large wafers. In this case since I have a partner, one person will handle the silica and the other person will handle the titania. During the course, we found that characterizing and measuring six individual samples was feasible and reasonable per person. So, after six samples are obtained they are then placed in a glass petri dish without the top and go into the plasma cleaner.
The plasma cleaner is first given power and the pump is turned on. We make sure all values are closed and allow the pressure to drop to 250. Then the rf level is dialed from off to high and we try to maintain a pressure of 350 at this point by opening the value slightly. This is kept for approximately 15 minutes. After the time has expired, we dial the rf level from high to off and turn off the pump. We then open the main valve to release the pressure inside and then turn off the power.
When the samples are done is the plasma cleaner, the silica needs to be analyzed by the ellipsometer. Titania has a high refractive index and a rough surface, thus is exempt from any measurements using the ellipsometer.
The ellipsometer is given power and approximately 10-15 minutes to warm up. The ellipsometer works with the computer to analyze data so the computer is also turned on. The correct program and file is selected and then a standard is taken every time the ellipsometer is used for that day.
After this, the six silica samples are then placed face up and the initial thickness is recorded in angstroms (Å). For each sample, three thickness measurements are recorded. When all silica samples are done being recorded, they are placed in glass vials. At this point, the titania samples are put in glass vials as well. Using a weighing scale, the mass of all samples are recorded. Once finished, we add approximately 3 drops of hydridomethylsiloxane (HMS) via syringe. The mass of HMS added to each sample is also recorded. Once this is done, all samples are placed in an oven set at 60℃ for 72 hours.
After the 72 hours, the samples are taken out of the oven and go into the hood to be cleaned. Throughout our research we have only determined two cleaning methods, the first method is to rinse the sample with toluene, acetone, water in that order. The second method is to rinse the sample with ethanol and water in that order. The cleaning method selected is based on which compound is added to the surface of our samples. In this case, after adding HMS, the first cleaning method is applied. When all samples are washed, then enter an oven set at 100℃ for a short time to get rid of any remaining water left on the sample. Once no more water is visible, samples are taken out and placed in a 24-well plate. At this point, all silica samples need to be characterized and recorded for thickness again. All titania samples simply only need to be characterized.
Characterization of samples is done using a static goniometer apparatus. To use the goniometer, the power to a light need only be turned on. After every other use, the water in the syringe is replaced with deionized water.
For the goniometer, all samples need three advancing and receding contact angle. Additionally, they need to be recorded from both the right and left side. This means for one sample, 12 contact angles are recorded. Once silica is done being characterized, they head over to the ellipsometer. Once titania is done, it is prepared for the next reaction.
When silica is being re-measured for thickness using the ellipsometer, the same procedure is followed. The only changes that need to be made are related to refractive index (Nf) and preset thicknesses. When the program loads, options for refractive index and preset thicknesses open. In this case, we have our initial thickness we previously recorded and enter the average initial thickness as thickness 2 with a Nf 2 of 1.46. Thickness 1 is set to 100 as a ballpark estimate and given a Nf1 of 1.40.
Once all measurements are done, they are placed in glass vials with Teflon tape wrapped around the ridges where the cap tightens and the same is done for the titania samples. After this, all samples are given .1 mL of platinum catalyst via syringe placed directly on the surface of our samples. Then a 50:50 mixture of our experimental compound and toluene is made in order to fill each vial with 2 mL. When this is accomplished, all samples go into the oven set at 60℃ for 72 hours.
After the 72 hours, the samples are taken into the hood and are rinsed accordingly using the proper cleaning method. After they have been cleaned, they enter the 100℃ oven for a short time and then enter their respective well plates. The same procedure follows for silica, these samples need to be characterized and re-measured for thickness. Titania samples only need to be characterized.
For silica, when re-measuring for thickness, the thickness 1 value would be set to the average HMS thickness recorded and the Nf1 value set to 1.40. The thickness 2 and Nf2 values remain the same.
The purpose of doing this research is to provide insight in controlling the surface properties of inorganic oxides as it has profound impacts on anti-fouling, adhesion, and other applications. Our goal is to analyze and interpret the data collected from contact angles and ellipsometry. We expect to learn more about different surface properties via an interfacial hydrosilylation reaction and how it further affects contact angle hysteresis. The main methods that will be applied throughout this research is ellipsometry and goniometry. The purpose of ellipsometry is to verify if the reaction took place. This is seen as the thickness of these samples increase. Goniometry looks at the angles made by adding or removing water on the surface. The hysteresis is analyzed by subtracting the advancing contact angle from the receding contact angle. This tells us how homogeneous or uniform the surface of our samples are. A high hysteresis value is indicative of a surface that is not homogeneous and a low hysteresis value means that the surface is rather homogeneous.
Recently, our work was presented at the ACS Conference in Orlando, FL. Additionally, my partner and I both presented in Dyson Society of Fellows at NYC and Pace Science Day.
I’m glad I was selected and began conducting research at such an early point in my college education. It is a privilege to work under Dr. Krumper and it pains me to see him leave Pace after all he has done for me. I was fortunate to have such an amazing and brilliant research partner like Giovanni throughout the course of our research. I have a lot of great memories from the time we started up until our last day. When I first started out, I was oblivious to how much work and technique was necessary for research. We made a lot of painful mistakes along the way that honestly made me want to quit research. It takes a lot of patience, repetition, and perseverance to achieve the desired results. Researchers don’t get enough credit for the work they have to put up with and do. I look forward to the next time I do research in the near future.
What I Learned
I have learned a lot with regard to this project, both conceptual understanding of the reactions and tactile research experience inside the lab. The research I’ve done has enlightened my comprehension when looking at surfaces that have specific properties. Lastly, my time in research has made me more excited about our future upcoming paper.