Final Blog Post Summer 2019

Giovanni Fardella

Summer 2019 Final Report

Hydosilation of (Poly)hydridomethylsiloxanes as an Approach to Mixed Surfaces

            Silicon is arguably one of, if not the most influential elements of our generation; the myriad of applications associated with silicon chemistry and engineering lends credence to its versatility. If you need further proof of this, look down at your computer or smartphone. The defining feature of these electronic devices is their complex circuitry and processers, which are made possible by their silicon semiconductors.

Chemically speaking, silicon is unique in that it acts in a similar manner to carbon, the hallmark element of organic matter. However, silicon differs from carbon in that its dipole moment, or a measure of the element’s ability to pull electrons towards it in a molecule through a bond, is less than carbon. Because of this fact, hydrogen-bonded to silicon can act as an anion, or a negatively charged atom, and dissociate from silicon. This detail was the inspiration for our experiment. We wanted to see whether or not the siloxane polymer, hydridomethylsiloxane (HMS), could undergo hydrosilation and be used as a base for subsequent reactions.

The reaction mechanism for hydrosilation is rather straight forward. In the presence of heat, the hydrogen atoms in HMS can dissociate from the silicon atom and form diatomic hydrogen gas. At the same time as the dissociation, a vinyl group may donate its two electrons and attack the silicon atom. This, in turn, forms a new bond with the vinyl compound and our siloxane polymer. We first reacted our HMS with a silica substrate. Upon characterization with a goniometer and ellipsometer, we ran a second reaction between our new HMS surfaces and the desired vinyl compound. By comparing ellipsometric thicknesses and contact angles, we were able to discern whether or not a reaction had occurred. We also ran a specific type of spectroscopy called X-ray Photoelectric Spectroscopy (XPS) in order to visualize and quantify the relative abundances of elements on the surface of our samples.

With the exception of two reactions, all of our experiments yielded desirable results that supported our initial hypotheses. The silica samples all show an increase in surface thickness after each reaction. Our contact angle measurements also showed changes that reflected the indicative surface chemistry of the added compounds. For example, upon reacting styrene with our surfaces, we saw a clear increase in the surface thickness, as well as hydrophilic contact angles and an increased hysteresis. XPS also demonstrated a clear increase in the carbon to silicon ratios, thereby supporting our previous characterization.

Out of the twelve reactions we ran, three, in particular, gave us the most trouble: 4-vinyl pyridine, allylamine, and perflourooctene. We were unable to detect any nitrogen atoms on the surfaces of our samples with XPS. This leads us to believe that their high basicity may have denatured our surfaces. Additionally, the XPS analysis of our perflourooctene samples yielded fluorine atoms on some surfaces, but not others. Contact angles for these surfaces were also heterogeneous among the sample set.

One interesting aspect of our surfaces is that we can perform several reactions in order to fine-tune the chemistry to our liking. This would yield samples with the characteristics of both compounds, or a mixed surface. In order to demonstrate this, we reacted to our perflourooctene samples with ethyl vinyl ether. Another advantage of this reaction is that we can run experiments with mixed reaction vessels (i.e, a reaction between two different types of vinyl compounds). with ethyl vinyl ether and styrene. Analysis of these reactions appears to indicate a successful experiment due to a clear shift in contact angles, as well as an increase in ellipsometric thicknesses.

Although our work for this summer has concluded, we would like to further expand upon our research by refining the process of hydrosilation via mixed reaction vessels. At the current moment, our research has applications in a myriad of fields ranging from mechanical engineering and medical implant technology. As I reflect on my research experience this summer, I have come to realize that the most important skill I learned is patience. Research can be extremely rewarding, but also terribly monotonous. My newfound patience helped me to persevere through the repetitive analysis and stay motivated throughout the summer. Moreover, I have really enjoyed my summer project and hope that I may continue to research with other professors in the near future.

Blog 2: Continuation of hydrosilation and modification with vinyl bearing siloxanes and perflouro-octene

As the summer has progressed, my research team and I have made great strides in our project. Within the past month alone, we have successfully engineered surfaces with multiple siloxane layers of varying structures. Via hydrosilation, we reacted tetravinyl-tetramethyl- tetrasiloxane, a cyclic siloxane, with our HMS surfaces. This was done in order to confirm whether or not can we layer siloxanes and induce chemistry similar to the HMS monolayer. Likewise, we also reacted a straight-chain, vinyl terminated siloxane polymer and obtained similar results.

Additionally, we have begun to build off of our siloxane monolayers with perflouro-octene. Our initial results with fluorine chemistry were varied as several of our samples were less than ideal; some samples supported our hypothesis while others did not. We had expected our samples to be more hydrophobic due to the conformation of perflouro-octene; the spiral structural conformation is the most stable and should have induced hydrophobic interactions. We will be rerunning this specific experiment in an effort to try and obtain more consistent results.

Moving forward, we hope to obtain data for reactions with vinyl amine and PEG (polyethylene glycol). Amine chemistry is extremely important with a wide array of applications across many fields. PEG is a polymer that has traditionally been used in the medical field due to its high hydrophilicity. PEG has been used in medical implant technology, hydrogels, and targeted drug delivery. It is my hope that we can obtain the chemicals before the end of the summer in order to be able to run these experiments and obtain meaningful data.

Blog 1: Hydrosilation of polyhydridomethyl siloxanes as an approach to mixed surfaces

Surface chemistry is an immensely important and often overlooked subset of chemical research. With how important tactile interactions are to our society, an increased focus on tactile interactions would allow us to fine tune surfaces in order to fulfill specific needs. However, the process of modification must be cost-effective and efficient to warrant further research; this is where my research comes in.

For the past year, I have been experimenting with a polymer called (poly)hydridomethylsiloxane, or HMS for short. This polymer is unique in that after coating a surface with it, we can perform subsequent reactions to fine tune the surface chemistry and achieve the desired function.  These subsequent reactions are called hydrosilations. So far, we’ve reacted a wide variety of chemicals with a vinyl functional group (i.e. a double bond) and characterized their effect on the surface. As for the surfaces we’ve used, we have focused on inorganic oxides. As the summer progresses and our research nears its end, we hope to finish our research and begin sorting through the wide array of data that we have collected.