Pondering Polymers

It’s an odd feeling to be graduating in less than a week.  I’m not sure it will truly hit me until I finish my last exam tomorrow.  Though I’m sad to move on, I am excited for the next big step in my education: Stanford University.  There, I will join one of the top ranked chemistry programs in the world and pursue a PhD.  I’ve got a lot of work ahead of me, but I look forward to tackling all sorts of new challenges while living on the West Coast.

Thank you to everyone who helped me out on my project: Mr. Dintersmith, Mr. and Mrs. Ayers, the W&M Charles Center, the Virginia Space Grant Consortium, Dr. Thompson, Luke Davis, the W&M Chemistry Department and my thesis committee.  You all have helped me take a firm step towards a life of learning and discovery.

I’ve been neglecting this blog the past couple weeks, but have been busier than I have all year working on the project.  Not doing research, but trying to get my thesis done.  As I churned out page after page, I found myself coming up with all sorts of new questions that I don’t have time now to pursue in the lab.  But after many long nights, I finally finished!  The final document is about 50 pages.

Of course, that’s not the end of the story, there was still the matter of the defense.  I had a jump on my presentation thanks to the honors colloquium I presented at in April.  Dr. Thompson tried to help go over potential questions I would receive.  The whole thing went down last Wednesday, and lasted over an hour.  I am thankful to all the professors who agreed to help me out.  I am also thankful to be done!  I was awarded high honors for my thesis.

As I mentioned before, one of the elements I’ve been trying to incorporate is polymer foam.  If we could metallize a foam with a hydrogenation catalyst, we could potentially create more surface area for the fuel cell reaction.  To create a foam, a chemical blowing agent is incorporated into the polymer.  At a certain temperature, the blowing agent decomposes into gaseous products, producing lots of small bubbles in the polymer that lead to foaming.  Azodicarbonamide (ACA) is one of the more common ones due to the high volume of gaseous products (carbon dioxide, nitrogen, some others) and low decomposition temperature (about 170°C).  This is a common process commercially, where polymers are produced by an extruder.  The extruder uses lots of high pressure and temperature to force the polymer out in whatever shape is desired.  We don’t have access to an extruder so we simply cast the dissolved polymer in solvent, then allow the solvent to evaporate.  Unfortunately, the latter method is not conducive to blowing agents because as you increase the temperature to decompose ACA, you accelerate the solvent evaporation.  If the polymer is not the correct viscosity when ACA breaks down, foaming will not occur: too runny and the gas will escape, too viscous and it won’t be able to alter the morphology.

I tried a lot of different combinations of ACA and solvent concentrations, I tried changing the solvent, and most of all I tried casting at different temperatures.  I had no success on polymer sheets.  I had some success when I put the polymer in a vial and was able to capture some of the bubbles, but the polymer still wasn’t able to return to its original shape after being deformed.

Finally, I went to one of our departmental seminars given by Masoud Agah, an engineering professor at Virginia Tech.  His group created what he called a “spider web” configuration for the polymer by spraying isopropyl alcohol on dissolved polymer.  The polymer is not soluble in alcohol or water, so it came out of solution as the fine mist of isopropyl alcohol landed on it.  I tried to reproduce this process on our polyimides.   At first the polymer went back into solution too quickly to be useful.  But then I switched completely to deionized water and saw some good results.

Not sure if it will have any benefit, given how late I got it to work.  But it goes to show you how sometimes you just have to keep your eyes open and a novel answer will present itself.

For any faithful readers out there, you are getting all the most exciting information straight from yours truly.  However, I’m pleased to report the research has gotten some extra publicity this past semester.  Most exciting for me was being interviewed for a William & Mary News story about 2009 Dintersmith Fellows.  I spoke with Mr. Jim Ducibella, who was both friendly and interested in what I’ve been doing.  He put together a great summary.  Some of it was even based on this website, so it will look pretty familiar.

http://www.wm.edu/news/stories/2009/dintersmith-fellows-explore-many-different-worlds-123.php#4

More significantly, our research has been published in Materials and Devices for Flexible and Stretchable Electronics, a publication from the Materials Research Society Symposium Dr. Thompson presented at last April.

Davis, Luke M., Stukenbroeker, Tyler S., Abelt, C. J., Scott, J. L., Orlova, E., Thompson, D. W.: Latent Patterned Surface Metallization of Silver Ion-Doped Polyimide Films, in Materials and Devices for Flexible and Stretchable Electronics, edited by Neville Moody (Mater. Res. Soc. Symp. Proc. Volume 1192E, Warrendale, PA, 2009).

Finally, our paper has been accepted to be presented next March at the 239th ACS National Meeting in San Francisco.  All of this is pretty run of the mill stuff for professional researchers, but for now, I find it very exciting.

It’s been a while!  After the summer ended it took me a little while to get back in the swing of things with a new courseload.  I always forget to appreciate how relaxing the summertime is.  Recently, I’ve been hard at work applying to graduate school.  It’s a pretty straightforward process, but it bogs down after so many applications.

I have gotten to work on a few things in lab.  The major focus at the end of the summer was trying to identify quantitatively how much of the silver was migrating.  As you can see from the TEM image a few posts ago, we are getting a layer of silver approximately 100nm deep.  Some of our calculations indicate that this layer should be thicker if it includes all the silver.  What could have happened to the rest?  Either is is not being reduced or it is not migrating.  Were we to determine one of these was occurring, it would open up a whole new set of questions.

At this point we are satisfied with the process, so this is more like troubleshooting than reworking anything significant.  To date we’ve not had much success diagnosing the problem, so we will probably have to resort to more TEM imaging early next semester.  Even if we can’t get 100% of the silver to migrate, however, we are still pleased with the current results.

Now that we are a week into the school year, I won’t be updating this blog as much.  I will continue to work towards a thesis with the silver 6FDA/ODA-DABA films and pursue the ACA foaming project as well.

I would like to extend a warm thank-you to anyone who has kept up with the blog.

Furthermore, the summer was made possible by the generosity of Mr. Ted Dintersmith, as well as John and Betty Ayers.  The opportunites they have provided to students like myself are crucial for promoting undergraduate research at William & Mary and training young scientists across this country. Thank you.

Although I may not be posting reguarly, I will continue to monitor the site for comments.  I would love to hear from you.

As I mentioned previously, our look at palladium-metalized films has applications to fuel cells.  I’d like to give a brief overview of what exactly that means.  A fuel cell produces electricity.  But unlike a battery, it requires a constant supply of new reactants to do so.  It operates using two separate chemical reactions, one called oxidation and the other reduction.  Electrons are forced to flow from the oxidation reaction to the reduction reaction.  This flow is harnessed into electrical energy.

One of the most common types of fuel cells is the hydrogen fuel cell.  This works by converting hydrogen and oxygen gases into water.  The fuel cell separates the hydrogen into protons and electrons and incorporates them into the water molecules.  See the link at the end of the post for an illustration.  For this reaction to work, we need two things.  First, the protons must be allowed to pass through a membrane separating the hydrogen and oxygen.  Of course, this membrane must be selective or else the electrons generated would pass through as well and hydrogen would be reformed, rather than water.  Several types of polymers are capable of this selectivity.  The most common one is called Nafion, and is produced by Dupont.

The second obstacle is overcoming the activation enegery.  Although the overall reaction is energetically favored (it releaseses engery, in the form of electricity), the half reactions require a catalyst.  Platinum and palladium are both capable of catalyzing the hydrogen separation.  Thus, our research into polymer metalization could help to create palladium-metalized, selective, polymer membranes for more efficient fuel cells.

Illustration (courtesy of GM Volt blog)

A quick update on the TEM.  I watched as Dr. Wei Cao operated the TEM and took some very nice pictures including the one below.  It is a cross section, so the darkest area is the silvered surface of the film.  To the right is the interior of the polymer and to the left is the resin that the sample is housed in. We expected to see more silver in the bulk (interior) of the polymer, but it appears all the reduced silver has migrated to the surface.  This is a promising result.

The visit to Jefferson Lab last Friday was a success.  Josh, a master’s student in the lab, and I drove down to the Newport News Facility and met Brandt, a technician there.  He helped us mount our samples and operated the SEM.  Josh ran his samples in the morning, and used the oportunity to learn how to run the instrument.  That was just the refresher I needed to jump on the instrument and run my samples without any help.  I enjoy working with the SEM because it’s a break from just strict cut and dry science.  When you are looking at a sample, you are constantly adjusting to get the best picture you can.  You never no what you might find, and exploring all the interesting features you come across is like looking at a foreign planet no one has ever seen before.  Here is one of my pictures.

Recently, Dr. Thompson and I have been talking about fuel cell applications for our polyimide metalization technique.  There is a nice description of fuel cells on Wikipedia, perhaps I will try to explain their operation in a later post.  The element we are concerned with is the proton exchange membrane.  If we apply our same metalization techniques to palladium and include a foaming agent, we could create a “metalized foam” to catalyze the key reaction.  So far we aren’t having much luck getting our polymers to foam, but we’ll keep trying.

Last summer I was also working in the Thompson lab.  My favorite part was being trained to use the Scanning Electron Microscope (SEM).  Light is made up of photons that have a wavelength between 400 and 700 nanometers.  Thus, the image from an optical microscope cannot have a resolution higher than that wavelength.  Electrons have a smaller wavelength than photons and allow you to see a sample in greater detail.  The SEM fires electrons at a sample, which results in the expulsion of secondary electrons.  A detector picks up these secondary electrons and can form an image.  There are numerous concerns when operating the SEM.  First you have to focus the beam of high energy electrons impacting the sample.  Second, you must choose how energetic those electrons are: too low and you won’t see anything, too high and the sample will heat up and obscure the display.  Additionally there are concerns about the strict vacuum in the SEM and maintaining an ion-free environment.  When operated correctly, the SEM is excellent at producing a 3D image of microscopic samples.

Transmission Electron Microscopy is somewhat similar.  It works by firing the same type of high energy electrons at a sample.  TEM, however, requires a sample that has been sliced on the order of hundreds of nanometers.  This allows the electrons to penetrate the sample and be detected on the other side.  It is basically like holding a flashlight behind a thin slice and seeing where it comes through.  Again, however, the electrons have a better resolution than photons in light.  TEM typically has slightly better resolution than the SEM.  However, it cannot process 3D samples and is typically used for cross sectional analysis.

Now the SEM has been moved from the WM campus to Jefferson Lab in Newport News.  I hope to drive down to their facility on Thursday and look at some of my films.  Additionally, I am prepping films for TEM analysis.  This involved embedding them in a resin and then using a super fine meat slicer, called a microtome.  Hopefully these instruments will give us a clearer picture of what is going on in our films.