Week 8 and 9 Results

The product of the PAN/DMF electrospinning was a relatively dense mat of white nanofibers. Technically speaking, this was the intended product; however, in order to unlock the conductive properties of the nanofiber so that it could be used in a capacitor, calcination was required. Calcination is the specific process of heating PAN/DMF nanofibers up to the immensely hot temperature of 580°C in order to stabilize their molecular structure. This stabilization is a result of the cyclic voltammetry that PAN undergoes at this temperature; it becomes both very brittle and very resistant to chemical or physical change.

Before Calcination

After Calcination

 














The two samples were also put under a Scanning Electron Microscope. The following images are ordered from highest zoom to lowest zoom.

After Calcination

Before Calcination

As you can see, the post-calcination nanofibers are much more condensed than that of its pre-calcination counterpart. Also, the post-calcination nanofibers are much more brittle, and have clearly defined angles in the curves of an individual strand. This ultimately allows for the nanofibers to be used as a conductive substance because it allows for a high energy density in the nanofiber electrode.


After the successful calcination of the PAN/DMF nanofibers, the resulting black sheet of nanofibers was divided into several disk-shaped electrodes. These electrodes, when combined with an electrolytic solution of sulfuric acid and an insulating separator, would make a capacitor. Ensuring that all components were thoroughly covered in the sulfuric acid, two of the disk-shaped electrodes were separated by an insulating separator, and then attached to two separate pieces of graphite that would serve as connectors for the two halves of the capacitor. The resulting capacitor was then covered by two small slabs of acrylic so that it would remain isolated from its surroundings.

• The created capacitor was then attached to a data collector, which proceeded to run various tests on it. The first test, called Charge Discharge, measured the total energy that could be stored in the capacitor. The second, PotentiostaticEIS, measured the internal resistance of the capacitor. The third and final test, titled Cyclic Voltammetry, measured the stability of the sample over a wide range of currents.

Cyclic Voltammetry

Charge Discharge

PotentiostaticEIS

• Based upon the performance tests and analysis, the capacitor exhibited a capacitance of 240.7 milliFarads. This translates to 100 Farads per gram, the standard units used in capacitance. For a relatively small capacitor (the size of a human thumb) this capacitance is extremely efficient compared to the typical capacitance of a capacitor, 185 microFarads [10].

Week 7 - Well Design

While our testings with the K'nex electrospinner seem to be doing quite, we've realized that the well holding the polymers we are testing is not the most ideal shape. The height of the well just reached the spindles on the gear and the area of 64 square centimeters resulted in more polymer to be tested than necessary. Because of the flat shape, when polymer was poured in, it would fill the entire bottom before actually reaching the spindles on the gears. This caused a large percent of our polymer solutions to become a waste as they were no way near spindles. It takes time and money to create polymer solutions; therefore it was necessary to create a new well that would require the least amount of polymer to be used as possible.

New Well Design

This new well design has a cylindrical shape in order to fit with the electrospinner's gears. It also reduces that amount of polymer needed to reach the spindles. There is a small rod projecting out of one side of the well that will allow the copper wire to feed into the solution. This was, the electrical current can run through the solution and the copper wire is not as exposed as it used to be, reducing the likelihood of someone getting shocked. The rod was placed at a raised angle so as to not allow the solution to flow out of the well. All that remains now is to wait for the well to be 3D-printed and test it out. Hopefully all this well won't react with the solution and we can continue electrospinning.

*The well design was created by Travis Weiss

Week 6 Progress

Ultimately, our goal is to create a sample of nanofiber that is capable of being used in a capacitor. Unfortunately, we ran into a few complications in the past week. Our initial test-run had been spun using PEO; however, in order to obtain a sample that could be calcified, and thus used in a capacitor, we needed to spin a sample using PAN (Poly-Acrylic Nitrile).

Today, during a PAN trial, instead of collecting a usable sample, we obtained a spider web type of structure that extended from the collector plate down. Upon consulting with Dr. Kalra, it was determined that the most likely cause for this was the moisture in the air. Apparently, when the air contains too much moisture, the gaseous water particles interfere with the electric field that directs the nanofiber jet to the collection plate. Using a meter, we determined that the air has a humidity percentage of 48%. To cope with this, we injected pure oxygen into an enclosed box to drive the moisture out of the air. When the box reached only 20% moisture, we ran the spinner again, however, the sample didn’t spin as it should have. At this point, the sample of PAN and DMF had become a gelatinous solid because so much DMF had evaporated out of the solution. It takes a full day to properly stir a solution, so that concluded this week’s tests. 

Week 5 Results

During lab on May 2, the group began our first actual trail on the electrospinner. This time we had ample time for nanofibers to form. For this test, we once again used the PEO polymer, however, this one dated more recently to April 27, 2012. All other variables to the electrospinner remained the same, with the gears being seven centimeters apart and a total of 12 strings attached to the gears, with the exception of the shiny side of the aluminum foil facing upwards, away from the gears. 


While this trail was successful, we decided we needed to better optimize the tray holding the PEO so we would not need to pour as much polymer. Not only do we want to make the tray smaller, but we also want to the tray to be closer to the gears. This will allow less polymer to be used, as well as, attach to the strings of the gears faster. 


If you observe the attached video, you can see the nanofibers begin to form and attach to the foil. The sharp white lines that show occasionally are the nanofibers. 

Once we were able to attain nanofibers, we took a sample down to our advisor's lab to view it under a high-powered microscope. The resulting images (shown below) displays a magnified view of what our first batch of nanofibers actually look like!

 

Week 4 Results

During lab on April 25, the group began our first tests on the electrospinner. Unfortunately, due to problems with strings attached to the gears, we were only able to have the electrospinner run for about 10 to 15 minutes. Initially the original width between the gears was greater than the pan holding the polymer, meaning we were required to restitch the strings on the gears twice. The second time, the strings would not stay attached to the gear, meaning I had to consistently restring the gears. Due to this time constraint, it gave little time for nanofibers to form that would be noticeable.

For this test, we used a polymer provided to us by our advisor of five weight percent PEO H₂O SSA (with no salt) dating back to February 16, 2012. The gears were separated seven centimeters apart from the inside of each gear and with a total of 12 strings able to hold the polymer droplets. The aluminum foil was place above the gears, with the shinier part of the foil facing down towards the gears and polymer. Inside the aluminum foil was a sheet of copper mesh that assisted in collecting nanofibers. If you look closely you can see droplets of polymer attached to the strings. However, the sheerness of the polymer would make it difficult to see any nanofibers heading for the aluminum and with time constraints, there is little chance any nanofibers can be seen on the aluminum by the naked eye.

The Electrospinning Process

While looking around on YouTube, I found a few interesting videos that highlight a few aspects of electrospinning:

The first video (below) shows an actual stream of nanofiber coming out of a charged syringe. At first, the stream is very well-defined, ; however, it soon becomes blurry due to rapid movement. This movement is an observable phenomenon in which the charged fiber forms a natural cone in an attempt to distance itself from the rest of its own identically charged length.

http://www.youtube.com/watch?v=87uRQ7KwbB0

As a side note, just as the nanofiber solution leaves the charged syringe, another natural phenomenon can be observed in the form of a Taylor Cone (labeled in the picture below). A Taylor Cone is fascinating because it refers the the tendency for a droplet of liquid/solution to deform from its normal spherical shape in the presence of excessive charge. This deformity causes the solution to be stretched into a fiber that measures in the nanometer scale, and thus creates nanofibers.

http://www.chromacademy.com/Electrospray-Ionization-ESI-for-LC-MS.asp?tpm=1_1

One other video caught my interest because it adequately describes the process through which we have decided to electrospin. As shown in the previous YouTube video, a typical elctrospinning setup includes one charged syringe, and thus, only one jet of nanofiber. This setup works, but is not efficient because it could take ninety minutes or more to create enough fiber to have a workable sample. However, as shown in the video below at time 1:50, various groups are in the process of designing a more efficient method of electrospinning. We have taken this type of design as our model, and hope to optimize it for the most efficient production of quality nanofibers. While the segment of the video from 1:50 - 2:12 deals with the basis behind our design, the rest of the video provides a general overview to the entire proces of nanofiber production.

http://www.youtube.com/watch?v=zhZ2u_tZFP4&feature=related

April 25th Events

Today Matt and I went to lab to create our first batch of polymer solution, which will eventually be tested in our K'Nex electrospinner. It was rather simple to create the solution, as we just collected the components, carefully massed them on a high precision scale, and mixed them together. The solution consisted of 4.5 grams of dimethylformamide and .5 grams of polyacrylontrile. Below is a picture of the finished solution:

This solution has undergone various testings at Drexel in the past, and once electrospun a nanofilm of this solution will calcinate into carbon nanofibers at approximately 800 degrees celsius. Later in the week, (once the components are completely in solution) Matt and I will use this solution in electrospinning (with an electrospinner from another lab) and practice our first calcination.

Meanwhile, Nikita and Travis have successfully completed their initial design for our K'Nex Electrospinner! While there will be optimizations to be made based on electrospinning tests, the base design is complete and the group is right on schedule with making a successful K'Nex electrospinner, and using it to electrospin a polymer solution that will be calcinated into carbon nanofibers. In lab later today our group will be conducting the first tests on this electrospinner, and noting improvements that need to be made. Later Nikita will add pictures and data from the first electrospinning trial.


-Nick Pescatore