PDMS
Removal from PFA Carrier Film
Transfer onto Acrylic Ring
Material Flexibility
Carbon Grease
Application
Consistent Thickness & Geometry
Carbon Nanotubes
RDEA Sample
Rolling efficiency
Electrode Connection
Lack of Displacement
DEA Samples
High-Voltage Failure
Displacement Measurement
PDMS
Consistent Manufacturing
Creating PDMS with consistent curing ratios, thickness, and size dimensions was very easy, but the difficulty came down to creating a sheet with a large candidate section. Pomona’s Physics chemical prep room made for a semi-sterile environment, but not enough to have clean and effective sheets of PDMS. Often, there were bubble deformities that had not popped before it began to solidify. Although the blade coater was cleaned between each use, somehow there still came to be tiny pieces of old PDMS bunched up and laying on top of our new samples. Both these issues creating divots, peaks, and nonuniform thickness.
There were also small flecks of dust that were incorporated into the mixture in the stirring stage, but without a controlled environment with no airflow this was inevitable. These dust particles also added to nonuniform thicknesses, and are suspected to have impacted the structural integrity of PDMS sheets. If a piece of dust was large enough to reach through the entire PDMS layer, the voltage delivery would not be according to plan and could even burn through the PDMS material (see DEA Samples : High Voltage Failure below).
Other impurities consisted of fingerprints and oils due to user error.
Removal from PFA Carrier Film
Although PFA carrier film was the best option for removing cured PDMS, there were still many challenges to it. The minimal thickness of our PDMS (.05mm) made it difficult to pull off the film without ripping, and although it differed for each curing ratio the overall process was tedious and had many scrapped pieces.
At the beginning stages of the lab, the PDMS sheets were peeled off and attempted to be placed on acrylic rings. Pulling the PDMS off required the experimentalists to touch the material with bare hands, resulting in residue. Gloved hands would not work due to the sticky nature of PDMS and latex. Often, when pulling the elastomer it would rip at the film-PDMS interface.
One method was attempted, where the PDMS/PFA sheet was submerged in warm water to loosen the elastomer easier, and then would be dried and applied to the acrylic ring. The water would also work to rinse off any dust particles on the surface. Unfortunately this process did not work better than the regular peeling method.
Improvements were made, and the removal process became that explained in the lab’s Methods section: attaching the acrylic ring + tape to the desired area of elastomer, then removing it from the PFA backing – several times the elastomer would stress and strain, leaving ripples in the PDMS sample.
PFA films are easily reusable in this material creation, but trying to remove the PDMS would often times cause the PFA to become dented or folded, irreversibly. If it were used again once being bent it would compromise the blade coating thickness and even PDMS curing.
Transfer onto Acrylic Ring
As stated above, removing the PFA backing caused large issues even when attached with the acrylic ring. The acrylic ring had double sided tape on the edges so the PDMS would stick better in those areas. It was attempted before to just have a PDMS-acrylic interface, but the elastomer only had friction to temporarily stay stuck to the acrylic and not adhere. Once the PDMS stuck to the tape and the PFA backing was removed, there was no efficient way to remove the resulting ripples in the outer edges of the desired material area. This may have caused discrepancies in our experiment, but with limited time it was not able to be avoided.
Material Flexibility
Sample 1 (10:1) had more curing agent in the mixture, making for a more rigid and sturdy piece of elastomer. Removing this from the PFA film was easier, but came with a large tradeoff of less movement under high voltage.
Sample 2 (20:1) had less curing agent in the mixture, making for a more flexible and pliable piece of elastomer. One downside of this was larger difficulty removing the sample from the PFA film because it would rip much easier under strain.
Making samples with different curing agent ratios made a difference, but overall for this experiment, Sylgard 184 product is not a suitable material once fully cured. The force generated by the capacitance was less than that of the intrinsic material force, and the material showed to be too stiff to see any movement, specifically in the RDEA test. Recommendations for future projects would be to find a material with more flexibility to see movement and easily remove off PFA film.
Carbon Grease
Application
Finding the right tool to apply the carbon grease had its challenges – a glass stirring rod had easy cleaning at the end but was advised not to use for tool longevity and continuously left a score on the grease from the curved end; a Q-tip was easily disposable but caused for much waste, cotton fibers would be left behind during spreading, and the same curved-end score in the grease also occurred; a metal spatula’s sharp corners could poke through and destroy the PDMS sample, and is difficult to apply in a circle. In the end after testing all tools, the metal spatula was deemed best fitting for most-even application
Initial application of carbon grease was done on a table with only the 0.125 inch thickness of the acrylic ring. Once contact was made with carbon grease application, the pressure that was put on the PDMS caused the other uncoated side to stick to the table. Upon removal, the sample ripped at point of contact. Improvements were made by placing the acrylic ring at a better height to have leeway for grease application pressure.
Consistent Thickness & Geometry
Applying a consistent thickness of carbon grease was done based on experimentalists’ estimation and intuition, but the actual thickness and evenness was not able to be verified. Carbon grease application could have been attempted via blade-coating, but the logistics of the machine would have made cleanup very difficult and possibly permanently tainting the machine. The consistency of the grease was also predicted to be unsuccessful when blade-coated, leaving patches of uneven application.
Geometry of the hand-painted carbon grease was again estimated by the experimentalists, applied in a relatively uniform circle to the best of their abilities.
Carbon Nanotubes
Carbon nanotubes would have been the most optimal electrode material, but due to safety reasons was omitted from the experiment. Using carbon nanotubes in a controlled environment with the necessary safety equipment would have allowed for blade-coating a uniform and thin layer of electrode material, and would have been more pliable and flexible under strain in the voltage tests.
DEA Samples
High-Voltage Failure
Our very first successful sample of PDMS-carbon grease DEA was tested on a voltage sweep up to 1.2 kV, but failed between 1.1 kV and 1.2kv. As you can see in the video, sparks fly and smoke appears. This is around the breakdown voltage we predicted for our PDMS, so from that point on, the experiment had a 1kV cutoff range, compared to the aspirational testing level of 3kV.
The initial test on Sample 1 was pushed to 500 V, and a spark was seen. Immediately lowering the voltage, there appeared to be no smoke or damage so tests continued. Tests were successful after that with that sample, maintaining its condition up to 1 kV. unfortunately, video of this voltage failure was not captured.
RDEA Sample
Lack of Displacement
Once creating an effectively rolled and applying a voltage sweeping 0 to 1 kV, movement was not visible under any voltage. We observed then observed some smoke, and it was assumed that there was a short in the circuit somewhere, most likely the electrode connection port. The next two samples also did not show any movement, when we measured capacitance with an LCR meter we found that the capacitance roughly aligned with what we expected. This means that they were functioning capacitors, so the lack of movement was concluded to be the PDMS material’s rigidity overpowering the electrostatic force. This was verified by testing the displacement of flat samples at different curing agent ratios.
INSERT VIDEO
Displacement Measurements
As discussed above under PDMS: Material Flexibility, Sylgard 184 is an unsuitable material once fully cured for this experiment, whether it be rolled or single-layer DEAs. Movement was much more visible for the single layer DEAs, but measurement of its displacement on a microscopic scale had its challenges.
If movement was occurring ono a nanometer scale, it could have been attempted to be measured on the displacement sensor. However, these tiny movements were predicted to be too small to effectively move the sensor and get a true measurement. Attaching one end of the PDMS section to the sensor would not have made for stable connection or facilitated effective movement. Instead, a more conventional measurement method was taken and explained below.
A grid as small as a printer could deliver was placed under the sample, and deformation of the PDMS was identifiable via grid changes. The units of the grid sizes were measured with calipers, measured in a 10×10 area and reconfirmed in a single-cell measurement. Being on such a small scale, the margin of error for each measurement was considerable.
Having the sample be a thickness above the grid also made for some optical errors when considering displacement measurements, because the distance from DEA to paper could be estimated but was not confirmed nor measured due to time constraints.
Many displacements on the grid were partial cell movements, so to the best of the experimentalists’ abilities was estimated to be 25% increment movements per direction. Future corrections for this error would be to have an automated non-contact displacement measuring tool functioning on a microscopic level, or a efficient and trustworthy way for experimentalists to see real displacement values on a grid.