-- GregKatz? - 19 Aug 2008

Tuesday, Aug 19

Conductive PDMS casting attempts

  • Took 3% wafer out of mold. This one was allowed to sit for 3 hours with weight and 2 hours without weight before being heat cured for 15 minutes at 85 C. It had one small section of small bubbles similar to the previous 5% sample. The rest of the sample was mostly smooth except for some tears distributed throughout the sample. These tears are not circular like the bumps/bubbles but long and skinny. They also go all the way through the sample. They also tend to have some curve or even an s shape to them.
  • Took 1% wafer out of mold. This one sat for 2 hours with weight and then sat over the weekend without weight and cured. This sample still had some problems especially in the good parts of the wafer. It had the same sort of small bubble-like roughness as previous samples. I felt as I was taking the sample out of the mold that it was getting stuck and ripping in these small circular areas. Under the microscope the wedges actually look really good. The bubble areas have no wedges at all and often are holes all the way through, but everywhere around these damaged areas the wedges are good. The bubble areas seem random except that they are more common in the parts of the mold that are deeper.
  • I am a bit stuck now since even at a low carbon concentration and without any heating at all, there was still imperfections in the mold. Possibly the worst thing is that the molds are made dirty because of the imperfections leave residue and this is very hard, possibly impossible to clean.

General strength of clamping force

  • Tried playing with 1% carbon and conductive ink dipped cantilever samples on frames at high voltage. Just from judging by eye, it seems that there is some difference in adhesive strength between 1% and 3% carbon whereas there was no difference between 3% and 5%. Also, the 3% seemed just as strong as the conductive ink dipped sample. My preliminary conclusion is that 3% carbon is enough to get some force and adding much more carbon is not worth it, but less may not be as good.

  • DSCF0010.avi: Movie of 3% carbon-sylgard clamping at just the cantilevered tip

  • DSCF0014.avi: Movie of 3% carbon-sylgard pdms clamping at 5kV sideview

  • Tried aluminum on Laurel's ball joint feet. The electrostatics actually do a decent job of pulling the foot flat against a surface at a few millimeters away with the 10kV portable supply.

Wednesday, Aug. 20

  • Tried casting 3% carbon with a tissue instead of a transparency so that the sample can "breathe". I degassed before and after pouring.
  • Sanjay and I did some encouraging tests with aluminized mylar on a frame behind "squeegee" wedges. The combo was easily holding a 50g weight on glass and the wooden door.
  • Laser CAMMMed more frames for the force sensor test set-up
  • Made high voltage insulating wires with new alligator clips.

Thursday, Aug. 21

  • Tried to make a aluminzed mylar sheet for testing on the force plate but I made the aluminum leads too thin and they burnt out under high voltage.
  • The casting with a tissue on it actually worked really well.
  • Tried casting 3% carbon with transparency again, but this time with less weight. The proess was compressed air and degas mold. Mix 30g sylgard with 1g carbon. Thinky mix for 2min then defoam in thinky 1min. Spread on wafer. Degas in wafer. Sandwich in transparencies. Squeeze down between flat surfaces briefly and not with too much force. Let cure without weight at room temperature but with top transparency still attached for about 16 hours. Remove top transparency and let cure at room temperature for another 24 hours.

Friday, Aug. 22

  • Made two test fixtures for electroadhesive force testing on Noe's set-up.
  • Changed the glass test surface on the testing arm. Needed it to be bigger.

Sunday, Aug. 24

  • Took the last casting attempt out of the mold and it looked excellent. It reproduced the surface perfectly and left no residue. Under the microscope the chisel tips look very good. The only problem is that the backing layer is 0.8mm thick. Ideally that would probably be more like 0.4mm or less. So I tried casting another one today pushing down with a little more weight for a little bit longer.
  • Tested to make sure that the casting was indeed conductive. On a mylar frame it did show electroadhesive force similar to what I have been seeing.
  • Made another test fixture for the force testing set-up.

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