Experimental Trial: Phase 2Experimental Trial: Phase 2This project involves the development of a microfluidics device which would function to meet our goals, and which could be fabricated by us. It is very important to consider the manufacturing process when working towards a final proposed design. This is important because manufacturing constraints are the largest limitation to our design. We were able to design, fabricate, and test two prototypes of the phase two design. Both prototypes met some of our goals, and fell short of achieving others.Our testing set up consisted of a (size?) syringe to inject liquid into the inputs of our device, and water colored with food coloring. We found that lighter shades of orange,red, and green showed up the best against the silicon wafer. For both prototypes, we injected liquid into each of the 5 inputs, and recorded the result. We also tried injecting liquid into the outputs and observed the results.The first experimental prototype had several large problems, making it very difficult to test. The PDMS layers were thicker than we had anticipated, and therefore theinterconnects did not transfer from the mold to the PDMS layer. The result was that our layers were not connected to each other, and the top layer sealed the channels from the outside. This limited us to testing the channels that were oriented only in the horizontal direction. This problem also made it difficult to inject liquid into the inputs, since the top layer of PDMS sealed them off. We solved this problem by poking through the top layer with the syringe, and injecting the liquid into the input, under the top layer. This technique worked, but had limitations. We observed no capillary action in the channels, meaning that the liquid would only move through them with applied pressure. This required a seal between the syringe and the top layer of PDMS, otherwise the injected liquid would flow out around the needle and not into the channels. This problem was corrected by sealing the channel with the needle in it using applied pressure from a finger.Once we were able to inject liquid into the channels we observed some success in moving the liquid through from input to output. Unfortunately, there were many air bubbles between the PDMS layers, causing the liquid to spread out and fill the air bubble instead of staying in the channel. Many of the problems we encountered during fabrication and experimentation were corrected for the second prototype.The second prototype had many improvements over the first trial. Each layer wasthe correct thickness, allowing for interconnects between layers. The layers were aligned with good accuracy, meaning the interconnects connected the channels on both the top and bottom, and the inputs and outputs were open on the top layer. There were no air bubbles between PDMS layers. With the more accurate fabrication of the design we were able to achieve several of our goals in testing. We successfully got liquid to flow in all five channels using applied pressure from the syringe. We were able to push liquid all the way through two of the five channels. We also observed two colors of liquid one on top of the other, as designed, proving that our channels were accurately fabricated.We observed some of the same problems that we had encountered with the testingof the first prototype. We observed no capillary action, so we had to jam the needle into the end of each channel to obtain a seal. In doing this, the layers sometimes delaminated near the end of the channel. We once again corrected this problem by applying pressurebehind the needle opening with a finger. Our biggest problem with getting fluid to flow through the channels occurred at the interconnects. We could not get fluid to flow vertically in any of the trials. In the channels that included vertical interconnects, the liquid would stop flowing when it reached the interconnect. To deal with this we applied more pressure to the fluid and the layers delaminated around the interconnect. This problem could have been caused by either our design or the fabrication of our
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