Step 4: Bond Top and Bottom Layers

step4-1.png
  • The next step involves using a thin layer of Ecoflex 0030 to bond the top and bottom halves of the sensor. If the layer is too thick, it will plug the channels. To ensure a thin, uniform layer a spincoater is used.
  • The spincoater should be set to 2000 RPM for 60 Seconds.
  • As done in the previous step, mix a small amount of EcoFlex 0030 and degas it.
  • Refer to the Bill of Materials section for vendor information for EcoFlex.

 

 

 

 

 

 

Add Adhesive Layer
step4-2.jpg
  • Place the bottom mold into the spincoater and spin briefly to test that the vacuum works. The spincoater chuck should be completely covered by the mold to ensure a good seal.
  • Peel off the transparency at this time and remove any excess elastomer around the edges.
step4-3.jpg
  • Pour the EcoFlex onto the mold, making sure to wet as much of the surface as possible.
step4-4.jpg
  • Run the spincoater program for the full 60 seconds at 2000 RPM. 
step4-5.jpg
  • In the meantime, demold the top half of the sensor (the one with the channel grooves) from its mold.
Set New Layer in Oven
step4-6.jpg
  • Remove the bottom mold from the spincoater, and place it in the 60 oC oven for 40 seconds.
step4-7.jpg
step4-8.jpg
Align Layers
step4-9.png
  • Next the two layers need to be aligned correctly. Holding the bottom half steady, the top half will be lowered gently onto it. The side that contains the channels will be face down.
step4-10.jpg
step4-11.jpg

 

step4-12.jpg
  • Similar to how the transparencies were applied, slowly lower top piece from one end to the other, being careful to keep alignment and to avoid trapping air bubbles. Use tweezers to guide the top half.
  • Use the tweezers to push out any bubbles that do appear as well.
step4-13.jpg
  • Try to avoid “scooting” or going backwards if possible.
step4-14.jpg
  • Once you reach the end, use tweezers to align the top piece to the pegs again.
  • Cure in the oven for 5-10 minutes.

 

Bibliography

Mengüç et al. (2013) Soft Wearable Motion Sensing Suit for Lower Limb Biomechanics Measurements.

Mengüç et al. (To appear in 2014) Wearable Soft Sensing Suit for Human Gait Measurement.

Miserez et al. (2008) The Transition from Stiff to Compliant Materials in Squid Beaks.

Muth et al. (2014) Embedded 3D Printing of Strain Sensors within Highly Stretchable Elastomers.

Vogt, D. M., Park, Y. L., & Wood, R. J. (2013). Design and Characterization of a Soft Multi-Axis Force Sensor Using Embedded Microfluidic Channels.

Contributors

Yiğit Mengüç