Fabrication Process of Silicone-based Dielectric Elastomer Actuators

The overall goal of this procedure is to fabricate robust dielectric elastomer actuators. In this video the fabrication of an in-plane actuator. Consisting of a silicone membrane stretched on a frame is shown.

with compliant electrodes stamped on both sides. Thanks to their large actuation strengths, dielectric elastomer actuators have many potential applications. However the manual production processes used to fabricate them have limited their usage in commercial products.

The main advantage of this technique is the ability to manufacture reproducible and robust actuators with precisely defined shapes. The use of low-loss silicone elastomers allows for a fast actuation response. Although the procedure presents the fabrication of an actuator, the same technique can be used to fabricate dielectric elastomer generators and stretchable strain sensors.

To begin sacrificial layer casting cut a 400 millimeter long sheet of high quality 125 micron thick polyethylene terephthalate or PET from the roll. Lay the PET substrate on the vacuum table and turn on the vacuum pump. Place the profile rod applicator on the automatic film coater and set the coating speed to five millimeters per second.

Then put two milliliters of sacrificial layer solution in front of the profile rod and start the coater machine. Next, retract the film applicator but leave the vacuum pump running and leave the PET substrate on the vacuum plate. Let the layer dry in air for two minutes.

For silicone membrane casting add 15 grams of silicone base and 1.50 grams of crosslinker to a mixing pot. Then add 10 grams of silicone solvent to decrease the viscosity. Mix the silicone mixture with the planetary mixer.

Use a two minute mixing cycle at 2, 000 RPM plus a two minute degassing cycle at 2, 200 RPM. Next set the height of a universal applicator to 225 microns. Place the applicator at the top of the PET sheet and set the film applicator speed to three millimeters per second.

It is critical to obtain defect free membranes by avoiding the inclusion of dust particles during the casting process. We do this by working in a clean environment and by carefully cleaning the substrate before coating the membrane. Transfer 10 milliliters of the silicone mixture from the mixing pot to the PET substrate with a syringe.

Start the automatic applicator to apply silicone over the complete PET substrate. Turn off the pump and wait for five minutes to let the solvent evaporate from the cast layer. Transfer the membrane onto a glass plate and place in the oven for 30 minutes at 80 degrees Celsius.

After 30 minutes remove the membrane from the oven and leave it to cool down at room temperature for an additional five minutes. Then cover it with a thin PET foil to protect the surface from contaminants. Fabricate the prestretched support and membrane support and cut the cast silicone membrane/PET substrate sandwich as described in the text protocol.

Fix the laser cut prestretched support onto the cut silicone membrane circle adhesive side down, such that the adhesive is in contact with the silicone surface. Prepare a bath of boiling water and submerge the assembly including the silicone membrane and the adhesive support into it. Whilst submerged, gently and slowly peel the PET substrate away from the silicone membrane until they are completely separated.

Remove the silicone membrane from the water bath and let it dry. A nitrogen gun can be used to speed up the drying process. Measure the thickness of the membrane with the transmission interferometer according to the manufacturer's protocol.

Set the prestretcher to a diameter of 45 millimeters and place the prestretched support silicone membrane on the stretcher fingers, adhesive side down. Cut the prestretched support between the stretcher fingers. Then place the radial ruler on the stretcher and rotate the prestretcher annulus anticlockwise to increase the diameter of the prestretcher to 58.5 millimeters to equibiaxially prestretch the membrane by a factor of 1.3.

Next remove the cover film from the PMMA membrane holder exposing the adhesive. Stick the PMMA membrane holder onto the prestretched membrane surface. Cut around the membrane holder to remove the prestretched membrane from the stretcher.

Then measure the final thickness of the prestretched membrane with the transmission interferometer. To set up the pad-printing machine install the cliche with the desired electrode pattern on the magnetic block. Place the cliche block on top of the ink-filled ink cup.

And install the assembly in the machine. Place the aligner plate on the printer base. Initiate a printing cycle on the pad-printing machine.

Which will apply the electrode design on the aligner plate. Visually inspect the overlap of the printed electrode and the etched reference structure of the aligner plate. Move the X-Y fader stage to correct for any misalignment.

Visually inspect the alignment with the reference structure and continue moving the platform position and printing electrodes until a perfect superposition of the printed pattern on the reference structure is obtained. Place a prestretched membrane on the printer base. On the pad printing machine launch a printing cycle to stamp the electrode on top of the membrane.

Stamp the membrane twice to ensure a sufficient electrode thickness of about four microns. After repeating the printing process until all prestretched membranes are stamped, place the membranes with the stamped electrode in an oven at 80 degrees Celsius for 30 minutes. Then place one of the printed membranes upside-down on the printer base exposing the back side of the membrane.

Initiate a series of two printing cycles to pattern the bottom electrode. To finish the actuator place the membranes in the oven at 80 degrees Celsius for 30 minutes to crosslink the bottom electrode. To create the electrical connections first remove the protective backing of the actuator frame to expose the adhesive.

Then apply an 18 millimeter by 2.5 millimeter piece of tape on the part of the actuator frame that will come into contact with the bottom electrode and fold it to the side of the frame to provide an accessible electrical contact. Then slide the actuator frame inside the membrane holder and gently press the membrane with fingers to stick it to the adhesive of the actuator frame. With a scalpel cut the membrane at the border between the membrane holder and actuator frame and remove the membrane holder.

Apply a second piece of 18 millimeter by 2.5 millimeter conductive tape on the contact zone of the top electrode. Finally place a wire on each piece of conductive tape to make an electrical connection. Connect the two wires to a high-voltage source and apply a two Hertz square signal of two kilovolts amplitude.

The dry film thickness of the casted silicone membrane depends on the gap setting of the applicator but also on the coding speed. The influence of the speed is more important for thicker membranes. Application of an electric field above 100 volts per micron at a frequency of one Hertz shows that the actuator can achieve large deformations.

The diametral actuation stretch of the actuator shows a quadratic dependence relative to the applied direct current voltage. After watching this video you should have a good understanding on how to fabricate planar dielectric elastomer actuators with short response times. An advantage of using low-mechanical-loss silicone elastomers.

The key point of this procedure is the ability to make reproducible actuators with well defined electrodes. Our fabrication process shows a possible route towards a large-scale fabrication of dielectric elastomer actuators.