so far my attempt where mainly trying to make usable linear actuator by stacking pouch that can contract.

but this might not be super efficient as you need to have a lot of high voltage circuitry to drive each pouch.

a better approach might be to use the pouch as a compressor to put under pressure the oil and use more standard hydraulic muscle driven by the pouch. This allows some flexibility by using a flexible tube to route the fluid where needed.

i had no epoxy glue at the time nor sturdy elastomer sheet but my workshop improved a bit over the years. The new design would probably be a watertight pouch containing a sponge and one aluminum sheet on each side. The sponge would act as a spring to pump back the fluid once the voltage is removed.

The second advantage of that design being that the force due to the accumulating charge on the capacitor plate increase as the plate get closer. The springy sponge would counteract that to allow for a smoother operation. They would be conceived similarly to these kind of pressure wedge https://fr.aliexpress.com/item/32916566419.html 

since i got slightly better at math, here are the formula i needed :

actually putting in some numbers (50 Kv, 5mm distance, void dielectric constant we get pressure around 2Pa... we would need some kind of hydraulic lever to convert that to a usable force but thats a start