A water-powered osmotic microactuator

Abstract

This paper presents a microactuator that utilizes osmosis to produce mechanical actuation without consuming any electrical energy. The microactuator is made of cellulose acetate with cylindrical chamber of 500 to 2000 μm in diameter and of 200 to 1000 μm in depth. Sodium chloride is chosen as the osmotic driving agent to be placed inside the chamber. A semipermeable diaphragm made of cellulose acetate is processed at the bottom of the chamber to control the water flow. Either a cellulose acetate diaphragm or an impermeable diaphragm made of vinylidene chloride and acrylonitrile copolymer is spin-coated on top of the chamber as the actuation diaphragm. Using the principle of osmosis, this water-powered, osmotic microactuator can employ high osmotic pressure (a chemical potential) up to 35.6 MPa to provide hydrostatic pressure for mechanical actuation. Experimental measurements show that up to 800 μm vertical diaphragm movement (diaphragm size of 800 μm in diameter) and constant volume expansion rate of 4.5 to 11.5 nL/h can be achieved. When integrated with other microfluidic devices, this osmotic microactuator could serve as a clean, compact and inexpensive fluidic actuation source.