Application of sensitive hydrogels in flow control

Abstract

For any polymer gel, the amount of solvent uptake is dependent upon the chemical nature of the gel and the nature of its environment— solvent composition, temperature, pH, and so on. We discuss the use of different hydrogels based on crosslinked poly(N-isopropylacrylamide) and copolymers with basic or acidic groups as materials for flow control. The design of a chemo-mechanical valve is described. The liquid flows directly through a gel actuator, which consists of a cylinder filled with small particles of the sensitive crosslinked polymer. The flow rate as well as the pressure drop is measured in dependence on the solvent properties. The sensitivity of the gels as well as the time behavior of the valve-function is correlated with the dependence of the degree of swelling on the environment and the swelling and shrinking kinetics of the gels. The stimulus must permeate the gel itself before a gel can respond to the stimulus. By NMR-imaging it is possible to follow the transport processes inside the gel in real-time. With the presented experimental arrangement we could show that sensitive polymers can be used for controlling the flow in dependence on temperature, pH and content of organic solvents in water. Furthermore, the synthesis of a photo-crosslinkable sensitive polymer is described, synthesized and suggestions for an application of thin layers of this polymer in micro-system techniques are made. Copyright © 2000 John Wiley & Sons, Ltd.