Abstract

Thermally actuated controlled shape changes in soft materials is a challenge as the material shows non-linear expansion characteristics. CTE of many materials is not properly available. In order to focus the expansion of the soft solid into large displacements a confined geometry is created to amplify the shape changes. Here we use an elastomer (PDMS sheet) confined between two rigid layers, which when locally heated using resistive heating expands into the micromolded channels, resulting into a massive relative displacement compared to the case of an unconfined geometry. This principle is used to make microfluidic valves which are electrically controlled (using a 3.3V-5V cellphone battery) and close in less than 100 ms. They operate within a power range of 140-160 mW generated by the specifically designed resistive heating element (in-house made ink) screen printed on the chip. We investigate the parameters of the heating element design, height dimensions and flow conditions through the valves. This technique helps us to make multiple valves along the fluidic pathway with arbitrary positioning. The size of these really help to make the devices portable as one does not need a separate controller for the actuating the valves.