Characterization and evaluation of ionic liquids for use in rapidly-actuated hydraulic microvalves

Abstract

Elastomeric membrane-based microvalves, especially pneumatically-actuated valves, are a core technology responsible for the proliferation of micro total analysis systems (μTAS) due to enabling the precise metering and mixing required by lab-on-a-chip applications. Hydraulic actuation is a promising actuation strategy, analogous to pneumatic actuation, useful in environments where the portability and power requirements of pneumatic actuation systems is non-ideal. Central to the function of hydraulic valves for active applications that require rapid and repeatable actuation, such as microfluidic pumping, are the viscosity, evaporation profile and the hygroscopic nature of the hydraulic fluid. Here the properties of a series of 1-methyl-3-butylimidizaolium (BMIM)-based ionic liquids (ILs) and water are investigated for application in self-contained hydraulically-actuated microfluidic (SCHAM) devices. Evaporation and water uptake of SCHAM devices was monitored daily over a one-month period, with IL-based SCHAMs providing superior performance compared to water-based SCHAMs. Evaporation and water uptake profiles of IL-filled devices were recorded over a six-week time period, subjected to thermocycling of one-week periods between −20 °C and 60 °C, with IL-based SCHAMs exhibiting superior stability in comparison to water-based SCHAMs. As a proof of concept, a SCHAM pump using [BMIM][BF4] was fabricated utilizing a simple and inexpensive rapid prototyping method, and tested over a range of actuation times (150 ms–350 ms, with pumping rates of 5.0 ± 0.1 μL min–1 to 2.6 ± 0.1 μL min–1, respectively). To the best of our knowledge, this is the first demonstration of an IL-filled SCHAM device utilizing active valve elements to attain fluidic transfer.