Ionogel-based light-actuated valves for controlling liquid flow in micro-fluidic manifolds

Abstract

We present the fabrication, characterisation and performance of four novel ionic liquid polymer gels (ionogels) as photo-actuated valves incorporated into microfluidic manifolds. The ionogels incorporate benzospiropyran units and phosphonium based ionic liquids. Each ionogel is photo-polymerised in-situ in the channels of a poly(methyl methacrylate) micro-fluidic device, generating a manifold incorporating four different micro-valves. The valves are actuated by simply applying localised white light irradiation, meaning that no physical contact between the actuation impulse (light) and the valve structure is required. Through variation of the composition of the ionogels, each of the micro-valves can be tuned to open at different times under similar illumination conditions. Therefore, flows through the manifold can be independently controlled by a single light source. At present, the contraction process to open the channel is relatively rapid (seconds) while the recovery (expansion) process to re-close the channel is relatively slow (minutes), meaning that the valve, in its current form, is better suited for single-actuation events.

Modular microfluidic valve structures based on reversible thermoresponsive ionogel actuators

“…[13] It is well known that lower crosslinking density results in increased water uptake, however this can result in a weaker mechanical stable gel. Therefore a compromise between physical-mechanical integrity (high degree of crosslinking) and extent of actuation (low degree of crosslinking) was established for this ionogel material in our previous publications.…”

Swelling and shrinking behaviour of photoresponsive phosphonium-based ionogel microstructures

“…18 The %H of all the photopolymerised microstructures was measured after 30 min (Figure 3b, Figure 4) of white light irradiation following the same protocol described above. In all cases, the [P 6,6,6,14 ][NTf 2 ] microstructures exhibit the greatest %H reduction, followed by [P 6,6,6,14 ][dca] and [P 6,6,6,14 ][Cl].…”

“…15 We have recently published several papers on phosphonium-based ILs, and their use in ionogels. 16,17,18 In this paper, we report the synthesis of photoresponsive poly(Nisopropylacrylamide) ionogels functionalised with spiropyran chromophores, and examine their ability to be photopatterned into complex microstructures using a performance is determined by the swelling and shrinking behaviour, and therefore it is one of the basic properties that needs to be considered if it is to form the basis of a useful polymer actuator. 8 Due to the large surface-area-to-volume ratio of the photopatterned microstructures compared to bulk macro scaled gel structures, the rates of water diffusion into and out of the gel are highly accelerated.…”

Bending kinetics of a photo-actuating nematic elastomer cantilever

“…1 This ability makes LCEs attractive candidates for a variety of applications in robotics, photonics, and microfluidics. It has been demonstrated that modified LCEs can exhibit thermal, 2-5 electrical, 6 and photo-induced 7,8 actuation; based on these achievements, a number of devices such as microvalves, 9 optical tweezers, and microgrippers 10 among others have been reported. Photo-induced actuation in particular is attractive because it can be triggered by an external "remote" stimulus (rather than by direct heating, which is inconvenient for most practical applications) and because the speed and periodicity of the stimulus can be finely controlled.…”