Resonant oscillation of droplets under an alternating electric field to enhance solute diffusion.

This study investigates a novel microfluidic mixing technique that uses the resonant oscillation of coalescent droplets. During the vertical contact-separation process, solutes are initially separated as a result of the combined effects of diffusion and gravity. We show that the application of alternating current (AC) voltage to microelectrodes below the droplets causes a resonant oscillation, which enhances the even distribution of the solute.

Simultaneous detection of the shuttling motion of liquid metal droplets in channels under alternating pressure and capacitive sensor signals.

Implementing a signal-switching mechanism for the selective use of integrated sensors and actuators plays a crucial role in streamlining the functionality of miniaturized devices. Here, a liquid metal droplet (LMD)-based signal-switching mechanism is introduced to achieve such functionality. Pressure modulation with a 100-μm spatial resolution enabled precise control of the position of the LMDs within a channel.

Enhancement of solute diffusion in microdroplets using microrotors under rotational magnetic field.

In vertical contact control (VCC), a microdroplet array selectively contacts with an opposite microdroplet array. Generally, VCC is useful for the dispenser mechanism based on solute diffusion between microdroplet pairs. However, sedimentation due to gravity can cause an inhomogeneous distribution of solutes in microdroplets.

Threshold magnetic field as a universal criterion for the selective transport of magnetized particles in microdroplets.

Transportation of magnetized particles (MPs) against gravity is possible by applying a magnetic field to the particles. This transport phenomenon of MPs in microdroplets can be quantitatively assessed by determining the contribution of individual forces acting on the MPs. We studied the selective transportation of MPs in microdroplets.

Rotation and transportation of liquid crystal droplets for visualizing electric properties of microstructured electrodes.

The spatial resolution of typical sensor probes is sufficient for measuring the average electric properties of microelectrical devices, but they are unable to measure the distribution with a spatial precision. Liquid crystal droplets (LCDs) are promising candidate for visualizing the distribution. When voltage is applied, the LCDs show rotational and translational behaviors which depend on the location of LCDs within the devices.

Temperature gradient sensing mechanism using liquid crystal droplets with 0.1-mK-level detection accuracy and high spatial resolution.

We proposed the detection mechanism of the micro-levels of temperature gradient in a micro-electromechanical system using the unidirectional rotation of cholesteric-liquid crystal (Ch-LC) droplets. Ch-LC droplets in the presence of an isotropic phase subjected to a heat flux rotate with a speed proportional to the magnitude of the temperature gradient. We further quantified the temperature gradient-to-torque conversion efficiency to apply the thermomechanical cross-correlation to the detection of temperature gradient.

Liquid metal droplet shuttling in a microchannel toward a single line multiplexer with multiple sensors.

Multiple sensors and actuators integrated in a small space, especially an elongated thin structure, require equivalent number of signal lines between microdevices, but there is limited space for signal wires. Thus, we propose a mechanism using a single microchannel where a liquid metal droplet moves and shuttles. A shuttling droplet switches multiple terminals of signal lines along a microchannel based on a traditional switching mechanism using a liquid metal droplet.

Steady rigid-body rotation of cholesteric droplets and their dumbbell-shaped aggregates driven by heat flux along the helical axes.

We investigated the steady unidirectional rotation of cholesteric (Ch) droplets driven by a heat flux. The droplets coexisted with the isotropic (Iso) phase and possessed a helical molecular arrangement. When a heat flux was transported along the helical axis, the droplets and their dumbbell-shaped aggregates exhibited steady rigid rotation.

Smooth transportation of liquid metal droplets in a microchannel as detected by a serially arranged capacitive device.

Gallium alloy liquid metals (Galinstan) possessing fluidity, electric conductivity, and low toxicity are attractive for use in flexible devices and microfluidic devices. However, the oxide skin of Galinstan in the atmosphere adheres to the microchannel surface, preventing the transportation of Galinstan in the channel. To tackle the problem of the adhesion of Galinstan to microchannel, we introduced liquid with Galinstan into a channel with a diameter of 1000 μm.

Heat-Driven Rigid-Body Rotation of a Mixture of Cholesteric Liquid Crystal Droplets and Colloids.

We show that cholesteric (Ch) liquid crystal droplets with cylindrically symmetric orientation dispersing in an isotropic (Iso) phase exhibited unidirectional rotation under a heat flux along the symmetry axis. By introducing colloidal particle adhesive to the Ch droplet surface, we traced the translational motion of the colloids and found that the colloids rotated unidirectionally around the center of each Ch droplet. The director configuration of the droplets was not distorted either spatially or temporally, while the colloids rotated constantly.

A thermomechanical coupling in cholesteric liquid crystals: Unidirectional rotation of double-twist cylinders driven by heat flux.

We made aggregates of cholesteric liquid crystalline Cylinders with Double-Twist orientational structure (DTC) and investigated their rigid-body rotation under a temperature gradient, focusing on how the rotational speed should depend on the cylinder size. The experimental results showed that the angular velocity of the DTC aggregates linearly increased with the height of the cylinders and was inversely proportional to the base area. With a phenomenological equation, we analyzed the torque caused by the heat flux and its balance with the viscous friction, and found that the simple analysis well explained the size-dependence of the rotation of the DTC aggregates.

Formation and dynamics of the aggregates of cholesteric double-twist cylinders.

We succeeded in driving the unidirectional rigid-body rotation of cholesteric (Ch) double-twist cylinder (DTC) droplets under a heat flux along the cylindrical symmetry axis. To directly observe the rigid-body rotation of DTC droplets, in each of which the center of the rotation and the symmetry axis of the structure correspond, we fabricated DTC aggregates that comprise several DTCs with intact structures. Given a steady heat flux, the DTC aggregates metastabilized by the shape and the surface anchoring show a unidirectional rigid-body rotation with a constant angular velocity.

Unidirectional rotation of cholesteric droplets driven by UV-light irradiation.

We investigated the novel photo-induced dynamics of azobenzene-doped cholesteric (Ch) droplets coexisting with the isotropic (Iso) phase. When the hemispherical Ch droplets initially stuck to glass substrates were irradiated by UV-light, they were parted from the substrates due to the surface disordering caused by the photo-isomerization of azobenzene. Then, the spherical droplets floating in the Iso phase exhibited an unexpected motion - a continuous and unidirectional rotation along the light propagation direction.