Organization of Particle Islands through Light‐Powered Fluid Pumping

Abstract

The field of active matter holds promise for applications in particle assembly, cargo and drug delivery, and sensing. In pursuit of these capabilities, researchers have produced a suite of nanomotors, fluid pumps, and particle assembly strategies. Although promising, there are many challenges, especially for mechanisms that rely on chemical propulsion. One way to circumvent these issues is by the use of external energy sources. Herein, we propose a method of using freely suspended nanoparticles to generate fluid pumping towards desired point sources. The pumping rates are dependent on particle concentration and light intensity, making it highly controllable. Using these directed flows, we further demonstrate the ability to reversibly construct and move colloidal crystals.

Light-Induced Dynamic Control of Particle Motion in Fluid-Filled Microchannels

“…A particularly useful feature of the system is the ability to control the trajectories of particles transported along the channel. In a previous report, 32 the repositioning of the beam of UV light caused a shift of the convective pattern generated by the light and concurrent relocation of a cluster of particles aggregated on the bottom of the fluidic chamber. In the system considered here, by relocating UV light, we can control the speed and the direction of the net flow locally within a channel.…”

“…We adjust R in our model to match temperature variations observed in the experiments. A typical temperature rise due to the irradiation is Δ T = T – T 0 ≈ 1 K, and the corresponding value for R is 1.5 × 10 3 K/m . We note that the periodic boundary conditions prescribed along the direction of the flow in the channel are valid when the effects of local heating by UV irradiation (and concurrent convective flows) have negligible contributions to the net flow close to the boundary.…”

“…A typical temperature rise due to the irradiation is ΔT = T − T 0 ≈ 1 K, and the corresponding value for R is 1.5 × 10 3 K/m. 32 We note that the periodic boundary conditions prescribed along the direction of the flow in the channel are valid when the effects of local heating by UV irradiation (and concurrent convective flows) have negligible contributions to the net flow close to the boundary. Therefore, the irradiation zones for different scenarios considered in this study are always kept far away from the periodic boundaries along the x direction.…”

“…Here, n is the local normal to the irradiated bottom wall of the channel. The magnitude of the heat flux into the fluid, R , depends on the geometry and size of the fluidic channel, material properties of the coating and the fluid, and the wavelength and the intensity of the incident UV radiation. , The size of the rectangular irradiated zone on the bottom is 1 mm × 2 mm. We adjust R in our model to match temperature variations observed in the experiments.…”

“…Consequently, the particles do not need to be altered, which is a significant advantage of the method. The mechanism of fluid motion generated through the coupling of light and heat − is general and can be applied to both nano- and microscopic particles and enables the sorting of heterogeneous mixtures of particles by size and density . It is worth emphasizing that light provides a particularly useful means of manipulating flow since the stimulus can be applied remotely, patterned with a photomask, and readily translated to irradiate specified locations of the chamber.…”