Light-Induced Convective Segregation of Different Sized Microparticles

Abstract

Using computational modeling, we design a facile method for sorting particles of different sizes in a fluid-filled microchamber. The microchamber is inclined at an angle with respect to the horizontal direction and contains suspended gold nanoparticles as well as the microparticles. With the application of ultraviolet light, the heat generated by illuminating the gold nanoparticles gives rise to thermal buoyancy effects, which drive the flow of the fluid in the chamber. This thermally driven, convective flow can be tailored by varying the intensity of the imposed light and the concentration of the gold nanoparticles in the solution. The competition between the drag force imposed by the fluid flows and the gravitational forces acting on the different sized particles produces the separation of the particles along the chamber’s bottom, inclined wall. The separation distance between the particles can be increased by increasing the angle of inclination and the relative difference in the particle sizes. This system provides a label-free, membrane-less, and low-cost approach for sorting particles vital to a wide range of applications.

Colloidal Assembly and Separation under UV‐Induced Convective Flows and on Inclines

“…Manna et al. predicted that on an incline plane, because of the competing effects of gravity and convective fluid flow, particles of different sizes will settle out at heights where the two effects cancel out [25] . Our experiments bear this out and the setup is shown in Figure 7.…”

“…Larger particles will sometimes become trapped in a bed of smaller particles, which can be alleviated by moving the irradiation point uphill incrementally. It is also of note that the flow center becomes slightly shifted downhill away from the irradiation point due to the effect of gravity [25] . Upon turning off the light, all the particles move to the bottom of the cell.…”

“…In our case, the fluid flow is effectively pushing the particles. Starting at the bottom wall, where the fluid velocity is zero due to the no‐slip boundary condition, the flow increases with increasing distance from the wall, reaching the maximum velocity at the quarter of the height of the chamber (see Figure 1B) [25] . As a result, larger particles experience higher fluid velocities because they extend further into the bulk fluid (see Figure 4).…”

Titania-Based Micro/Nanomotors: Design Principles, Biomimetic Collective Behavior, and Applications

“…Sen and Balazs showed that in the presence of light, freely suspended TiO 2 nanoparticles generate photothermal flow fields that pump inert microparticles towards the light, with flow rates tightly controlled by nanoparticle concentration and light intensity [46]. Using these directed flows, they further demonstrated the reversible construction and transport of colloidal crystals (Figure 3C), as well as facile methods for sorting microparticles of different sizes and densities [50]. In another report, the convective flows induced by illuminating a selected area with near infrared (NIR) light was demonstrated (Figure 3D) [51].…”

A Review on Optoelectrokinetics-Based Manipulation and Fabrication of Micro/Nanomaterials

“…To address real-world needs for manipulation and fabrication of micro/nanomaterials, a number of micro-/nano-scaled methods have been presented. Typical examples include microfluidic [14,15], acoustic [16,17], electrokinetics [18,19], magnetic [20,21], optical [22,23], thermal [24,25], and atomic force microscope [26,27] approaches. An emerging topic on the manipulation and fabrication of micro/nanoparticles is about how to develop a novel mechanism that can complement what a single technique can offer.…”