Marangoni force-driven manipulation of photothermally-induced microbubbles

Abstract

The generation and manipulation of microbubbles by means of temperature gradients induced by low power laser radiation is presented. A laser beam (λ = 1064 nm) is divided into two equal parts and coupled to two multimode optical fibers. The opposite ends of each fiber are aligned and separated a distance D within an ethanol solution. Previously, silver nanoparticles were photo deposited on the optical fibers ends. Light absorption at the nanoparticles produces a thermal gradient capable of generating a microbubble at the optical fibers end in non-absorbent liquids. The theoretical and experimental studies carried out showed that by switching the thermal gradients, it is possible to generate forces in opposite directions, causing the migration of microbubbles from one fiber optic tip to another. Marangoni force induced by surface tension gradients in the bubble wall is the driving force behind the manipulation of microbubbles. We estimated a maximum Marangoni force of 400nN for a microbubble with a radius of 110 μm.

Low-temperature laser-stimulated controllable generation of micro-bubbles in a water suspension of absorptive colloid particles

“…and T m = 24 °C the result (19) dictates that the temperature necessary for bubble nucleation (~180 °C, see the 1st paragraph of this Sec. 3.1) can be realized at the beam center if 0 0.5 -0.6 W, Q ≥…”

“…This force appears due to the slight difference in the temperature conditions along the bubble surface [16], and its manifestations are observed and employed in many situations where the concentrated light is absorbed in organic liquids containing the absorptive particles [17][18][19][20].…”

“…This enabled efficient regulation of the bubbles' generation, evolution and motion by means of the easily controllable properties of the laser radiation. The bubbles formed ensembles and quasi-ordered structures and were kept together within the most heated area of water, which was explained based on the effective thermocapillary force owing to the temperature-induced surface tension inhomogeneity (Marangoni force [16][17][18][19]). However, the repulsive interaction between the bubbles was associated with the double electric layers at the bubble-water interfaces that are hardly controllable.…”

Steady-State 3D Trapping and Manipulation of Microbubbles Using Thermocapillary

“…The equilibrium position is located at a distance d, measured from the tip of the fiber OF T until the bubble geometrical center. Optical forces are not taken into account because their magnitudes are three orders of magnitude smaller than the buoyancy force and six orders of magnitude smaller than the Marangoni force F M [19].…”

“…However, they require rather large optical powers >100 mW; besides, they did neither show steady-state trapping nor stably manipulation. Recently, our research group has demonstrated both the generation and quasi-steadystate trapping and manipulation of single microbubbles in optical fibers using the Marangoni effect [19,20].…”