Coupled laser molecular trapping, cluster assembly, and deposition fed by laser-induced Marangoni convection

Abstract

A coupled mechanism for molecular aggregation in a thin water solution film by laser-tweezers is suggested based on (i) simulation of light intensity distribution and (ii) order of magnitude analysis of heat and mass transport induced by Marangoni convection. The analysis suggests that the laser induced temperature distribution develops within 1 ms and Marangoni convection flow commences within 0.01-1 s, which increases by 1-2 orders of magnitude the mass transfer of dissolved molecules into the laser focus where they are trapped and aggregate by attractive van der Waals forces. This mechanism, considered for the particular case of polymer assembly, suggests that it can also be successfully applied for assembling other types of clusters and molecular aggregates from solutions.

Insight into plasmonic hot-electron transfer and plasmon molecular drive: new dimensions in energy conversion and nanofabrication

“…This surface tension gradient may be the origin of the slip flow along the particle surface to the substrate, known as the Marangoni convective flow (Figure 18d). 59 Here, we note that the 2D temperature profiles in Figure 18a are typical for this scale in which a point-like heat source (~100 nm) is surrounded by an almost infinite-scale heat sink (cm × cm ×~100 μm). Because the high-temperature region is confined, thermal convection is predicted to be slow (Figure 18e).…”

“…In addition to buoyancy-driven thermal convection, Marangoni convection can occur as a result of surface tension gradients generated by temperature gradients formed at interfaces. 59 These processes contribute to the transport of molecules and small particles, resulting in accumulation and crystallization under appropriate conditions. Apart from this migration or flow, microbubbles can form if Au NPs and NSs are strongly heated in a liquid environment.…”

Light at work: The use of optical forces for particle manipulation, sorting, and analysis

“…A completely different mechanism propels droplets or bubbles on the surface of a liquid with thermal gradients created by laser absorption. It is a consequence of the difference of contact angles (surface tension) on the opposite sides of the object, which can move it up to hundreds of micrometers along the surface (so-called Marangoni effect or thermocapillary force) [254][255][256][257][258][259].More detailed comparison of various micro-manipulation techniques, their ranges of applicable forces, spatial and temporal resolutions, and additional features can be found in reviews [14,216,217,260]. …”

Laser trapping dynamics of 200 nm-polystyrene particles at a solution surface

“…Actually, these Heating Effects were occasionally pointed out for conventional laser trapping experiments. [22][23][24] These Heating Effects possibly become dominant with the increase in laser power, since local temperature becomes higher with the increase in the power. The direct observation of the trapping behavior with a CCD camera provided us a crucial insight to these Heating Effects.…”