Subnanometer imaging and controlled dynamical patterning of thermocapillary driven deformation of thin liquid films

Abstract

Exploring and controlling the physical factors that determine the topography of thin liquid dielectric films are of interest in manifold fields of research in physics, applied mathematics, and engineering and have been a key aspect of many technological advancements. Visualization of thin liquid dielectric film topography and local thickness measurements are essential tools for characterizing and interpreting the underlying processes. However, achieving high sensitivity with respect to subnanometric changes in thickness via standard optical methods is challenging. We propose a combined imaging and optical patterning projection platform that is capable of optically inducing dynamical flows in thin liquid dielectric films and plasmonically resolving the resulting changes in topography and thickness. In particular, we employ the thermocapillary effect in fluids as a novel heat-based method to tune plasmonic resonances and visualize dynamical processes in thin liquid dielectric films. The presented results indicate that light-induced thermocapillary flows can form and translate droplets and create indentation patterns on demand in thin liquid dielectric films of subwavelength thickness and that plasmonic microscopy can image these fluid dynamical processes with a subnanometer sensitivity along the vertical direction.

Contactless thin-film rheology unveiled by laser-induced nanoscale interface dynamics

“…Since Thus in presence of thermocapillarity with 0 T γ ∂ ∂ < , the induced flow should be radially directed away from the heating laser and due to mass conservation, the resulting toroidal flow should produce a beam-centred dimple on the top of the drop interface. [19][20][21] In the viscous regime, 58 ) to a position below the top of the non-deformed drop (negative height), demonstrating that a dimple has indeed been induced. Then this dimple relaxes much slower than expected from radiation pressure effects.…”

“…These requirements prompted the emergence of contactless micro-rheology techniques. Among all the various methods advanced, those based on the analysis of interface deformation have attracted attention for several important reasons: (i) most of the targeted properties of the liquid can be deduced from the analysis of both the dynamical and stationary deformations of the interface in different regimes (inertial, overdamped, …); (ii) Interfacial deformations can be triggered without any contact using several ways: from natural thermal fluctuations, 14 by capillary levelling, 13,15 by applying an electrostatic stress, 16,17,18 by triggering tangential thermal gradient and thermocapillary stresses, 19,20,21 or by irradiating the interface using the radiation pressure of an acoustic 22,23,24 or a laser beam. 25 , 26 The fluctuation method is based on the analysis of light scattering by broadband thermal fluctuations at the free surface and then it requires long signal acquisition durations.…”

Optical Manipulation of Soft Matter

“…[ 65 ] By leveraging the interaction between light, liquid, and substrate, the surface profile and thickness of the liquid film can be modulated through optical‐force‐induced deformation or photothermal‐induced deformation (Figure 5b,c). [ 66 ] Local irradiation can be used to achieve dynamic patterning of thin liquid films, [ 67 ] and there is potential for further development of programmable optical manipulation of thin liquid films to construct tunable optical metasurfaces [ 68 ] and optofluidic reservoir computers. [ 69 ]…”

Thin liquid film as an optical nonlinear-nonlocal medium and memory element in integrated optofluidic reservoir computer

“…In the following we use these values unless specified otherwise and assume that the initial configuration of the liquid film forms 90 o with the vertical silica walls. thermocapillary [19][20][21] (TC) driven deformation of optically thin gas-liquid interface [22,23], to predict and characterize a set of new effects in optofluidic integrated photonic components, and then leverage these nonlinear effects to achieve RC capabilities. Fig.…”