Quantitative Spreading Kinetics of a Three Molecular Layer Liquid Patch

Abstract

The late stage kinetics of the spreading of a smectic nanodrop on a solid surface was investigated by direct and real time imaging of a three molecular layer patch using the SEEC microscopy. Experimental data do not conform to the only available theory, which covers only weakly stratified liquids. A new model is proposed, in remarkable agreement with experiments, in which the spreading mechanism appears to be a quasi-static process ruled by solid/liquid interactions, 2D Laplace pressure, and separate edge and surface permeation coefficients.

Mechanism of Lipid Nanodrop Spreading in a Case of Asymmetric Wetting

“…Such drops quickly evolve towards trilayered patches surrounded by a monolayer. Using the surface enhanced ellipsometric contrast [26][27][28] with an optical microscope working at a fixed magnification, the history of every molecular layer can be properly traced from this stage to the final structure, which is a single molecular monolayer disk with typically 200 m diameter. Over most of the experiment duration, coexistence of a monolayer and a trilayer is observed.…”

From Permeation to Pore Nucleation in Smectic Stacks

“…A very thin film added on this support generates interferences which make the extinction property disappear, and the film appears brighter than the bare surface in reflected light. The SEEC technique provides a height resolution better than 0.1 nm, so that direct and real-time visualization of all 8CB layers, including the diffuse one, becomes possible, with a much higher lateral resolution than ellipsometry or X-ray reflectivity . Optical observations were achieved through a polarization microscope (Leica DMRX PlanApo Pol Fluotar 20 × 0.5 objective lens).…”

“…The SEEC technique provides a height resolution better than 0.1 nm, so that direct and real-time visualization of all 8CB layers, including the diffuse one, becomes possible, with a much higher lateral resolution than ellipsometry or X-ray reflectivity. 16 Optical observations were achieved through a polarization microscope (Leica DMRX PlanApo Pol Fluotar 20 × 0.5 objective lens). The solid support was cleaned using UV/ozone for 30 s and then set on a heating stage with ±0.5 °C of accuracy.…”

“…The central trilayer is the sum of a bilayered patch and a dense liquid-like monolayer. The whole structure was elucidated by X-ray reflectivity, ellipsometry, and SEEC experiments . The trilayer is surrounded by a gas-like monolayer which is topologically connected to the dense monolayer in the trilayer stack. , This monolayer may be the upper one, as in Figure a, or the lower one, as in Figure b .…”

“…In the following, we will focus on the shape of the shrinking bilayer during late-stage spreading. With 8CB, two behaviors may be observed: (i) for temperatures close to the solid/smectic transition (21.5 °C), the bilayer shrinks without particular event; , (ii) at higher temperatures (above 22.5 °C), holes with a bilayer thickness appear in the trilayer and grow during bilayer shrinking, leaving a monolayer on the surface. This is the case in the experiments reported herein.…”