Contact Line Motion on Nanorough Surfaces: A Thermally Activated Process

Abstract

The motion of a solid-liquid-liquid contact line over nanorough surfaces is investigated. The surface nanodefects are varied in size, density, and shape. The dynamics of the three-phase contact line on all nanorough substrates studied is thermally activated. However, unlike the motion of a liquid-vapor interface over smooth surfaces, this thermally activated process is not adequately described by the molecular kinetic theory. The molecular parameters extracted from the experiments suggest that on the nanorough surfaces, the motion of the contact line is unlikely to simply consist of molecular adsorption-desorption steps. Thermally activated pinning-depinning events on the surface nanodefects are also important. We investigate the effect of surface nanotopography on the relative importance of these two mechanisms in governing contact line motion. Using a derivation for the hysteresis energy based on Joanny and de Gennes's model, we evaluate the effect of nanotopographical features on the wetting activation free energy and contact line friction. Our results suggest that both solid-liquid interactions and surface pinning strength contribute to the energy barriers hindering the three-phase contact line motion. For relatively low nanodefect densities, the activation free energy of wetting can be expressed as a sum of surface wettability and surface topography contributions, thus providing a direct link between contact line dynamics and roughness parameters.

Ion‐Specific Oil Repellency of Polyelectrolyte Multilayers in Water: Molecular Insights into the Hydrophilicity of Charged Surfaces

“…Figure 2 a shows that the resulting PEMs can be readily wetted by water in air, with a q w/a value of 15-208, and is a result of the effective hydration of the surface ionic groups. After 72 hours of aging at 60 8C in air, the q w/a values increased to about 518 and 348for (PDDA/ PSS) 3.5 and (PDDA/PSS) 4 PEMs, respectively, thus suggesting that the surface hydrophilicity of the PSS capping is weaker and more vulnerable to air aging than the PDDA capping. When oil is utilized instead of air to challenge water wetting on the resulting PEMs, as shown in Figure 2 b, the PDDAcapped surfaces remain easily wetted by water (q w/o % 428), while water wetting on the PSS-capped surfaces becomes noticeably poorer, with q w/o decreasing from 1108 to an equilibrium value of 978 over time.…”

“…From the XPS data, we estimated that 25-35 % of the QA + groups and 70-80 % of the BS À groups are uncompensated for on the (PDDA/PSS) 3.5 and (PDDA/PSS) 4 PEM surfaces obtained in 1.0 m NaCl. Figure 2 a shows that the resulting PEMs can be readily wetted by water in air, with a q w/a value of 15-208, and is a result of the effective hydration of the surface ionic groups.…”

“…Here they were alternatingly deposited onto silicon wafers in the presence of 1.0 m NaCl and the resulting PEMs were denoted as (PDDA/PSS) n where "n" represents the bilayer numbers. In this work, we mainly studied (PDDA/ PSS) 3.5 and (PDDA/PSS) 4.0 PEMs with a surface roughness of less than 3 nm (see Figure S1 in the Supporting Information), so the impact of the surface roughness on surface wetting was ignored. The surface compositions of as-prepared (PDDA/ PSS) n PEMs were examined by X-ray photoelectron spectroscopy (XPS; see Figure S2 and Table S1 in the Supporting Information).…”

“…[2d] the BS À groups (i.e., their SO 3 À moieties) on PSS-capped surfaces are expected to be more strongly hydrated than the QA + groups on PDDA-capped 4.0 PEMs, obtained in 1.0 NaCl, are compared with the PDDA-capped and PSS-capped PEMs, obtained in dilute NaCl, with similar thickness and roughness. [9] All the data are obtained from XPS measurements.…”

Crossover from shear-driven to thermally activated drainage of liquid-infused microscale capillaries

“…The interplay between thermal motion and nanoscale surface features can lead to nontrivial wetting processes that are induced by thermal fluctuations of the contact line [17][18][19][20][21][22][23][24][25][26]. A few different approaches have been proposed to model the effect thermal motion and nanoscale surface defects s d ≤ 1 nm have on the dynamics of wetting.…”