Polymer nano-doplets forming liquid bridges in chemically structured slit pores: A computer simulation

Using a coarse-grained bead-spring model of flexible polymer chains, the structure of a polymeric nanodroplet adsorbed on a chemically decorated flat wall is investigated by means of Molecular Dynamics simulation. We consider sessile drops on a lyophilic (attractive for the monomers) region of circular shape with radius R_D while the remaining part of the substrate is lyophobic. The variation of the droplet shape, including its contact angle, with R_D is studied, and the density profiles across these droplets also are obtained. In addition, the interaction of droplets adsorbed on two walls forming a slit pore with two lyophilic circular regions just opposite of one another is investigated, paying attention to the formation of a liquid bridge between both walls. A central result of our study is the measurement of the force between the two substrate walls at varying wall separation as well as the kinetics of droplet merging. Our results are compared to various phenomenological theories developed for liquid droplets of mesoscopic rather than nanoscopic size.Comment: 8 pages, 9 figures, accepted in J. Chem. Phys. 200

Toward an experimental proof of superhydrophobicity enhanced by quantum fluctuations freezing on a broadband-absorber metamaterial

Previous theoretical works suggested that superhydrophobicity could be enhanced through partial inhibition of the quantum vacuum modes at the surface of a broadband-absorber metamaterial which acts in the extreme ultraviolet frequency domain. This effect would then compete with the classical Cassie-Baxter interpretation of superhydrophobicity. In this article, we first theoretically establish the expected phenomenological features related to such a kind of "quantum" superhydrophobicity. Then, relying on this theoretical framework, we experimentally study patterned silicon surfaces on which organosilane molecules were grafted, all the coated surfaces having similar characteristic pattern sizes but different profiles. Some of these surfaces can indeed freeze quantum photon modes while others cannot. While the latter ones allow hydrophobicity, only the former ones allow for superhydrophobicity. We believe these results lay the groundwork for further complete assessment of superhydrophobicity induced by quantum fluctuations freezing.Comment: 10 pages, 5 figures, final version, accepted for publication in Journal of Applied Physic

Spreading on Heterogeneous Substrates

International audienceIn this article, we consider the wetting properties of surfaces coated by organic monolayers. These monolayers are either incomplete or chemically heterogeneous. Dynamics of relaxation of the advancing contact angle and high lateral resolution spectroscopic ellipsometry (HRSE) serve to characterize the surfaces and the spreading of branched hydrocarbon or of silicon oils droplets. Influence of the heterogeneity concentration on the friction coefficient (partial wetting regime) or on the pseudo diffusion coefficient (complete wetting regime) of the liquid molecules is presented. Comparisons are given with computer simulation results

Spreading on Heterogeneous Substrates

In this article, we consider the wetting properties of surfaces coated by organic monolayers. These monolayers are either incomplete or chemically heterogeneous. Dynamics of relaxation of the advancing contact angle and high lateral resolution spectroscopic ellipsometry (HRSE) serve to characterize the surfaces and the spreading of branched hydrocarbon or of silicon oils droplets. Influence of the heterogeneity concentration on the friction coefficient (partial wetting regime) or on the pseudo diffusion coefficient (complete wetting regime) of the liquid molecules is presented. Comparisons are given with computer simulation results