ORCID Profile
0000-0001-9599-5589
Current Organisations
Johannes Gutenberg Universität Mainz
,
Max Planck Institute for Polymer Research
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Publisher: AIP Publishing
Date: 04-10-2016
DOI: 10.1063/1.4963792
Abstract: Classical density functional theory is applied to investigate the validity of a phenomenological force-balance description of the stability of the Cassie state of liquids on substrates with nanoscale corrugation. A bulk free-energy functional of third order in local density is combined with a square-gradient term, describing the liquid-vapor interface. The bulk free energy is parameterized to reproduce the liquid density and the compressibility of water. The square-gradient term is adjusted to model the width of the water-vapor interface. The substrate is modeled by an external potential, based upon the Lennard-Jones interactions. The three-dimensional calculation focuses on substrates patterned with nanostripes and square-shaped nanopillars. Using both the force-balance relation and density-functional theory, we locate the Cassie-to-Wenzel transition as a function of the corrugation parameters. We demonstrate that the force-balance relation gives a qualitatively reasonable description of the transition even on the nanoscale. The force balance utilizes an effective contact angle between the fluid and the vertical wall of the corrugation to parameterize the impalement pressure. This effective angle is found to have values smaller than the Young contact angle. This observation corresponds to an impalement pressure that is smaller than the value predicted by macroscopic theory. Therefore, this effective angle embodies effects specific to nanoscopically corrugated surfaces, including the finite range of the liquid-solid potential (which has both repulsive and attractive parts), line tension, and the finite interface thickness. Consistently with this picture, both patterns (stripes and pillars) yield the same effective contact angles for large periods of corrugation.
Publisher: American Association for the Advancement of Science (AAAS)
Date: 17-01-2020
Abstract: We monitor the self-cleaning process on a single-particle level and quantify the involved forces.
Publisher: Royal Society of Chemistry (RSC)
Date: 2022
DOI: 10.1039/D1SM01297E
Abstract: We investigate the shrinkage of a surface-grafted water-swollen hydrogel under shear flows of oils by laser scanning confocal microscopy.
Publisher: Wiley
Date: 2023
DOI: 10.1002/DRO2.42
Abstract: The friction force opposing the onset of motion of a drop on a solid surface is typically considered to be a material property for a fixed drop volume on a given surface. However, here we show that even for a fixed drop volume, the static friction force can be tuned by over 30% by preshaping the drop. The static friction usually exceeds the kinetic friction that the drop experiences when moving in a steady state. Both forces converge when the drop is prestretched in the direction of motion or when the drop shows low contact angle hysteresis. In contrast to static friction, kinetic friction is independent of preshaping the drop, that is, the drop history. Kinetic friction forces reflect the material properties.
Publisher: Springer Science and Business Media LLC
Date: 06-11-2017
DOI: 10.1038/NPHYS4305
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Doris Vollmer.