Dynamics of Droplets Moving on Lubricated Polymer Brushes

Abstract

Understanding the dynamics of drops on polymercoated surfaces is crucial for optimizing applications such as selfcleaning materials or microfluidic devices. While the static and dynamic properties of deposited drops have been well characterized, a microscopic understanding of the underlying dynamics is missing. In particular, it is unclear how drop dynamics depends on the amount of uncross-linked chains in the brush, because experimental techniques fail to quantify those. Here we use coarse-grained simulations to study droplets moving on a lubricated polymer brush substrate under the influence of an external body force. The simulation model is based on the many body dissipative particle dynamics (MDPD) method and designed to mimic a system of water droplets on poly(dimethylsiloxane) (PDMS) brushes with chemically identical PDMS lubricant. In agreement with experiments, we find a sublinear power law dependence between the external force F and the droplet velocity v, F ∝ v α with α < 1; however, the exponents differ (α ∼ 0.6−0.7 in simulations versus α ∼ 0.25 in experiments). With increasing velocity, the droplets elongate and the receding contact angle decreases, whereas the advancing contact angle remains roughly constant. Analyzing the flow profiles inside the droplet reveals that the droplets do not slide but roll, with vanishing slip at the substrate surface. Surprisingly, adding lubricant has very little effect on the effective friction force between the droplet and the substrate, even though it has a pronounced effect on the size and structure of the wetting ridge, especially above the cloaking transition.

Adsorption-Driven Deformation and Footprints of the RBD Proteins in SARS-CoV-2 Variants on Biological and Inanimate Surfaces

“…Molecular Dynamics (MD) simulations can provide highly valuable insight into the function of biological systems with high resolution, ,,− and, in particular, on the interaction with different surfaces. − From a molecular simulations viewpoint, the comparison of VoCs behavior with different surfaces is still in its infancy. Pioneering studies on relevant hydrophobic, hydrophilic, skin, and coinage surfaces have been performed for the WT spike, − , and recent research has focused only on the RBD interactions to very specific nanomaterials that can be degraded by macrophages .…”