Dynamics of Droplets Moving on Lubricated Polymer Brushes

Abstract

Understanding the dynamics of drops on polymer-coated surfaces is crucial for optimizing applications such as self-cleaning materials or microfluidic devices. While the static and dynamic properties of deposited drops have been well characterised, a microscopic understanding of the underlying dynamics is missing. In particular, it is unclear how drop dynamics depends on the amount of uncrosslinked 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 polydimethylsiloxane (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 $v$, $F\propto v^{\alpha }$ with $\alpha <1$; however, the exponents differ ($\alpha \sim 0.6-0.7$ in simulations versus $\alpha \sim 0.25$ 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.

References in corpus (27)

• Beyond traditional coatings, a review on thermal sprayed functional and smart coatings
• Vapour-liquid coexistence in many-body dissipative particle dynamics
• Oleoplaning droplets on lubricated surfaces
• Dissipative particle dynamics for interacting systems
• Origin of line tension for a Lennard-Jones nanodroplet
• Static and Dynamic Properties of Dissipative Particle Dynamics
• Droplets move over viscoelastic substrates by surfing a ridge
• Film dynamics and lubricant depletion by droplets moving on lubricated surfaces
• Wetting and phase separation in soft adhesion
• Soft wetting and the Shuttleworth effect, at the crossroads between thermodynamics and mechanics
• No-go theorem in many body dissipative particle dynamics
• Do liquid drops roll or slide on inclined surfaces?
• Viscoelastic and poroelastic relaxations of soft solid surfaces
• Statics and dynamics of a cylindrical droplet under an external body force
• Phase Separation in Wetting Ridges of Sliding Drops on Soft and Swollen Surfaces
• Statics of polymer droplets on deformable surfaces
• Drops on polymer brushes -- advances in thin-film modelling of adaptive substrates
• Cloaking Transition of Droplets on Lubricated Brushes
• The rolling and slipping of droplets on superhydrophobic surfaces
• Capillarity of soft amorphous solids: a microscopic model for surface stress
• Non-equilibrium configurations of swelling polymer brush layers induced by spreading drops of weakly volatile oil
• Stick-slip Dynamics in the Forced Wetting of Polymer Brushes
• Variational approach to contact line dynamics for thin films
• Unidirectional Droplet Propulsion onto Gradient Brushes without External Energy Supply
• Droplet transport in a nanochannel coated by hydrophobic semiflexible polymer brushes: the effect of chain stiffness
• Antidurotaxis Droplet Motion onto Gradient Brush Substrates
• Droplet motion with contact-line friction: long-time asymptotics in complete wetting

Cited by in corpus (1)

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