SPP 2171 Summer School: Dynamic Wetting of Flexible, Adaptive, and Switchable Substrates

Oleophilic polymer brushes serve as liquid-infused slippery surfaces that facilitate e.g. the motion of water drops. Similarly, they can act as flexible surface-grafted transport layers for oil in advanced lubrication techniques. In this lecture, I discuss the wetting properties of poly n-alkyl methacrylate bottle brushes with variable length of the n-alkyl side chains. Brushes with short...

Stimulus-responsive polymer brushes exhibit a remarkable ability to adapt and transform their properties in response to specific external triggers. Here, we investigate the wetting behaviour of oil on hydrophobic temperature-responsive poly( n-octadecyl methacrylate) (PODMA) brushes below and above the bulk melting temperature. Upon depositing a hexadecane droplet on top of PODMA brushes at...

The wetting properties of solid surfaces are extremely important for many daily and industrial processes, like for example inkjet printing, painting, and adhesion of bacteria or viruses on catheter and medical devices [1]. While significant progress has been made in describing the static properties of drops on surfaces, the wetting dynamic is less understood. In particular, the dependence of...

A drop impacting on a substrate deforms before the wetting occurs and a thin film of air is formed between the liquid and surface. When a drop gets sufficiently close to the surface within a few micrometers, it will most likely contact the underlying surface in a time on the order of 0.02 s. For experiments done under the same conditions, the time that the wetting occurs varies. Here, we...

Recently, there is much interest in droplet condensation on soft or liquid or liquidlike substrates. Droplets can deform soft and liquid interfaces resulting in a wealth of phenomena not observed on hard, solid surfaces (e.g., increased nucleation, interdroplet attraction). Here, we describe a unique collective motion of condensate water droplets that emerges spontaneously when a solid...

Studying wetting phenomena is of great importance across a wide range of scientific disciplines. As a fundamental research area, wettability dynamics of adaptive and responsive substrates gained significant attention. These substrates include polyelectrolyte multilayers (PEM), Poly-N-isopropylacrylamide (PNIPAM) microgels (MG), and Polydimethylsiloxane pseudo-brushes (PDMS brushes), among...

Droplets resting on soft flexible sheets deform into a lens-like shape, presenting exciting opportunities for developing tunable fluidic lenses. Building upon our previously established droplet model, which utilises the boundary element method (BEM), we continue to explore dynamic wetting on thin, flexible sheets. Our research focuses on the intricate interplay between the mechanical...

Polymer brushes swell completely in good solvents and partially in good vapours. The spreading of volatile liquids on brush layers is governed by subtle combination of hydrodynamic flow, vapour transport and swelling kinetics.
We studied the wetting dynamics of alkanes on oleophilic polymer brush layers of poly-lauryl methacrylate (PLMA), synthesised via surface initiated activators...

Electro-dewetting (EDeW) was introduced as a novel method to modify surface wetting properties. By using ionic surfactants like dodecyl tetrethyl ammonium bromide (DTAB), the wettability of hydrophilic silicon oxides on a conductive Si substrate can be controlled through an applied electric potential, resulting in an increased contact angle. This behavior is significantly influenced by the pH...

Traditionally, investigations of Coulomb explosions have focused on charged microdrops levitated using quadrupole electric fields, i.e., a Paul trap. In a surprising twist, our work introduces a simple method to observe Coulomb explosions, with no drop levitation and no external electric field. Instead, we generate a charged water drop using a conventional micropipette, which we then deposit...

Control over physical and chemical properties such as porosity and wettability during 3D printing allows for fabrication of functional materials with gradient properties for many applications such as controlled water imbibition and condensation. Common methods for fabrication of functional materials with gradient properties via Digital Light Processing (DLP) 3D printing such as VAT exchange1,2...

When water droplets move over a hydrophobic surface, they and the surface become oppositely charged by what is known as slide electrification. This effect can be used to generate electricity, but the physical and especially the chemical processes that cause droplet charging are still poorly understood. The most likely process is that at the base of the droplet an electric double layer forms...

The dewetting and equilibration of liquids on soft solids is studied and compared quantitatively with numerical simulations from our tandem project using the experimentally derived input parameters. The size of the explored liquid structures is well below the capillary length and in the range of the elastocapillary length. For these studies, we use a system consisting of a 120 nm thick liquid...

The study of wetting mechanisms on patterned surfaces is critical for surface cleaning and functional surface design. We accurately characterize the complete wetting and Cassie-Baxter wetting states on nano-pillar patterned surfaces through an ATR-FTIR-based optical method. The dynamic evolution of the wetting state transitions is also monitored in situ. In addition, through experimental...

The understanding of wetting phenomena plays a crucial role in many daily processes. For example, dirt repelling surfaces can be achieved by a hydrophobic coating. Typically, the wetting properties of such a coating are characterized by measurements of the advancing and receding contact angles by sessile drop goniometry [1]. This method provides only information on selected points and local...

Polymer brushes with lubricants show significant potential in reducing contact angle hysteresis, yet the microscopic wetting phenomena and underlying mechanisms remain poorly understood. Our study focuses on observing and analyzing the formation and deformation processes of microscopic wetting ridges to elucidate the macroscopic reduction of contact angle hysteresis and the dynamic wetting...

We investigate the influence of substrate softness on biofilm growth amending the thin-film
model developed by Trinschek et al for rigid solid substrates [1] by the inclusion of a simple
description of an elastic substrate [2]. Wettability (described in the mesoscopic model by
a wetting energy) is a key factor in the transition between arrested and continuous spread-
ing on rigid...

After the discovery of biomolecular condensates in biological cells, research in
this field has increased dramtatically. Cells use those condensate droplets as well
as membranes to structure their interior. The interaction between membrane and
droplet can lead to topological changes in cells like fission or fusion of membranes,
which are little understood.
In this talk, we will present a...

Colloids suspended in a primary fluid can be made to aggregate by adding a small amount of an immiscible secondary liquid: the three types of interfacial tension in this system conspire to form liquid bridges between the colloids that bind the colloids together, see as illustrated. The resulting mixtures vary from viscous fluids to elastic gels, with various promising applications, e.g. in the...

Sliding water drops on hydrophobic insulating surfaces leads to charge separation at the three-phase contact line [1]. Although slide electrification has been investigated thoroughly, understanding the exact mechanism is still a challenge. Electron transfer, formation of the electrical double layer structure, and adsorption of ions have been associated to this phenomenon [2]. Slide...

We investigate the effect of polydispersity on the properties of curved linear
brushes in good solvent and for molten brushes. To this end, we extend the strong stretching
theory for polydisperse brushes to curved geometries and investigate the polymer chain end profiles,
bending moduli and other properties for experimentally relevant polymer chain length distributions
of the Schulz-Zimm...

Nowadays, there are many applications where knowledge of surface wettability is needed. For example, these are microfluidic devices, oil/water separation, drug delivery, etc. There are two approaches to control the wettability properties of materials: changing their topography or modifying them with different surface groups. Changing the surface topography, which can be achieved by applying...

Infuse a nanostructured surface with a thin oil-film, and now you have prepared a dance floor for droplets to waltz on! We recently discovered when droplets condense on lubricated surfaces, they spontaneously dance in serpentine, self-avoiding fashions (left), before switching to circling motions, like whirling dervishes in a trance (right, bottom). The driving force behind this dance is the...

The phenomenon of wetting holds considerable significance, particularly when examined at the microscale, where it underpins a plethora of technological and fundamental advancements. In this study, we employ Atomic Force Microscopy to delve into the size-dependency of microdroplets, focusing on a scale where surface forces and gravity effects are minimal. To achieve this, we employ a...

We present a mesoscopic thin-film model in gradient dynamics form for binary liquid mixtures on brush-covered substrates incorporating volatility in a narrow gap. Thereby, we expand models established in [1, 4–6] by incorporating two substances present in each of three bulk phases - liquid, brush and gas. We discuss the different contributions to the free energy, thereby employing...