Vapor Swelling of Polymer Brushes Compared to Nongrafted Films

Does the Topology of Polymer Brushes Determine Their (Vapor-)Solvation?

When the topology of polymer brushes is changed from linear to cyclic or looped, many of the brush properties will be improved. Yet, whether such a topology variation also affects the (vapor-)solvation and swelling of brushes has remained unclear. In fact, in a recent publication, Vagias and co-workers (Macromolecular Rapid Communications 2023, 44 (9), 2300035) reported an unequal swelling for linear and cyclic brushes and challenged theoreticians to develop a new Flory-Huggins theory that includes topology effects. In this letter, we address this challenge and employ molecular dynamics simulations to study the vapor swelling of linear, looped, and cyclic brushes. We find that the emergence of equal or unequal swelling for different topologies depends on the definition of the grafting density that is kept constant in the comparison. When suitably defined, the degree of swelling is independent of the topology, and the Flory-Huggins theory for brushes will describe brush swelling for all topologies in the present study.

Thermally Activated Swelling and Wetting Transition of Frozen Polymer Brushes:a New Concept for Surface Functionalization

Functional polymer brush coatings have great potential for various industrial applications thanks to their ability to adapt to environmental stimuli, providing tunable surface properties. While existing approaches rely on polymer-solvent interactions and their response to external stimuli, changes in the intrinsic physical properties of the polymer also play a critical role in modulating brush behavior. In this context, the melting transition of a semicrystalline oleophilic poly-octadecylmethacrylate (P18MA) brush coating is shown to drive a swelling and wetting transition upon exposure to various liquid alkanes. The top surface of this polymer displays a somewhat higher melting temperature than the bulk, enabling separate control of the bulk-driven swelling and surface-driven wetting transitions. Laser-induced heating enables reversible on-demand activation of both transitions with micrometer lateral resolution. These findings suggest a new concept of polymer brush-based functional surfaces that allow for controlled fluid transport via separately switchable surface barriers and bulk transport layers based on a suitable choice of polymer-polymer and polymer-solvent interactions.

Exploring Scent Distinction with Polymer Brush Arrays

The ability to distinguish scents, volatile organic compounds (VOCs), and their mixtures is critical in agriculture, food safety, and public health. This study introduces a proof-of-concept approach for VOC and scent distinction, leveraging polymer brush arrays with diverse chemical compositions designed to interact with various VOCs and scents. When VOCs or scents are exposed to the brush array, they produce distinct mass absorption patterns for different polymer brushes, effectively creating "fingerprints". Scents can be recognized without having to know the absorption of their individual components. This allows for a scent distinction technique, mimicking scent recognition within a mammalian olfactory system. To demonstrate the scent distinction, we synthesized different polymer brushes, zwitterionic, hydrophobic, and hydrophilic, using surface-initiated photoinduced electron transfer-reversible addition-fragmentation chain-transfer polymerization with eosin Y and triethanolamine as catalysts. The polymer brushes were then exposed to vapors of different single-compound VOCs and complex scents consisting of many VOCs, such as the water-ethanol mixture, rosemary oil, lavender oil, and whiskey scents. Quartz crystal microbalance measurements with dissipation monitoring (QCM-D) show a clear difference in brush absorption for these diverse VOC vapors such that distinct fingerprints can be identified. Our proof-of-concept study aims to pave the way for universal electronic nose sensors that distinguish scents by combining mass absorption patterns from polymer brush-coated surfaces.

Response to Comment on "Vapor Lubrication for Reducing Water and Ice Adhesion on Poly(dimethylsiloxane) Brushes": Organic Vapors Influence Water Contact Angles on Hydrophobic Surfaces

Fast removal of water drops from solid surfaces is important in many applications such as on solar panels in rain, in heat transfer, and for water collection. Recently, a reduction in lateral adhesion of water drops on poly(dimethylsiloxane) (PDMS) brush surfaces after exposure to various organic vapors was reported. It was attributed to the physisorption of vapor and swelling of the PDMS brushes. However, it was later pointed out that a change in the interfacial energies by vapor adsorption could also have caused low drop adhesion. To find out how strongly each effect contributes, contact angles of water drops on three hydrophobic surfaces in different vapors are measured. In water-soluble vapors, a substantial decrease is observed in contact angles. This decrease can indeed be explained by a vapor-induced change in the interfacial tensions. The very low contact angle hysteresis on PDMS surfaces in saturated n-hexane and toluene vapor cannot be explained by a change in interfacial tensions. The observation supports the hypothesis that these vapors adsorb into the PDMS and form a lubricating layer. It is hoped that these findings help to solve fundamental problems and contribute to applications, such as anti-icing, heat transfer, and water collection.