Ville Jokinen

Water condensation on superhydrophobic surfaces can generate spontaneous droplet jumping, enabling rapid condensate removal and improved thermal and mass transfer. Although this effect has been extensively demonstrated on densely packed nanostructures, the capability of microscale textures to support jumping condensation remains poorly understood. By systematically varying cone pitch within a series of microcone arrays with comparable cone geometries, we observe previously unreported spacing‐dependent transition between jumping and non‐jumping regimes. In the jumping regime, we identify a geometric threshold below which sub‐10 µm droplets are rapidly removed, and above which jumping is suppressed, resulting in slower dynamics and larger departing droplets. In situ optical and environmental scanning electron microscopies provide evidence supporting a mechanistic interpretation of this transition: dense arrays favor full Cassie droplets, which depart cleanly, while wider spacing favors partial Cassie droplets that retain a localized wet region initiating new nucleation. Our findings establish a mechanistic link between the morphology of condensing microdroplets and the macroscopic jumping dynamics that govern performance in anti‐fogging, water harvesting, and heat‐transfer applications.

Omniphobic surfaces are capable of repelling a wide range of liquids, including low-surface-tension oils. This contrasts with superhydrophobic surfaces, which only repel water and other liquids with high surface tension. One problem with omniphobic surfaces is that the fabrication processes tend to be more complicated and include more steps than those of superhydrophobic surfaces. The reason is the re-entrant pillar geometries that are required for omniphobicity. In this study, we present two streamlined, proof-of-concept fabrication processes that create doubly re-entrant pillar structures in a single, uninterrupted, multi-step etching process executed in one plasma reactor and requiring only one lithography step. The key innovation is a self-aligning process that uses plasma-deposited fluoropolymer (C₄F₈) as a freestanding structural component of the overhang, rather than merely a hydrophobic coating, enabling complete fabrication without tool changes. We show that the fabricated surfaces reliably repel low-surface-tension liquids, including 2-propanol and ethanol, as demonstrated by high dynamic contact angles, low sliding angles, and droplet rebound upon impact. In the best-performing sample, the advancing contact angle for 2-propanol was measured at 164°, with a receding contact angle of 135°, and droplets rebounded from the surface.

Superhydrophobic surfaces hold great promise for various engineering applications. However, their fragility and limited durability in real-world scenarios pose significant challenges. Here, a durable superhydrophobic and icephobic surface is fabricated using the metal-assisted chemical etching method to create silicon nanowires within inverted pyramidal microstructures. Mechanical robustness is introduced by applying a hard coating to the structure through titanium film deposition, followed by annealing in a nitrogen atmosphere, which forms titanium silicide and titanium nitride. The hard-coated surfaces can endure up to 60 g of sand abrasion or 20 icing-shearing cycles while still retaining their superhydrophobic properties (advancing and receding contact angles of approximately 150°) and icephobic properties (ice adhesion strength of approximately 10 kPa).

Superhydrophobic (SHB) glass capillaries are fabricated by depositing thin alumina and its conversion into grass-like alumina. The capillaries repel water and biofluids including blood which indicates their applications in blood contacting devices.

Understanding the friction forces acting on droplets moving across non-wetting surfaces is essential for advancing applications in fluid transport and microfluidics. In this study we quantify droplet friction on both superhydrophobic and superheated (Leidenfrost) substrates using two complementary experimental approaches: inclined plane dynamics and cantilever force sensing. We identify distinct friction regimes governed by contact-line pinning, viscous dissipation, and aerodynamic drag over a broad range of velocities and viscosities. A force-based scaling law captures the transition between these regimes as a function of the capillary number, integrating contact-line effects, internal dissipation, and aerodynamic contributions. Our model is further validated through white light interferometry and high-speed reflective interference contrast microscopy, which reveal the structure and evolution of the thin air or vapor layers beneath the droplets. These findings offer a comprehensive framework for predicting droplet behavior on non-wetting surfaces and inform the design of surfaces for reduced friction in engineering and microfluidic systems.

Control of cell adhesion is essential for biomedical devices, biosensors, and anti‐fouling coatings. Here, adhesion of A549 epithelial cells is systematically evaluated on silicon substrates with tunable wettability (superhydrophilic to superhydrophobic) and topography (smooth, nanostructured, and micropillared). Superhydrophobic surfaces stabilize a trapped air plastron that minimizes solid–liquid contact, enabling plastron‐mediated physical repellency of cells . The most cell‐repellent surface, composed of 5 µm micropillars with a 7.4% solid–liquid contact fraction, reduced cell density by ≈83% versus a smooth hydrophobic control and ≈95% versus a hydrophilic control at 4 h, and by ≈90% and ≈93%, respectively, after 24 h of incubation, corresponding to an approximate tenfold decrease in cell adhesion. Micropillar arrays outperform nanostructures in resisting cell attachment, owing to large air‐filled gaps exceeding 10 µm that physically prevent cell adhesion. A trade‐off is observed: lower solid‐fraction micropillars provide greater short‐term repellency but lose the plastron over time, enabling delayed fouling, whereas higher‐fraction structures preserve the air layer beyond 72 h but are initially less cell‐repellent due to higher effective cell contact area and smaller air gaps. These results establish that optimized microscale superhydrophobic textures achieve superior and time‐dependent bio‐repellency and introduce a rational design strategy for non‐fouling materials.

Superhydrophobic surfaces find applications in numerous biomedical scenarios, requiring the repellence of biofluids and biomolecules. Plastron, the trapped air between a superhydrophobic surface and a wetting liquid, plays a pivotal role in biofluid repellency. A key challenge, however, is the often short-lived plastron stability in biofluids and the lack of knowledge surrounding it. Plastron stability refers to the duration for which a surface remains in the Cassie state before transitioning to the fully wetting Wenzel state. Here, a submersion test with real-time optical monitoring is used to determine the plastron lifetime of different superhydrophobic surfaces upon immersion in various biofluids. We find that biofluids of all types exhibit shorter plastron lifetimes compared to pure water, which is attributed to their lower surface tension and biomolecular adsorption through hydrophobic-hydrophobic interactions. Proteins and glucose are identified as the major contributors to plastron dissipation in fetal bovine serum-based biofluids. Plastron minimizes the solid-liquid interface, reducing biomolecular adsorption, making its stability crucial for biofluid repellence. Thus, the effects of surface texture, feature size, Cassie solid fraction, Wenzel dimensionless roughness, and surface chemistry on plastron stability are investigated. Our key findings indicate that prolonged plastron stability and thus enhanced biofluid repellency are achieved through a combination of larger plastron volumes, increased Wenzel roughness degrees, greater Cassie solid fractions, and smaller feature sizes. We demonstrate that with optimized parameters, our surface design can maintain plastron stability and sustain a consistent solid-liquid area fraction for over 120 h in complex biofluids containing high levels of protein and glucose, underscoring a robust design for long-term use in biomedical and antifouling applications. This research is essential for advancing the design of superhydrophobic surfaces that effectively resist biofouling in diverse medical and engineering settings.

Bosch etching and photoresist micromasks were used to create nanojungle black silicon (b-Si) with heights over 10 μm. This nanojungle b-Si shows superior superhydrophobic robustness compared to traditional nanograss b-Si.