The formation of a bridging gas capillary between superhydrophobic surfaces in water gives rise to strongly attractive interactions ranging up to several micrometers on separation. However, most liquids used in materials research are oil-based or contain surfactants. Superamphiphobic surfaces repel both water and low-surface-tension liquids. To control the interactions between a superamphiphobic surface and a particle, it needs to be resolved whether and how gas capillaries form in non-polar and low-surface-tension liquids. Such insight will aid advanced functional materials development. Here, we combine laser scanning confocal imaging and colloidal probe atomic force microscopy to elucidate the interaction between a superamphiphobic surface and a hydrophobic microparticle in three liquids with different surface tensions: water (73 mN m−1), ethylene glycol (48 mN m−1) and hexadecane (27 mN m−1). We show that bridging gas capillaries are formed in all three liquids. Force-distance curves between the superamphiphobic surface and the particle reveal strong attractive interactions, where the range and magnitude decrease with liquid surface tension. Comparison of free energy calculations based on the capillary menisci shapes and the force measurements suggest that under our dynamic measurements the gas pressure in the capillary is slightly below ambient. © 2023, The Author(s).

Forces exerted at surfaces and interphases due to formation of gaseous (air or vapor) bridges describe the extreme liquid repellence in superhydrophobicity (SH) and amphiphobicity. The neighboring research areas of liquid capillary bridges and that of interactions between hydrophobic surfaces are highly valuable reference systems. We review recent findings with particular focus on the three-phase contact line and surface forces. Although macroscopic contact angles (>150°), low contact angle hysteresis (<10°, but can be high; parahydrophobic or petal type) and low roll-off angle (≤5–10°) are adequate criteria for SH and superamphiphobicity (SA) for most studies, a detailed understanding requires a view related to mechanisms. Experimental studies of liquid drop–substrate and particle–substrate adhesion in hydrophobic, SH, and SA systems are summarized by relating measured forces to the wetting tension, γcosθ. A low wetting tension value is a necessary but not sufficient criterion for SH and SA systems. The picture emerging from detailed force distance studies is that extreme liquid repellence in SH and SA systems is a progression of liquid repellence due to hydrophobicity, in which force curves can be explained by capillary forces of constant volume of the gaseous capillary. In SH and SA, neither the capillary force equation assuming constant volume nor constant pressure of the gaseous capillary explains experimental force measurements as the capillary increases in both volume and pressure. In recent experimental studies, a transition is observed into nonconstant volume and pressure which suggests an SH and SA wetting transition from constant volume or pressure to a capillary growth as driven by the γA and the PV works but also by forces at the three-phase contact SLV (solid-liquid-vapor) line, viz. pinning forces, Fpin and Fdepin, and line energy, (τL)SLV, terms. Supported by calculations of the different contributions, we suggest this transition being an appropriate definition for the onset of (appreciable) SH and SA. © 2019 The Author(s)

The increasing utilization of wood-based products raises new demands for improved durability, for example an enhanced liquid repellence. Superhydrophobic or superamphiphobic surfaces have been widely fabricated. Less attention has been paid to such modifications on wood and the changes of its hygroscopic or solvoscopic properties. In this work, wood veneers were surface modified by hydrophobized silicone nanofilaments. Results revealed that the surface-modified wood showed a superamphiphobic behavior, i.e. it repelled water, ethylene glycol and hexadecane with contact angles greater than 150° and roll-off angles of less than 10°. Most importantly, a plastron effect was observed when the surface-modified wood was submerged in water, ethylene glycol or hexadecane, which reduced the liquid sorption rate and extent to various degrees. By comparing the measured permeabilities and the estimated diffusive mass flux and supported by Hansen solubility parameters and the degrees of swelling, it is concluded that diffusion is the major cause for the liquid uptake in the surface-modified wood. Moreover, the interaction between the liquid and the modified layer (the solubility of the liquid in the modified layer) also needs to be considered, especially in hexadecane. © 2020 The Authors

Sensorineural hearing loss due to aging, noise exposure, trauma or drug ototoxicity is irreversible because cochlear hair cells and neurons cannot regenerate. Recently, therapeutic strategies involving nanoparticles have been developed as innovative drug delivery systems. Thermodynamically stable liquid crystalline nanoparticles based on the polar lipid glycerol monooleate (GMO NP, cubosomes), nontoxic and able to encapsulate both hydrophilic and hydrophobic compounds, were produced and tested for biocompatibility in an immortalized Organ of Corti derived cell line (OC-k3), through cell viability and cytomorphological assays, and Western blot expression profiles of apoptotic markers. Overall, the GMO NP were biocompatible in OC-k3 at the doses and time tested, supporting previous data obtained in a neuronal cell line (PC12). The results encourage further tests on GMO NP-mediated drug release with improved target specificity and could be useful to develop innovative therapies against sensorineural hearing loss.

The formation of a bridging gas meniscus via cavitation or nanobubbles is considered the most likely origin of the submicrometer long-range attractive forces measured between hydrophobic surfaces in aqueous solution. However, the dynamics of the formation and evolution of the gas meniscus is still under debate, in particular, in the presence of a thin air layer on a superhydrophobic surface. On superhydrophobic surfaces the range can even exceed 10 μm. Here, we report microscopic images of the formation and growth of a gas meniscus during force measurements between a superhydrophobic surface and a hydrophobic microsphere immersed in water. This is achieved by combining laser scanning confocal microscopy and colloidal probe atomic force microscopy. The configuration allows determination of the volume and shape of the meniscus, together with direct calculation of the Young-Laplace capillary pressure. The long-range attractive interactions acting on separation are due to meniscus formation and volume growth as air is transported from the surface layer.

Superhydrophobic surfaces in the Cassie-Baxter wetting state retain an air layer at the surface which prevents liquid water from reaching into the porous surface structure. In this work we explore how addition of ethanol, which reduces the surface tension, influences the wetting properties of superhydrophobic and smooth hydrophobic surfaces. Wetting properties are measured by dynamic contact angles, and the air layer at the superhydrophobic surface is visualized by laser scanning confocal microscopy. Colloidal probe atomic force microscopy measurements between a hydrophobic microsphere and the macroscopic surfaces showed that the presence of ethanol strongly affects the interaction forces. When the macroscopic surface is superhydrophobic, attractive forces extending up to a few micrometers are observed on retraction in water and in 20 vol % ethanol, signifying the presence of a large and growing gas capillary. Submicrometer attractive forces are observed between the probe particle and a smooth hydrophobic surface, and in this case a smaller gas capillary is formed. Addition of ethanol results in markedly different effects between superhydrophobic and hydrophobic surfaces. In particular, we show that the receding contact angle on the superhydrophobic surface is of paramount importance for describing the interaction forces.

An innovative approach to improve drug delivery is the use of glycerol monooleate nanoparticles. Numerous studies describe their high versatility, low toxicity and ability to carry relatively high loads of conjugated compounds including scarcely soluble ones, providing sustained drug release and increasing drug diffusion and half-life. Despite a growing interest in their potential use for therapeutic applications, there are surprisingly few literature data concerning the toxic effects of these nanoparticles at high concentrations in vitro and in vivo, and their effects on cell metabolism. We produced and characterized from a physical-chemical point of view glycerol monooleate nanoparticles and tested them on the PC12 cell line, a rat model of neuronal differentiation. The toxicity of these nanoparticles was evaluated by molecular methods on cell viability, cell cycle, nanoparticle uptake and induction of apoptosis. The results showed that glycerol monooleate nanoparticles up to 100 μg/mL had no toxic effects on PC12 cells, did not induce significant changes in the cell cycle nor cause apoptosis. The nanoparticles entered PC12 cells 8 h after treatment, successfully delivering the conjugate compound inside cells. Overall, glycerol monooleate nanoparticles did not exhibit significant toxicity on PC12 cell line in concentrations up to 100 µg/mL, supporting their therapeutic use as drug delivery systems.