Long-term stability of aerophilic metallic surfaces underwater.

Aerophilic surfaces immersed underwater trap films of air known as plastrons. Plastrons have typically been considered impractical for underwater engineering applications due to their metastable performance. Here, we describe aerophilic titanium alloy (Ti) surfaces with extended plastron lifetimes that are conserved for months underwater.

Ferrofluid Microdroplet Splitting for Population-Based Microfluidics and Interfacial Tensiometry.

Ferrofluids exhibit a unique combination of liquid properties and strong magnetic response, which leads to a rich variety of interesting functional properties. Here, the magnetic-field-induced splitting of ferrofluid droplets immersed in an immiscible liquid is presented, and related fascinating dynamics and applications are discussed. A magnetic field created by a permanent magnet induces instability on a mother droplet, which divides into two daughter droplets in less than 0.

Uncertainties in contact angle goniometry.

The most widely used method to quantify the wetting properties of surfaces is by measuring contact angles. Even though contact angle goniometry is a powerful technique for characterizing wetting properties, it is not accurate for very hydrophobic surfaces. As the technique relies on image processing, it has inherent errors due to optical limitations, especially near the three-phase contact line.

Friction and Wetting Transitions of Magnetic Droplets on Micropillared Superhydrophobic Surfaces.

Reliable characterization of wetting properties is essential for the development and optimization of superhydrophobic surfaces. Here, the dynamics of superhydrophobicity is studied including droplet friction and wetting transitions by using droplet oscillations on micropillared surfaces. Analyzing droplet oscillations by high-speed camera makes it possible to obtain energy dissipation parameters such as contact angle hysteresis force and viscous damping coefficients, which indicate pinning and viscous losses, respectively.

Oscillating Ferrofluid Droplet Microrheology of Liquid-Immersed Sessile Droplets.

The damped oscillations of liquid-immersed ferrofluid sessile droplets were studied with high-speed imaging experiments and analytical modeling to develop a novel microrheology technique. Droplet oscillations were induced with an external magnetic field, thereby avoiding transients in the resulting vibrational response of the droplet. By following the droplet relaxation with a high-speed camera, the frequency and relaxation time of the damped harmonic oscillations were measured.

Complexes of Magnetic Nanoparticles with Cellulose Nanocrystals as Regenerable, Highly Efficient, and Selective Platform for Protein Separation.

We present an efficient approach to develop cellulose nanocrystal (CNC) hybrids with magnetically responsive FeO nanoparticles that were synthesized using the (Fe/Fe) coprecipitation. After 2,2,6,6-tetramethylpiperidine-1-oxyl radical (TEMPO)-catalyzed oxidation of CNC, carbodiimide (EDC/NHS) was used for coupling amine-containing iron oxide nanoparticles that were achieved by dopamine ligand exchange (NH-FeO NPs). The as-prepared hybrids (FeO@CNC) were further complexed with Cu(II) ions to produce specific protein binding sites.

Free-decay and resonant methods for investigating the fundamental limit of superhydrophobicity.

The recently demonstrated extremely water-repellent surfaces with contact angles close to 180° with nearly zero hysteresis approach the fundamental limit of non-wetting. The measurement of the small but non-zero energy dissipation of a droplet moving on such a surface is not feasible with the contemporary methods, although it would be needed for optimized technological applications related to dirt repellency, microfluidics and functional surfaces. Here we show that magnetically controlled freely decaying and resonant oscillations of water droplets doped with superparamagnetic nanoparticles allow quantification of the energy dissipation as a function of normal force.

Switchable static and dynamic self-assembly of magnetic droplets on superhydrophobic surfaces.

Self-assembly is a process in which interacting bodies are autonomously driven into ordered structures. Static structures such as crystals often form through simple energy minimization, whereas dynamic ones require continuous energy input to grow and sustain. Dynamic systems are ubiquitous in nature and biology but have proven challenging to understand and engineer.