Sizhu Wu

Multifunctional ultrathin aluminum foil: oil/water separation and particle filtration

We present here a kind of novel multifunctional ultrathin aluminum foil which consists of large-area regular micropore arrays covered with nanostructures. These multiscale micro/nanostructures show underwater superoleophobic ability (contact angle > 150°) and oil/water separation function. The novel foils were realized by one-step femtosecond laser irradiation, which is a simple and promising method for preparing special micro/nanostructures due to its high precision, excellent controllability, one-step processing and compatible with various materials. In addition, the micropore arrayed aluminum foil also shows robust filtering performance for particles with different sizes, exhibiting multifunctional applications. This work provides a new way for the construction of aluminum foil-based micropore arrays which can be applied in high-efficiency oil/water separation, particle sorting, and other broader fields.

Biomimetic surfaces with anisotropic sliding wetting by energy-modulation femtosecond laser irradiation for enhanced water collection

Biological rice leaf surfaces show a distinct anisotropic sliding property by means of three-level macrogrooves and micro/nanostructures, and they have many potential applications in biomimetic cell movement control, water transportation, and microfluidic devices. However, fabricating artificial three-level biosurfaces with a controllable anisotropic sliding property by a simple and effective method remains a challenge. Herein, we report a simple method to prepare hierarchical groove structures (macro and micro/nano) on polydimethylsiloxane (PDMS) films using energy-modulation femtosecond laser scanning. The macrogrooves for anisotropic control were realized by larger-energy (>0.40 J cm−2) laser scanning, whereas the micro/nanostructures for superhydrophobic ability were fabricated by small-energy (0.08 J cm−2) laser scanning. The processed surface shows a sliding angle (SA) difference of 6° between the perpendicular and parallel directions, which is comparable to that of the natural rice leaf. To quantitatively investigate the anisotropic wettability, surfaces with a different period (100 to 600 μm) and height (30 to 100 μm) were systematically fabricated by adjusting the scanning space and pulse energy. Finally, the distinct ability of the dynamic water droplet anisotropic sliding and size-constrained fog deposition on the anisotropic biosurfaces was demonstrated. The collection efficiency of water on the anisotropic surface with a rotation of 5 and 10 degrees is four times and eighty times higher than that on an isotropic surface.

Three-level cobblestone-like TiO2 micro/nanocones for dual-responsive water/oil reversible wetting without fluorination

In this work, a kind of three-level cobblestone-like anatase TiO2 microcone array was fabricated on titanium sheets by femtosecond laser-induced self-assembly. This three level structure consisted of cobblestone-like features (15–25 μm in height and 20–35 μm in diameter), ∼460 nm ripple-like features, and smaller particles (10–500 nm). The formation of microcone arrays can be ascribed to the interaction of alternant laser beam ablation. TiO2 surfaces display dual-responsive water/oil reversible wetting via heat treatment and selective UV irradiation without fluorination. It is indicated that three-level scale surface roughness can amplify the wetting character of the Ti surface, and the mechanism for reversible switching between extreme wettabilities is caused by the conversion between Ti-OH and Ti-O. Moreover, the double-faced superhydrophobic and double-faced superhydrophilic Ti samples were constructed, which exhibited stable superhydrophobicity and underwater superoleophobicity in water-oil solution, ...

One-step facile fabrication of controllable microcone and micromolar silicon arrays with tunable wettability by liquid-assisted femtosecond laser irradiation

Micro/nanostructured silicon surfaces are attracting more and more research attention because of the wide range of applications in optoelectronic devices, microelectronics, microfluidics, and biomedical devices. Despite numerous efforts for fabricating a variety of micro/nanostructures, a one-step, facile and effective method for preparing diverse, three-dimensional micro/nanostructures is still desired. In this paper, a new approach based on liquid (ethanol and sucrose solution) assisted femtosecond laser irradiation on silicon substrates was proposed for the preparation of controllable microcones and micromolars arrays. Their height can be controlled from 3.3 to 17.6 μm for microcones and 5.9∼33.7 μm for micromolars by adjusting the pulse energy. The processed surfaces are superhydrophilic (25.05∼2.46°), superoleophilic (7.22∼0°), and underwater superoleophobic (124.9∼169.2°). The surfaces further demonstrate many distinct functions such as fog collecting and volatilizing, droplet storage and transportation, and liquid directional transfer. Our proposed method features rapidness, simplicity and easiness of large-area fabrication, which may find enormous potential applications in many fields such as microfluidic devices, fluid microreactors, biomedicine, and chemical–biological sensors.

Switchable Underwater Bubble Wettability on Laser-Induced Titanium Multiscale Micro-/Nanostructures by Vertically Crossed Scanning

We present here a kind of novel multiscale TiO2 square micropillar arrays on titanium sheets through vertically crossed scanning of femtosecond laser. This multiscale micro-/nanostructure is ascribed to the combination of laser ablation/shock compression/debris self-deposition, which shows superaerophobicity in water with a very small sliding angle. The laser-induced sample displays switchable bubble wettability in water via heating in a dark environment and ultraviolet (UV) irradiation in alcohol. After heating in a dark environment (0.5 h), the ablated titanium surface shows superaerophilicity in water with a bubble contact angle (BCA) of ∼4°, which has a great ability of capturing bubbles in water. After UV irradiation in alcohol (1 h), the sample recovered its superaerophobicity in water and the BCA turns into 156°. The mechanism of reversible switching is believed as the chemical conversion between Ti-OH and Ti-O. It is worth noting that our proposed switching strategy is time-saving and the switch wetting cycle costs only 1.5 h. Then we repeat five switching cycles on the reversibility and the method shows excellent reproducibility and stability. Moreover, laser-induced samples with different scanning spacing (50-120 μm) are fabricated and all of them show switchable underwater bubble wettability via the above tunable methods. Finally, we fabricate hybrid-patterned microstructures to show different patterned bubbles in water on the heated samples. We believe the original works will provide some new insights to researchers in bubble manipulation and gas collection fields.

In situ tunable bubble wettability with fast response induced by solution surface tension

Underwater bubble wettability is attracting more and more research attention due to its important applications in the fields of water treatment, anti-fouling and drag-reduction. However, the realization of in situ tunable bubble wettability on smart materials remains challenging. In this work, we proposed a facile method to realize in situ tunable bubble wettability on titanium surfaces via controlling the alcohol volume fraction in aqueous solution. By continuously adding alcohol into pure water, the bubble contact angle on the as-prepared sample is gradually in situ tuned from superaerophilicity to superaerophobicity. This mechanism could be ascribed to the underwater competition between the air and alcohol molecules inside the micro/nanotextures induced by the variation of the solution surface tension. This tuning strategy is suitable for a variety of materials as long as the solute is soluble in water and can reduce the surface tension of a mixed solution in a wide range. By utilizing the proposed strategy, we conduct a demonstrative experiment on the samples with in situ tunable bubble wettability to show the light on–off function in liquid, which can be used as an optical switch. Furthermore, a through-microholes-array titanium foil was fabricated for the selective passing/blocking of bubbles in the liquid medium. Finally, the underwater superaerophilic titanium foil could be used for collecting gas in a solution medium.