Jian-Nan Wang

One-step preparation of regular micropearl arrays for two-direction controllable anisotropic wetting.

In this paper, one simple method to control two-direction anisotropic wetting by regular micropearl arrays was demonstrated. Various micropearl arrays with large area were rapidly fabricated by a kind of improved laser interference lithography. Specially, we found that the parallel contact angle (CA) theta(2) decreased from 93 degrees to 67 degrees as the intensity ratio of four laser beams increased from 2:1 to 30:1, while the perpendicular CA theta(1) determined by the thickness of the resin remained constant. This was interpreted as the decrease of height variations Delta h from 1100 to 200 nm along the parallel direction caused by the increase of the intensity ratio. According to this rule, both theta(1) and theta(2) could be simultaneously controlled by adjusting the height variation Delta h and the resin thickness. Moreover, by combining appropriate design and low surface energy modification, a natural anisotropic rice leaf exhibiting CAs of 146 degrees +/- 2 degrees/153 degrees +/- 3 degrees could be mimicked by our anisotropic biosurface with the CAs 145 degrees +/- 1 degrees/150 degrees +/- 2 degrees. We believe that these controlled anisotropic biosurfaces will be helpful for designing smart, fluid-controllable interfaces that may be applied in novel microfluidic devices, evaporation-driven micro/nanostructures, and liquid microdroplet directional transfer.

Biomimetic Graphene Surfaces with Superhydrophobicity and Iridescence

Triggered by the fantastic functions and bright appearance of biological systems in nature, enormous efforts have been devoted to biomimetic fabrication. For instance, butterfly wings and red rose petals have attracted increasing attention due to their excellent water repellency and splendid structural color. Consequently, colorful superhydrophobic surfaces have become a hot topic with significance in both fundamental research and practical applications. Previous studies have shown that hierarchical micro-/nanostructures on biosurfaces play a critical role in the multifunctional acquisition. On the one hand, the highly rough textures trap a wealth of air bubbles at the interface preventing a water droplet from spreading; thus, the surfaces exhibit a high water contact angle (CA>1508). Along this line, a variety of water-repellent surfaces with multiscale structures have been achieved by classical “top-down” and “bottomup” approaches. On the other hand, as inspired by many natural species that use structural color as a warning or protection, the surface microstructures are not randomly distributed but rigidly arranged in periodic micro-patterns, and therefore triggered light diffraction and scattering contribute to the brilliant appearance. However, due to technical challenges in the fabrication of uniform and well-defined nanostructures in the long-range order, most of the superhydrophobic surfaces hardly show any structural color. To date, only a few attempts to such multifunctional surfaces have been realized. For instance, Gu et al. fabricated colloidal photonic crystal films with both structural color and superhydrophobicity at the cost of long time and high temperature. Jiang et al. reported multicolor superhydrophobic coatings that depend on metal ions for the appearance of color; in their study, individual samples exhibited a single color. Wu et al. fabricated superhydrophobic surfaces with iridescence by employing multiple procedures including interference, surface modification, and chemical plating. Consequently, a facile and convenient approach for surfaces with superhydrophobicity and iridescent structural color is in urgent need. Unlike the classical slippery superhydrophobic surface represented by the famous self-cleaning lotus leaf, rose petals possess a sticky superhydrophobicity, exhibiting both a high water contact angle (CA>1508) and strong adhesion. Because of the adhesive force, flowers are able to maintain a fresh appearance, as a water droplet cannot roll off effortlessly but stays stably on the surface without any movement. To date, by tailoring the chemical composition, the geometrical structure, or interfacial capillary and van der Waals forces, superhydrophobic surfaces with high adhesion were successfully prepared. Due to their representativeness in wetting behavior and their research value in various realms, such as liquid transportation in microfluidic systems and biomedical applications, high-adhesion surperhydrophobic surfaces become increasingly important. Recently, graphene has attracted much attention due to its unique single atom-layer structure, which contributes to its wide applications in nanoelectronics, sensing devices, energy storage, and even tissue engineering. For example, graphene has proven to be a promising biocompatible scaffold that could accelerate the specific differentiation of human mesenchymal stem cells (hMSCs) into bone cells. In this case, the cell adhesion on the graphene surface plays a critical role in the long-term differentiation; therefore, a precise control of the surface wettability of graphene becomes a significant issue. Generally, superhydrophobic graphene substrates could be fabricated by using an irregular stack of graphene oxides (GO) prepared by chemical oxidation of graphite. In this procedure, to reduce the surface energy, the hydrophilic oxygen-containing groups on the GO surface have to be removed beforehand. To the best of our knowledge, modulation of the wetting property of graphene by micro-/nanostructuring and simultaneous control of chemical composition have not been realized. Moreover, despite the pioneering biomimetic fabrications of periodic micro-/nanostructures based on a wide range of materials, a bioinspired graphene surface with properties comparable to natural surfaces has not been reported yet. [a] J.-N. Wang, R.-Q. Shao, Dr. Y.-L. Zhang, L. Guo, Prof. H.-B. Sun State Key Laboratory on Integrated Optoelectronics College of Electronic Science and Engineering Jilin University 2699 Qianjin Street, Changchun 130012 (P. R. China) Fax: (+86)431-85168281 E-mail : yonglaizhang@jlu.edu.cn hbsun@jlu.edu.cn [b] H.-B. Jiang, D.-X. Lu, Prof. H.-B. Sun College of Physics Jilin University 2699 Qianjin Street, Changchun 130012 (P. R. China) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/asia.201100882.

Solvothermal synthesis of nanoporous polymer chalk for painting superhydrophobic surfaces.

Reported here is a facile synthesis of nanoporous polymer chalk for painting superhydrophobic surfaces. Taking this nanoporous polymer as a media, superhydrophobicity is rapidly imparted onto three typical kinds of substrates, including paper, transparent polydimethylsiloxane (PDMS), and finger skin. Quantitative characterization showed that the adhesion between the water droplet and polymer-coated substrates decreased significantly compared to that on the original surface, further indicating the effective wetting mode transformation. The nanoporous polymer coating would open a new door for facile, rapid, safe, and larger scale fabrication of superhydrophobic surfaces on general substrates.

A simple strategy to realize biomimetic surfaces with controlled anisotropic wetting

The study of anisotropic wetting has become one of the most important research areas in biomimicry. However, realization of controlled anisotropic surfaces remains challenging. Here we investigated anisotropic wetting on grooves with different linewidth, period, and height fabricated by laser interference lithography and found that the anisotropy strongly depended on the height. The anisotropy significantly increased from 9° to 48° when the height was changed from 100 nm to 1.3 μm. This was interpreted by a thermodynamic model as a consequence of the increase of free energy barriers versus the height increase. According to the relationship, controlled anisotropic surfaces were rapidly realized by adjusting the grooves’ height that was simply accomplished by changing the resin thickness. Finally, the perpendicular contact angle was further enhanced to 131°±2° by surface modification, which was very close to 135°±3° of a common grass leaf.

Controllable assembly of silver nanoparticles induced by femtosecond laser direct writing

Abstract We report controllable assembly of silver nanoparticles (Ag NPs) for patterning of silver microstructures. The assembly is induced by femtosecond laser direct writing (FsLDW). A tightly focused femtosecond laser beam is capable of trapping and driving Ag NPs to form desired micropatterns with a high resolution of ∼190 nm. Taking advantage of the ‘direct writing’ feature, three microelectrodes have been integrated with a microfluidic chip; two silver-based microdevices including a microheater and a catalytic reactor have been fabricated inside a microfluidic channel for chip functionalization. The FsLDW-induced programmable assembly of Ag NPs may open up a new way to the designable patterning of silver microstructures toward flexible fabrication and integration of functional devices.

Reversible switching between isotropic and anisotropic wetting by one-direction curvature tuning on flexible superhydrophobic surfaces

In this letter, we report a kind of smart surfaces with reversible switching between isotropy and anisotropic wetting, which was realized by one-direction curvature tuning on flexible superhydrophobic surfaces. Along the curvature change, the wettability of this flexible film was changed from isotropic state (150°/150°) into anisotropic state confirmed by its anisotropic contact angles (150°/160°) and sliding properties (30°/65°). Further investigation revealed that the surface wettability was changed from composited pinned state into transitional state. This was attributed to the increase in roughness factor and the decrease in the contact area between the water droplet and the pillar array. At last, we demonstrate that the wetting states between isotropy and anisotropy on this flexible superhydrophobic film could be reversibly switched by curvature for many times (>10).