Yanlin Song

Applications of Bio-Inspired Special Wettable Surfaces

In this review we focus on recent developments in applications of bio-inspired special wettable surfaces. We highlight surface materials that in recent years have shown to be the most promising in their respective fields for use in future applications. The selected topics are divided into three groups, applications of superhydrophobic surfaces, surfaces of patterned wettability and integrated multifunctional surfaces and devices. We will present how the bio-inspired wettability has been integrated into traditional materials or devices to improve their performances and to extend their practical applications by developing new functionalities.

Bio-Inspired Strategies for Anti-Icing

Undesired ice accumulation leads to severe economic issues and, in some cases, loss of lives. Although research on anti-icing has been carried out for decades, environmentally harmless, economical, and efficient strategies for anti-icing remain to be developed. Recent researches have provided new insights into the icing phenomenon and shed light on some promising bio-inspired anti-icing strategies. The present review critically categorizes and discusses recent developments. Effectively trapping air in surface textures of superhydrophobic surfaces weakens the interaction of the surfaces with liquid water, which enables timely removal of impacting and condensed water droplets before freezing occurs. When ice already forms, ice adhesion can be significantly reduced if liquid is trapped in surface textures as a lubricating layer. As such, ice could be shed off by an action of wind or its gravity. In addition, bio-inspired anti-icing strategies via trapping or introducing other media, such as phase change materials and antifreeze proteins, are discussed.

Robust Prototypical Anti-icing Coatings with a Self-lubricating Liquid Water Layer between Ice and Substrate

A robust prototypical anti-icing coating with a self-lubricating liquid water layer (SLWL) is fabricated via grafting cross-linked hygroscopic polymers inside the micropores of silicon wafer surfaces. The ice adhesion on the surface with SLWL is 1 order of magnitude lower than that on the superhydrophobic surfaces and the ice formed atop of it can be blown off by an action of strong breeze. The surface with self-lubricating liquid water layer exhibits excellent capability of self-healing and abrasion resistance. The SLWL surface should also find applications in antifogging and self-cleaning by rainfall, in addition to anti-icing and antifrosting.

Superhydrophobic surfaces cannot reduce ice adhesion

Understanding the mechanism of ice adhesion on surfaces is crucial for anti-icing surfaces, and it is not clear if superhydrophobic surfaces could reduce ice adhesion. Here, we investigate ice adhesion on model surfaces with different wettabilities. The results show that the superhydrophobic surface cannot reduce the ice adhesion, and the ice adhesion strength on the superhydrophilic surface and the superhydrophobic one is almost the same. This can be rationalized by the mechanical interlocking between the ice and the surface texture. Moreover, we find that the ice adhesion strength increases linearly with the area fraction of air in contact with liquid.

Anti-icing Coating with an Aqueous Lubricating Layer

In this paper, an anti-icing coating with an aqueous lubricating layer is reported. This anti-icing coating can be directly applied to various substrates, and the ice adhesion strength on the coated surfaces can be lowered greatly as compared to uncoated substrates. We demonstrate for the first time that the formed ice on this anti-icing coating can be blown off by a wind action in the wind tunnel with a controlled temperature and wind velocity. Moreover, the low ice adhesion of the anti-icing coating can be maintained even when the temperature is lowered to -53 °C. The robustness and durability of the anti-icing coating are proved by the icing/de-icing experiments. The results show that the anti-icing coating with an aqueous lubricating layer is of great promise for practical applications.

A Biomimetic Potassium Responsive Nanochannel: G-Quadruplex DNA Conformational Switching in a Synthetic Nanopore

Potassium is especially crucial in modulating the activity of muscles and nerves whose cells have specialized ion channels for transporting potassium. Normal body function extremely depends on the regulation of potassium concentrations inside the ion channels within a certain range. For life science, undoubtedly, it is significant and challenging to study and imitate these processes happening in living organisms with a convenient artificial system. Here we report a novel biomimetic nanochannel system which has an ion concentration effect that provides a nonlinear response to potassium ion at the concentration ranging from 0 to 1500 microM. This new phenomenon is caused by the G-quadruplex DNA conformational change with a positive correlation with ion concentration. In this work, G-quadruplex DNA was immobilized onto a synthetic nanopore, which undergoes a potassium-responsive conformational change and then induces the change in the effective pore size. The responsive ability of this system can be regulated by the stability of G-quadruplex structure through adjusting potassium concentration. The situation of the grafting G-quadruplex DNA on a single nanopore can closely imitate the in vivo condition because the G-rich telomere overhang is attached to the chromosome. Therefore, this artificial system could promote a potential to conveniently study biomolecule conformational change in confined space by the current measurement, which is significantly different from the nanopore sequencing. Moreover, such a system may also potentially spark further experimental and theoretical efforts to simulate the process of ion transport in living organisms and can be further generalized to other more complicated functional molecules for the exploitation of novel bioinspired intelligent nanopore machines.

Bioinspired colloidal photonic crystals with controllable wettability.

Because of the combinatorial advantage of their unique light manipulation properties and potential applications in novel optical devices, colloidal photonic crystals (PCs), the periodic arrangement of monodispersed latex spheres, have attracted interest from researchers. In particular, colloidal PCs exhibit structural colors based on interference effects within their periodic structures. The wavelength of these colors lies in the visible range, making them particularly attractive for a variety of applications. Colloidal PCs are extensively used in templating, catalysis, and chromatographic separations. Inspired by biological PCs with both structural color and specific wettability, researchers have fabricated colloidal PCs with controllable wettability as described in this Account. The wettability can be adjusted by the intrinsic roughness of colloidal crystals in combination with the tunable chemical composition of latex surfaces. Changes in the chemical composition of the latex surface under external stimuli, such as light, electricity, and heat, can reversibly control the wettability of PCs. Furthermore, the hierarchical structure of latex particles can effectively alter the water adhesive force of superhydrophobic colloidal PCs. Patterned PCs with a variety of wettabilities can be assembled using inkjet printing from well-designed latex suspensions. By combining their structural color and specific wettability, we also exemplify some of the promising applications of colloidal PCs as templates for the construction of hierarchical structures, as indicators for controllable transport of liquid droplets, and as color-based sensors for the monitoring changes in their environment. These findings offer innovative insights into the design of novel colloidal PCs and will be of great importance for further applications of these materials.

Colorful humidity sensitive photonic crystal hydrogel

A colorful humidity sensitive photonic crystal (PC) hydrogel was facilely fabricated by infiltrating acrylamide (AAm) solution into a P(St–MMA–AA) PC template and subsequently photo-polymerizing. The color of the samples was sensitive to humidity; it could reversibly vary from transparent to violet, blue, cyan, green and red under various humidity conditions, covering the whole visible range. This could be attributed to the humidity sensitivity of the samples stopband, with a maximum change of 240 nm resulting from the varying humidity. Furthermore, the color response showed good stability under cyclic humidity experiments. As-prepared PAAm–P(St–MMA–AA) PC hydrogel successfully combined the humidity sensitivity of PAAm and structure color of the PC template, which suggested a promising composite material as an economical alternative to traditional humidity sensors, and also provided a new insight into the design and development of novel composite functional materials based on a PC template.

Bio-Inspired Photonic-Crystal Microchip for Fluorescent Ultratrace Detection†

Ultratrace detection attracts great interest because it is still a challenge to the early diagnosis and drug testing. Enriching the targets from highly diluted solutions to the sensitive area is a promising method. Inspired by the fog-collecting structure on Stenocara beetles back, a photonic-crystal (PC) microchip with hydrophilic-hydrophobic micropattern was fabricated by inkjet printing. This device was used to realize high-sensitive ultratrace detection of fluorescence analytes and fluorophore-based assays. Coupled with the fluorescence enhancement effect of a PC, detection down to 10(-16) mol L(-1) was achieved. This design can be combined with biophotonic devices for the detection of drugs, diseases, and pollutions of the ecosystem.

Anti-icing surfaces based on enhanced self-propelled jumping of condensed water microdroplets

A spontaneous and controllable removal of condensed microdroplets at high supersaturation via self-propelled jumping is achieved by introducing a designed micropore array on a nanostructured superhydrophobic surface. The fabricated surface was demonstrated to delay the ice formation for 1 hour at -15 °C with a supersaturation of 6.97.