Dong Wu

Curvature‐Driven Reversible In Situ Switching Between Pinned and Roll‐Down Superhydrophobic States for Water Droplet Transportation

Artifi cial superhydrophobic surfaces [ 1–10 ] with water contact angles (CAs) greater than 150 ° have been intensively investigated due to their unique “anti-water” property that could be utilized in a wide range of applications. [ 11–13 ] Recent development of intelligent devices, such as microfl uidic switches and biomedicine transporters, makes strong demands on surface wettability control, therefore, responsive surfaces have become a signifi cant issue for superhydrophobic studies. Up to now, various smart surfaces have been successfully developed as reversible switches for wettability control through a micronanostructured surface on a responsive material. [ 14–25 ] These unique tunings of surface wettability greatly contributed to refi ned control of surface wettability. With the thorough understanding of superhydrophobic phenomenon, superhydrophobic surfaces have been classifi ed into fi ve states [ 26 ] according to the details of CA hysteresis, which have been well verifi ed on different samples based on experimental results. [ 1 , 8 , 27–29 ]

High numerical aperture microlens arrays of close packing

Closed-packed high numerical aperture (NA) microlens arrays (MLA) are highly desirable for high resolution imaging and high signal-to-noise-ratio detection in micro-optical and integrated optical applications. However, realization of such devices remains technically challenging. Here, we report high quality fabrication of curved surfaces and MLAs by taking the full advantage of surface self-smoothing effect by creating highly reproducible voxels and by adopting an equal-arc scanning strategy. MLA of approximately 100% fill ratio and NA of 0.46, much greater than those ever reported, 0.13, is demonstrated, whose excellent optical performance was approved by the sharp focusing and high resolution imaging.

Remote manipulation of micronanomachines containing magnetic nanoparticles

We report remote manipulation of micronanomachines containing magnetic nanoparticles. Surface-modified Fe(3)O(4) nanocrystals were synthesized as doping agents of the photopolymerizable resin, which was pinpoint written by femtosecond laser-induced two-photon photopolymerization to create microsprings. Owing to the nature of superparamagnetism of Fe(3)O(4) nanoparticles, force exerted to the microsprings relies sensitively on the field gradient of the external ferromagnet, and various motions like elongation, bending, and swing are achieved in a well-controllable remote manner. As a noncontact, sensitive, easy, and environmentally friendly approach, the magnetic driving of micronanomachines may play an important role for nano and biological applications.

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.

A facile approach for artificial biomimetic surfaces with both superhydrophobicity and iridescence

Biomimetic surfaces are attracting more and more research attention because of the amazing characteristics of living biological species, such as iridescence in flowers of hibiscus trionum and tulipa, and superhydrophobicity on the lotus leaf. Despite numerous efforts for producing the fascinating micro-nanostructures that present either iridescence or superhydrophobicity, there is almost no reports on artificial surfaces that posses both simultaneously apart from a few examples on self-organized colloidal particles. Here, we report bio-inspired charming photonic surface structures consisting of regular micro-needle arrays covered with nano-metal protrusions, which are prepared by multibeam interference patterning plus electroless plating. The multibeam laser approach features rapidness, simplicity and ease of large-area fabrication, for example fabrication of a uniform area of 600 mm2 took less than 1 min. The attained hierarchical artificial surface layers exhibit not only superhydrophobic ability, but also brilliant iridescence, which may be useful as a novel type of decoration layer for buildings, cars, and even clothes.

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.

High efficiency multilevel phase-type fractal zone plates

Three kinds of high efficiency phase-type fractal zone plates were rapidly (in tens of minutes) fabricated by femtosecond laser two-photon photopolymerization. Their theoretical maximal diffractive efficiencies of 24.5%, 12.52%, and 18.76% were predicted both by numerical simulation and analytical deduction and were verified by the measured values of 20.5%, 9.1%, and 13%, respectively. The characteristic of multifoci and the improved imaging ability for phase-type fractal lens was also demonstrated. Moreover, to further enhance the diffractive efficiency, a four-level fractal phase lens, whose diffraction efficiency reached as high as 37.6%, was proposed and realized.

Phase lenses and mirrors created by laser micronanofabrication via two-photon photopolymerization

The phase lens, also called kinoform, a promising focusing component in an integrated micro-optical system, was produced by femtosecond laser fabrication via two-photon photopolymerization. Kinoforms consisting of two-, four-, eight-level subzones with level thicknesses of 475, 238, and 119nm demonstrate diffraction efficiencies of 30%, 54%, and 68%, respectively, which are comparable with the theoretical limit and with those from the commercial phase lenses. In addition, a reflective diffractive micromirror was proposed and realized with the aid of electroless plating. These works show the promising prospect of femtosecond laser fabrication in manufacturing optical micronanodevices and their integrated system with optical quality.

100% Fill-Factor Aspheric Microlens Arrays (AMLA) With Sub-20-nm Precision

Substitution of a single aspheric microlens (array) for a complex multilens system results in not only smaller size, lighter weight, compacter geometry, and even possibly lower cost of an optical system, but also significant improvement of its optical performance such as better imaging quality. However, fabrication of aspheric microlens or microlens array is technically challenging because conventional technologies used for macro-sized aspheres like single-point diamond milling, and those for spherical microlens like thermal reflow, are not capable of defining a complicated lens profile in an area as small as several to tens of micrometers. Here we solve the problem by using femtosecond laser micro-nanofabrication via two photon polymerization. Not only well-defined single lens, but also 100% filling ratio aspheric microlens array were readily produced. The average error of the lens profile is only 17.3 nm deviated from the theoretical model, the smallest error reported so far.

Self-organization of polymer nanoneedles into large-area ordered flowerlike arrays

Combination of top-down and bottom-up process is crucial for fabricating ordered complex micronanostructures. Here we report a simple, rapid, and versatile approach to demonstrate this useful concept, which involves the joint use of multibeam interference patterning and capillary force self-organization. Regular hydrophobic arrays of four-peddle nanoflowers consisting of bent needles with 300 nm tip diameters are readily produced. A “domino model” based on the balance of the capillary and support forces were proposed to interpret realization of large-area homogeneity of the array. The technology, promising for preparing more complex and functional structures, may find broad utilization in nano and biological researches.