Shile Feng

Temperature-triggered directional motion of tiny water droplets on bioinspired fibers in humidity

We designed a kind of smart bioinspired fiber using the N-isopropylacrylamide (NIPAAm) polymer, with roughness and curvature features similar to those of wetted spider silk. The motion of tiny water droplets can be manipulated reversibly in directions by the effective cooperation of multi-gradients such as roughness, curvature and temperature-responsive wettability.

Controlled Smart Anisotropic Unidirectional Spreading of Droplet on a Fibrous Surface.

Smart anisotropic-unidirectional spreading is displayed on a wettable-gradient-aligned fibrous surface due to a synergetic directing effect from the aligned structure and the ratio of hydrophilic components.

Radial Wettable Gradient of Hot Surface to Control Droplets Movement in Directions

A radial wettable gradient was fabricated on the surface of graphite plate by a simple one-step anodic oxidation process. It was found that the direction and value of the wettable gradient could be easily controlled by adjusting current and oxidation time gradient. With the increase of surface temperature, droplets on surface not only exhibited the transition of boiling mode, but also showed the controlled radial spreading, evaporation and movement behaviors. These phenomena could be attributed to the cooperation of wettability force, hysteresis force and vapor pressure (Leidenfrost effect). Especially, the controlled radial convergence or divergence of droplets with high velocity were realized on the surfaces with either inside or outside radial gradient, which would have crucial applications in the design of microfluidic devices and the exploration of the biotechnology.

Photo-controlled water gathering on bio-inspired fibers

We report photo-controlled water gathering on bio-inspired fibers. We have designed a bio-inspired fiber using azobenzene (Azo) polymer materials, with roughness and a curvature similar to the spindle-knots of wetted spider silk. We demonstrate that the cooperation between roughness and curvature and the photo-responsive wettability play a key role in water gathering after Vis or UV irradiation, which regulate effectively the separation of water droplets away from the spindle-knots or the coalescence towards the spindle-knots, respectively. This study offers an insight into the design of novel gradient surfaces that may drive tiny droplets to move in as-desired directions, which could potentially be extended to the realms of fluid-control in micro-scale engines, sub-micron masks, heat transfer, water-collecting devices and systems.

Dynamic Magnetic Responsive Wall Array with Droplet Shedding-off Properties

Directional control of droplets on a surface is an important issue for tasks of long-range liquid-transport, self-cleaning and water repellency. However, it is still challenging to control the structure motions in orientations so as to control the shedding-off of droplets. Herein, we report a novel dynamic magnetic responsive wall (DMRW) array on PDMS (polydimethylsiloxane) -based surface. The walls can easily tilt through the effect of the external magnet because of the magnetic material in the DMRW. The droplets can be shed off directionally on the surface. Particularly, with the shape recovery and flexible properties, it achieves simultaneous control of the tilt angles (0-60°) of DMRW for shedding-off of droplets with different volumes (1-15 μL) under magnetic action on DMRW. The mechanism of droplet shedding-off on DMRW is elucidated by theory of interfaces. It offers an insight into design of dynamic interface for water repellency. This strategy realizes the preparation of multifunctional, tunable and directional drive functions.

Water-assisted fabrication of porous bead-on-string fibers

We use the Rayleigh instability technique and breath figure method to fabricate porous bead-on-string fibers and regulate the size and distribution of the pores by controlling the resin reaction conditions. Interestingly, a variety of bead-on-string fibers , with smooth, less porous, homogenous porous, gradient porous and dented microstructures could be easily prepared.

Controlling of Water Collection Ability by an Elasticity-Regulated Bioinspired Fiber

A special artificial spider silk is presented which is fabricated by using both an elastic polymer and a fiber, and the water collection behavior is investigated. Through exerting tension in varying degree, the length of the three-phase contact line (TCL) and the area of spindle knot can be regulated readily, which makes a great contribution to the improvement of collecting efficiency and water-hanging ability. The water-hanging ability can be predicted at a given stretching ratio according to the given expression of the TCL. As a result, liquid capture or release of distinct measure can be achieved via exerting tension. This research is helpful to design smart materials for developing applications in fogwater collection, dehumidification, high-efficiency humidity control, and controllable adhesion.

Controlled droplet transport to target on a high adhesion surface with multi-gradients

We introduce multi-gradients including Laplace pressure gradient, wettable gradient and wettable different gradient on a high adhesion surface via special wedge-pattern and improved anodic oxidation method. As a result of the cooperative effect mentioned above, controlled directional motion of a droplet on a high adhesion surface is realized, even when the surface is turned upside down. The droplet motion can be predicted and the movement distances can be controlled by simply adjusting the wedge angle and droplet volume. More interestingly, when Laplace pressure gradient is introduced on a V-shaped wettable gradient surface, two droplets can move toward one another as designed.

Controlled transportation of droplets and higher fog collection efficiency on a multi-scale and multi-gradient copper wire

Via a one-step gradient anodic oxidation, a copper wire with a multi-scale structure and multi-gradient was successfully fabricated, which could realize self-propulsion of droplets and with a well-controlled transport distance. Compared to the previous study, herein, the wire exhibited not only a longer transport distance of the droplet, but also a much higher water collection efficiency.

Selective oxidation of carbon to enhance both tensile strength and interfacial adhesion of carbon fiber

ABSTRACT Among the various techniques utilized for surface modification of carbon fiber, the most practical one for commercial production is anodization due to its controllable oxidation level in a continuous process. During the traditional process, the adhesion between the fiber and epoxy resin can be improved, but at the expense of reducing tensile strength. Here, we present a novel anodic oxidation method, i.e., the carbon atoms on the ridges are selectively oxidized and those in the grooves remain intact. In this way, the longitudinal grooves on the fiber surface become shallow and the tensile strength of fiber shows an obvious increase by comparison with the carbon fiber oxidized via traditional oxidation method. More importantly, due to the high density of oxygen-containing groups on the ridges, the fiber shows great wetting properties and strong adhesion to epoxy resin.