Photothermal responsive slippery surfaces based on laser-structured graphene@PVDF composites.

Photothermal responsive slippery surfaces with switchable superwettability are promising in the fields of biomedicine, self-cleaning, anti-corrosion, and lab-on-a-chip systems. However, the development of a light switchable slippery surface that combines high-performance photothermal materials with hierarchical microstructures of special orientation remains challenging, which limits the applications in anisotropic droplet manipulation. Herein, we demonstrate a photothermal responsive slippery surface based on laser-structured graphene and polyvinylidene difluoride composites (L-G@PVDF) for controllable droplet manipulation. The L-G@PVDF film exhibits high light absorption (∼95.4%) in the visible and NIR region. After lubricating with paraffin, the resultant surface shows excellent self-healing ability and light-responsive wettability change due to the photothermal effect of L-G@PVDF and the hot melting effect of paraffin. Additionally, by introducing anisotropic grooved structures, the paraffin-infused L-G@PVDF surface displays anisotropic wettability that further affects droplet manipulation under light irradiation. Also, the photothermal responsive slippery property endows the paraffin-infused L-G@PVDF surface with excellent anti-frosting and de-icing capability. Moreover, the smart paraffin-infused L-G@PVDF surface can be combined with a microfluidics chip for light-driven automatic sampling. This study offers insight into the rational design of photothermal responsive slippery surfaces for controllable droplet manipulation.

Airflow Enhanced Solar Evaporation Based on Janus Graphene Membranes with Stable Interfacial Floatability.

Solar interfacial evaporation has been recognized as a versatile energy conversion protocol for cutting-edge applications such as water treatment and power generation (e.g., hydro voltaic effect). Recently, to enhance water evaporation rates, water temperature and evaporation area have been considered as essential ingredients, and thus photothermal materials and three-dimensional hierarchical structures have been developed to promote light-to-heat conversion efficiency and enhance interfacial evaporation. However, less attention has been paid to the airflow effect, because the interfacial floatability of photothermal membranes should be considered under air blast. Here, inspired from the stable interfacial floatability of lotus leaves, we report the airflow enhanced solar interfacial evaporation approach using a graphene-based Janus membrane. Laser-induced graphene (LIG) film was treated unilaterally by O2 plasma, forming a LIG/oxidized LIG (LIG-O) Janus membrane with distinct wettability on two sides. Higher water evaporation rate of 1.512 kg m-2 h-1 is achieved. The high solar interfacial evaporation performance can be attributed to the two advantages: (i) the combination of microscale capillary water transporting and nanoscale light trapping; (ii) hydrophobic/hydrophilic Janus membrane for stable interfacial floatability under airflow. Our approach is feasible for developing high-performance solar interfacial evaporation devices for practical clean energy utilization.

Kraft Mesh Origami for Efficient Oil-Water Separation.

Inspired from fish scales that exhibit unique underwater superoleophobicity, artificial porous membranes featuring similar wettability have been successfully developed for oil-water separation. However, most of the superoleophobic meshes are workable only for underwater oil/water separation and become disabled in air. In this article, we reported the facile fabrication of underwater superoleophobic kraft mesh and demonstrated efficient oil-water separation using kraft mesh origamis. Kraft paper that features porosity, natural hydrophilicity, and relatively high elasticity and tear resistance has been found to be an ideal candidate for developing underwater superoleophobic origami. Direct laser drilling has been employed to make microhole arrays on the kraft paper, forming a flexible mesh. The hydrophilic nature and the hierarchical microstructures that consist of microhole arrays and porous microfiber networks make the resultant kraft mesh superoleophobic underwater, enabling oil-water separation. More importantly, the kraft mesh can retain a large amount of water (2.5 times its weight under dry conditions) owing to its porous and hydrophilic structure. Thus, the wet kraft mesh became a slippery surface for oil droplets when it was taken out of the water. This unique feature makes it possible to directly fish out oil droplets from water using a simple kraft mesh origami. Direct laser drilling of paper mesh for flexible origami may open up a new route to the rational design and fabrication of oil-water separation devices.

Directly drawing high-performance capacitive sensors on copying tissues.

We report here a facile, green and cost-effective fabrication of high-performance capacitive pressure sensors by drawing loop-and disc-shaped graphite electrode arrays on copying tissues. Graphene oxide enhanced foam-like paper is prepared as an efficient dielectric layer. The paper-based capacitive pressure sensor enables sensitive detection of finger touch, motion and proximity.

Laser-structured Janus wire mesh for efficient oil-water separation.

We report here the fabrication of a Janus wire mesh by a combined process of laser structuring and fluorosilane/graphene oxide (GO) modification of the two sides of the mesh, respectively, toward its applications in efficient oil/water separation. Femtosecond laser processing has been employed to make different laser-induced periodic surface structures (LIPSS) on each side of the mesh. Surface modification with fluorosilane on one side and GO on the other side endows the two sides of the Janus mesh with distinct wettability. Thus, one side is superhydrophobic and superoleophilic in air, and the other side is superhydrophilic in air and superoleophobic under water. As a proof of concept, we demonstrated the separation of light/heavy oil and water mixtures using this Janus mesh. To realize an efficient separation, the intrusion pressure that is dominated by the wire mesh framework and the wettability should be taken into account. Our strategy may open up a new way to design and fabricate Janus structures with distinct wettability; and the resultant Janus mesh may find broad applications in the separation of oil contaminants from water.