We report the facile fabrication of a functional nanoporous multilayer film with wettability that is reversibly tunable between superhydrophobicity and superhydrophilicity with UV/visible irradiation. Our approach controls surface roughness with an electrostatic self-assembly process and makes use of the photoresponsive molecular switching of fluorinated azobenzene molecules. Selective UV irradiation onto the nanostructured substrate was used to realize substrates with erasable and rewritable patterns of extreme wetting properties. Our findings will open up new avenues for external stimuli-responsive smart surfaces.

Organic thin-film transistors (OTFTs) have attracted considerable attention because of their potential applications in large-area, flexible, and printed electronics. To achieve OTFT devices with desirable properties, recent research has primarily focused on molecular design, [1,2] dielectric-semiconductor interfacial engineering, [3][4][5] and device optimization. [6][7][8][9][10][11] The use of conjugated polymer blends as active materials has brought a new way to tune and optimize the electronic properties of devices; for example, ambipolar field-effect charge transport has been reported in binary blends of p-and n-type conjugated polymers or oligomers. [12,13] Semiconducting and insulating polymer blends have also attracted increasing interest, because they can combine the electronic properties of semiconducting polymers with the low cost and excellent mechanical characteristics of insulating polymers. However, the presence of the insulating component tends to degrade the device performance by diluting the current density of the film. [14,15] To the best of our knowledge, the only effective approach to overcome this drawback is controlling the blended films to form vertically phase-separated structures, to keep the connectivity of the semiconducting layer in the presence of insulating components. In recent works, the composites with this structures have been used in OTFTs to fabricate low-voltage-driven devices, to improve environmental stability or reduce semiconductor cost. [16][17][18][19][20][21] However, the phase-separation process in polymer blends is very complicated. The final morphology in the blend films is highly sensitive to many factors, including the solvent evaporation rate, solubility parameters, film-substrate interactions, the surface tension of the components, and the film thickness. Vertical phase separation can only take place under extreme conditions. [22,23] Therefore, to develop a more facile and general method for realizing high-performance, low-semiconductor-cost devices is of great technological and academic significance.In this paper, we show that the percolation threshold of semiconducting/insulating polymer blends can be drastically decreased by depositing them from a marginal solvent with temperature-dependent solubility. Morphology and crystallinestructure studies reveal that the excellent electronic performance of the devices derives from the efficient charge transport and the good connectivity observed in highly crystalline, interconnected nanofibrillar networks of semiconductors embedded in an insulator matrix.Semiconductor/insulator-blend mother solutions were prepared by blending poly(3-hexylthiophene) (P3HT) and amorphous polystyrene (PS) in dichloromethane (CH 2 Cl 2 ), which is a marginal solvent for P3HT.[24] To completely dissolve P3HT, the CH 2 Cl 2 solution was kept at approximately 40 8C. For comparison, chloroform (CHCl 3 ), which is a good solvent for P3HT, was used as a reference. Thin films with different P3HT and PS ratios were fabricated on a silicon substrat...

With the aim of enhancing the field‐effect mobility of self‐assembled regioregular poly(3‐hexylthiophene), P3HT, by promoting two‐dimensional molecular ordering, the organization of the P3HT in precursor solutions is transformed from random‐coil conformation to ordered aggregates by adding small amounts of the non‐solvent acetonitrile to the solutions prior to film formation. The ordering of the precursor in the solutions significantly increases the crystallinity of the P3HT thin films. It is found that with the appropriate acetonitrile concentration in the precursor solution, the resulting P3HT nanocrystals adopt a highly ordered molecular structure with a field‐effect mobility dramatically improved by a factor of approximately 20 depending on the P3HT concentration. This improvement is due to the change in the P3HT organization in the precursor solution from random‐coil conformation to an ordered aggregate structure as a result of the addition of acetonitrile. In the good solvent chloroform, the P3HT molecules are molecularly dissolved and adopt a random‐coil conformation, whereas upon the addition of acetonitrile, which is a non‐solvent for aromatic backbones and alkyl side chains, 1D or 2D aggregation of the P3HT molecules occurs depending on the P3HT concentration. This state minimizes the unfavorable interactions between the poorly soluble P3HT and the acetonitrile solvent, and maximizes the favorable π–π stacking interactions in the precursor solution, which improves the molecular ordering of the resulting P3HT thin film and enhances the field‐effect mobility without post‐treatment.

We report the fabrication of a roselike nanostructured vanadium oxide (V2O5) film with photoinduced surface wettability switching by carrying out the drop-casting of a suspension of V2O5 particles synthesized with the sol−gel method. Although a pure V2O5 film is slightly hydrophilic, the addition of alkylamine renders the nanostructured V2O5 film superhydrophobic owing to the intercalation of alkyl chains between the V2O5 layers. UV exposure switches the wettability of the V2O5 surface to superhydrophilic with a water contact angle of almost 0°, and storage in the dark reconverts the irradiated surface back to its initial superhydrophobic state. This extraordinary wetting transition is ascribed to the cooperation between the photosensitivity of V2O5 and the surface roughness of its nanostructure, which has submicron- to micron-scale apertures. Our approach provides not only the possibility of producing large homogeneous or patterned surfaces with tunable wettability, but also potential uses in catalysts, electrodes, switchable smart devices, etc., in various fields for future industrial applications.

Rice leaves can directionally shed water droplets along the longitudinal direction of the leaf. Inspired by the hierarchical structures of rice leaf surfaces, synthetic rice leaf‐like wavy surfaces are fabricated that display a tunable anisotropic wettability by using electrostatic layer‐by‐layer assembly on anisotropic microwrinkled substrates. The nanoscale roughness of the rice leaf‐like surfaces is controlled to yield tunable anisotropic wettability and hydrophobic properties that transitioned between the anisotropic/pinned, anisotropic/rollable, and isotropic/rollable water droplet behavior states. These remarkable changes result from discontinuities in the three‐phase (solid–liquid–gas) contact line due to the presence of air trapped beneath the liquid, which is controlled by the surface roughness of the hierarchical nanostructures. The mechanism underlying the directional water‐rolling properties of the rice leaf‐like surfaces provides insight into the development of a range of innovative applications that require control over directional flow.