Publikationen

The development of switchable white-light emitters is extremely challenging but urgently needed for various applications. We describe a class of switchable fluorescent polymeric nanoparticles (SFPNs) that can alternate their emission color among stable white, cyan, or pink. These SFPNs consist of a dye with cyan-light emission and a spiropyran (SP) derivative with photochromism. When the SP derivative is transferred to its merocyanine state, fluorescence resonance energy transfer (FRET) occurs from the cyan dye to the merocyanine one. In a rational design of transfer efficiency, a stable white-light emission is achieved. This white-light emission can be switched to the cyan-light one upon photoirradiation or pink-light one by solvent-induced swelling. Such multi-color fluorescent alternation is reversible and therefore allows for data encryption. Because of the facile synthesis, excellent long-term stability, fast photo-responsibility, high-contrast fluorescence, and outstanding switchability of these nanoparticles, we envision that they should have great potential in various applications such as high-resolution imaging, white luminescence, and data encryption.

Both phototriggered growth and removal of polymer chains from surfaces are efficient ways to finely tune interface properties. Combining these two capabilities in one system with independent control can significantly increase the feasibility of photoregulation on surface modification but has not been reported yet. Herein we describe a novel approach to control both the growth and the detachment of polymer brushes independently by light with different wavelengths. The approach is based on a nitrodopamine-based initiator (NO2–BDAM) which contains a catechol structure for surface modification, alkyl bromide group for radical polymerization, and o-nitrophenyl ethyl moiety for photolysis. When dimanganese decacarbonyl (Mn2(CO)10) was applied together with NO2–BDAM as an initiating system, visible light (460 nm) can be used to trigger the site-specific growth of polymer brushes. Resulting polymer brushes can be selectively removed by UV light (360 nm). This method is suitable for different monomers on various substrates, suggesting a facile and robust method to regulate surface properties.

Abstract Collection of two optically pure enantiomers in a single crystallization process can significantly increase the chiral separation efficiency but this is difficult to realize. Now a self-reporting strategy is presented for visualizing the crystallization process by a dyed self-assembled inhibitor made from the copolymers with tri(ethylene glycol)-grafting polymethylsiloxane as the main chain and poly(N6-methacryloyl-l-lysine) as side chains. When applied with seeds together for the fractional crystallization of conglomerates, the inhibitors can label the formation of the secondary crystals and guide the complete separation process of two enantiomers with colorless crystals as the first product and red crystals as the second. This method leads to high optical purity of d/l-Asn⋅H2O (99.9 % ee for d-crystals and 99.5 % for l-crystals) in a single crystallization process. It requires a small amount of additives and shows excellent recyclability.

Novel polymeric inhibitors with lower critical solution temperatures in water were prepared and used to mediate the crystallization of racemic asparagine monohydrate, leading to chiral separation with 88.6 ee%. They could be recollected by simply elevating the temperature with a high yield of around 95% and reused without compromising the stereoselectivity and stability.

Abstract Switchable organic fluorescent materials are attracting much interest in many fields including flexible display, information storage, anti-counterfeit, and bioimaging, due to their prominent properties and relatively low cost. Herein, a class of novel photoswitchable fluorescent polymeric nanoparticles (PFPNs) toolbox that shows switchable full-colored emission including white light is described. This nanoparticles toolbox consists of a series of reversibly photoswitchable and non-PFPNs with red, green, and blue fluorescence, and is built up from three primary fluorescent dyes and a photochromic diarylethene molecule, through a facile one-pot miniemulsion method. The as-prepared PFPNs display the merits of high fluorescence resonance energy transfer efficiency and fluorescence quantum yield, rapid responsiveness, prominent photoreversibility, and brilliant long-term fluorescence stability (≈6 weeks). They enable switchable emission between white light and any visible color on-demand in both solution and film states. Their potential in complex fluorescent encryption and photoswitchable white light-emitting diode is described and its great potential in anti-counterfeiting technology, data encryption, and the next generation of optoelectronic materials is foreseen.

Abstract Earthworms are able to pass through sticky soil without inducing stains through a self-forming thick lubricating layer on their rough skins. To mimic this earthworm-like lubricating capability, an attempt to create a textured structure on the surface of liquid-releasable polymer coatings by a “breath figure” process is described herein. The resulting coatings exhibit fast and site-specific release behavior under external triggers such as solid-based friction. The released oil is then stabilized by the surface texture to form thick lubricating layers, reducing friction and enhancing wear resistance. Moreover, the coatings also exhibit excellent antifouling property in a sticky soil environment. Because the lubricating layer can be regenerated after consumption, the potential of this self-replenished lubricating mechanism in preparing friction-reduction, antiwear, and antifouling coatings used in solid-based environments is therefore envisioned.

Here, model blister-like soft thermo-pneumatic artificial muscles with the embedded nanofibers impregnated with ethanol are developed. The muscles are essentially blister-like thermo-pneumatic soft actuators (BTSAs), which deflect in response to heat supplied to their bottom. The resulting deflections are on the scale of 1 cm, and the BTSAs are operational for several cycles. They are able to raise the artificial rigid scales, spines or fur/thin fibers attached to them emulating animals such as pangolin, hedgehog and porcupine. They are also capable of removing the stickiest adhesive tapes attached to them, and thus hold great promise for biomedical applications where artificially grown skin patches should be removed from an underlying substrate without being damaged. The theory of the BTSA proposed in this work is in reasonable agreement with the acquired experimental data.

Abstract Active nanocomposites are created with liquid inclusions that contain plasmonic gold nanoparticles inside a polymeric matrix. The alkylthiol-coated gold particles are designed to reversible agglomerate at certain temperatures, which changes the plasmonic coupling and thus optical properties. It is found that particles confined to the liquid inclusions inside the active composite retain this capability and cause macroscopic, temperature-dependent color change of the solid. The transition is fully reversible for at least 100 times and tunable in temperature via particle size and ligand. This method is suitable to “package” responsive dispersion in solid composites to exploit their dynamic properties in materials.

We demonstrate that rapid nanoparticle self-assembly is possible in organic solvents if the temperature is above the melting point of the particles' ligand shell. Flow experiments coupled to small-angle X-ray scattering reveal the agglomeration kinetics and agglomerate structures of alkylthiol-coated gold nanoparticles at different temperatures, interparticle potentials, and times. Our experiments allow to discriminate between the effects of long-range and short-range interactions on self-assembly: crystalline agglomerates formed for a wide range of potentials, but only at temperatures where the short-ranged mobility was sufficient. Rapid superlattice formation in less than 3 s was observed for strongly attractive potentials at high temperatures, implying an assembly rate that is sufficient for large-scale material synthesis. Strong attraction between the particles did not impede high-quality self-assembly when short-ranged mobility was provided by ligands above a specific temperature.

Metal grids with submicron line diameters are optically transparent, mechanically flexible, and suitable materials for transparent and flexible electronics. Printing such narrow lines with dilute metal nanoparticle inks is challenging because it requires percolation throughout the particle packing. Here, we print fully connected submicron lines of 3.2 nm diameter gold nanoparticles and vary the organic ligand shell to study the relation between colloidal interactions, ligand binding to the metal core, and conductivity of the printed lines. We find that particles with repulsive potentials aid the formation of continuous lines, but the required long ligand molecules impede conductivity and need to be removed after printing. Weakly bound alkylamines provided sufficient interparticle repulsion and were easy to remove with a soft plasma treatment after printing, so that grids with a transparencies above 90% and a conductivity of 150 Ω sq–1 could be printed.