Scientific publications

Abstract Developing a novel strategy to synthesize photoresponsive polymers is of significance owing to their potential applications. We report a photoinduced strain-assisted synthesis of main-chain stiff-stilbene polymers by using ring-opening metathesis polymerization (ROMP), activating a macrocyclic π-bond connected to a stiff-stilbene photoswitch through a linker. Since the linker acts as an external constraint, the photoisomerization to the E-form leads to the stiff-stilbene being strained and thus reactive to ROMP. The photoisomerization of Z-form to E-form was investigated using time-dependent NMR studies and UV/Vis spectroscopy. The DFT calculation showed that the E-form was less stable due to a lack of planarity. By the internal strain developed due to the linker constraint through photoisomerization, the E-form underwent ROMP by a second generation Grubbs catalyst. In contrast, Z-form did not undergo polymerization under similar conditions. The MALDI-TOF spectrum of E-form after polymerization showed the presence of oligomers of >5.2 kDa.

Abstract In recent years, various hydrogels with a wide range of functionalities have been developed. However, owing to the two major drawbacks of hydrogels—air-drying and water-swelling—hydrogels developed thus far have yet to achieve most of their potential applications. Herein, a bioinspired, facile, and versatile method for fabricating hydrogels with high stability in both air and water is reported. This method includes the creation of a bioinspired homogeneous fusion layer of a hydrophobic polymer and oil in the outermost surface layer of the hydrogel via a double-hydrophobic-coating produced through quenching. As a proof-of-concept, this method is applied to a polyacrylamide hydrogel without compromising its mechanical properties. The coated hydrogel exhibits strong resistance to both drying in air and swelling in multiple aqueous environments. Furthermore, the versatility of this method is demonstrated using different types of hydrogels and oils. Because this method is easy to apply and is not dependent on hydrogel surface chemistry, it can significantly broaden the scope of next-generation hydrogels for real-world applications in both wet and dry environments.

Physical entanglement of polymer chains is an interaction that is believed to be too weak to build polymer networks for hydrogelation. Herein, we report a cluster strategy for preparing a class of fundamentally new hydrogels that are crosslinked by only entanglement interaction of polymer chains. The entanglement cluster is created by in situ polymerization of the monomer (acrylamide) in polyacrylamide nanogels to form long inter-connected polyacrylamide chains passing through nanogels. The as-prepared hydrogels can swell high content of water to achieve very low polymer fractions (∼1 wt%). Although they contain an ultrahigh water content and possess an ultra-soft nature (low to ∼10 Pa storage modulus), these physical entanglement hydrogels (PEH) are tough and stretchable (>6 times) due to the free-sliding dynamics of the entanglement-cluster crosslinking interaction. Moreover, this free-sliding nature allows PEH to fully recover their mechanical properties after lyophilization–rehydration treatment. Because of their novel properties, PEH should be promising for various applications.

The design of novel ratiometric nanoprobes with two well-resolved fluorescence bands for accurate imaging of lysosomal hypochlorous acid (HClO) is significant to understand its biological and pathological behaviors. Herein, we develop a single-dye-doped self-referenced ratiometric nanoprobe (SSRN) for imaging of HClO in lysosomes under a single-wavelength excitation (λex = 405 nm). The referenced unit (benzothiazole moiety) and HClO-responsive unit (rhodamine B) are integrated into the single dye (HB-Py) to achieve the self-referenced ratiometric effect. The well-dispersed SSRN are prepared by a simple coprecipitation of the morpholine moiety modified amphiphilic polymers (CO-720-MA) and HB-Py. Of note, the two well-resolved fluorescence bands (∼130 nm) of SSRN could provide accurate imaging of analyte in live cells. Additionally, other distinct merits with SSRN are also simultaneously realized, including high water solubility, high sensitivity (detection limit: 52 nM), excellent selectivity, good biocompatibility and excellent photostability. Significantly, benefiting from the morpholine moiety, this nanoprobe SSRN can specially locate lysosomes and enable ratiometric imaging of exogenous/endogenous HClO in lysosomes.

Disulfide bonds are commonly exploited as dynamic crosslinks to fabricate degradable self-healing hydrogels. However, the low energy dissipation capability and low density of disulfide crosslinks in the hydrogel networks give these hydrogels poor mechanical properties, slow and non-autonomous self-healing, and incomplete polymer degradation. This paper reports a strategy for synthesizing multifunctional hydrogels by copolymerizing 2,3-dimercapto-1-propanol and meso-2,3-dimercaptosuccinic acid, yielding a dynamic poly(disulfide) backbone and numerous rapidly reversible physical crosslinks (H-bonds and ionic interactions). The high-density disulfide bonds and multiphysical crosslinkers synergistically provide the hydrogels with extremely fast self-healing in air and underwater, extraordinary stretchability, and complete and fast degradability. The hydrogels show various functionalities including three-dimensional printability in air and underwater, good electrical conductivity, non-cytotoxicity and bio-tissue adhesion. This strategy opens a new route for exploiting degradable self-healing multifunctional hydrogels with extraordinary features for biomedical and engineering applications.

Natural organic structures form via a growth mode in which nutrients are absorbed, transported, and integrated. In contrast, synthetic architectures are constructed through fundamentally different methods, such as assembling, molding, cutting, and printing. Here, we report a photoinduced strategy for regulating the localized growth of microstructures from the surface of a swollen dynamic substrate, by coupling photolysis, photopolymerization, and transesterification together. Photolysis is used to generate dissociable ionic groups to enhance the swelling ability that drives nutrient solutions containing polymerizable components into the irradiated region, photopolymerization converts polymerizable components into polymers, and transesterification incorporates newly formed polymers into the original network structure. Such light-regulated growth is spatially controllable and dose-dependent and allows fine modulation of the size, composition, and mechanical properties of the grown structures. We also demonstrate the application of this process in the preparation of microstructures on a surface and the restoration of large-scale surface damage.

Abstract It is challenging to post-tune the sensitivity of a tactile force sensor. Herein, a facile method is reported to tailor the sensing properties of conductive polymer composites by utilizing the liquid-like property of dynamic polymer matrix at low strain rates. The idea is demonstrated using dynamic polymer composites (CB/dPDMS) made via evaporation-induced gelation of the suspending toluene solution of carbon black (CB) and acid-catalyzed dynamic polydimethylsiloxane (dPDMS). The dPDMS matrices allow CB to redistribute to change the sensitivity of materials at the liquid-like state, but exhibit typical solid-like behavior and thus can be used as strain sensors at normal strain rates. It is shown that the gauge factor of the polymer composites can be easily post-tuned from 1.4 to 51.5. In addition, the dynamic polymer matrices also endow the composites with interesting self-healing ability and recyclability. Therefore, it is envisioned that this method can be useful in the design of various novel tactile sensing materials for many applications.

Hybrid electronic materials combine inorganic metals and semiconductors with π-conjugated polymers. The orientation of the polymer molecules in relation to the inorganic components is crucial for electrical material properties and device performance, but little is known of the configuration of π-conjugated polymers that bind to inorganic surfaces. Highly curved surfaces are common when using nanoscale components, for example, metal nanocrystal cores covered with conductive polymers. It is important to understand their effect on molecular arrangement. Here, we compare the molecular structures and electrical conductivities of well-defined nanoscale gold spheres and rods with shells of the covalently bound polythiophene PTEBS (poly[2-(3-thienyl)-ethyloxy-4-butylsulfonate]). We prepared aqueous sinter-free inks from the particles and printed them. The particles formed highly conductive films immediately after drying. Films with spherical metal cores consistently had 40% lower conductivities than films based on nanorods. Raman and X-ray photoelectron spectroscopy revealed differences in the gold–sulfur bonds of PTEBS on rods and spheres. The fractions of bond sulfur groups implied differences in the alignment of PTEBS with the surface. More polymer molecules were bound in an edge-on configuration on spheres than on rods, where almost all polymers aligned “face-on” with the metal surface. This leads to different interface resistances: gold–polythiophene–gold interfaces between rods with π–π-tacked face-on PTEBS apparently foster electron transport along the surface-normal direction, while edge-on PTEBS does not. Molecular confinement thus increases the conductivity of hybrid inks based on highly curved nanostructures.

Aqueous redox flow batteries using electroactive organic materials are currently attracting significant attention. However, the influence of supporting electrolytes on the aqueous solubility, electrochemical reversibility and chemical stability of the organic components has rarely been investigated. Here, a new electrolyte design strategy towards enhanced solubility and chemical stability of active materials is proposed by using interaction-mediating species. 3 molality aqueous imidazolium chlorides, with high ionic conductivity and water-like flowability, enable a record aqueous solubility of 4.3 M for a commercially available nitroxyl radical and reversible 2e− reaction of unmodified methyl viologen at moderate concentrations. With 0.6 M electrolyte, flow cell shows remarkable chemical stability of the nitroxyl radical, excellent cycling stability over 250 cycles at 80 mA cm−2, and a peak power density of 121.6 mW cm−2 at 175 mA cm−2. Furthermore, nitroxyl radical catholyte with a concentration of 3 M is tested in a flow cell. It maintains an impressive steady energy efficiency of 65% at 30 mA cm−2. This work paves a new way for the development of high performance aqueous electrolytes based on organic materials.

Abstract Conductive inkjet printing with metal nanoparticles is irreversible because the particles are sintered into a continuous metal film. The resulting structures are difficult to remove or repair and prone to cracking. Here, a hybrid ink is used to obviate the sintering step and print interconnected particle networks that become highly conductive immediately after drying. It is shown that reversible conductive printing is possible on low-cost cardboard samples after applying standard paper industry coats that are adapted in terms of surface energy and porosity. The conductivity of the printed films approaches that of sintered standard inks on the same substrate, but the mobility of the hybrid particle film makes them less sensitive to cracks during bending and folding of the substrate. Damages that occur can be partially repaired by wetting the film such that particle mobility is increased and particles move to bridge insulating gaps in the film. It is demonstrated that the conductive material can be recovered from the cardboard at the end of its life time and be redispersed to recycle the particles and reuse them in conductive inks.