Zhilong Su

Photo-crosslinked nanofibers of poly(ether amine) (PEA) for the ultrafast separation of dyes through molecular filtration

Molecular filtration is very attractive in the industrial applications of separation and water treatment, but it is challenging to realize fast separation due to the low transport rates and filtrate loss within the membranes in commercial ultrafiltration. We here demonstrated a novel example that a nanofiber membrane of poly(ether amine) (PEA) can be used in the separation of hydrophilic dyes through fast molecular filtration. Two types of PEA nanofiber membrane (PEA-NF) were fabricated through the electrospinning process, which were further photo-crosslinked through the UV-induced dimerization of coumarin groups. Regardless of their charge state, the obtained PEA-NF membranes exhibited strong adsorption to Ponceau S (PS), Rose Bengal (RB), Orange G (OG), Ponceau SX (PSX), and Bismarck brown Y (BY), and with weak adsorption to Methylene Blue trihydrate (MB), and Rhodamine 6G (R6G). Based on the unique selective adsorption to the hydrophilic dyes, PEA-NF membranes can separate mixtures of PS/MB in aqueous solution through molecular filtration with a very high flux rate of 2870 L m−2 h−1. In addition, the PEA-NF membranes are easily regenerated and keep the high separation efficiency over ten adsorption–washing cycles. The integration of the fast separation, easy regeneration and low-cost give PEA-NF membranes potential applications such as separation and water purification.

One-pot approach to synthesize hyperbranched poly(thiol–ether amine) (hPtEA) through sequential “thiol–ene” and “epoxy–amine” click reactions

We here demonstrated a novel strategy of a one-pot approach to synthesize hyperbranched poly(thiol–ether amine) (hPtEA) through sequential “thiol–ene” and “epoxy–amine” click reactions, both of which were well traced using in situ1H-NMR spectra. The obtained hPtEA, with a high branching degree (DB) of 0.83 and a molecular weight (Mn) of 8.6 × 103, was composed of a large amount of hydroxyl groups in the backbone and amino groups in the periphery. Moreover, hPtEA could be further functionalized orthogonally due to the difference in the chemistry between the hydroxyl and amino groups. So fluorescent anthracene (AN) and carboxyl (SA) groups were introduced to the periphery and backbone of hPtEA, respectively, and the amphiphilic and zwitterionic hPtEA (SA-hPtEA-AN) was obtained. The resulting SA-hPtEA-AN could self-assemble into microspheres in aqueous solution with uniform sizes of 750 nm in diameter, and was further cross-linked through photo-dimerization of the AN groups. The microgel of SA-hPtEA-AN is fluorescent and responsive to environmental stimuli such as temperature and pH, and can be used in the encapsulation and controlled release of guest molecules. In addition, the controlled release of guest molecules from the microgel of SA-hPtEA-AN can be monitored by its fluorescence change.

In situ polymerization induced supramolecular hydrogels of chitosan and poly(acrylic acid-acrylamide) with high toughness

A novel type of supramolecular hydrogel was developed by in situ polymerization of acrylic acid (AA) and acrylamide (AM) monomers in the aqueous solution of chitosan (CS), in which nanofiber-structured CS and polyelectrolyte chains of poly(acrylic acid-acrylamide) P(AA-r-AM) form the dynamic cross-linked network through the electrostatic interaction of ions. 1H NMR, WAXD, SEM and TEM were used to trace the formation of this supramolecular hydrogel, and revealed that CS chains aggregate into a nanofiber when the copolymerization of AA and AM proceeded. The obtained hydrogels exhibited good comprehensive mechanical properties. With the excellent fatigue resistance and a high toughness of ∼500 J m−3, the tensile strength and elongation of hydrogel-5 are 120 kPa and 1600%, respectively. The obtained supramolecular hydrogel can self-heal and exhibited no residual strain after continuous deformation-resting processes and loading–unloading tests. Furthermore, the obtained hydrogels can be used to adsorb metal ions in water, interestingly their tensile modulus enhanced several times after adsorption of metal ions.

Light-reversible hierarchical patterns by dynamic photo-dimerization induced wrinkles

Hierarchical patterns are playing an increasing role for various fields due to their integrated functions. Herein we created a novel library of multi-scale complex patterns where hierarchical wrinkles can be dynamically generated and eliminated by in situ photo-control. Atom Force Microscopy (AFM) results and UV-vis kinetics manifest that the change of surface modulus induced by dynamic photo-dimerization of the anthracene-containing polymer (PAN) top-layer plays a crucial role in triggering the morphology switch of the resulting wrinkled surface with self-healing, tunable adhesion and wettability properties. Based on the temporal and spatial characteristics of dynamic photo-dimerization, the ordered and hierarchical patterns can be obtained through adapting selective exposure and photolithography. Furthermore, a series of hierarchical patterns in which the smaller-scale wrinkles can be prescriptively generated on the assigned micro-pillar arrays, making up sets of Braille characters, was demonstrated for Braille text refreshable typography through photo-reversible formation and erasure. This novel and effective approach for photoreversible hierarchical wrinkle patterns offers great promise for smart devices and surfaces with dynamic tunable morphology and surface properties on demand in response to light stimuli without altering the bulk properties.

Ultralarge Nanosheets Fabricated by the Hierarchical Self-Assembly of Porphyrin-Ended Hyperbranched Poly (ether amine) (TPP-hPEA)

An ultralarge sheet with remarkable lateral dimensions of 10 µm × 10 µm-20 µm × 20 µm is fabricated by the hierarchical self-assembly of porphyrin-ended hyperbranched poly(ether amine) (tetraphenylporphyrin (TPP)-hPEA) in solution. The obtained TPP-hPEA amphiphiles can self-assemble from ultrathin single-layered nanosheets with a thickness of 4 nm to ultralarge multilayered nanosheets with thicknesses from 30 to 70 nm. The lateral dimensions increase from 2 × 2 µm to 5 × 5 µm, and eventually to 10 × 10 µm. In-situ dynamic light scattering and UV-vis spectroscopy studies suggest a hierarchical growth self-assembly mechanism with a self-assembly process that relies on π-π stacking. This 2D self-assembly method provides a significant potential guide for the preparation of ultralarge nanosheets in solution.