Junjie Wu

Mussel-Inspired Chemistry for Robust and Surface-Modifiable Multilayer Films

In this article, we report a bioinspired approach to preparing stable, functional multilayer films by the integration of mussel-inspired catechol oxidative chemistry into a layer-by-layer (LbL) assembly. A polyanion of poly(acrylic acid-g-dopamine) (PAA-dopamine) bearing catechol groups, a mussel adhesive protein-mimetic polymer, was synthesized as the building block for LbL assembly with poly(allylamine hydrochloride) (PAH). The oxidization of the incorporated catechol group under mild oxidative condition yields o-quinone, which exhibits high reactivity with amine and catechol, thus endowing the chemical covalence and retaining the assembled morphology of multilayer films. The cross-linked films showed excellent stability even in extremely acidic, basic, and highly concentrated aqueous salt solutions. The efficient chemical cross-linking allows for the production of intact free-standing films without using a sacrificial layer. Moreover, thiol-modified multilayer films with good stability were exploited by a combination of thiols-catechol addition and then oxidative cross-linking. The outstanding stability under harsh conditions and the facile functionalization of the PAA-dopamine/PAH multilayer films make them attractive for barriers, separation, and biomedical devices.

Rapid sintering of silver nanoparticles in an electrolyte solution at room temperature and its application to fabricate conductive silver films using polydopamine as adhesive layers

Here we demonstrate a new route to achieve the sintering of silver nanoparticles (Ag NPs) at room temperature. The as-prepared Ag NPs coalesced when they were immersed in electrolyte solutions, such as NaCl and MgSO4. The square resistances of Ag NPs thin films decreased from tens of kiloohms to lower than 1 ohm after treatment with electrolyte solutions for 10 s. Conductive Ag NPs thin films can be created on various substrates coated by polydopamine, a mussel-inspired polymer, viasilver-plating followed by treatment with electrolyte solutions at room temperature.

Mussel Inspired Modification of Polypropylene Separators by Catechol/Polyamine for Li-Ion Batteries

Inspired by the remarkable adhesion of mussel, dopamine, a mimicking adhesive molecule, has been widely used for surface modification of various materials ranging from organic to inorganic. However, dopamine and its derivatives are expensive which impede their application in large scale. Herein, we replaced dopamine with low-cost catechol and polyamine (only 8% of the cost of dopamine), which could be polymerized in an alkaline solution and deposited on the surfaces of various materials. By using this cheap and simple modification method, polypropylene (PP) separator could be transformed from hydrophobic to hydrophilic, while the pore structure and mechanical property of the separator remained intact. The uptake of electrolyte increased from 80% to 270% after the hydrophilic modification. Electrochemical studies demonstrated that battery with the modified PP separator had a better Coulombic efficiency (80.9% to 85.3%) during the first cycle at a current density of 0.1 C, while the discharging current density increased to 15 C and the discharge capacity increased by 1.4 times compared to the battery using the bare PP separator. Additionally, the modification allowed excellent stability during manifold cycles. This study provides new insights into utilizing low-cost chemicals to mimic the mussel adhesion and has potential practical application in many fields.

High‐Strength Cellulose/Poly(ethylene glycol) Gels

Cellulose gel membranes have been prepared by a pre-gelation method employing cellulose solutions in aqueous NaOH-thiourea obtained at low temperature. The cellulose gels were then swollen by low-molecular-weight polyethylene glycol (PEG; MW<1000 g mol(-1)), and the morphology, structure and mechanical properties of the cellulose/PEG gels were studied by various techniques. The gels exhibit high mechanical performance, and the tensile strength of the gel membranes increases sharply with an increase in the molecular weight of PEG from 200 to 800 g mol(-1). Moreover, their elongation at break remains stable at 100 %. PEG800 efficiently improves the optical transmittance of the gel membranes at ambient temperature, which is about five times greater than that of a normal cellulose hydrogel membrane. A strong hydrogen-bonding interaction occurs between PEG and cellulose leading to a homogeneous structure, high mechanical strength and good transparency of the gel membranes.

Multi-membrane hydrogel fabricated by facile dynamic self-assembly

Multi-membrane hydrogels are newly promising carriers in biomedical fields. We fabricate alginate-based onion-like multi-membrane hydrogels starting from a template gel-core to shells through a dynamic self-assembly method, and investigate the influence of various factors on the formation of the complex system in detail. By precisely controlling the process of preparation, multi-layered hydrogels of different shapes either with or without defined internal space between separated layers can be prepared. And a pulse-like delivery of macromolecule has been achieved by this architecture.

Micro–nano hierarchically structured nylon 6,6 surfaces with unique wettability

A micro-nano hierarchically structured nylon 6,6 surface was easily fabricated by phase separation. Nylon 6,6 plate was swelled by formic acid and then immersed in a coagulate bath to precipitate. Micro particles with nano protrusions were generated and linked together covering over the surface. After dried up, the as-formed surface showed superhydrophilic ability. Inspired by lotus only employing 2-tier structure and ordinary plant wax to maintain superhydrophobicity, paraffin wax, a low surface energy material, was used to modify the hierarchically structured nylon 6,6 surface. The resultant surface had water contact angle (CA) of 155.2+/-1.3 degrees and a low sliding angle. The whole process was carried on under ambient condition and only need a few minutes.

Low-cost mussel inspired poly(catechol/polyamine) coating with superior anti-corrosion capability on copper.

A low-cost mussel inspired approach was developed to produce anti-corrosion coating on copper substrate. Catechol (CA) and polyamine (PA) were spontaneously polymerized to form adhesive coating of poly(cetechol/polyamine) (P(CA/PA)) onto copper surface and then P(CA/PA) was grafted by 1-dodecanethiol. The SEM, contact angle, XPS, FTIR and TG results demonstrated the formation of uniform, compact and thermal stable coatings through multiple interactions and chemically grafting. Electrochemical tests indicated of Cu-P(CA/PA)-SH possessed a highest corrosion potential of -81mV, a lowest corrosion current density of 0.15μA/cm(2), and a highest coating resistance of 57.19kΩcm(2), and also exhibit great long-term stability whether in solution immersion or salt spray tests. The remarkable anti-corrosion capability of Cu-P(CA/PA)-SH could be ascribed to the synergistic effect of the hydrophobicity, good stability, and strong wet adhesion of the mussel-inspired coating. This study provides an effective and cheap way for material protection and may give inspiration in the fields of material, biology and medicine relating to surface and interface engineering.

Directional and Path-Finding Motion of Polymer Hydrogels Driven by Liquid Mixing

The spreading of a miscible liquid with a low surface tension on a water surface generates the directional motion of submerged polymer hydrogels, which could be attributed to convective flows resulting from the gradient of surface tension along the surface (Marangoni effect). The direction and velocity of this motion can be well controlled by altering the driving conditions. Furthermore, a spherical hydrogel can smartly find the path to walk through a microfluidic maze when liquid mixing occurs near the maze exit. This convenient chemical driving approach to transporting submerged objects in a desired way may be useful in microfluidics, micromechanics, and other applications.

Solvent free nanoscale ionic materials based on Fe3O4 nanoparticles modified with mussel inspired ligands

Mussels exhibit robust adhesion capability with varied materials mainly due to the strong affinity of catechol moieties in their adhesive proteins. Nanoscale ionic materials (NIMs) are special organic-inorganic hybrid materials comprising a charged oligomer corona attached to inorganic nanoparticle cores, which can behave from glassy solids to liquids in the absence of any solvent. Herein, Fe3O4 nanoscale ionic materials (NIMs) exhibiting inorganic-organic core-shell structure and liquid-like behavior were obtained by using a mussel-inspired bifunctional ligand of 3,4-dihydroxybenzenepropanoic acid (DHPA), which could link Fe3O4 nanoparticles core and cationic organic shell, respectively. A simplified one-step aqueous co-precipitation method to prepare DHPA decorated Fe3O4 nanoparticles is developed, which shows advantages in productivity and is more environmental friendly compared with the traditional core preparation first and then surface modification. This research proposes a simple and effective approach to obtain solvent-free NIMs with tailorable core-shell structure using versatile adhesion of mussel mimetic adhesives and various available ion pairs.