Mussel‐Inspired One‐Pot Synthesis of a Fluorescent and Water‐Soluble Polydopamine–Polyethyleneimine Copolymer

Inspired by the molecular mechanics of mussel adhesive formation, a novel water‐soluble fluorescent macromolecule (polydopamine–polyethyleneimine (PDA–PEI)) is prepared by one‐pot copolymerization of dopamine (DA) and PEI. In this method, DA is polymerized to form PDA, which is then coupled with PEI mainly through Michael addition. The fluorescence property of PDA–PEI is mainly attributed to the Michael addition of PEI on the 5,6‐dihydroxyindole (DHI) units of PDA, where PEI can form hydrogen bonds with oxidative products such as DHI and force the DHI units to twist out of plane, resulting in a decrease in the intra‐ and intermolecular coupling of PDA. In addition, the influence of various metal cations on the fluorescence of the PDA–PEI copolymer is investigated. This work may facilitate the development of new strategies for controlling the emission characteristics of PDA.

     

Simple but Strong: A Mussel‐Inspired Hot Curing Adhesive Based on Polyvinyl Alcohol Backbone

The strong adhesion ability of mussel foot‐byssal proteins (Mfps) has inspired scientists to develop novel materials for strong and reversible adhesion, coating, antifouling, and many other applications. However, in many cases, the high costs and the tedious preparation steps of such bioinspired materials hamper the process to push them into practical application. Here a simple but effective way (one step) is presented to synthesize a mussel‐inspired glue from two cheap commercially available materials: polyvinyl alcohol (PVA) and 3,4‐dihydroxybenzaldehyde (DBA). This bioinspired hot curing adhesive exhibits a strong bonding ability as high as 17.3 MPa on stainless steel surfaces, which surpasses most of the commercially available adhesives.

     

Mussel‐Inspired Dendritic Polymers as Universal Multifunctional Coatings

A rapid and universal approach for multifunctional material coatings was developed based on a mussel‐inspired dendritic polymer. This new kind of polymer mimics not only the functional groups of mussel foot proteins (mfps) but also their molecular weight and molecular structure. The large number of catechol and amine groups set the basis for heteromultivalent anchoring and crosslinking. The molecular weight reaches 10 kDa, which is similar to the most adhesive mussel foot protein mfp‐5. Also, the dendritic structure exposes its functional groups on the surface like the folded proteins. As a result, a very stable coating can be prepared on virtually any type of material surface within 10 min by a simple dip‐coating method, which is as fast as the formation of mussel byssal threads in nature.     

Breath Figures of Nanoscale Bricks: A Universal Method for Creating Hierarchic Porous Materials from Inorganic Nanoparticles Stabilized with Mussel‐Inspired Copolymers

High‐performance catalysts and photovoltaics are required for building an environmentally sustainable society. Because catalytic and photovoltaic reactions occur at the interfaces between reactants and surfaces, the chemical, physical, and structural properties of interfaces have been the focus of much research. To improve the performance of these materials further, inorganic porous materials with hierarchic porous architectures have been fabricated. The breath figure technique allows preparing porous films by using water droplets as templates. In this study, a valuable preparation method for hierarchic porous inorganic materials is shown. Hierarchic porous materials are prepared from surface‐coated inorganic nanoparticles with amphiphilic copolymers having catechol moieties followed by sintering. Micron‐scale pores are prepared by using water droplets as templates, and nanoscale pores are formed between the nanoparticles. The fabrication method allows the preparation of hierarchic porous films from inorganic nanoparticles of various shapes and materials.

     

Fabrication of Mussel‐Inspired Highly Adhesive Honeycomb Films Containing Catechol Groups and Their Applications for Substrate‐Independent Porous Templates

Porous surface patterns are used in a wide variety of practical applications. Honeycomb‐patterned porous polymer films are good templates for preparing porous surfaces due to their simple fabrication and the arrangement of pores on the surface. Catechol groups include in adhesive protein of mussels have attracted much attention due to their highly and substrate‐independent adhesive properties. In this paper, highly and substrate‐independent adhesive honeycomb‐patterned porous polymer films are prepared by using amphiphilic copolymer having catechol moieties. Furthermore, porous surface patterns are transferred on various organic or inorganic substrates by wet etching with using adhesive honeycomb films as templates.

     

Tuning the low critical solution temperature of polymer brushes grafted on single‐walled carbon nanotubes and temperature dependent loading and release properties

A nondestructive method was developed for grafting and retrieving polymer brushes from single‐walled carbon nanotubes (SWCNT)s based on mussel‐inspired chemistry. Thermo‐responsive polymer brushes were grafted on SWCNTs by coating the tubes with polydopamine as a reactive underlayer and sequential surface‐initiated atom transfer radical polymerization of oligo(ethylene glycol) methacrylate (OEGMA, M_n = 475) and 2‐(2'‐methoxyethoxy)ethyl methacrylate (MEO2MA). Copolymer brushes were retrieved from the SWCNTs using 1 M NaOH to destroy the crosslinked polydopamine coating, and after that, the pristine properties of the SWCNTs were preserved. The low critical solution temperature (LCST) and molecular weight of the copolymer were measured using a nephelometer and gel permeation chromatograph, respectively. The loading and release behavior of Rhodamine 6G on responsive polymer‐grafted SWCNTs demonstrates that the copolymer brushes confer the SWCNTs an LCST dependence. This method can accurately confirm the molecular weights and polydispersity of stimuli‐responsive polymers grafted on any other nanoparticles and predict their controlled release behavior. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1807–1814     

CuSO4/H2O2‐Induced Rapid Deposition of Polydopamine Coatings with High Uniformity and Enhanced Stability

Mussel‐inspired polydopamine (PDA) deposition offers a promising route to fabricate multifunctional coatings for various materials. However, PDA deposition is generally a time‐consuming process, and PDA coatings are unstable in acidic and alkaline media, as well as in polar organic solvents. We report a strategy to realize the rapid deposition of PDA by using CuSO₄/H₂O₂ as a trigger. Compared to the conventional processes, our strategy shows the fastest deposition rate reported to date, and the PDA coatings exhibit high uniformity and enhanced stability. Furthermore, the PDA‐coated porous membranes have excellent hydrophilicity, anti‐oxidant properties, and antibacterial performance. This work demonstrates a useful method for the environmentally friendly, cost‐effective, and time‐saving fabrication of PDA coatings.     

Low‐Voltage Pulsed Electric Field Sterilization on a Microfluidic Chip

A polyimide substrate based microfluidic chip with thousands of comb‐shaped microelectrodes has been designed, fabricated, and tested for sterilization of bacteria by using pulsed electric field. The performance of bacteria sterilization as functions of the electric field strength, pulse number and width, treatment buffer, bacteria growth status, and bacteria enrichment by positive dielectrophoresis has been experimentally investigated on the microfluidic chip. Experimental results show that only 100 V are sufficient to obtain good sterilization of Escherichia coli. Higher electric field strength, bacteria enrichment by positive dielectrophoresis, longer pulse time, buffer with fewer components and nutritions, and suitable bacteria growth status also improve the sterilization of bacteria. In addition, configuration of the microelectrode array affects bacteria sterilization. This microfluidic device allows one to preconcentrate bacteria to a region with high electric field strength by using positive dielectrophoresis, and subsequently kill the enriched bacteria by applying a pulsed electric field through the same microelectrode array.     

Reactive Polymer Coatings: A General Route to Thiol‐ene and Thiol‐yne Click Reactions

Reactive polymer coatings were synthesized via chemical vapor deposition (CVD) polymerization process. These coatings decouple surface design from bulk properties of underlying materials and provide a facile and general route to support thiol‐ene and thiol‐yne reactions on a variety of substrate materials. Through the reported technique, surface functions can be activated through a simple design of thiol‐terminated molecules such as polyethylene glycols (PEGs) or peptides (GRGDYC), and the according biological functions were demonstrated in controlled and low‐fouling protein adsorptions as well as accurately manipulated cell attachments.     

Salt‐Induced Fabrication of Superhydrophilic and Underwater Superoleophobic PAA‐g‐PVDF Membranes for Effective Separation of Oil‐in‐Water Emulsions

Conventional polymer membranes suffer from low flux and serious fouling when used for treating emulsified oil/water mixtures. Reported herein is the fabrication of a novel superhydrophilic and underwater superoleophobic poly(acrylic acid)‐grafted PVDF filtration membrane using a salt‐induced phase‐inversion approach. A hierarchical micro/nanoscale structure is constructed on the membrane surface and endows it with a superhydrophilic/underwater superoleophobic property. The membrane separates both surfactant‐free and surfactant‐stabilized oil‐in‐water emulsions under either a small applied pressure (<0.3 bar) or gravity, with high separation efficiency and high flux, which is one to two orders of magnitude higher than those of commercial filtration membranes having a similar permeation property. The membrane exhibits an excellent antifouling property and is easily recycled for long‐term use. The outstanding performance of the membrane and the efficient, energy and cost‐effective preparation process highlight its potential for practical applications.     

High‐Efficiency Perovskite Solar Cells Enabled by Anatase TiO2 Nanopyramid Arrays with an Oriented Electric Field

One‐dimensional (1D) nanostructured oxides are proposed as excellent electron transport materials (ETMs) for perovskite solar cells (PSCs); however, experimental evidence is lacking. A facile hydrothermal approach was employed to grow highly oriented anatase TiO₂ nanopyramid arrays and demonstrate their application in PSCs. The oriented TiO₂ nanopyramid arrays afford sufficient contact area for electron extraction and increase light transmission. Moreover, the nanopyramid array/perovskite system exhibits an oriented electric field that can increase charge separation and accelerate charge transport, thereby suppressing charge recombination. The anatase TiO₂ nanopyramid array‐based PSCs deliver a champion power conversion efficiency of approximately 22.5 %, which is the highest power conversion efficiency reported to date for PSCs consisting of 1D ETMs. This work demonstrates that the rational design of 1D ETMs can achieve PSCs that perform as well as typical mesoscopic and planar PSCs.     

In Situ Generated Janus Fabrics for the Rapid and Efficient Separation of Oil from Oil‐in‐Water Emulsions

A cotton fabric was coated with a polymer that contains both poly(dimethyl siloxane) (PDMS) and poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA). When the repeat unit number of PDMS is about three‐fold that of PDMAEMA and the fabric is exposed to air, the fabric is superhydrophobic because PDMS in the coating covers the PDMAEMA chains. Upon contact with an oil‐in‐water emulsion, the water‐soluble PDMAEMA rises to the top and the side in contact with the emulsion becomes hydrophilic. The emerged PDMAEMA chains then cause the emulsion droplets to coagulate, and the aggregated oil fills the pores on the superhydrophobic side of the fabric. The oil‐impregnated side remains hydrophobic even upon prolonged contact with water. Thus, a Janus fabric is elegantly generated in situ and sustained. This easy‐to‐prepare Janus fabric rapidly and efficiently separates oil from emulsions and may find practical applications.     

Reproducing Superhydrophobic Leaves as Coatings by Micromolding Surface‐Initiated Polymerization

Micromolding surface‐initiated polymerization enables the fabrication of polymer coatings that reproduce the microscale surface topography of superhydrophobic leaves onto solid supports. Here, the surfaces of superhydrophobic leaves from Trifolium repens and Aristolochia esperanzae are molded and reproduced as the topography of a partially fluorinated polymer coating through the surface‐initiated ring‐opening metathesis polymerization of 5‐(perfluorooctyl)norbornene (NBF8). The polymer coatings have thicknesses exceeding 100 μm, which can be tailored by the amount of monomer added to the mold. These coatings are robustly bound to the substrate, contain compositions not found in nature, and achieve superhydrophobicity that is comparable to the actual leaf.

     

Collapse of Poly(methacrylic acid) Hydrogels in Response to Simultaneous Stimulation by an Electric Field and Complex Formation

Complex formation of poly(methacrylic acid) hydrogels with linear poly(ethylene glycol) has been studied at different pH values and in the presence of an electric field. The fastest contraction of the gel samples was observed under simultaneous action of electric field and complex formation.

Dependence of the volume ratio V/V₀ of PMAA sample on time: Sample in the absence of an electric field immersed in 0.1 M PEG solution at (1) pH 8.2, (2) at pH 5.1, and in the presence of an electric field (3) in water and (4) 0.1 M PEG solution at pH 5.1.     

Polytetrafluoroethylene‐jacketed stirrer modified with graphene oxide and polydopamine for the efficient extraction of polycyclic aromatic hydrocarbons

Steel stirrers jacketed with polytetrafluoroethylene can be regarded as an ideal substrate for stirrer bar sorptive extraction. However, it is still a great challenge to immobilize graphene onto a polytetrafluoroethylene stirrer due to the high chemical resistance of the surface of a polytetrafluoroethylene stirrer. We describe here a method to modify the surface of polytetrafluoroethylene stirrers with graphene. In this work, graphene was used as the sorbent due to its excellent adsorption capability for aromatic compounds, such as polycyclic aromatic compounds. Graphene was successfully immobilized onto polytetrafluoroethylene‐stirrer by a bio‐inspired polydopamine functionalization method. The graphene‐modified polytetrafluoroethylene‐stirrer shows good stability and tolerance to stirring, ultrasonication, strong acidic and basic solutions, and to organic solvents. The multilayer coating was characterized by scanning electronic microscopy and Fourier transform infrared spectroscopy. After the optimization of some experimental conditions, the graphene‐modified polytetrafluoroethylene stirrer was used for the stirrer bar sorptive extraction of polycyclic aromatic hydrocarbons, in which the binding between the polycyclic aromatic hydrocarbons and the graphene layer was mainly based on π–π stacking and hydrophobic interactions. The graphene‐modified polytetrafluoroethylene‐stirrer‐based stirrer bar sorptive extraction and high‐performance liquid chromatography method was developed for the determination of polycyclic aromatic hydrocarbons with great extraction efficiency, with enrichment factors from 18 to 62. The method has low limits of detection of 1–5 pg/mL, wide linear range (5–100 and 10–200 pg/mL), good linearity (R ≥ 0.9957) and good reproducibility (RSD ≤ 6.45%). The proposed method has been applied to determine polycyclic aromatic hydrocarbons in real dust samples. Good recoveries were obtained, ranging from 88.53 to 109.43%.     

Graft‐Copolymer‐Based Approach to Clear,Durable, and Anti‐Smudge Polyurethane Coatings

Clear anti‐smudge coatings with a thickness of up to tens of micrometers have been prepared through a graft‐copolymer‐based approach from commercial precursors. The coatings repel water, diiodomethane, hexadecane, ink, and an artificial fingerprint liquid. In addition, they can be readily applied onto different substrates using different coating methods. These coatings could find applications in protecting hand‐held electronic devices from fingerprints, windows from stains, and buildings from graffiti.     

Mesoscopic Morphology of Proton‐Conducting Polyelectrolyte Membranes of Nafion® Type: A Self‐Consistent Mean Field Simulation

Summary: A SCMF simulation is presented for a coarse‐grained model of Nafion®. Based on a number of simplifying assumptions, this study predicts distinct morphological changes in the material upon alteration of temperature and water content. We found that the hydration level corresponding to the microphase segregation depends on the temperature of the system. Spherical clusters constituting the hydrophilic microphase of the membrane at relatively low water content (but above the transition point) grow in size, coalesce and form a network of channels responsible for the ionic transport at higher hydration levels. This hydrophilic phase is shielded from the hydrophobic matrix by the sidechains of Nafion®, their end‐groups being turned towards the water clusters. The results obtained are similar to those reported from dissipative particle dynamics studies and support the “cluster‐network” model for the low hydration levels and the “sponge” model at higher hydration levels. The simulation approach chosen proved to be effective for the mesoscopic structure analysis of the heterogeneous polymeric material.

Schematic representation of the structure of Nafion®‐water blends.     

Two‐Photon Voltmeter for Measuring a Molecular Electric Field

We present a new approach for determining the strength of the dipolar solute‐induced reaction field, along with the ground‐ and excited‐state electrostatic dipole moments and polarizability of a solvated chromophore, using exclusively one‐photon and two‐photon absorption measurements. We verify the approach on two benchmark chromophores N,N‐dimethyl‐6‐propionyl‐2‐naphthylamine (prodan) and coumarin 153 (C153) in a series of toluene/dimethyl sulfoxide (DMSO) mixtures and find that the experimental values show good quantitative agreement with literature and our quantum‐chemical calculations. Our results indicate that the reaction field varies in a surprisingly broad range, 0–10⁷ V cm^?1, and that at close proximity, on the order of the chromophore radius, the effective dielectric constant of the solute–solvent system displays a unique functional dependence on the bulk dielectric constant, offering new insight into the close‐range molecular interaction.     

Oxidation of CO Catalyzed by a Cu Cluster: Influence of an Electric Field

Adsorption ability and reaction rate are two essential parameters that define the efficiency of a catalyst. Herein, we implement density functional theory (DFT) and report that CO can be oxidized by a pyramidal Cu cluster with an associated reaction barrier E_b=1.317 eV. In this case, our transition state calculations reveal that the barrier can be significantly lowered after superimposing a negative electric field. Moreover, when the field intensity corresponds to F=?0.010 au, the magnitude of E_b=0.698 eV is equivalent to—or lower than—those of typical catalysts such as Pt, Rh, and Pd. The superimposition of a positive field is found to enhance the release of the nascent CO₂ molecule. Our study demonstrates that small Cu clusters have better adsorption ability than the corresponding flat surface while the field can be used to enhance the purification of the exhaust gas.