Polymer Nanosheet Research Articles

Liquid/Liquid Interfacial Synthesis of a Click Nanosheet.

A liquid/liquid interfacial synthesis is employed, for the first time, to synthesize a covalent two-dimensional polymer nanosheet. Copper-catalyzed azide-alkyne cycloaddition (CuAAC) between a three-way terminal alkyne and azide at a water/dichloromethane interface generates a 1,2,3-triazole-linked nanosheet. The resultant nanosheet, with a flat and smooth texture, has a maximum domain size of 20 μm and minimum thickness of 5.3 nm. The starting monomers in the organic phase and the copper catalyst in the aqueous phase can only meet at the liquid/liquid interface as a two-dimensional reaction space; this allows them to form the two-dimensional polymer. The robust triazole linkage generated by irreversible covalent-bond formation allows the nanosheet to resist hydrolysis under both acidic and alkaline conditions, and to endure pyrolysis up to more than 300 °C. The coordination ability of the triazolyl group enables the nanosheet to act as a reservoir for metal ions, with an affinity order of Pd2+ >Au3+ >Cu2+ .

高分子ナノシートの湿潤・乾燥による凹凸形状への追従性の評価

高分子ナノシートの湿潤・乾燥による凹凸形状への追従性の評価

Glue-Free Stacked Luminescent Nanosheets Enable High-Resolution Ratiometric Temperature Mapping in Living Small Animals.

In this paper, a microthermograph, temperature mapping with high spatial resolution, was established using luminescent molecules embedded ultrathin polymeric films (nanosheets), and demonstrated in a living small animal to map out and visualize temperature shift due to animal's muscular activity. Herein, we report super flexible and self-adhesive (no need of glue) nanothermosensor consisting of stacked two different polymeric nanosheets with thermosensitive (Eu-tris (dinaphthoylmethane)-bis-trioctylphosphine oxide: EuDT) and insensitive (Rhodamine 800) dyes being embedded. Such stacked nanosheets allow for the ratiometric thermometry, with which the undesired luminescence intensity shift due to focal drift or animal's z-axis displacement is eliminated and the desired intensity shift solely due to the temperature shift of the sample (living muscle) can be acquired. With the stacked luminescent nanosheets, we achieved the first-ever demonstration of video filming of chronologically changing temperature-shift distribution from the rest state to the active state of the muscles in the living animal. The polymer nanosheet engineering and in vivo microthermography presented in the paper are promising technologies to microscopically explore the heat production and heat transfer in living cells, tissues, and organisms with high spatial resolution beyond what existing thermometric technologies such as infrared thermography have ever achieved.

Sulfur‐Enriched Conjugated Polymer Nanosheet Derived Sulfur and Nitrogen co‐Doped Porous Carbon Nanosheets as Electrocatalysts for Oxygen Reduction Reaction and Zinc–Air Battery

Among the rising 2D soft materials, conjugated polymer nanosheets are one of the most promising and new classes of polymeric materials, which are rarely developed because of the challenge in controlling the dimensionality and lack of synthetic strategies. In this study, one kind of sulfur‐enriched conjugated polymer nanosheet (2DP‐S) with a high aspect ratio of up to ≈400 is successfully synthesized. On the basis of structural characterization, as‐prepared 2DP‐S possesses the chemical identity of cruciform‐fused polymeric backbone consisting of quinoidal polythiophene and poly(p‐phenylenevinylene) along horizontal and vertical directions, respectively, by sharing two alternating single–double carbon–carbon bonds in each repeat unit. The unique structural conformation of 2DP‐S renders carrier mobilities of up to 0.1 ± 0.05 cm2 V−1 s−1, a figure inferred from Terahertz time domain spectroscopy. Moreover, upon thermal treatment, 2DP‐S is readily converted into N/S dual‐doped porous carbon nanosheets (2DPCs) under ammonia atmosphere, whose N/S ratio can be rationally controlled by adjusting the activation time. The catalytic performance of the oxygen reduction reaction of as‐prepared 2DPCs is well tunable by the rationally controlled N/S contents. These results offer a new pathway for exploring heteroatom‐doped porous carbons applicable for energy conversion and storage.

Synthesis and Mechanism Insight of a Peptide-Grafted Hyperbranched Polymer Nanosheet with Weak Positive Charges but Excellent Intrinsically Antibacterial Efficacy.

Antimicrobial resistance is an increasingly problematic issue in the world and there is a present and urgent need to develop new antimicrobial therapies without drug resistance. Antibacterial polymers are less susceptible to drug resistance but they are prone to inducing serious side effects due to high positive charge. Herein we report a peptide-grafted hyperbranched polymer which can self-assemble into unusual nanosheets with highly effective intrinsically antibacterial activity but weak positive charges (+ 6.1 mV). The hyperbranched polymer was synthesized by sequential Michael addition-based thiol-ene and free radical mediated thiol-ene reactions, and followed by ring-opening polymerization of N-carboxyanhydrides (NCAs). The nanosheet structure was confirmed by transmission electron microscopy (TEM) and atomic force microscopy (AFM) studies. Furthermore, a novel "wrapping and penetrating" antibacterial mechanism of the nanosheets was revealed by TEM and it is the key to significantly decrease the positive charges but have a very low minimum inhibitory concentration (MIC) of 16 μg mL(-1) against typical Gram-positive and Gram-negative bacteria. Overall, our synthetic strategy demonstrates a new insight for synthesizing antibacterial nanomaterials with weak positive charges. Moreover, the unique antibacterial mechanism of our nanosheets may be extended for designing next-generation antibacterial agents without drug resistance.

Cobalt/nitrogen co-doped porous carbon nanosheets as highly efficient catalysts for the oxygen reduction reaction in both basic and acidic media

Cobalt/nitrogen co-doped porous carbon nanosheets as highly-efficient catalysts for ORR in both basic and acidic electrolytes have been prepared by using cobalt porphyrin based conjugated microporous polymer nanosheet as a precursor.

73 Smart polymer functionalized graphene nano-devices for thermo-switch controlled biodetection

In this work, we have developed a general methodology for constructing an activatable biosensor utilizing a thermo-responsive polymer (Yavuz et al., 2009) and two-dimensional nano-sheet. We have de...

Development of a ubiquitously transferrable silver‐nanoparticle‐loaded polymer nanosheet as an antimicrobial coating

Ultra-thin polymer films (nanosheets) fabricated by a layer-by-layer (LbL) method possess unique properties such as high flexibility, adhesive strength, and transparency, and can be peeled off from a substrate and attached to various surfaces via a water-soluble supporting film. Therefore, flexible and transferrable LbL nanosheets are convenient tools as coating materials. Here, we fabricated a novel antimicrobial coating material by embedding silver nanoparticles (AgNPs) in an LbL nanosheet composed of layers of chitosan and sodium alginate (Ag-LbL nanosheet) by means of a photo-reduction method. Optimizing the amount of irradiated energy applied led to robust antimicrobial efficacy against methicillin-resistant Staphylococcus aureus (MRSA), sufficient to meet ISO standards (ISO 22196), while maintaining the flexibility and adhesive potency of the LbL nanosheet. Thus, the Ag-LbL nanosheet is a promising coating material that can provide antimicrobial efficacy to various surfaces.

Effect of polymerization on hierarchical self-assembly into nanosheets.

The oligomers consisting of phenyl-capped bithiophene and tetra(ethylene glycol)s linked by azide-alkyne Huisgen cycloaddition were synthesized. The relationship between the degree of polymerization and self-assembling ability was investigated in o-dichlorobenzene and dimethyl sulfoxide. From the absorption spectrum, it was confirmed that the critical degree of polymerization (CDP) for thiophene unit aggregation was 4. The morphology of the aggregated product was observed by atomic force microscopy. The oligomers 4mer and 5mer could not self-assemble into well-defined structures due to the weak driving force for the self-assembly. In the cases of 6mer and 7mer, aggregates with nonwell-defined and nanosheet structures coexisted. In the cases of 8mer and 9mer, the nanosheet was the main product. The critical point between 7mer and 8mer could be confirmed by different aggregation behaviors in the cooling process of the solution (nonsigmoidal and sigmoidal). In the cases of 8mer and 9mer, polymer folding prior to intermolecular self-assembly, which was supported by sigmoidal aggregation behavior, leads to the nanosheet formation. On the contrary, shorter oligomers than 8mer experience intermolecular aggregation prior to intramolecular polymer folding, which was supported by the nonsigmoidal aggregation behavior. This is the first report to prove the existence of CDP for folded polymer nanosheet formation which requires hierarchical self-assembly, i.e., polymer folding followed by intermolecular self-assembly.

Smart-Polymer-Functionalized Graphene Nanodevices for Thermo-Switch-Controlled Biodetection.

In this work, we have developed a general methodology for constructing an activatable biosensor utilizing a thermoresponsive polymer and two-dimensional nanosheet. We have demonstrated the detection of four different types of biological compounds using the smart PEGMA (poly(ethylene glycol) methyl ether methacrylate), oligonucleotides, and graphene oxide nanoassembly. The activity of the functional nanodevice is controlled with a thermo-switch at 39 °C. In this design, the nanosized graphene oxide serves as a template for fluorophore labeled probe oligonucleotides while quenching the fluorescence intensities dramatically. On the other hand, the PEGMA polymer serves as an activatable protecting layer covering the graphene oxide and entrapping the probe oligonucleotides on the surface. The PEGMA polymers are hydrophobic above their lower critical solution temperature (LCST) and therefore interact strongly with the hydrophobic surface of graphene oxide, creating a closed configuration (OFF state) of the nanodevice. However, once the temperature decreases below the LCST, the polymer undergoes conformational change and becomes hydrophilic. This opens up the surface of the graphene oxide (open configuration, ON state), freeing the encapsulated payload on the surface. We have tuned the activity of the nanodevice for the detection of a sequence-specific DNA, miR-10b, thrombin, and adenosine. The activity of our functional system can be decreased by ∼80% with a thermo-switch at 39 °C. Our approach can be extended to other antisense oligonucleotide, aptamer, or DNAzyme based sensing strategies.

Elucidation of Internal Fine Structure of "Polymer Nanosphere" in the Interfacial Particle Film

Transition behavior from a monolayer on the water surface to a single particle layer of a ternary comb copolymer with highly hydrophobic carbazole units and both hydrogenated and fluorinated side-chains have been investigated by surface pressure−area (π−A) isotherm and atomic force microscopic (AFM) observation. Moreover, we fabricated a polymer nanosphere multilayered organization consisting of such polymer nanoparticles by the Langmuir–Blodgett (LB) technique, and estimated the particle arrangement by performing out-of-plane X-ray diffraction (XRD) analysis. This polymer monolayer is able to form the polymer nanosheet with amorphous layers. The multiparticle layered organization of polymer nanosphere is fabricated from the single particle layer by the LB technique. These layer structures have highly regular arrangement along the c-axis. Further, we investigated molecular arrangement inside of polymer particles by performing in-plane XRD analysis and fluorescence spectroscopy. This copolymer formed side-chain crystals inside the particles. Fluorocarbon chains had a short spacing of 5.0 A for the two-dimensional side-chain lattice whereas hydrocarbon chains formed sub-cell at short spacing of 4.2 A. In addition, aggregated structure of carbazole rings is formed by π-π interaction.

Fabrication and Structural Estimation of “Polymer Nanosphere Multilayered Organization”

We have newly constructed “multi-particle layered organization” of aromatic polyamide (poly-(N- alkylated benzamide), abbrev . PABAn , n : carbon number of side-chains) derivatives having both a rigid main chain and a flexible side chains by a Langmuir-Blodgett (LB) technique. This organization is composed of the build-up particle layers with highly regular arrangement along the c -axis. The particle arrangement of this organization of polymer nanosphere was estimated by performing out-of plane X-ray diffraction (XRD), and atomic force microscopic (AFM) observation. In addition, it is also proposed that ternary comb copolymers with carbazole units and both hydrogenated and fluorinated side-chains are candidates of newly typed “polymer nanosheet” material. These copolymers with high hydrophobic carbazole contents also formed single particle layer at air/water interface and “multi-particle layered organization” was constructed by a LB technique. Therefore, it was found that “multi-particle layered organization of polymer nanosphere” and “polymer nanosheet” are simultaneously formed by same component copolymer materials with hydrophobic carbazole units.

Layered Ultrathin Ion Conductive Membrane Using Polymer Nanosheet with Amine Group

Layered ultrathin ion conductive membrane was prepared using poly (N-dodecylacrylamide-co-N-(2-(2-(2-aminoethoxy)ethoxy)ethyl)acrylamide) (p(DDA/ DONH)) polymer nanosheet. The polymer forms a stable monolayer at the air-water interface and is transferable to a solid substrate using the Langmuir-Blodgett technique. The multilayer film showed a clear layered structure with 2.0 nm periodicity confirmed by X-ray diffraction measurements. The polymer nanosheet showed ion conductivity of 0.85 × 10−3 S/cm at 100% RH with 20°C through the layer plane direction.

Role of Solubility Parameters in Understanding the Steric Stabilization of Exfoliated Two-Dimensional Nanosheets by Adsorbed Polymers

In this paper we show that graphene, hexagonal boron nitride, and molybdenum disulfide can all be exfoliated and stabilized against aggregation in solvents that cannot alone exfoliate these materials, provided that dissolved polymers are present. In each case we demonstrate this steric stabilization for a range of polymers. To understand this, we have derived an expression for the free energy of adsorption of polymer chains onto the surface of nanosheets in a solvent environment. Critically, we express all energetic interactions in terms of the Hildebrand solubility parameters of solvent, polymer, and nanosheet. This allows us to predict the dispersed nanosheet concentration to display a Gaussian peak when plotted against polymer Hildebrand parameter. This is borne out by experimental data. The model correctly (within ∼2 MPa1/2) predicts the peak to occur when polymer and solvent solubility parameters match. In addition, the model describes both the peak width and the dependence of nanosheet concentration on polymer molecular weight. Because of the wide availability of solubility parameters for solvents, polymers, and many nanomaterials, this work is of practical importance for the production of polymer–nanosheet composite dispersions. However, more importantly it extends our understanding of the conditions required for steric stabilization and provides simple rules which define the required combination of solvent and polymer to best stabilize a given type of nanomaterial or colloid.

Morphological Transition from Nanosheet to Nanosphere of Ternary Comb Copolymers with Carbazole Rings Induced by an Increase in Surface Pressure

Fax: +81-48-858-3503, e-mail: fujimori@fms.saitama-u.ac.jp Transition behavior from a monolayer on the water surface to a single particle layer of a ternary comb copolymer containing carbazole rings have been investigated by surface pressure-area isotherm, atomic force microscopy, X-ray diffraction. This polymer monolayer is able to form the “polymer nanosheet” with amorphous layers and strong interaction between main-chains prepared by the Langmuir-Blodgett (LB) technique. Further, the single particle layer is able to form the multi-particle layered organization of “polymer nanosphere” by the LB technique. This ternary comb copolymers were synthesized by radical copolymerization with hydrogenated and fluorinated long-chain vinyl compounds. Poly(N-vinylcarbazole) homopolymer formed a single particle layer on the water surface immediately after spreading. Spontaneous “particulation” behavior is accelerated by incorporation of carbazole units in ternary copolymer films. Organized molecular film of these copolymers formed a monolayer on the water surface below 10 m Nm

Molecular Optical Switch Based on Polymer Nanosheet Assembly Operated at Visible Wavelength

Abstract We constructed a molecular optical switch, which controls the photocurrent direction using a polymer nanosheet assembly. Two polymer nanosheet photodiodes composed of ruthenium complex (sensitizer) and ferrocene (donor) polymer nanosheet pair and anthracene (sensitizer) and dinitrobenzene (acceptor) polymer nanosheet pair, respectively, were assembled on the ITO electrode. Selective excitation of ruthenium by 450 nm generated cathodic photocurrent, whereas excitation of anthracene at 389 nm generated anodic photocurrent. The results indicate that the current flow direction in the assembled film can be controlled by the irradiation wavelength.

Layered Ultrathin Proton Conductive Film Based on Polymer Nanosheet Assembly

As described in this paper, a layered ultrathin proton conductive film was prepared using a poly(N-dodecylacrylamide-co-2-acrylamido-2-methylpropanesulfonic acid) (p(DDA/AMPS)) polymer nanosheet. The surface pressure-area isotherm revealed that p(DDA/AMPS) formed a stable monolayer at the air-water interface. The polymer monolayer was transferred onto a solid substrate using the Langmuir-Blodgett technique. X-ray diffraction measurements of a 30-layer film of p(DDA/AMPS) showed clear Kiessig fringes and one Bragg peak, which indicate that the multilayer film took a uniform layered structure. The monolayer thickness was determined as 1.85 nm from the Bragg peak. The proton conductivity of p(DDA/AMPS) polymer nanosheet through the layer plane direction was studied with changing temperature and relative humidity. The proton conductivity of the multilayer film was on the order of 1 × 10⁻⁵ S/cm at 100% RH with 20 °C and increased to 1 × 10⁻² S/cm at 70 °C. The proton conductivity of the multilayer film showed a more than 10 times higher value than that of the spin-coated film because of the formation of a uniform and consecutive hydrophilic nanochannel through the hydrophilic region in the multilayer film.

Electrochemical charging and photochemical discharging in heterodeposited polymer nanosheet assembly

We demonstrate electrochemical charge storage and photochemical release of the charge in heterodeposited polymer nanosheets assemblies. Two kinds of redox polymer nanosheets, those containing ruthenium dipyridyl complex (p(DDA/Rubpy32+)) and ferrocene derivative (p(DDA/Fc)), respectively were heterodeposited onto an ITO electrode using the Langmuir–Blodgett technique. The heterodeposited assembly forms a clear bilayer structure in which p(DDA/Rubpy32+) is located in an inner layer and p(DDA/Fc) in an outer layer. The electrochemical property of the heterodeposited assembly was studied by cyclic voltammetry measurement and compared with their single component film. The cyclic voltammogram of p(DDA/Rubpy32+) monolayer film showed a redox peak of Rubpy32+/3+ reaction around 1.1 V (vs.Ag/AgCl), and that of p(DDA/Fc) monolayer showed a redox peak of Fc0/+1 around 0.4 V. On the other hand, the cyclic voltammogram of the bilayer film showed no oxidation current around 0.4 V, and large oxidation currents were observed from 0.9 V. In the heterodeposited assembly, the p(DDA/Fc) layer was separated from the electrode about 5 nm by the inner p(DDA/Rubpy32+) layers. Therefore the oxidation of Fc moieties occurred by mediation of the inner p(DDA/Rubpy32+) layers, which started around 0.9 V. On the other hand, reduction of Fc+ by scanning the potential to cathodic direction was not observed, because reduction of Fc+ is thermodynamically unable for Rubpy32+. As the results, the outer p(DDA/Fc) layers store charges as Fc+ by one potential cycle (electrochemical charging). Moreover, we demonstrate the Fc+ reduction by using the photoinduced electron transfer from an excited ruthenium complex to Fc+ (photochemical discharging). The repeatability of the charging-discharging process was about 5 times. To improve the repeatability, Prussian blue (PB) nanoparticles were used instead of the p(DDA/Fc) layers. PB nanoparticles were assembled on a solid substrate using a cationic polymer nanosheet, poly(N-dodecylacrylamide-co- N-(2-(2-(2-aminoethoxy)ethoxy)ethyl)acrylamide) (p(DDA/DONH)) as a template. A hybrid heterodeposited assembly was prepared using p(DDA/Rubpy32+) as an inner layer and p(DDA/DONH) templated PB as an outer layer. The hybrid heterodeposited assembly stored and released charges by a similar process with the p(DDA/Rubpy32+)-p(DDA/Fc) heterodeposited polymer nanosheets assembly. The repeatability of the charging-discharging process in the hybrid heterodeposited assembly was increased compared to that in the p(DDA/Rubpy32+)-p(DDA/Fc) heterodeposited assembly due to the high stability of the oxidized form of PB. The high repeatability of the hybrid heterodeposited assembly indicates that the assembly is applicable to molecular-memory and battery.

Surface modification of a flexible polyimide film using a reactive fluorinated polymer nanosheet

This paper describes an effective approach to surface modification of a flexible polyimide film using a reactive fluorinated polymer nanosheet. N-(1 H,1 H-pentadecafluorooctyl)methacrylamide copolymers containing carboxyl group as a reactive moiety form stable monolayer on the water surface and highly ordered reactive polymer nanosheets can be fabricated by the Langmuir–Blodgett technique. This reactive fluorinated polymer nanosheet was utilized to modify the surface properties of polyimide film through its immobilization using thermal treatment. The modification process was studied by X-ray photoelectron spectroscopy (XPS) and modified PI surface was characterized by contact angle measurements and atomic force microscopy (AFM).

Sealing effect of a polysaccharide nanosheet for murine cecal puncture

Recent developments in nanobiotechnology have led us to develop a method of producing a free-standing polymer nanosheet composed of polysaccharides (ie, polysaccharide nanosheet) with a thickness of tens of nanometers. Owing to its enormous aspect ratio, the polysaccharide nanosheet is semi-absorbent and has a physical adhesive strength 7.5-fold greater than that of conventional films of >1 microm thickness. Herein, we have investigated the therapeutic sealing effect of this polysaccharide nanosheet on murine cecal puncture as a wound dressing material. Murine cecum was punctured and then overlapped with the polysaccharide nanosheet. Thereafter, we evaluated its sealing effect on bacterial peritonitis as well as the protection offered by the polysaccharide nanosheet against bacterial permeability using an in vitro transmembrane assay. The 39-nm-thick polysaccharide nanosheet overlapped tightly the perforated cecum. No adhering agents were required because of the ability of the polysaccharide nanosheet to adhere to the tissue surface by physical adsorption (eg, van der Waals interaction). Sealing the perforated cecum with the polysaccharide nanosheet increased survival rate without postoperative adhesion by comparison with untreated mice (90 vs 30%; P < .01). These data were supported by the improvement in peritonitis related to bacterial counts, white blood cell counts, and the serum tumor necrosis factor level. Moreover, using an in vitro transmembrane assay, we showed that the polysaccharide nanosheet inhibited effectively bacterial penetration. We have demonstrated the potential clinical benefits of the nanosheet-type biomaterial that can be used for repairing a cecal colotomy without chemical bonding agents.