Fabrication and characterization of dry conducting polymer actuator by vapor phase polymerization of polypyrrole.

A trilayered dry conducting polymer actuator was fabricated via application of a polypyrrole (PPy) coating on both sides of a solid polymer electrolyte film using vapor phase polymerization (VPP). The solid polymer electrolyte film was prepared by incorporation of different weight ratios of dodecylbenzene sulfonic acid sodium salt in poly(vinyl alcohol) (PVA) by solvent casting. The successful polymerization of PPy was confirmed by Fourier transform infrared spectroscopy; a uniform PPy coating on the solid polymer electrolyte film surface was also observed by scanning electron microscopy. The dry PVA/PPy actuator demonstrated good actuation behavior at a low applied voltage of 1-3 V. The actuator bending displacement was found to increase with an increase in the applied voltage. The VPP approach in this study provides a very effective method for achieving a uniform polymer coating in the fabrication of a dry conducting polymer actuator.

Cycloaddition reactions: a controlled approach for carbon nanotube functionalization.

Controlled functionalization of carbon nanotubes (CNTs) through the use of cycloaddition reactions is described. By employing various cycloaddition reactions, a wide range of molecules could be coupled onto CNTs without disruption of the structural integrity as well as with a statistical distribution of functional groups onto the surface of the CNTs. The cycloaddition reactions represent an effective and tailored approach for preparing CNT-based advanced hybrid materials that would be useful for a wide range of applications from nanobiotechnology to nanoelectronics.

Core-shell morphology and characterization of carbon nanotube nanowires click coupled with polypyrrole.

Core-shell nanowires having multiwalled carbon nanotubes (MWNT) as a core and polypyrrole (PPy) as a shell were synthesized using Cu(I)-catalyzed azide-alkyne cycloaddition click chemistry. According to transmission electron microscopy measurements, the uniform PPy layers of 10-20 nm in thickness were formed well on the MWNT's surface. In particular 'grafting from' click coupling was more effective in obtaining uniform and stable core-shell nanowires as well as in the reaction yield, compared to 'grafting to' click coupling. This is due to chemical bond formation between PPy and MWNT in equal intervals along the longitudinal direction of the MWNT, achieved by 'grafting from' click coupling. As a result, the core-shell nanowires were very stable even in the sonication of nanowires and showed an enhanced electrical conductivity of 80 S cm(-1), due to the synergetic interaction between MWNTs and PPy, which is higher than the conductivity of pure MWNTs and pure PPy. In addition, the core-shell nanowires could show better NO2 gas sensing properties compared to pure MWNTs and pure PPy as well as MWNT/PPy composites prepared by in situ polymerization. The synthesized core-shell nanowires would play an important role in preparing electrical and sensing devices.

Synthesis and characterization of polyurethane-grafted single-walled carbon nanotubes via click chemistry.

Polyurethane (PU)-grafted carbon nanotubes were synthesized by the coupling of alkyne moiety decorated single walled carbon nanotube (SWCNT) with azide moiety containing PU using Cu(I) catalyzed Huisgen [3 + 2] cycloaddition click chemistry. The azide moiety containing poly(s-caprolactone)diol was synthesized by ring-opening polymerization and further used for PU synthesis. Alkyne-functionalizion of SWCNT was completed by the reaction of p-aminophenyl propargyl ether with SWCNT using a solvent free diazotization procedure. Nuclear magnetic resonance, Fourier transform infrared, and Raman spectroscopic measurements confirmed the functionalization of SWCNT. Scanning electron microscopy and transmission electron microscopy images showed an excellent dispersion of SWCNTs, and specially debundling of SWCNTs could be observed due to polymer assisted dispersion. A quantitative grafting was successfully achieved even at high content of functional groups.

Synthesis and characterization of multi-walled carbon nanotubes functionalized with hyperbranched poly(urea-urethane).

Two types of hyperbranched poly(urea-urethane)-functionalized multi-walled carbon nanotubes (GHPU) have been synthesized in the presence of bis- and tris-hydroxy terminated carbon nanotubes (MWNT-OH). For comparison of the grafting efficiency on carbon nanotubes, pure hyper-branched poly(urea-urethane)s (HPUs) were also synthesized to prepare pristine carbon nanotubes-reinforced nanocomposites (HPNTs). Better MWNT dispersion in the polymer matrix was obtained for GHPU than for HPNT, and the effect was superior in the case of highly branched GHPU from tris-hydroxy-functionalized MWNTs, compared to GHPU from bis-hydroxy-functionalized MWNTs. TEM measurements for GHPUs clearly showed hyperbranched polymer-wrapped MWNT structures. Crystallization of hyperbranched polymers in GHPU was more developed than that of the HPNT nanocomposites, although MWNT-induced crystallization was observed for both the GHPU and HPNT samples. The hyperbranched polymer-grafting effect on MWNTs resulted in greater enhancement of the mechanical properties of GHPU at the same nanotube loading, compared to the case of HPNT nanocomposites. However, a too highly branched structure was found to lower the crystallization and mechanical properties of both the GHPUs and HPNTs.

Application of shape memory polyurethane in orthodontic.

A shape memory polymer wire for orthodontic application was prepared by melt-spinning of polyurethane block copolymer (PU) which was synthesized in a two-step process from a reaction of 4,4'-methylene bis(phenylisocyanate), poly(ε-caprolactone)diol (PCL), and 1,4-butanediol. An orthodontic test using the PU wire was carried out in an orthodontic model with a metal bracket. High shape recovery force of 70 gf for PU wire at 40 wt% hard segment content could be preserved for even 1 month after a shape recovery force test at a constant temperature of 50°C. The shape recovery force decreased exponentially during the initial 2 h, but reached an equilibrium shape recovery force of 50 gf after about 20 days. It was found that this shape recovery force was sufficient to correct misaligned teeth in the orthodontic test. The shape memory PU wire possesses strong potential as a novel orthodontic appliance with esthetically appealing appearance.

Assembly of gold nanoparticles on single-walled carbon nanotubes by using click chemistry.

Azide moiety-functionalized gold nanoparticles were conjugated with acetylene functionalized single-walled carbon nanotubes by employing copper-catalyzed Huisgen's [3+2] dipolar cycloaddition 'click chemistry' reaction. Evidences of conjunction were observed by TEM, EDX and Raman images.

Functionalization of single-walled carbon nanotubes with azides derived from amino acids using click chemistry.

Single-walled carbon nanotubes (SWCNTs) were chemically functionalized with amino acid-based moieties. The covalent functionalization of alkyne-derived SWCNTs with well defined azides derived from amino acids was accomplished through Cu(I)-catalyzed Huisgen [3+2] dipolar cycloaddition click chemistry. Transmission electron microscopy, Raman spectroscopy, and infrared spectroscopic measurements confirmed the functionalization of SWCNTs by organic molecules derived from amino acids, and the resulting material showed some good solubility in the organic solvents such as tetrahydrofuran, CH2Cl2, and CHCl3.

Functionalization of graphene with self-doped conducting polypyrrole by click coupling.

The synthesis of self-doped conducting polypyrrole-grafted graphene sheets (GS-PPy) for non-volatile memory applications is reported. First, the alkyne-modified graphene sheets (GS-alkyne) were covalently functionalized with a water-soluble polymer containing numerous anionic SO3(-) dopants by a copper-catalyzed click reaction. Then, polypyrrole was covalently grafted onto the functionalized graphene sheets by chemical oxidative polymerization to produce GS-PPy hybrids. The GS-PPy hybrids showed a uniform coating of PPy on the GS sheets, good dispersion in aqueous solutions, high electrical conductivity, and red-shifted absorption peak in the UV/Visible spectra. The non-volatile memory device composed of a Al/(GS-PPy/poly(vinyl alcohol))/Al structure, produced by spin coating of the aqueous GS-PPy/poly(vinyl alcohol) solution, showed a good write-once read-many times memory behavior, which was due to good electrical and optical absorption properties of the GS-PPy hybrids. The findings of this study provide a potential solution for the fabrication of water-soluble graphene-based hybrids for non-volatile resistive-memory-based applications.

The synergistic effect of the combined thin multi-walled carbon nanotubes and reduced graphene oxides on photothermally actuated shape memory polyurethane composites.

We evaluated the synergistic effect of the hybrid-type nanocarbon, consisting of 1D thin-walled carbon nanotubes (TWNTs) and 2D reduced graphene oxide (RGO), on the shape memory performance of hyperbranched polyurethane composites. The shape recovery of the resulting composites was activated via a photothermal process using a near-infrared laser. The best laser-induced shape recovery performance was achieved for the composites with a 7/3 of TWNT/RGO ratio and a 1wt.% of nanocarbon content. Such result can be explained by good dispersion of TWNTs and RGO in the hyperbranched polymer as well as three-dimensionally enhanced interconnection between carbon nanotubes and graphenes. The optically active TWNTs with a high optical absorption section exhibited high ability of transferring laser-induced thermal energy to polymer matrix whereas RGO provided a high mechanical property to polymer matrix. The tensile modulus and electrical conductivity of the composites also showed a similar dependence on the TWNT/RGO composition ratio as the photothermal shape recovery. Our study demonstrated an effective conversion from light, thermal to mechanical work by irradiating shape memory polymer composite containing hybrid-type fillers using a near-infrared laser.

Synthesis of a hybrid assembly composed of titanium dioxide nanoparticles and thin multi-walled carbon nanotubes using "click chemistry".

A hybrid assembly composed of thin multi-walled carbon nanotubes (t-MWCNT) and titanium dioxide (TiO(2)) has been prepared by using "click" chemistry for photocatalytic applications. TiO(2)-decorated t-MWCNT hybrids with anatase phase TiO(2) were obtained from the reaction of an azide moiety-containing TiO(2) with alkyne-functionalized t-MWCNTs. The hybrids were systematically characterized using Fourier transform infrared spectroscopic (FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectrum (EDX), and X-ray diffraction (XRD) measurements. The nanohybrid has been proved to be highly active and robust for photocatalytic degradation of methyl orange. The click coupling approach is a simple and convenient route to efficiently assemble TiO(2) on the surface of carbon nanotubes, and can be extended to obtain many other nanoparticle hybrids based on carbon nanotubes.

Synthesis of multi-walled carbon nanotube/polyhedral oligomeric silsesquioxane nanohybrid by utilizing click chemistry.

A new hybrid material consisting of a polyhedral oligomeric silsesquioxane (POSS) and carbon nanotube (CNT) was synthesized by a simple and versatile approach entailing click coupling between azide moiety-functionalized POSS and alkyne-functionalized multi-walled CNTs. This approach provides a simple and convenient route to efficiently functionalize a wide variety of nanoscale nanostructure materials on the surface of CNTs.

Functionalization of carbon nanotubes via Cu(I)-catalyzed Huisgen [3+2] cycloaddition "click chemistry".

Functionalization of carbon nanotubes is essential for achieving their mechanical, electrical, and biological functions and enhancing their dispersion in a polymer matrix. Cycloaddition reactions can play a significant role as an emerging route in this direction. This minireview focuses on covalent functionalization of carbon nanotubes using a facile approach via a Cu(I)-catalyzed Huisgen [3+2] cycloaddition reaction. Through this reaction, an enormous variety of molecules can be coupled onto carbon nanotubes in a very controlled manner, and may be utilized for many potential applications from nanoelectronics to bio-applications.

Enhanced dispersion of carbon nanotubes in hyperbranched polyurethane and properties of nanocomposites.

Hyperbranched polyurethane (HBPU) nanocomposites with multi-walled carbon nanotubes (MWNTs) were prepared by in situ polymerization on the basis of poly(ε-caprolactone)diol as the soft segment, 4,4'-methylene bis(phenylisocyanate) as the hard segment, and castor oil as the multifunctional group for the hyperbranched structure. A dominant improvement in the dispersion of MWNTs in the HBPU matrix was found, and good solubility of HBPU-MWNT nanocomposites in organic solvents was shown. Due to the well-dispersed MWNTs, the nanocomposites resulted in achieving excellent shape memory properties as well as enhanced mechanical properties compared to pure HBPU.