Synthesis of CdSe–Poly(N‐vinylcarbazole) Nanocomposite by Atom Transfer Radical Polymerization for Potential Optoelectronic Applications

A hybrid inorganic–polymer nanocomposite using CdSe nanocrystals with high electron mobility has been successfully synthesized by atom transfer radical polymerization (ATRP). First the hydroxyl‐coated CdSe nanoparticles (i.e., CdSe–OH) were prepared via a wet chemical route. A polymerization initiator was then prepared for ATRP of N‐vinylcarbazole. FT‐IR, ¹H NMR, and XRD analyses confirmed the successful synthesis of CdSe–poly(N‐vinylcarbazole) (PVK) nanohybrid. UV–Vis spectra and photoluminescence data revealed that grafting of PVK onto the surface of CdSe nanocrystals would reduce the band gap of PVK and cause the red shift of emission peak. TEM and SEM micrographs exhibited CdSe nanoparticles that were well‐coated with PVK polymer.

     

Photoinduced Energy Transfer from Poly(N‐vinylcarbazole) to Tricarbonylchloro‐(2,2′‐bipyridyl)rhenium(I)

This work investigates the photoinduced energy transfer from poly(N‐vinylcarbazole) (PVK), as a donor material, to fac‐(2,2′‐bipyridyl)Re(CO)₃Cl, as a catalyst acceptor, for its potential application towards CO₂ reduction. Photoluminescence quenching experiments reveal dynamic quenching through resonance energy transfer in solid donor/acceptor mixtures and in solid/liquid systems. The bimolecular reaction rate constant at solution–film interfaces for the elementary reaction of the excited state with the quencher material could be determined as 8.8(±1.4)×10¹¹ L mol^?1 s^?1 by using Stern–Volmer analysis. This work shows that PVK is an effective and cheap absorber material that can act efficiently as a redox photosensitizer in combination with fac‐(2,2′‐bipyridyl)Re(CO)₃Cl as a catalyst acceptor, which might lead to possible applications in photocatalytic CO₂ reduction.     

Poly(N‐vinylcarbazole) chemically modified graphene oxide

A new soluble donor‐acceptor type poly(N‐vinylcarbazole)‐covalently functionalized graphene oxide (GO‐PVK) has been synthesized by reaction of DDAT (S‐1‐dodecyl‐S′‐(α,α′‐dimethyl‐α″‐aceticacid)trithiocarbonate)‐PVK with GO‐toluene‐2,4‐diisocynate. The incorporation of sufficient amount of PVK chains makes the modified GO nanosheets readily dispersible in organic solvents. The resulting material exhibits an enhanced solubility of 10 mg/mL in organic solvents. Covalent grafting of PVK onto the edge and surface of GO nanosheets did not change the carbazole absorption in the ultraviolet region, but substantially reduced the absorption intensity of GO in the visible region. The intensity of the emission band of GO‐PVK at 437 nm was a little bit quenched when compared with that of DDAT‐PVK, suggesting intramolecular quenching from PVK to GO. Such intramolecular quenching process may involve energy or electron transfer between the excited singlet states of the PVK moiety and the GO moiety. The HOMO/LUMO values and the energy bandgap of GO‐PVK experimentally estimated by the onset of the redox potentials are ?5.60, ?3.58, and 2.02 eV, respectively. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2642–2649, 2010     

Electrically Conductive Poly(DL‐lactide)/Chitosan/Polypyrrole Complexes

Summary: The fabrication of novel conductive poly(DL ‐lactide)/chitosan/polypyrrole complex membranes is reported. Using poly(DL ‐lactide)/chitosan blends as matrices and polypyrrole as a conductive component, several kinds of membranes with various compositions are prepared. A percolation threshold of polypyrrole as low as 1.8 wt.‐% is achieved for some membranes by controlling the chitosan proportion between 40 and 50 wt.‐%. SEM images exhibit that the membranes with a low percolation threshold show a two‐phase structure which consists of poly(DL ‐lactide) and chitosan phases. Dielectric measurements indicate that there is limited miscibility between the poly(DL ‐lactide) and chitosan but polypyrrole is nearly immiscible with the other two components. Based on the structural characteristics of the membranes, the polypyrrole particles are suggested to be localized at the interface between two phases.

Dependence of conductivity of complex membranes on the PPy content. (○) PDLLA/PPy, (▪) PDLLA/ch(10)/PPy, (▵) PDLLA/ch(20)/PPy, (•) PDLLA/ch(30)/PPy, (□) PDLLA/ch(40)/PPy, and (▴) PDLLA/ch(50)‐PPy.     

Grafting Efficiency of Hydroxy‐Terminated Poly(methyl methacrylate) with Multiwalled Carbon Nanotubes

Summary: Poly(methyl methacrylate)s (PMMAs) containing a terminal hydroxy group or multiple hydroxy groups as pendants were grafted to multiwalled carbon nanotubes (MWNTs) by esterification in toluene at 100 °C. The recovered polymer with a low level of MWNTs and the PMMA‐g‐MWNTs with up to 12 wt.‐% grafted polymer were characterized using spectroscopic, microscopic, and thermogravimetric analyses. The percentage of polymer present in the PMMA‐g‐MWNT samples is very low based upon the concentration of the acid groups in the tubes.

The grafting of hydroxy‐terminated PMMA to MWNTs by esterification.     

Organic electroluminescent devices using europium complex‐doped poly(N‐vinylcarbazole)

Electroluminescence (EL) properties of europium (Eu) complex‐doped poly(N‐vinylcarbazole) (PVK) were investigated. A device structure of glass substrate/indium‐tin oxide/hole‐injection layer/Eu complex‐doped PVK/hole‐blocking layer/electron transport layer/electron‐injection layer/Al was employed. Red emission originating from Eu complex was observed. Relatively high luminance of 50 cd/m² and an efficiency of 0.2% were obtained. Copyright © 2004 John Wiley & Sons, Ltd.     

Core–Shell PbI2@WS2 Inorganic Nanotubes from Capillary Wetting

Multiwall WS ₂ nanotube templates were used as hosts to prepare core–shell PbI₂@WS₂ nanotubes by a capillary‐wetting method. Conformal growth of PbI₂ layers on the inner wall of the relatively wide WS₂ nanotubes (i.d. ca. 10 nm) leads to nanotubular structures which were not previously observed in narrow carbon nanotube templates. Image simulation after structural modeling (see picture) showed good agreement with the experimental HRTEM image.

     

Sulfur‐Impregnated Core–Shell Hierarchical Porous Carbon for Lithium–Sulfur Batteries

Core–shell hierarchical porous carbon spheres (HPCs) were synthesized by a facile hydrothermal method and used as host to incorporate sulfur. The microstructure, morphology, and specific surface areas of the resultant samples have been systematically characterized. The results indicate that most of sulfur is well dispersed over the core area of HPCs after the impregnation of sulfur. Meanwhile, the shell of HPCs with void pores is serving as a retard against the dissolution of lithium polysulfides. This structure can enhance the transport of electron and lithium ions as well as alleviate the stress caused by volume change during the charge–discharge process. The as‐prepared HPC‐sulfur (HPC‐S) composite with 65.3 wt % sulfur delivers a high specific capacity of 1397.9 mA h g^?1 at a current density of 335 mA g^?1 (0.2 C) as a cathode material for lithium–sulfur (Li‐S) batteries, and the discharge capacity of the electrode could still reach 753.2 mA h g^?1 at 6700 mA g^?1 (4 C). Moreover, the composite electrode exhibited an excellent cycling capacity of 830.5 mA h g^?1 after 200 cycles.     

Microwave‐Assisted Synthesis of Crosslinked Poly(vinyl alcohol) Nanocomposites Comprising Single‐Walled Carbon Nanotubes,Multi‐Walled Carbon Nanotubes,and Buckminsterfullerene

We report a facile method to accomplish the crosslinking reaction of PVA with SWNTs, MWNTs, and C‐60 using MW irradiation. Nanocomposites of PVA crosslinked with SWNT, MWNT and C‐60 were prepared expeditiously by reacting the respective carbon nanotubes with 3 wt.‐% PVA under MW irradiation, maintaining a temperature of 100 °C, representing a radical improvement over literature methods to prepare such crosslinked PVA composites. This general preparative procedure is versatile and provides a simple route to manufacture useful SWNT, MWNT and C‐60 nanocomposites.

     

Creep Resistant Polymer Nanocomposites Reinforced with Multiwalled Carbon Nanotubes

Poly(propylene) (PP) nanocomposites filled with shorter‐ and longer‐aspect‐ratio multiwalled carbon nanotubes (MWNTs) were compounded using a twin‐screw extruder and an injection moulding machine. It is shown that with only 1 vol.‐% of MWNTs, creep resistance of PP can be significantly improved with reduced creep deformation and creep rate at a long‐term loading period. Additionally, the creep lifetime of the nanocomposites has been considerably extended by 1 000% compared to that of a neat PP. Three possible mechanisms of load transfer were considered that could contribute to the observed enhancement of creep resistance, which are: (1) fairly good interfacial strength between MWNTs and polymer matrix, (2) increasing immobility of amorphous regions due to nanotubes acting as restriction sites, and (3) high aspect ratio of MWNTs. DSC results showing crystallinity changes in the specimens before and after creep deformation present evidence to confirm these mechanisms. Our results should lead to improved grades of creep resistant polymer nanocomposites for engineering applications.

     

Magneto‐Optical Studies of HgTe/HgxCd1−xTe(S) Core–Shell Nanocrystals

The synthesis and magneto‐optical properties of HgTe nanocrystals capped with Hg_xCd_1?xTe(S) alloyed shells have been investigated. The magneto‐optical measurements included the use of optically detected magnetic resonance (ODMR) and circular polarized photoluminescence (CP‐PL) spectroscopy. The PL spectra suggest the existence of luminescence events from both the core HgTe and the Hg_xCd_1?xTe(S) shells. The continuous‐wave (cw) and time‐resolved ODMR measurements revealed that the luminescence at the shell regime is associated with a trap‐to‐band recombination emission. The electron trap is comprised of a Cd–Hg mixed site, confirming the existence of an alloyed Hg_xCd_1?xTe(S) composition. The ODMR data and the CP‐PL measurements together revealed the g‐values of the trapped electron and the valence band hole.     

Multifunctional Poly(N‐vinylcarbazole)‐Based Block Copolymers and their Nanofabrication and Photosensitizing Properties

The synthesis of poly(N‐vinylcarbazole)‐based block copolymers functionalized with rhenium diimine complexes or pendant terpyridine ligands is reported. The copolymers are synthesized by reversible addition–fragmentation chain transfer (RAFT) polymerization, and they exhibit interesting morphological properties as a result of the phase separation between different blocks. The rhenium complex polymer block may function as a photosensitizer, while the terpyridine‐containing polymer block can be used as the template for nanofabrication by selective deposition of zinc complexes.

     

Waveguiding properties in dye‐doped submicron poly(N–vinylcarbazole) fibers

Dye‐doped submicron poly(N‐vinylcarbazole) fibers having mean diameters of 290–430 nm were fabricated via electrospinning and their waveguiding properties were investigated. The middle of each fiber's length was excited with UV light and guided photoluminescence (PL) was measured at the end of each of the fibers for different propagation lengths. The spectral shapes of the guided PL differed depending on the fiber diameter because of leakage of light into the substrate. We propose a model that reproduces the PL attenuation with increasing propagation lengths and includes the temporal PL decay due to photobleaching and the size of the excitation area. The calculated propagation loss coefficient in the fibers was 6.3 × 10^?3?1.4 × 10^?1 µm^?1 with λ = 430–500 nm. The propagation loss was inherent in the fiber itself because the re‐absorption loss coefficient of the doped dye was <1.3% of the propagation loss coefficient. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1237–1244     

Nanotube Friendly Poly(N‐isopropylacrylamide)

Poly(N‐ispropylacrylamide) [PNIPAM] is a widely studied polymer for use in biological applications due to its lower critical solution temperature (LCST) being so close to the human body temperature. Unfortunately, attempts to combine carbon nanotubes (CNTs) with PNIPAM have been unsuccessful due to poor interactions between these two materials. In this work, a PNIPAM copolymer with 1 mol‐% pyrene side group [p‐PNIPAM] was used to produce a thermoresponsive polymer capable of stabilizing both single and multi‐walled carbon nanotubes (MWNTs) in water. The presence of pyrene in the polymer chain lowers the LCST less than 4 °C and the interaction with nanotubes does not show any influence on LCST. Moreover, p‐PNIPAM stabilized nanotubes show a temperature‐dependent dispersion in water that allows the level of nanotube exfoliation/bundling to be controlled. Cryo‐TEM images, turbidity, and viscosity of these suspensions were used to characterize these thermoresponsive changes. This ability to manipulate the dispersion state of CNTs in water with p‐PNIPAM will likely benefit many biological applications, such as drug delivery, optical sensors, and hydrogels.

     

Multiwalled carbon nanotubes covalently functionalized with poly(N‐vinylcarbazole) via RAFT polymerization: Synthesis and nonliner optical properties

The poly(N‐vinylcarbazole)‐grafted MWNTs (MWNT‐PVK) hybrid materials were synthesized in the presence of S‐1‐Dodecyl‐S′‐(α, α′‐dimethyl‐α″‐acetic acid) trithiocarbonate (DDAT)‐covalently functionalized multiwalled carbon nanotubes (MWNT‐DDAT) as reversible addition–fragmentation chain transfer (RAFT) agent. Incorporation of the PVK moieties onto the MWNTs surface can considerably improve the solubility and processability of MWNTs. For all MWNT‐PVK hybrid materials, they are soluble in some common organic solvents such as toluene, THF, chloroform, DMF and others. In contrast to the UV/Vis spectrum of DDAT‐PVK, which was synthesized by use of DDAT as RAFT agent under the same synthetic condition, in the visible region, the absorption spectrum of MWNT‐PVK exhibited a typical electronic absorption characteristics of solubilized carbon nanotubes, in which the absorbance decreases gradually in the range of 350–600 nm. At the same level of linear transmission the MWNT‐PVK with 79.2% PVK moieties in the material structure possesses best optical limiting performance in comparison with the other MWNT‐PVK composites, MWNTs and C₆₀. The significant NLO responses manifest the MWNT‐PVK materials suitable candidate for viable optical limiting devices. Light scattering, originating from the thermal‐induced microplasmas and/or microbubbles, is responsible for the optical limiting. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3161–3168, 2010     

Selective Localization and Migration of Multiwalled Carbon Nanotubes in Blends of Polycarbonate and Poly(styrene‐acrylonitrile)

Multiwalled carbon nanotubes (MWNTs) have been introduced into blends of polycarbonate (PC) and poly(styrene‐acrylonitrile) (SAN) by melt mixing in a microcompounder. Co‐continuous blends are prepared by either pre‐compounding low amounts of nanotubes into PC or SAN or by mixing all three components together. Interestingly, in all blends, regardless of the way of introducing the nanotubes, the MWNTs were exclusively located within the PC phase, which resulted in much lower electrical resistivities as compared to PC or SAN composites with the same MWNT content. The migration of MWNTs from the SAN phase into the PC phase during common mixing is explained by interfacial effects.

     

A Mechanochemical Approach to Nanocomposites Using Single‐Wall Carbon Nanotubes and Poly(L‐lysine)

A simple method to fabricate polymer nanocomposites with single‐walled carbon nanotubes is reported, in which the nanotubes were reacted with poly(L ‐lysine) by using high‐speed vibration milling. The nanocomposites obtained were characterized by Fourier transform infrared (FT‐IR), UV–Vis spectroscopy, and thermogravimetric methods. The morphology as well as the dispersion of the carbon nanotubes were determined by scanning and transmission electron microscopy.