Xinlin Tuo

A novel polyelectrolyte with branched azo side chains: Synthesis, characterization and self-assembled nanostructures

A novel polyelectrolyte (PEAPB 6 P-AA) functionalized with branched azo side chains has been synthesized. Aggregation of the azo chromophores of PEAPB 6 P-AA in H 2 O/tetrahydrofuran (THF) mixed solvent was detected from its influences on UV-vis spectra and photoresponsive behavior. Micelle-like nanoparticles were found when the concentration of PEAPB 6 P-AA increased to above 0.2 mmol . L -1 in the mixed solvent (THF/H 2 O = 1:20 vol.-%). Multilayers of the micelle-like nanoparticles and poly(diallyldimethylammonium chloride) (PDAC) were fabricated by an electrostatic layer-by-layer self-assembly process. Particularly high wettability of the multilayer surfaces was observed, which affirmed the self-assembled micelle-like structure of the particles.

Synthesis and fluorescent properties of a novel europium(III) complex with terpyridine-capped poly(ethylene glycol)

Abstract Terpyridine-capped poly(ethylene glycol) (PEG) was synthesized as a novel polymeric ligand and rare earth complex was prepared from Eu(NO 3 ) 3 and the telechelic macromolecules. The structure of the complex was characterized by 1 H NMR, FT-IR, UV-vis and fluorescence spectroscopy. Strong fluorescent emission of the complex was observed at 593 and 616 nm upon the excitation of 300 nm. The fluorescent emission was quenched upon addition of trace amount of diethyl chlorophosphate (DCP). And the observed K sv values for DCP were measured to be 0.568×10 3 and 0.89×10 3 L/mol for quenching at 593 and 616 nm, which indicated the detection limit for DCP was about 0.014 mmol/L. These results showed that the terpyridine-lanthanide complex could be an effective chemosensor with a potential application in the detection of organophosphates.

Polystyrene microsphere-based lanthanide luminescent chemosensor for detection of organophosphate pesticides

Abstract Fluorescent microspheres of polystyrene-based Eu(III) complexes were prepared from TentaGel resin, 2,6-bisbenzimidazolylpyridine and europium nitrate. The microspheres were characterized by FTIR spectroscopy, elemental analysis, XPS measurements and fluorescence spectroscopy. Characteristic red emission under irradiation of 365 nm light from a hand-held UV lamp was observed for the microspheres either in a solution or solid-state. Fluorescent quenching was observed when the microspheres were exposed to a trace amount of diethyl chlorophosphate (DCP) in the dispersion. The material and property can be potentially used to fabricate chemosensor in the detection of organophosphates.

Ab initio calculations of the effects of H+ and NH4+ on the initial decomposition of HMX

In this work, the effects of H(+) and NH(4)(+) on the initial decomposition of HMX were investigated on the basis of the B3P86/6-31G** and B3LYP/6-31G* calculations. Three initial decomposition pathways including the N-NO(2) bond fission, HONO elimination and C-N bond dissociation were considered for the complexes formed by HMX with H(+) (PHMX1 and PHMX2) or with NH(4)(+) (AHMX). We found that H(+) and NH(4)(+) did not evidently induce the HMX to trigger the N-NO(2) heterolysis because the energy barrier of N-NO(2) heterolysis was found to be higher than the bond dissociation energy of N-NO(2) homolytic cleavage. Meanwhile, the transition state barriers of the HONO elimination from the complexes were found to be similar to that from the isolated HMX, which means that the HONO elimination reaction of HMX was not affected by the H(+) and NH(4)(+). As for the ring-opening reaction of HMX due to the C-N bond dissociation, the calculated potential energy profile showed that the energy of the complex (AHMX) went uphill along the C-N bond length and no transition state existed on the curve. However, the transition state energy barriers of C-N bond dissociation were calculated to be only 5.0 kcal/mol and 5.5 kcal/mol for the PHMX1 and PHMX2 complexes, respectively, which were much lower than the C-N bond dissociation energy of isolated HMX. Moreover, among the three initial decomposition reactions, the C-N bond dissociation was also the most energetically favorable pathway for the PHMX1 and PHMX2. Our calculation results showed that the H(+) can significantly promote the initial thermal decomposition of C-N bond of HMX, which, however, is influenced by NH(4)(+) slightly.

A new approach to the preparation of poly(p-phenylene terephthalamide) nanofibers

Poly(p-phenylene terephthalamide) (PPTA) nanofibers were prepared via a polymerization induced self-assembly process with the assistance of methoxy polyethylene glycol (mPEG) for stability and dispersity. In the traditional process of the solution polycondensation of p-phenylenediamine (PPD) and terephthaloyl chloride (TPC), PPTA will aggregate and precipitate with the chain growth due to the liquid crystalline characteristic. The introduction of mPEG can control the aggregation degree of PPTA molecules and stabilize the formed aggregates, which drives the self-assembly of PPTA molecules and results in the formation of nanofibers. The obtained nanofibers specialized by the great length–diameter ratio were characterized in detail. The effects of mPEG addition on the formation and the performance of the fibers were all studied in the work. The nanofibers can disperse in variety of organic solvents and water. Moreover, the nanofibers can be deposited for the formation of thin films with excellent transparency and thermal stability, which has great potential applications such as the separator of lithium ion battery.

Large-Scale Self-Organized Growth of (001) Surface-Oriented Colloidal Crystals by Edge Meniscus Effect

Millimeter-sized films of (100) facing face-centered crystals (fcc) of colloidal nanoparticles have been fabricated by self-assembly on silicon substrates and studied by both optical and scanning electron microscopy. The top surface layer sometimes also reconstructs to form a 1 x n (n varies from 2-7) superstructure. Such (100) oriented regions of the colloidal film are apt to concentrate near the edge of the substrate, and changing the width of the substrate could control the areas of the (100)-oriented domains. The formation of the square packing surface pattern is related to the shape of the meniscus at the edges of the substrate, where the particles suffer additional shear force and higher evaporation, which can be used to control the location and size of the square arrangement of nanoparticles.

HOMOLYTIC C–H BOND DISSOCIATION ENERGIES OF HTPB BINDER NETWORK

The C–H bond dissociation energies (BDEs) of hydroxyl-terminated polybutadiene (HTPB) binder have been computed using ab initio and density functional theory methods. Five different HTPB carbon radicals were produced by the ruptures of different C–H bonds. The structural analysis of radicals and the calculated BDEs showed that the studied C–H bonds could be divided into three groups. It was found that the weakest C–H bonds were those on the tertiary carbon atom linked to a vinyl function. The next were those on the secondary carbon attached to a vinyl function. The dissociation of these two kinds of C–H bonds determines the structure of the ultimate products during the aging of HTPB binder. The most stable C–H bonds were those in the methylene that were attached to the saturated carbon atoms.

Selective Fusion, Solvent Dissolution, and Local Symmetry Effects in Inversion of Colloidal Crystals to Ordered Porous Films

Polystyrene-methacrylic core-shell nanospheres, self-assembled into face-centered-cube-like colloidal crystals with their (001) planes parallel to the substrate, have been transformed into ordered pore structures by a toluene treatment. Detailed analysis by transmission electron microscopy reveals that the morphological transformation is preceded by an internal neck formation due to selective fusion of the polystyrene-rich core material, at the contacts between the nanoparticles, followed by the selective dissolution of the polystyrene-rich cores. We have demonstrated the importance of local symmetry and compactness of the nanospheres assembly in determining the nature of the neck formation and the existence of multiscale ordered pore structures in the square facing colloidal crystals. The pseudo layer-by-layer nature of the selective dissolution of square arranged nanosphere multilayers is responsible for the observed three-dimensional pore structures.

AB INITIO STUDY OF THE MOLECULAR STRUCTURE AND THERMAL CIS–TRANS ISOMERIZATION OF 3,3′-DIAMINO-4,4′-AZOFURAZAN AND 3,3′-DIAMINO-4,4′-AZOXYFURAZAN

In this work, we carried out the density functional theory (DFT) calculations in order to understand the molecular structures and thermal trans–cis isomerization of 3,3′-diamino-4,4′-azofurazan (DAAzF) and 3,3′-diamino-4,4′-azoxyfurazan (DAAF). We found that the azo group oxidation of DAAzF leading to the formation of DAAF induced evidently the twist of azofurazan molecule and weakened one of CN bonds connecting the furazan rings and azo group. This means that DAAzF is more stable than DAAF. In addition, the oxidation of azo group has a significant influence on the energy difference between trans- and cis-isomer of azofurazan. The energy difference between the isomers of DAAF is only about half of that of DAAzF. Furthermore, the thermal trans–cis isomerization of DAAzF and DAAF was found to follow a different mechanism: an inversion mechanism for DAAzF and a rotation mechanism for DAAF. By analyzing the reversible trans–cis isomerization process, we firstly proposed that a self-desensitization effect could be responsible for the low sensitivity of azofurazan. This new desensitization mechanism may be useful in the design of novel high energetic density material.

Controllable growth of (001) surface-oriented colloidal crystals by edge meniscus effect

Colloidal crystal films have been fabricated on silicon substrates using a flow-controlled vertical deposition (FCVD) method. Scanning electron microscopy shows that large areas of the colloidal crystal films can exhibit regular square arrangement or related 1×n superstructure induced by the surface relaxation of colloidal spheres. They are shown to be the (100) facing crystals of face centred cubic (FCC) structure. Their formation is related to meniscus bending at the edge of the wafer, which can be controlled by varying the width of the substrate or the wetting properties of the backing substrate. This (100) surface-oriented colloidal crystal could be used as a template to fabricate square arrangements of nanopore and nanodot arrays.