Synthesis and characterization of fluorinated polyacrylate latex emulsified with novel surfactants

The fluorinated polyacrylate latex were successfully prepared with semi- continuous seeded emulsion polymerization of butyl acrylate (BA), methyl methacrylate (MMA) and hexafluorobutyl methacrylate (HFMA) which was initiated with potassium persulfate (KPS) initiator and emulsified with the novel mixed surfactants of sodium lauryl glutamate (SLG) and alkylphenol ethoxylates (OP-10). The structure of the resultant latex was confirmed by Fourier transform infrared spectroscopy (FTIR). The particle size of the latex was measured by Zetatrac dynamic light scattering detector. The film of latex was tested by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and contact angle (CA). The optimum conditions of preparing the novel fluorinated polyacrylate latex are optimized and the results are as follows: the amount of emulsifiers is 4.0%; mass ratio of SLG to OP-10 is 1:1, the amount of the initiator is 0.6%. The mass ratio of MMA to BA is 1:1 and the amount of HFMA is 7.0%. In this case, the conversion is high and the polymerization stability is good. In addition, the water resistance and thermal properties of the latex films were improved significantly in comparison with the film of the latex prepared without the fluorinated monomer.     

聚氨酯交联改性聚丙烯酸酯压敏胶的研究

采用溶液自由基共聚法合成了含有羟基的(甲基)丙烯酸酯共聚物(PA),采用预聚法合成了端-NCO基聚氨酯(PU)预聚体,然后将PA和PU预聚体混合均匀后制备PUA压敏胶。考察了n(-NCO)∶n(-OH)比例、不同相对分子质量(Mn)的聚丙二醇(PPG)和不同类型的聚醚合成的PU预聚体对PUA压敏胶性能的影响。实验结果表明,改性PUA压敏胶的剥离强度随着PU预聚体用量的增加而逐渐降低,最大降幅为8N/30mm左右,但残胶现象可消除;当n(-NCO)∶n(-OH)=3∶2、m(PA)∶m(PU)=10∶1且PPG的Mn为400时,所制取的PUA压敏胶的持粘性较未改性PA压敏胶提高了267%,但初粘性则有所降低;对Mn均为400的聚乙二醇(PEG)和PPG而言,由PEG400合成的PUA压敏胶比由PPG400合成的PUA压敏胶改性效果更好。     

Field emission from non-uniform carbon nanotube arrays

Regular arrays of carbon nanotubes (CNTs) are frequently used in studies on field emission. However, non-uniformities are always present like dispersions in height, radius, and position. In this report, we describe the effect of these non-uniformities in the overall emission current by simulation. We show that non-uniform arrays can be modeled as a perfect array multiplied by a factor that is a function of the CNTs spacing.     

Micromorphology and mechanism of polyurethane/polyacrylate membranes modified with epoxide group

Polyurethane/polyacrylate (PUA) composite emulsions were synthesized based on the presence of preformed polyurethane chains. Glycidyl methacrylate (GMA), an acrylate monomer, was introduced into the system. Surface tension measurements assured the surface activities of the polyurethane emulsion. Dynamic light scattering (DLS) result showed that the average diameters and polydispersity were increased with the increment of GMA content. X-ray photoelectron spectroscopy (XPS) result indicated that the upper surface was rich in PU phase. The peak deconvolution results of XPS also confirmed the formation of PUA. The crosslinking degree and tensile strength were both enhanced due to the reaction between the carboxyl groups and the epoxide groups. Thermo gravimetric analysis (TGA) of the membranes showed that the thermal stability enhanced and the decomposition temperature was much higher than the pure PU membrane. X-ray diffraction (XRD) analysis, together with differential scanning calorimetry (DSC) results, demonstrated the amorphous nature of the PU matrix. Atomic force microscopy (AFM) observation performed the extremely flat membrane.     

Dispersion behaviour of laser-synthesized nanometric SiC powders in aqueous medium with ammonium polyacrylate

The dispersion behaviour of laser-synthesized nanometric SiC powders in water using ammonium polyacrylate (molecular WEIGHT=10,000) as dispersant was investigated. The influence of oxidation, presoaking time, ammonium polyacrylate (NH₄PA) concentration, and pH on suspension stability and coagulation rate of aggregates was determined. The stabilization mechanism is discussed. Excellent dispersion stability was obtained for oxidized (500 °C) powders containing 2.45 wt.% NH₄PA at pH 9.25 after a lengthy aging treatment.     

聚氨酯-聚丙烯酸酯互穿聚合物网络压敏胶及其耐热性研究

为了提高丙烯酸酯压敏胶的耐热性能,本文采用聚氨酯/聚丙烯酸酯(PU/PAA)互穿聚合物网络(IPN)技术对丙烯酸酯压敏胶进行改性,研制出一种软化点达到125℃左右的耐热压敏胶。分析讨论了不同制备工艺因素对该压敏胶性能的影响,并对其耐热性机理进行了探讨。     

Fluorescent coumarin derivatives with large stokes shift, dual emission and solid state luminescent properties: An experimental and theoretical study

Coumarin derivatives containing 8-benzothiazole (C-2) and its difluoroboron bound derivative (C-3) were prepared. Both derivatives show dual emission at 322 nm and 513 nm and large Stokes shift (188 nm), compared to the unsubstituted coumarin (C-1), which shows emission at 356 nm with small Stokes shift of 46 nm. C-2 and C-3 show fluorescence in solid state, in contrast the C-1 is non-fluorescent in the solid state. The excited state intramolecular proton transfer (ESIPT) process of C-2 was fully rationalized by DFT/TDDFT calculations with optimization of the ground state (S₀) and excited state (S₁) geometries. TDDFT calculations propose that the large Stokes shift of C-2 and C-3 are due to the re-distribution of the frontier molecular orbitals at excited states. Study of the potential energy curve of C-2 indicated that the dual emission of the C-2 is due to the simultaneous S₁ and S₃ emission, not the rotamer of the enol form.     

Effect of sodium polyacrylate on mechanical properties and microstructure of metakaolin-based geopolymer with different SiO2/Al2O3 ratio

The mechanical properties and microstructure of geopolymer are affected by the molar ratio of SiO₂/Al₂O₃. Meanwhile, organic polymer has the effect of improving the toughness of geopolymer, which depends on the SiO₂/Al₂O₃ ratio of geopolymer inevitably. Therefore, it is important to investigate the effect of the organic polymer on the mechanical properties and microstructure of geopolymer with varying SiO₂/Al₂O₃ ratio for using organic polymer to modify geopolymer. In this work, the SiO₂/Al₂O₃ ratios of metakaolin-based geopolymers are adjusted to 2.0, 2.5, 3.0, 3.5 and 4.0 by adding silica fume and β-Al₂O₃, with Na₂O/SiO₂, H₂O/SiO₂ being maintained at 0.2, 4.0, respectively. The geopolymers with each SiO₂/Al₂O₃ ratios are modified by addition of 0, 0.4, 0.8, 1.2 and 1.6?wt% of sodium polyacrylate (PAAS).The mechanical properties of these samples are measured and the rate of change is used to characterize the effect of PAAS on the metakalin-based geopolymers. The mechanism is also shown by 29Si NMR, XPS and FTIR. The results show that the effects of polymer on the mechanical properties of metakaolin-based geopolymer are affected by SiO₂/Al₂O₃ ratio and the effect becomes less obvious with SiO₂/Al₂O₃ ratio increasing from 2.0 to 4.0. Incorporation of PAAS can reduce the degree of polymerization of [SiO]₄ or [AlO]₄ in geopolymer and form the Si?O?C bond, which are two main reasons for polymer improving the toughness of geopolymer. But these effects decrease when the SiO₂/Al₂O₃ ratio of geopolymer increases from 2.0 to 4.0, which is corresponding to the effect on the mechanical properties. The toughening effect of organic polymer on geopolymer depends on the SiO₂/Al₂O₃ ratio of geopolymer, and only the geopolymer with lower SiO₂/Al₂O₃ ratio (no more than 2.5 in this work) can be significantly toughening modified by organic polymer. Therefore, it is necessary to consider the SiO₂/Al₂O₃ ratio of the geopolymer when geopolymer modified by organic polymer is designed.     

Electrochemical characterizations on MnO2 supercapacitors with potassium polyacrylate and potassium polyacrylate-co-polyacrylamide gel polymer electrolytes

MnO₂·nH₂O supercapacitors with potassium polyacrylate (PAAK) and potassium polyacrylate-co-polyacrylamide (PAAK-co-PAAM) gel polymer electrolytes (GPEs) having the weight compositions of polymer:KCl:H₂O = 9%:6.7%:84.3% have been characterized for their electrochemical performance. Compared with the liquid electrolyte (LE) counterpart, the GPE cells exhibit remarkable (50–130%) enhancement in specific capacitance of the oxide electrode, and the extent of the enhancement increases with increasing amount of the carboxylate groups in the polymers as well as with increasing oxide/electrolyte interfacial area. In situ X-ray absorption near-edge structure (XANES) analysis indicates that the oxide electrodes of the GPE cells possess higher Mn-ion valences and are subjected to greater extent of valence variation than that of the LE cell upon charging/discharging over the same potential range. Copolymerization of PAAK with PAAM greatly improves the cycling stability of the MnO₂·nH₂O electrode, and the improvement is attributable to the alkaline nature of the amino groups. Both GPEs exhibit ionic conductivities greater than 1.0 × 10⁻¹ S cm⁻¹ and are promising for high-rate applications.     

由4-氨基二苯醚合成三苯二噁嗪荧光染料

以4-氨基二苯醚为原料合成了10个新结构三苯二口恶嗪型荧光染料,测定了它们在甲苯、氯仿、DMF、丙酮和乙醇中的吸收光谱和荧光光谱。结果表明,这些染料发色强度大(εm ax>7×104),荧光强度高(在甲苯中Ф=0.43~0.78),染料的摩尔消光系数、荧光量子产率和Stokes位移与溶剂极性参数ET之间呈线性变化关系。     

Facile electrosynthesis of nitro-group-substituted oligopyrene with bicolored emission

Nitro-group-substituted oligopyrene (ONP) film with fairly high electrical conductivity (1.25 × 10⁻¹ S cm⁻¹) and good thermal stability was electrochemically synthesized by direct anodic oxidation of its monomer 1-nitropyrene (NP) in boron trifluoride diethyl etherate (BFEE). The oxidation potential of NP in this medium was determined to be 1.12 V vs. SCE, which was lower than that in acetonitrile +0.1 mol L⁻¹ Bu₄NBF₄ (1.27 V vs. SCE). ONP films obtained from this medium showed good redox activity and structural stability in both BFEE and concentrated sulfuric acid. Fourier transform infrared spectra and theoretical calculations showed that the electropolymerization of the NP monomer mainly occurred at the C(3), C(6) and C(8) positions. The fluorescence spectra suggested that soluble ONP emits strong blue or green fluorescence when excited at 402 nm or 504 nm, respectively. Scanning electron microscopy showed that highly crystalline nitro-group-substituted oligopyrene was formed on the electrode surface. All these results indicate that as-prepared ONP film has many potential applications in various fields.     

Emulsion polymerization of an epoxy–acrylate emulsion stabilized with polyacrylate. II. Using the results of statistically designed experiments to deduce a possible polymerization mechanism

Epoxy–acrylate composite emulsions such as the one in this study can be used as metal coatings, etc. Many factors can influence the final quality of the product, and it is the aim of this study to highlight some of these factors. Statistically designed experiments were performed to investigate the influence of monomer level, the polymeric dispersant level, epoxy level, and the initiator level on particle size (light scattering), particle size distribution, and fractional conversion. It was found that the monomer level significantly influenced particle size and particle size distribution. The epoxy level and the monomer level influenced fractional conversion significantly. A qualitative model based on these observations is put forward to describe the mechanism of particle formation and polymerization. This model states that the high internal viscosity of the initial dispersed epoxy phase inhibits the formation of smaller particles and accelerates the polymerization rate during the first few minutes of polymerization by inducing a gel effect that inhibits termination and chain transfers of radical species. The addition of a monomer lowers the internal viscosity of the particles and causes them to break up into droplets containing dissolved epoxy, polyacrylate, and monomer. At the same time, radical species inside the smaller droplets can now undergo termination and chain transfer reactions. To confirm this model, polyacrylates of varying molecular masses were synthesized. Variation of the molecular masses of these polyacrylates resulted in variation in the viscosity of the dispersed phase. Polymerizations conducted with the polyacrylates confirmed the model observations. A dispersed phase with a high viscosity results in an increased polymerization rate, larger overall particle size, and a higher mass average molecular mass copolymer compared to lower molecular mass polyacrylates. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 368–381, 2000     

Fluorescent spongy carbon nanoglobules derived from pineapple juice: A potential sensing probe for specific and selective detection of chromium (VI) ions

Herein, we report, for the first time, the facile, green and one step hydrothermal synthesis of fluorescent spongy carbon nanoglobules (CNG) derived from pineapple juice as a sole carbon source without involving any strong acid treatment. The synthesized CNG not only exhibits hydrophilicity and can remain stable for several weeks but also demonstrates prominent blue color fluorescence under UV light (λ=365 nm). These CNG showed wide range of emission spectra in the visible region depending upon the different excitation wavelengths. The synthesized CNG were characterized in detail in terms of their morphological, structural, optical, compositional and thermal properties using numerous analytical and spectroscopic techniques. For application point of view, the perspective to utilize CNG as fluorescent sensing probe has also been explored with the introduction of various highly toxic metal ions and interestingly, it was observed that the fluorescence intensity of CNG was drastically quenched by chromium (VI) ions with high selectivity over the linear range of concentrations 0–18 µM with stern volmer constant 2.29×10⁴ M⁻¹. Such encouraging results revealed that simply prepared CNG are potential scaffold to fabricate highly sensitive and selective fluorescent sensors for the detection of highly hazardous and life threatening metal ions.     

Nitrous oxide emission from soils amended with crop residues

Crop residues incorporated in soil are a potentially important source of nitrous oxide (N₂O), though poorly quantified. Here, we report on the N₂O emission from 10 crop residues added to a sandy and a clay soil, both with and without additional nitrate (NO₃). In the sandy soil, total N₂O emission from wheat, maize, and barley residues was not significantly different from the control. The total N₂O emission from white cabbage, Brussels sprouts, mustard, sugar beet residues and broccoli ranged from 0.13 to 14.6 % of the amount of N added as residue and were higher with additional NO₃ than without additional NO₃. In the clay soil, similar effects of crop residues were found, but the magnitude of the N₂O emission was much smaller than that in the sandy soil: less than 1 % of the residue N evolved as N₂O. The C-to-N ratio of the residue accounted for only 22–34% and the mineralizable N content of the residue for 18–74% of the variance in N₂O emission. We suggest that the current IPCC methodology for estimating N₂O emission from crop residues may be considerably improved by defining crop specific emission factors instead of one emission factor for all crop residues. This revised version was published online in November 2006 with corrections to the Cover Date.     

A category for estimate of CH4 emission from rice paddy fields in China

Based on key factors influencing CH₄ fluxes from rice paddy fields in China, a category for estimation of total CH₄ emission was suggested and the constraints for the estimation were discussed in the paper. Recently, CH₄ fluxes measured in situ have been built up dramatically with the efforts of both Chinese scientists and those from abroad. After reviewing published data on CH₄ fluxes from rice paddy fields, we found that although there are many other influencing factors, water regime and organic manure application are two key factors controlling CH₄ emission; thus, rice paddy fields in China were classified by these two factors to estimate CH₄ emission. In the suggested category, the water regime of rice paddy fields was classified into mid-season aeration at least once during the period of rice growth (MSA), continuous flooding during the period of rice growth but well-drained after rice harvest (CFD), and permanent flooding (PF) even in winter, and fertilization was classified into mineral fertilizers only (MIN), amendment with organic manures at the rate of less than or equal to 15 t ha^-1 (MU < 15) and at the rate of higher than 15 t ha^-1 (MU > 15), and with rice straw or other fresh plant materials (RS). Combining both water regime and fertilization together, we classified rice paddy fields in China into 12 types. The seasonal mean CH₄ flux of each type of rice paddy field was calculated by the data available and showed that the lowest CH₄ flux was found in the type MSA-MIN, and the highest in PF-MU > 15. The total emission estimated by this category was 8.05 Tg CH₄ yr^-1 with a standard deviation of 3.69 Tg CH₄ yr^-1. This revised version was published online in August 2006 with corrections to the Cover Date.     

Theoretical investigation on the white-light emission from a single-polymer system with simultaneous blue and orange emission

White organic light-emitting devices (WOLEDs) have attracted considerable attention because of their good potential for various lighting applications. Among these devices, WOLEDs based on polymers (WPLEDs) are of particular interest. We report here a theoretical investigation of the white-light emission from a single-polymer system with simultaneous blue (polyfluorene as a blue host) and orange (2,1,3-benzothiadiazole-based derivative as an orange dopant) emission. A variety of theoretical methods are used and evaluated to calculate electronic and optical properties of polyfluorene and 2,1,3-benzothiadiazole-based derivatives. Simulated electronic and optical properties are found to agree well with available experimental measurements. The influence of the “CH”/N heterosubstitution on the electronic and optical properties of the 2,1,3-benzothiadiazole-based derivative is considered. Furthermore, we find that the electronic and optical properties of “CH”/N substitution derivatives can be tuned by symmetrically adding suitable electron-donating groups on N,N-disubstituted amino groups, implying good candidates as orange dopants in WPLEDs with polyfluorene as a blue-light-emitting host. Solvent (dichloromethane) effects on the electronic and optical properties of 2,1,3-benzothiadiazole-based derivatives have been investigated. In addition, low reorganization energy values of holes for designed 2,1,3-benzothiadiazole-based derivatives within the framework of the charge hopping model suggest them to be good hole transfer materials.     

A selective fluorescent chemosensor with 1, 2, 4-triazole as subunit for Cu (II) and its application in imaging Cu (II) in living cells

A chemosensor based on rhodamine B with 1, 2, 4-triazole as subunit was synthesized and characterized. It exhibits high selectivity and sensitivity for Cu²⁺ in ethanol/water (6:4, v:v) of pH 7.0 HEPES buffer solution and undergoes ring opening mechanism, and a 2:1 metal-ligand complex is formed. The chemosensor displays a linear response to Cu²⁺ in the range between 1.0 × 10⁻⁷ M and 1.0 × 10⁻⁶ M with a detection limit of 4.5 × 10⁻⁸ M. Its capability of biological application was also evaluated and the results show that this chemosensor could be successfully employed as a Cu²⁺-selective chemosensor in the fluorescence imaging of living cells.     

Lead-free zero-dimensional Cs2ZnBr4 perovskite single crystals with broadband emission covering visible spectrum

All-inorganic lead-free zero-dimensional (0D) metal halides perovskites with intriguing photoluminescent (PL) properties have aroused much interest due to their application in lighting and artificial illumination. Herein, 0D Cs₂ZnBr₄ perovskite single crystals were synthesized through simple solvothermal method. The phase purity, the electronic band structure and electronic density of states of Cs₂ZnBr₄ are investigated by X-ray diffraction (XRD) measurement and density functional theory (DFT) calculation. Under 430 nm blue light excitation, Cs₂ZnBr₄ single crystals exhibit broadband emission covering the visible region from 450 to 750 nm and large Stokes shift about 120 nm, originating from self-trapped excitons (STEs) radiative recombination. And Cs₂ZnBr₄ shows excellent thermal and air stability. These results indicate the potential application of Cs₂ZnBr₄ as environmental-friendly light emitters for solid state lighting and displaying.     

On the thermionic emission from nitrogen-doped diamond films with respect to energy conversion

Thermionic energy converters utilize thermal energy and efficiently transform it into more useful electrical energy. A key aspect in thermionic energy conversion is the emission of electrons at elevated temperatures, where the electron emitter is separated from the collector by a vacuum gap and a voltage is generated due to the temperature difference between the emitter and collector. In this study, nitrogen-doped diamond films with a negative electron affinity surface have been synthesized with plasma-assisted chemical vapor deposition, and the electron emission has been imaged using high-resolution electron emission microscopy. This study reports the measurement of a thermovoltage and current, i.e. energy conversion, at temperatures considerably less than 1000 °C.