Laser-induced thin film formation from a gaseous mixture of trimethylsilylacetylene and methyl acrylate

Under irradiation with N₂ laser light, gaseous trimethylsilylacetylene (TMeSiA) and a gaseous mixture of TMeSiA and methyl acrylate (MA) produced thin films on an incident optical quartz window of an irradiation vessel. The product yield decreased with increasing partial pressure of TMeSiA. From the analysis of FT-IR spectra and X-ray photoelectron spectra of the deposited films, it was shown that Si---C bond of TMeSiA was cleaved by a two-photon absorption of N₂ laser light to produce trimethylsilyl radical and the silanes, R(CH₃)Si=CH₂ (R: H₃C---, CHC---). Trimethylsilyl radical reacted with MA at C=C and C=O bonds to produce Si---C and Si---O bonds in the film deposited from the gaseous mixture. The silanes were polymerized in each other to produce a thin film from pure TMeSiA vapor. Under irradiation with a medium pressure mercury lamp, a gaseous mixture of TMeSiA and MA produced aerosol particles in addition to the film. Polymeric species of TMeSiA was more involved in the aerosol particles rather than in the film, suggesting that collisionally induced chemical reaction takes place efficiently between excited MA and TMeSiA molecules.     

Detecting trace pesticides in real time using single particle aerosol mass spectrometry

Pesticides are toxic substances and may cause unintentional harm if improperly used. The ubiquitous nature of pesticides, with frequent use in agriculture and the household, and the potential for harm that pesticides pose to non-target organisms such as wildlife, humans, and pets, demonstrate the need for rapid and effective detection and identification of these compounds. In this study, single particle aerosol mass spectrometry (SPAMS) was used to rapidly detect compounds from four classes of pesticides commonly used in agricultural and household applications. These include permethrin (pyrethroid class), malathion and dichlorvos (organophosphate class), imidacloprid (chloronicotinyl class), and carbaryl (carbamate class). Analytical standards of each compound were diluted and aerosolized using a nebulizer to create particles for analysis in the SPAMS instrument. The resultant dual-polarity time-of-flight mass spectra were then analyzed to identify the characteristic peaks of the compound in each sample. In addition, samples of commercial products containing pesticides, a commercial insecticide spray, containing permethrin, and a canine flea collar, containing carbaryl, were analyzed in their original form using SPAMS without any significant sample preparation. The characteristic mass spectral peaks of the active pesticides in these samples were identified using the mass spectra obtained earlier from the pesticide analytical standards. By successfully identifying pesticides in analytical standards and in commercial products, it is demonstrated herein that the SPAMS system may be capable of pesticide detection in numerous environmental and agricultural situations.     

Characterization of iodine species in the marine aerosol: To understand their roles in particle formation processes

In this contribution, iodine chemistry in the Marine Boundary Layer (MBL) is introduced. A series of methodologies for the measurements of iodine species in the gas and particle phases of the coastal atmosphere has been developed. Iodine species in the gas phase in real air samples has been determined in two field campaigns at the west coast of Ireland, indicating that gaseous iodo-hydrocarbons and elemental iodine are the precursors of new particle formation. Particulate iodine speciation from the same measurement campaigns show that the non-water-soluble iodine compounds are the main iodine species during the marine particle formation. A seaweed-chamber experiment was performed, indicating that gaseous I₂ is one of the important precursors that lead to new particle formation in the presence of solar light in the ambient air at the coastal tidal area.     

负载于二氧化硅上的小尺寸氧化亚铜物种促进丙烯选择性氧化生成丙烯醛

氧化物负载的含铜材料是丙烯选择性氧化制备丙烯醛的理想催化剂,一直以来都受到人们的广泛关注.然而,对于该催化体系的结构与性能之间的关系仍不是很清楚.因此,我们以碳酸钠为沉淀剂,通过沉积沉淀法将铜负载于高比表面的二氧化硅载体上,从而得到了均匀分散且小尺寸的Cu/SiO2催化剂.另外,采用浸渍法制得了相同负载量的分散不均匀、大尺寸的Cu/SiO2催化剂.丙烯选择性氧化反应活性测试发现,沉积沉淀法制备的催化剂比浸渍法制备的更有利于丙烯醛的生成,表现出了优异的催化性能:在300℃反应时,丙烯的转化率达到25.5%,丙烯醛的选择性达到66.8%,对应的丙烯醛的生成速率高达10.5 mmol·h^-1·gcat.^-1或111.2 mmol·h^-1·gCu^-1,远远超出了浸渍法制备的催化剂性能(1.7 mmol·h^-1·gcat.^-1或17.2mmol·h^-1·gCu^-1)和文献中报道的结果.结合高角度环形暗场扫描透射电子显微镜(HAADF-STEM)和X射线吸收精细结构(XAFS)技术,对沉积沉淀法制备的催化剂进行表征,发现在反应后铜物种的结构发生了明显的变化,由小尺寸的氧化铜(CuO)团簇转变为氧化亚铜(Cu2O)团簇,并且铜物种的尺寸没有明显的增大.为了进一步探索铜物种在预处理(氢气还原)以及催化反应时(丙烯+氧气)的结构变化,对不同方法合成的两种催化剂进行了原位X射线粉末衍射测试,发现不同尺寸的铜物种在还原和反应时都经历了从氧化铜(CuO)变为金属Cu再到Cu2O的结构变化,并且Cu2O在320 min的反应过程中可以稳定存在,说明它是该催化反应的活性物种.另外,通过原位双光束傅里叶变换红外光谱追踪反应时气体分子在催化剂表面的吸脱附状态,发现丙烯可以有效地吸附在小尺寸Cu/SiO2催化剂表面,随着Cu2O的形成,检测到了烯丙基中间体(CH2=CHCH2*)的产生,该物种可以与邻近Cu2O上的一个氧发生反应,从而生成丙烯醛,因此结合N2O滴定实验,我们可认为,高度分散的小尺寸的Cu2O物种是丙烯进行高效选择性氧化反应生成丙烯醛的活性物种.     

Tracking of mercury ions in living cells with a fluorescent chemodosimeter under single- or two-photon excitation

Tracking of Hg²⁺ in solutions as well as in living cells was conducted with a fluorescent chemodosimeter by measuring the spectral shift of its fluorescence under single- or two-photon excitation. The spectral hypsochromic shifts of this chemodosimeter when reacting with Hg²⁺ were found to be about 50 nm in acetonitrile/water solutions and 32 nm in Euglena gracilis 277 living cells. This chemodosimeter shows high sensitivity and selectivity, and is not influenced by the pH values. It can signal Hg²⁺ in solutions down to the ppb range under either single-photon excitation (SPE) at 405 nm or two-photon excitation (TPE) at 800 nm. However, with low cellular chemodosimeter concentrations, the SPE spectra were disturbed by the auto-fluorescence from the native fluorophore in the cell, while the TPE spectra were still of high quality since the two-photon absorption cross section of this chemodosimeter is much larger than that of the native fluorophores in the cell.     

Photophysical properties of rhodamine isomers: A two-photon excited fluorescent sensor for trivalent chromium cation (Cr)

We introduce a new rhodamine-based fluorescent chemosensor, FD8 which exhibits a distinct two-photon excited fluorescence (TPEF) on/off characteristic upon binding Cr³⁺ ions. By coordination with metal cation, conformation of FD8 changes from spirocyclic to open-ring, resulting in remarkable enhancement of absorption and fluorescence both in one- and two-photon excitations. As a result, a 29-fold enhancement of two-photon excited fluorescent intensity was observed when 10 eq. Cr³⁺ was added to the FD8 solution. The detection limit of Cr³⁺ cation concentration down to 1 μM (0.01 eq. of FD8) was achieved under our experimental condition. Besides the excitation within ultraviolet regime by fluorescence resonance energy transfer (FRET) mechanism, the TPEF on/off behavior further extends the excitation to near infrared regime (the biological optimal window of 700-1200 nm), and shows more effective sensitivity. The broad excitation wavelength, on/off fluorescence and high selectivity to Cr³⁺ enable FD8 to be a powerful Cr³⁺ cation sensor with potential application, especially in biological detection. To the best of our knowledge, this is the first report about two-photon fluorescent sensor for Cr³⁺ ions.     

Characterization of a novel particle into liquid sampler for analysis of single fluorescent aerosol particles through capillary electrophoresis

An approach to sample and analyze single aerosolized droplets (<10 nL) of solutions containing fluorescein isothiocyanate (FITC) labeled glycine (GLY) and glutamic acid (GLU) is demonstrated. The sampling approach is based on inertial impaction in which the sample particle is accelerated through a nozzle and directly into a small drop of buffered solution (20 mM borate, pH = 10) suspended at the end of a coaxial tube of stainless steel and a fused silica capillary. A spherical light scattering cell and laser (λ = 532 nm) is used to detect the arrival of particles at the buffered droplet. Upon dissolution and/or mixing, a portion of the sample is injected onto the fused silica capillary for subsequent chemical analysis by capillary electrophoresis (CE) and detection by laser-induced fluorescence (LIF). It was found that the inertial impaction approach sampled particles >1 μm diameter with an efficiency of 80% or greater. At 15 kV applied potential, the FITC conjugates of GLY and GLU could be resolved in less than 120 s allowing qualitative analysis of the contents of single dispersed particles. However, the extent to which the sample is diluted into the buffer droplet varied significantly on a per-particle basis that caused >80% R.S.D. in fluorescence peak heights. This aspect of the method would necessitate the use of internal standards for quantitative analysis of materials present within the particles. It is envisaged that further improvements to the device described may ultimately lead to analysis of the contents of single particles dispersed in earth's atmosphere.     

Chemical characteristics of aerosol insecticide deposition in indoor surfaces

We investigated the deposition rate of aerosol insecticide on through woollen surfaces inside a test chamber. Compared to floor surface, the deposition rate of aerosol insecticide active ingredient on table of 1 m high was up to 2.07 times for piperonyl butoxide, 1.64 times for tetramethrin and 2.95 times for permethrin represented by 0.51, 0.37 and 0.23 μg cm^?2 for the three molecules, respectively. Application of the household used cleaning to the woollen table surface decrease these concentrations by 61.32%, 45.01% and 59.80% for the three pesticides respectively, this cleaning procedure still not efficient for the floor surfaces. Moreover, indoor conditions permit the removal of 46.42%, 21.92% and 14.35% of the table surface deposition rate after one week, for the three pesticides, respectively. These conditions ensure the removal of only 28.72%, 20.69% and 24.05% of the three deposit molecules respectively on floor surface.     

Femtosecond laser ablation: Visualization of the aerosol formation process by light scattering and shadowgraphic imaging

The shockwave propagation and aerosol formation during femtosecond laser ablation (fs-LA) of dielectric materials (Li₂B₄O₇, Y:ZrO₂) in ambient air were monitored using shadowgraphy and light scattering. Three independent shockwave fronts were observed originating from (i) the instantaneous compression of ambient gas during the initial stage of fs-LA, (ii) a secondary compression caused by material ejection, and (iii) an air breakdown well above the target surface. In addition, particle size distributions were found to be multimodal implying the co-existence of condensational growth and supplementary particle production pathways such as phase explosion or critical point phase separation (CPPS). As a consequence, fs-LA of Li₂B₄O₇ resulted in the formation of primary aggregates reaching diameters of > 10 μm. In contrast, aggregates formed during fs-LA of Y:ZrO₂ covered a size range < 1 μm. Our data, furthermore, indicate the existence of a breakdown channel in the ambient atmosphere being capable to carry plasmatic, i.e. non-condensed matter beyond the primary shockwave barrier which may occasionally causes a spatial separation of material released. Assuming the Taylor-Sedov model of explosion to be valid the over-all energy dissipated in acoustic transients was found to exceed values of 50%.     

Monodisperse micron-sized cross-linked polystyrene particles. VI. Understanding of nucleated particle formation and particle growth

 The procedure of nucleated particle formation and particle growth in dispersion polymerization was studied with the intention of understanding the production of monodisperse polystyrene particles cross-linked with urethane acrylate (UA). The time required for the formation of primary particles was determined exactly from the turbidity measurement of the reaction mixture with the polymerization time. It could be found that differing from conventional divinyl cross-linkers, such as divinylbenzene, UA had a boundary concentration where the association and coagulation of preformed nuclei with other oligomers and/or nuclei effectively took place until the primary particle formed. Similarly to linear polystyrene particles, the particle number density of the primary particles cross-linked with UA remained constant to the final particles. This observation verifies the suggestion that the primary particles cross-linked with UA readily absorbed the monomers from the medium during the stage of particle growth. Received: 31 August 1999 Accepted: 7 January 2000     

A kinetic modeling of particle formation by gas antisolvent process: Precipitation of aspirin

Population balance equations (PBEs) are often integro-partial differential in nature due to complexities involved in nonconventional crystallization processes, especially gas antisolvent (GAS). The reason is that they include phenomena such as primary nucleation, secondary nucleation, crystal growth, agglomeration, and/or breakage of crystals. Therefore, the solution to such models has become rather difficult. Considering these difficulties, a powerful numerical algorithm was adopted in this paper to treat the population balance model for the precipitation of aspirin by the GAS process. This method was the combination of Lax–Wendroff and Crank–Nicholson numerical methods. It was used to investigate the effect of significant operating parameters, that is, antisolvent addition rate, process temperature, and solute concentration, on the final product properties for two solvents. The antisolvent addition rate was varied between 8 and 40 bar/min, the process temperature was kept constant at levels 37°C and 42°C, the solute concentration was manipulated at two levels, namely, 0.2 and 0.27 g solute/g solution, and methanol and acetone were used as the organic solvents. The results indicated the successful performance of the applied method in treating PBE, since smooth particle size distributions were produced, which were in an acceptable agreement with the experimental data of the investigated system.     

Red carbon dots as label-free two-photon fluorescent nanoprobes for imaging of formaldehyde in living cells and zebrafishes

Direct,in situ selective detection of intracellular formaldehyde(FA)is of great significance for understanding its function in FA-related diseases.Herein,red carbon dots(RCD)are reported as label-free two-photon fluorescent nanoprobes for detecting and imaging of FA.Upon addition of FA,the-NH2 groups of RCD could quickly and specially react with aldehydes to form Schiff base and then the strong fluorescence of RCD with blue-shift emission is recovery due to the destruction of the hydrogen bond interaction between RCD and water.In addition,the nanoprobes exhibit outsta nding photo stability,rapid response(<1 min),high sensitivity(~9.9μmol/L)and excellent selectivity toward FA over other aldehyde group compounds.Notably,owing to the good cell-membrane permeability and biocompatibility,as well as the large two-photon absorption cross-section,the as-prepared RCD can be used as label-free nanoprobes for selectively detecting and imaging FA in living cells and zebrafishes through one-photon and two-photon excitation.Moreover,RCD could stain the tissue of zebrafishes at depths interval of up to 240μm under two-photon excitation.This research implied that RCD are promising tools for directly and in situ imaging FA in vivo,thus providing critical insights into FA-related pathophysiological processes.     

Ratiometric two-photon excited photoluminescence of quantum dots triggered by near-infrared-light for real-time detection of nitric oxide release in situ

Probe-donor integrated nanocomposites were developed from conjugating silica-coated Mn²⁺:ZnS quantum dots (QDs) with MoS₂ QDs and photosensitive nitric oxide (NO) donors (Fe₄S₃(NO)₇⁻, RBS). Under excitation with near-infrared (NIR) light at 808 nm, the Mn²⁺:ZnS@SiO₂/MoS₂-RBS nanocomposites showed the dual-emissive two-photon excited photoluminescence (TPEPL) that induced RBS photolysis to release NO in situ. NO caused TPEPL quenching of Mn²⁺:ZnS QDs, but it produced almost no impact on the TPEPL of MoS₂ QDs. Hence, the nanocomposites were developed as a novel QDs-based ratiometric TPEPL probe for real-time detection of NO release in situ. The ratiometric TPEPL intensity is nearly linear (R² = 0.9901) with NO concentration in the range of 0.01∼0.8 μM, which corresponds to the range of NO release time (0∼15 min). The detection limit was calculated to be approximately 4 nM of NO. Experimental results confirmed that this novel ratiometric TPEPL probe possessed high selectivity and sensitivity for the detection of NO against potential competitors, and especially showed high detection performance for NIR-light triggered NO release in tumor intracellular microenvironments. These results would promote the development of versatile probe-donor integrated systems, also providing a facile and efficient strategy to real-time detect the highly controllable drug release in situ, especially in physiological microenvironments.     

Nature of mechanoradical formation and reactivity with oxygen in methacrylic vinyl polymers

The formation of mechanoradicals under anaerobic conditions and their reactivity with oxygen at room temperature is described for several methacrylic vinyl polymers. Observed electron spin resonance (ESR) spectra of the mechanoradicals formed were all essentially identical and are clearly assigned to a respective endchain radical. The ESR kinetics of the mechanoradical formation of polymethylmethacrylate (PMMA) and polymethacrylamide (PMAAm) exhibit an interesting contrast; the progressive changes in the radical concentration in PMMA as a function of duration of milling gradually decrease after reaching a maximum value, while those of PMAAm show a parabolic increase. This discrepancy has been ascribed to mechanoradicals of PMAAm that are strongly stabilized by intermolecular and intramolecular doubly hydrogen-bonded networks among the amide groups. Such interactions also are to lower the reactivity of the mechanoradicals with oxygen. Thus, the mechanoradicals of both PMAAm and PMAA do not give a single peroxy radical, but rather a mixture of the mechanoradical and peroxy radical even after exposure to air, while the mechanoradicals of other polymers are rapidly converted to the corresponding peroxy radicals. Such a difference was observed in experiments on the mechanical fracture of such polymers under aerobic conditions.     

Determination of acrolein and other carbonyls in cigarette smoke using coupled silica cartridges impregnated with hydroquinone and 2,4-dinitrophenylhydrazine

A new method for the determination of acrolein and other carbonyls in cigarette smoke using a dual cartridge system has been developed. Each cartridge consists of reagent-impregnated silica particles. The first contains hydroquinone (HQ) for the inhibition of acrolein polymerization, while the second contains 2,4-dinitrophenylhydrazine (DNPH) for the derivatization of carbonyls. Smoke samples were firstly drawn through the cartridge containing HQ-impregnated silica (HQ-silica) and then through the DNPH-impregnated silica (DNPH-silica). Acrolein in the sample was completely trapped in the first HQ-silica cartridge. Some other airborne carbonyls were also trapped by the HQ-silica, and those that pass through were trapped in the second DNPH-silica cartridge. Extraction was performed in the reverse direction to air sampling. When solvent was eluted through the dual-cartridges, excess DNPH was washed into the HQ bed where it reacted with acrolein and other trapped carbonyls to form the corresponding hydrazone derivatives. All of the hydrazones derived from airborne carbonyls were completely separated and measured using high-performance liquid chromatography. This HQ-DNPH-method can be applied for the determination of acrolein and other α,β-unsaturated aldehydes, such as crotonaldehyde, in cigarette smoke.     

气溶胶单粒子化学成分的实时测量

自行设计了国内第一台可实时测量气溶胶单粒子化学成分的气溶胶飞行时间质谱仪,并用该仪器对两类燃烧过程产生的气溶胶粒子进行了实时测量。实验结果展示了本仪器能够同时实现实时在线测量和单粒子检测,从而克服了传统的离线检测方法如色谱法、化学方法的局限性。     

Effects of surface charge density on emulsion kinetics and secondary particle formation in emulsifier-free seeded emulsion polymerization of methyl methacrylate

 Experiments were carried out to investigate the effects of surface charge density on emulsion kinetics and secondary particle formation in emulsifier-free seeded emulsion polymerization. Three monodisperse seed latices with different surface charge densities were prepared from styrene/NaSS comonomers using the two-stage shot-growth process. After purification of the seed latices, they were used in seeded emulsion polymerization of methyl methacrylate. The initial rate of poly-merization and the average number of radicals per particle for the high-charged seed latex system were lower than that of the low-charged case. The low rate of polymerization resulted from the low rate of radical adsorption in the beginning of the reaction due to the electrical repulsion between seeds and oligomeric radicals. In this case, because of the secondary particles, particle size distribution became bimodal. The low rate of radical adsorption and the formation of secondary particles reduced the average number of radicals per particle. The rate of polymerization (R _p) increased, but the rate of polymerization per particle (R _p/N _p) decreased. Received: 9 December 1996 Accepted: 7 March 1997     

The use of Si carriers for aerosol particle collection and subsequent elemental analysis by total-reflection X-ray fluorescence spectrometry

The adoption of polished Si carriers was studied for the sensitive elemental analysis of aerosol particles using total-reflection X-ray fluorescence (TXRF) spectrometry. The surface roughness of the Si carrier measured by atomic force microscopy was found to be smaller than those of glassy carbon and quartz glass carriers, which are commonly used for TXRF analysis. The detection limits of elements for the Si carrier were superior to those for the glassy carbon and the quartz glass carriers, presumably due to its smaller surface roughness. For example, the detection limit of Sr for the Si carrier was 9 pg, which was 100 times and 3 times lower than those for the glassy carbon and the quartz glass carriers, respectively. The Si carriers could be successfully applied to the direct aerosol particle collection by impaction and the subsequent elemental analysis by TXRF. From the results of the elemental analysis of aerosol particles, the variations in the concentrations of K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn Sr and Pb with time could be clarified.     

A two-photon excited luminescence of water-soluble rhodamine-platinum(II) complex: fluorescent probe specific for Hg2+ detection in live cell

The first example of cyclometalated platinum(II)-containing rhodamine probe (1) with two-photon induced luminescent properties was synthesized and investigated for mercury detection. A highly selective color change of 1, from light yellow to pink, is observed only in the presence of Hg²⁺ due to the formation of 1,3,4-oxadiazole ring in 2. This selectivity of Hg²⁺ with color changes can be observed easily by the naked-eye. Meanwhile, a remarkable turn-on and selective 20-fold fluorescent enhancement of 1 upon binding with Hg²⁺ over the other tested metal ions was observed. The water-soluble probe 1 was successfully applied in the visualizing of the site of Hg²⁺ accumulation as well as estimating of trace amounts of mercury ions in live HeLa cells by two-photon microscopy.     

Dispersion polymerization of methyl methacrylate: Mechanism of particle formation

The mechanism for the formation of micron-size polymer particles in the dispersion polymerization of methyl methacrylate was investigated by applying dynamic light scattering to monitor the evolution of the average particle size in the early stages of the polymerization. In addition, the contributions of physically adsorbed stabilizer and graft copolymer were evaluated by measuring the bound, unbound (adsorbed), and free stabilizer, and by determining the amount of added stabilizer required in seeded dispersion polymerizations. Twenty nanometer particles (termed nuclei) were the smallest particles detected and are considered to be formed by aggregation of growing polymer chains precipitating from solution as they exceed their critical chain length. Aggregation of these nuclei with themselves and their aggregates continues until mature and stable particles are formed. This occurs when sufficient stabilizer occupies the particle surface which includes both the polymeric stabilizer [poly(vinylpyrrolidone)] and its graft copolymer which is created in situ. The effects of process variables are discussed based on this mechanistic picture of the dispersion polymerization process. © 1994 John Wiley & Sons, Inc.