Polymerization rate and mechanism of ultrasonically initiated emulsion polymerization of n-butyl acrylate

The factors affecting the induction period and polymerization rate in ultrasonically initiated emulsion polymerization of n-butyl acrylate (BA) were investigated. The induction period takes only an instant in ultrasonically initiated emulsion polymerization of BA without any added initiator by enhancing the N2 flow rate. Increasing temperature, power output and SDS concentration, decreasing the monomer concentration results in further decreasing induction period and enhanced polymerization rate. Under optimized reaction conditions the conversion of BA reaches 92% in 11 min. The polymerization rate can be controlled by varying reaction parameters. The apparatus of ultrasonically initiated semi-continuous and continuous emulsion polymerization were set up and the feasibility was first studied. Based on the experimental results, a free radical polymerization mechanism for ultrasonically initiated emulsion polymerization was proposed, including the sources of the radicals, the process of radical formation, the locus of polymerization and the polymerization process. Compared with conventional emulsion polymerization, where the radicals come from thermal decomposition of a chemical initiator, ultrasonically initiated emulsion polymerization has attractive features such as no need for a chemical initiator, lower reaction temperature, faster polymerization rate, and higher molecular weight of the polymer prepared.     

Polystyrene/Fe3O4 magnetic emulsion and nanocomposite prepared by ultrasonically initiated miniemulsion polymerization

Ultrasonically initiated miniemulsion polymerization of styrene in the presence of Fe3O4 nanoparticles was successfully employed to prepare polystyrene (PS)/Fe3O4 magnetic emulsion and nanocomposite. The effects of Fe3O4 nanoparticles on miniemulsion polymerization process, the structure, morphology and properties of PS/Fe3O4 nanocomposite were investigated. The increase in the amount of Fe3O4 nanoparticles drastically increases the polymerization rate due to that Fe3O4 nanoparticles increase the number of radicals and the cavitation bubbles. Polymerization kinetics of ultrasonically initiated miniemulsion polymerization is similar to that of conventional miniemulsion polymerization. PS/Fe3O4 magnetic emulsion consists of two types of particles: latex particles with Fe3O4 nanoparticles and latex particles with no encapsulated Fe3O4 nanoparticles. Fe3O4 nanoparticles lower the molecular weight of PS and broaden the molecular weight and particle size distribution. Thermal stability of PS/Fe3O4 nanocomposite increases with the increase in Fe3O4 content. PS/Fe3O4 emulsion and nanocomposite exhibit magnetic properties. PS/Fe3O4 magnetic particles can be separated from the magnetic emulsion by an external magnetic field and redispersed into the emulsion with agitation.     

Study of interaction of aliphatic alcohols with primary radical cations of n-alkanes using MARY spectroscopy

MARY spectroscopy (the radical ion pair level crossing technique) was employed to probe the reaction of proton transfer from primary radical cations of n-alkanes to alcohol molecules in liquid solution. Alcohols were demonstrated to react with the primary radical cation of the solvent, leaving the counterion of the radical ion pair unaffected. The broadening of the zero field MARY line, tentatively attributed to the proton transfer reaction, was found to be independent of the proton affinity of the species in the studied systems, estimated from gas-phase data. The rate constant of the reaction is close to the diffusion controlled limit within the experimental accuracy for all the studied alcohol/solvent combinations.     

Radical generation process studies of the cationic surfactants in ultrasonically irradiated emulsion polymerization

Without any chemical initiators added, ultrasonically irradiated emulsion copolymerization of styrene and a cationic polymerizable surfactant (methacryloxyethyl dodecydimethyl ammonium bromide, C(12)N(+)) was successfully employed to prepare copolymer nanolatexes. Compared with the conventional ionic surfactants, C(12)N(+) has much higher initiation efficiency and C(12)N(+) system exhibits shorter induction period, much higher styrene conversions and polymerization rate R(p) in short reaction time. A radical trapping experiment and gas chromatograph-mass spectrograph analysis proved that under ultrasonic irradiation, C(12)N(+) undergoes bond scission between the two alkyl and ionic group, where both C-N bonds are weak along the chain, thereby producing much more original radicals to initiate the emulsion polymerization.     

Using pulsed wave ultrasound to evaluate the suitability of hydroxyl radical scavengers in sonochemical systems

Hydroxyl radical (OH) scavengers are commonly used in sonochemistry to probe the site and nature of reaction in aqueous cavitational systems. Using pulsed wave (PW) ultrasound with comparative sonochemistry we evaluated the performance of OH scavengers (i.e., formic acid, carbonic acid, terephthalic acid/terephthalate, iodide, methanesulfonate, benzenesulfonate, and acetic acid/acetate) in a sonochemical system to determine which OH scavengers react only in bulk solution and which OH scavengers interact with cavitation bubbles. The ability of each scavenger to interact with cavitation bubbles was assessed by comparing the pulse enhancement (PE) of 10 μM of a probe compound, carbamazepine (CBZ), in the presence and absence of a scavenger. Based on PE results, acetic acid/acetate appears to scavenge OH in bulk solution, and not interact with cavitation bubbles. Methanesulfonate acts as reaction promoter, increasing rather than inhibiting the degradation of CBZ. For formic acid, carbonic acid, terephthalic acid/terephthalate, benzenesulfonate, and iodide, the PE was significantly decreased compared to in the absence of the scavenger. These scavengers not only quench OH in bulk solution but also affect the cavity interface. The robustness of acetic acid/acetate as a bulk OH scavenger was validated for pH values between 3.5 and 8.9 and acetic acid/acetate concentrations from 0.5 to 0.1 M.     

Ultrasonically initiated emulsion polymerization of styrene in the presence of Fe2+

Ultrasonically initiated emulsion polymerization of styrene was carried out in the presence of Fe(2+). The addition of a small amount of Fe(2+) markedly enhanced the polymerization rate of styrene. In the presence of 50 microM Fe(2+), the conversion of monomer in the reaction time of 60 min was 2.4 times as high as that in the absence of Fe(2+). The increase in the polymerization rate was due to higher concentration of hydroxyl (*OH) radicals generated via Fenton reaction of Fe(2+) with hydrogen peroxide (H(2)O(2)), which was proved by a lower amount of H(2)O(2) in Fe(2+) aqueous solution compared with that in pure water during ultrasonic irradiation. However, the addition of excessive Fe(2+) had no further accelerating effect on the polymerization rate due to the reduction of *OH radicals by Fe(2+). So it is an effective way to add an appropriate amount of Fe(2+) to accelerate ultrasonically initiated emulsion polymerization of styrene.     

Enhancement of sonochemical degradation of phenol using hydrogen atom scavengers

Sonochemical degradation of phenol was found to be enhanced in the presence of the volatile hydrogen atom scavengers CCl4 and perfluorohexane. The non-volatile hydrogen atom scavenger iodate did not enhance phenol degradation. The first order rate constant for aqueous phenol degradation in separate experiments using different sonochemical probes increased in the presence of 150 microM CCl4 from 0.014 to 0.031 min(-1) (probe 1) and from 0.022 to 0.061 min(-1) (probe 2). In the presence of <1.5 microM C6H14, the first order rate constant increased from 0.014 to 0.032 min(-1) (probe 1). Hydroquinone was the major observed reaction intermediate both in the presence and absence of hydrogen atom scavengers. Hydroquinone yields were substantially higher in the presence of hydrogen atom scavengers, suggesting that hydroxyl radical pathways for phenol degradation were enhanced by the hydrogen atom scavengers. These additives may be useful in improving pollutant degradation efficiency or improving synthetic processes that rely on hydroxyl radical as a key intermediate.     

Theoretical mechanistic studies on the degradation of alizarin yellow R initiated by hydroxyl radical

The degradation of azo dyes has attracted many research efforts not only due to the resulting environmental problems but also because the azo compounds with various substituents may show different degradation mechanism. It has been computationally found here, for the first time, that the HO? initiated cleavages of C–N and N–N bonds of alizarin yellow R with carboxyl group are kinetically competitive. In view of the formation of HO? adducts, the C–N and N–N bond cleavages of the hydrazone tautomer of alizarin yellow R are also kinetically competitive, but the former is more thermodynamically favorable. This result is different from that previously reported for the hydrozone tautomers of Acid Orange 7 and Acid Orange 8 containing hydroxyl and azo groups in neighboring positions, which are favorable to follow C–N bond cleavage mechanism both kinetically and thermodynamically. The decarboxylation occurs via an attack of HO? to the benzene ring carbon connecting to the carboxyl group rather than a direct attack of HO? to the carboxyl carbon atom. The anion form has higher reactivity than the neutral form in all of the reactions investigated. In addition, a water molecule as a proton relay reagent could significantly reduce the energy barrier for the N–N bond cleavage of alizarin yellow R. Copyright © 2014 John Wiley & Sons, Ltd.     

Numerical analysis of quantitative measurement of hydroxyl radical concentration using laser-induced fluorescence in flame

The aim of the present work is to quantitatively measure the hydroxyl radical concentration by using LIF(laserinduced fluorescence) in flame.The detailed physical models of spectral absorption lineshape broadening,collisional transition and quenching at elevated pressure are built.The fine energy level structure of the OH molecule is illustrated to understand the process with laser-induced fluorescence emission and others in the case without radiation,which include collisional quenching,rotational energy transfer(RET),and vibrational energy transfer(VET).Based on these,some numerical results are achieved by simulations in order to evaluate the fluorescence yield at elevated pressure.These results are useful for understanding the real physical processes in OH-LIF technique and finding a way to calibrate the signal for quantitative measurement of OH concentration in a practical combustor.     

Study on ultrasonically assisted emulsification and recovery of copper(II) from wastewater using an emulsion liquid membrane process

The aim of this work was to study the emulsification assisted by ultrasonic probe (22.5 kHz) and investigate the removal of copper(II) ions from aqueous solution using water-in-oil-in-water (W/O/W) emulsion liquid membrane process (ELM). The membrane was prepared by dissolving the extractant bis(2-ethylhexyl)phosphoric acid (D2EHPA) and the hydrophobic surfactant sorbitan monooleate (Span 80) in hexane (diluent). The internal phase consisted of an aqueous solution of sulfuric acid. Effects of operating parameters such as emulsification time, ultrasonic power, probe position, stirring speed, carrier (D2EHPA) and surfactant (Span 80) concentrations volume ratios of organic phase to internal striping phase and of external aqueous phase to membrane (W/O) phase, internal phase concentration and choice of diluent on the membrane stability were studied. With ultrasound, the W/O emulsion lifetime were much higher than those reported previously by mechanical agitation. The effect of carrier and Cu(II) initial concentration on the extraction kinetics was also investigated. Nearly all of the Cu(II) ions present in the continuous phase was extracted within a few minutes. Additionally, the influence of H₂SO₄ concentration on the stripping efficiency was examined.     

Enhancement of thermal and mechanical properties of poly(MMA-co-BA)/Cloisite 30B nanocomposites by ultrasound-assisted in-situ emulsion polymerization

This study reports synthesis and characterization of poly(MMA-co-BA)/Cloisite 30B (organo-modified montmorillonite clay) nanocomposites by ultrasound-assisted in-situ emulsion polymerization. Copolymers have been synthesized with MMA:BA monomer ratio of 4:1, and varying clay loading (1–5 wt% monomer). The poly(MMA-co-BA)/Cloisite 30B nanocomposites have been characterized for their thermal and mechanical properties. Ultrasonically synthesized nanocomposites have been revealed to possess higher thermal degradation resistance and mechanical strength than the nanocomposites synthesized using conventional techniques. These properties, however, show an optimum (or maxima) with clay loading. The maximum values of thermal and mechanical properties of the nanocomposites with optimum clay loading are as follows. Thermal degradation temperatures: T_10% = 320 °C (4 wt%), T₅₀ = 373 °C (4 wt%), maximum degradation temperature = 384 °C (4 wt%); glass transition temperature = 64.8 °C (4 wt%); tensile strength = 20 MPa (2 wt%), Young’s modulus = 1.31 GPa (2 wt%), Percentage elongation = 17.5% (1 wt%). Enhanced properties of poly(MMA-co-BA)/Cloisite 30B nanocomposites are attributed to effective exfoliation and dispersion of clay nanoparticles in copolymer matrix due to intense micro-convection induced by ultrasound and cavitation. Clay platelets help in effective heat absorption with maximum surface interaction/adhesion that results in increased thermal resistivity of nanocomposites. Hindered motion of the copolymer chains due to clay platelets results in enhancement of tensile strength and Young’s modulus of nanocomposite. Rheological (liquid) study of the nanocomposites reveals that nanocomposites have higher yield stress and infinite shear viscosity than neat copolymer. Nonetheless, nanocomposites still display shear thinning behavior – which is typical of the neat copolymer.     

Exceptionally high decarboxylation rate of a primary aliphatic acyloxy radical determined by radical product yield analysis and quantitative 1H‐CIDNP spectroscopy

Symmetrical (RCO₂CO₂R; R = XCH₂CH₂) and asymmetrical (RCO₂CO₂R′; R = C₉H₁₉CH₂CH₂, R′ = CH₃ or m‐ClC₆H₄) primary diacyl peroxides were thermally decomposed under different conditions to analyze the decarboxylation rates of the thermally generated acyloxy radicals. Quantitative models of the geminate product yields, and qualitative and quantitative ¹H‐CIDNP spectroscopy were used to obtain the decarboxylation rate estimates. Results reported here suggest that, unlike short chain acyloxy radicals such as propanoyloxyl, long chain acyloxy radicals possess the highest decarboxylation rates of all known acyloxy radicals, estimated at (0.5–1.5) × 10¹² s^?1 between 80 and 140 °C. Given the nature of the dissociative state of acyloxy radicals, such rates appear to be the result of destabilization of the former by the steric bulk of the long chain substituents. Additionally, the rate of this order of magnitude suggests a nearly concerted decarboxylation of primary diacyl peroxides. Copyright © 2011 John Wiley & Sons, Ltd.     

Pickering emulsion polymerization of polyaniline/LiCoO2 nanoparticles used as cathode materials for lithium batteries

The oil in water (o/w) emulsions were prepared using aniline dissolved in toluene and LiCoO₂ particles as stabilizers (Pickering emulsions). Pickering emulsions are stabilized by adsorbed solid particles instead of emulsifier molecules. The mean droplet diameter of emulsions was controlled by the mass ratio M (oil)/M (solid particles). The emulsions showed great stability during 3 days. The composite materials containing LiCoO₂ and the conductive polymer polyaniline (PANI) have been prepared by means of polymerization of aniline emulsion stabilized by LiCoO₂ particles. The composite materials were characterized by nanosphere and nanofiber-like structures. The nanofiber-like morphology of the powdered material was distinctly different of the morphologies of the parent materials. The electrochemical reactivity of PANI/LiCoO₂ composites as positive electrode in a lithium battery was examined during lithium ion deinsertion and insertion by galvanostatic charge–discharge testing; PANI/LiCoO₂ (1:4) composite materials exhibited the best electrochemical performance by increasing the reaction reversibility and capacity compared to that of the pristine LiCoO₂ cathode. The first discharge capacity of PANI/LiCoO₂ (1:4) was 167 mAh/g, while that of LiCoO₂ was136 mAh/g.     

Surface modification of calcium carbonate: radical graft polymerization of vinyl monomers onto calcium carbonate surface initiated by azo groups introduced onto the surface

—The preparation of calcium carbonate modified by 12-hydroxystearate groups and the grafting of polymers onto the surface by the polymerization of vinyl monomers initiated by azo groups introduced onto the surface were investigated. The preparation of calcium carbonate modified by 12-hydroxystearate was achieved by the reaction of calcium chloride with sodium carbonate containing a small amount of sodium 12-hydroxystearate. The introduction of azo groups onto calcium carbonate was successfully achieved by the direct condensation of the carboxyl group of 4,4'-azobis(4-cyanopentanoic acid) with 12-hydroxystearate groups on the modified calcium carbonate using N,N'-dicyclohexylcarbodiimide as a condensing agent. It was found that the radical polymerization of vinyl monomers, such as methyl methacrylate (MMA), styrene, and N-vinylcarbazole (NVC), was initiated by azo groups introduced onto the surface, and the corresponding polymers were grafted onto the surface based on the propagation of polymer from the surface: the percentage of grafting of polyMMA, polystyrene, and polyNVC reached 5.7, 9.5 and 3.5%, respectively, at 70°C. The percentage of grafting was found to decrease with decreasing monomer concentration. The wettability of calcium carbonate surface was found to turn from hydrophilic to hydrophobic by the grafting of polymers.     

Comparison of hydroxyl radical formation in aqueous solutions at different ultrasound frequencies and powers using the salicylic acid dosimeter

Ultrasonic frequencies of 20 kHz, 382 kHz, 584 kHz, 862 kHz (and 998 kHz) have been compared with regard to energy output and hydroxyl radical formation utilising the salicylic acid dosimeter. The 862 kHz frequency inputs 6 times the number of Watts into water, as measured by calorimetry, with the other frequencies having roughly the same value under very similar conditions. A plausible explanation involving acoustic fountain formation is proposed although enhanced coupling between this frequency and water cannot be discounted. Using the salicylic acid dosimeter and inputting virtually the same Wattages it is established that 862 kHz is around 10% more efficient at generating hydroxyl radicals than the 382 kHz but both of these are far more effective than the other frequencies. Also, it is found that as temperature increases to 42 °C then the total dihydroxybenzoic acid (Total DHBA) produced is virtually identical for 382 kHz and 862 kHz, though 582 kHz is substantially lower, when the power levels are set at approximately 9 W for all systems. An equivalent power level of 9 W could not be obtained for the 998 kHz transducer so a direct comparison could not be made in this instance. These results have implications for the optimum frequencies chosen for both Advanced Oxidation Processes (AOPs) and organic synthesis augmented by ultrasound.     

Enhancement of single-molecule fluorescence using a gold nanoparticle as an optical nanoantenna

We investigate the coupling of a single molecule to a single spherical gold nanoparticle acting as a nanoantenna. Using scanning probe technology, we position the particle in front of the molecule with nanometer accuracy and measure a strong enhancement of more than 20 times in the fluorescence intensity simultaneous to a 20-fold shortening of the excited state lifetime. Comparisons with three-dimensional calculations guide us to decipher the contributions of the excitation enhancement, spontaneous emission modification, and quenching. Furthermore, we provide direct evidence for the role of the particle plasmon resonance in the molecular excitation and emission processes.     

Enhancement of deposition rate of titanium silicon oxide films on silicon using hexafluorotitanic acid by nitric acid

The deposition of titanium silicon oxide films on silicon using hexafluorotitanic acid and boric acid as sources is much enhanced by nitric acid incorporation. The deposition delay time is almost zero. The structure of the films is titanium silicon oxide examined by Fourier transform infrared spectrometer. By current-voltage measurement, the leakage current of the as-deposited film with a thickness of 458 Å is about 7.78×10^-6 Å/cm² at the electrical field of 1 MV/cm. By capacitance-voltage measurement, the effective oxide charge of the as-deposited film is 6.31×10¹⁰ cm^-2. The static dielectric constant and refractive index are about 13 and 1.98, respectively. Compared with that without nitric acid incorporation, the lower effective oxide charge is from a sharp interface due to in-situ etching of nitric acid. The higher leakage current is from the higher deposition rate and the higher dielectric constant is from higher titanium content. PACS 77.84.-s     

Synthesis and characterization of a nano-scaled barium cerate perovskite powder using starch as polymerization agent

The preparation of nano-sized BaCeO₃ powder using starch as a polymerization agent is described herein. Phase evolution during the decomposition process of a (BaCe)-gel was monitored by XRD. A phase-pure nano-sized BaCeO₃ powder was obtained after calcining of the (BaCe)-gel at 920 °C. The resulting powder has a specific surface area of 15.4 m²/g. TEM investigations reveal particles mainly in the size range of 30 to 65 nm. The shrinkage and sintering behavior of resulting powder compacts were studied in comparison to a coarse-grained mixed-oxide BaCeO₃ powder (S_BET = 2.1 m²/g). Dilatometric measurements show that the beginning of shrinkage of compacts from the nano-sized powder is downshifted by 300 °C compared to mixed-oxide powder. Compacts from the nano-sized powder reach a relative density of 91% after sintering at 1450 °C for 10 h.     

Study of the recast layer of a surface machined by sinking electrical discharge machining using water-in-oil emulsion as dielectric

Electrical discharge machining (EDM) caused a recast layer to form at the machined surface of the workpiece. The characteristics of the recast layer have a great relationship with the type of dielectric. The research work in this paper aims to acquire a profound knowledge of the recast layers of a surface machined by sinking EDM using water-in-oil (W/O) emulsion as dielectric. Scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive spectrograph (EDS) and micro hardness analysis were performed. The characteristics of the recast layer formed in W/O emulsion were investigated by comparing them with those of the recast layer formed in kerosene and de-ionized water dielectric. It was found that the recast layer formed in W/O emulsion exhibited larger surface roughness, thickness and micro hardness compared with that formed in kerosene and de-ionized water. Both carbide and oxide were detected in the recast layer formed in W/O emulsion whereas only carbide was detected in the recast layer formed in kerosene. Due to the higher supersaturation of gases in the melted material, the recast layer formed in W/O emulsion was found to possess more micro-voids than that formed in kerosene and de-ionized water.