Mechanistic aspects of sonochemical copolymerization of butyl acrylate and methyl methacrylate

Sonochemical fabrication of inorganic nanoparticles for applications in catalysis

Catalysis covers almost all the chemical reactions or processes aiming for many applications. Sonochemistry has emerged in designing and developing the synthesis of nano-structured materials, and the latest progress mainly focuses on the synthetic strategies, product properties as well as catalytic applications. This current review simply presents the sonochemical effects under ultrasound irradiation, roughly describes the ultrasound-synthesized inorganic nano-materials, and highlights the sonochemistry applications in the inorganics-based catalysis processes including reduction, oxidation, degradation, polymerization, etc. Or all in all, the review hopes to provide an integrated understanding of sonochemistry, emphasize the great significance of ultrasound-assisted synthesis in structured materials as a unique strategy, and broaden the updated applications of ultrasound irradiation in the catalysis fields.

Relationship between the radial dynamics and the chemical production of a harmonically driven spherical bubble

The sonochemical activity and the radial dynamics of a harmonically excited spherical bubble are investigated numerically. A detailed model is employed capable to calculate the chemical production inside the bubble placed in water that is saturated with oxygen. Parameter studies are performed with the control parameters of the pressure amplitude, the forcing frequency and the bubble size. Three different definitions of collapse strengths (extracted from the radius vs.time curves) are examined and compared with the chemical output of various species. A mathematical formula is established to estimate the chemical output as a function of the collapse strength; thus, the chemical activity can be predicted without taking into account the chemical kinetics into the bubble model. The calculations are carried out by an in-house code exploiting the high processing power of professional graphics cards (GPUs). The results shown that chemical activity can be approximated qualitatively from the values of relative expansion. This could be helpful in order to optimise chemical output of sonochemical reactors either from measurement data or simulations as well.

Role of External Field in Polymerization: Mechanism and Kinetics

The past decades have witnessed an increasing interest in developing advanced polymerization techniques subjected to external fields. Various physical modulations, such as temperature, light, electricity, magnetic field, ultrasound, and microwave irradiation, are noninvasive means, having superb but distinct abilities to regulate polymerizations in terms of process intensification and spatial and temporal controls. Gas as an emerging regulator plays a distinctive role in controlling polymerization and resembles a physical regulator in some cases. This review provides a systematic overview of seven types of external-field-regulated polymerizations, ranging from chain-growth to step-growth polymerization. A detailed account of the relevant mechanism and kinetics is provided to better understand the role of each external field in polymerization. In addition, given the crucial role of modeling and simulation in mechanisms and kinetics investigation, an overview of model construction and typical numerical methods used in this field as well as highlights of the interaction between experiment and simulation toward kinetics in the existing systems are given. At the end, limitations and future perspectives for this field are critically discussed. This state-of-the-art research progress not only provides the fundamental principles underlying external-field-regulated polymerizations but also stimulates new development of advanced polymerization methods.

Study of non-spherical bubble oscillations under acoustic irradiation in viscous liquid

The effect of dissipation on the shape stability of a harmonically excited bubble is investigated. The employed liquid is the highly viscous glycerine. The rate of the dissipation is controlled through the alteration of viscosity of the liquid by varying its temperature. The mean radius of the bubble during its radial oscillation is described by the Keller-Miksis equation. Two approaches are used to describe the surface oscillations. The first model solves the surface dynamics equations of each mode together with the transport equation of the vorticity in the liquid domain. The second model approximates the transport equation, which is a partial differential equation, with a boundary layer approximation reducing the required computational resources significantly. The comparison of the surface models shows qualitative agreement at low dissipation rate; however, at high viscosity the application of the full transport equation is mandatory. The results show that an increasing rate of dissipation can significantly extend the shape stable domains in the excitation frequency-pressure amplitude parameter plane. Nevertheless, the collapse strength is decreasing due to the highly damped oscillations. It has been found that an optimal range of dissipation rate in terms of temperature can be defined expressing a good compromise between the collapse strength and surface stability. The computations are carried out by an in-house GPU accelerated initial value problem solver.

Ultrasound-assisted synthesis and characterization of magnetite nanoparticles and poly(methyl methacrylate)/magnetite nanocomposites

Poly(methyl methacrylate)/magnetite (PMMA/Fe₃O₄) nanocomposites were prepared with a two-step technique involving sonication. Fe₃O₄ nanoparticles were synthesized by ultrasound-assisted co-precipitation, and then PMMA/Fe₃O₄ (1-5 wt%) nanocomposites were synthesized via ultrasound-assisted in-situ emulsion polymerization. Best physical properties of the nanocomposites for different Fe₃O₄ loadings were: tensile strength (2 wt%) = 40.28 MPa, Young's modulus (2 wt%) = 2.4 GPa, percentage elongation (2 wt%) = 2.24%, glass transition temperature (2 wt%) = 122.5 °C, thermal inflection point (2 wt%) = 383 °C, electrical conductivity (5 wt%) = 2.0 × 10^-13 S/cm, coercivity = 59.85 Oe (2 wt%), magnetic saturation (5 wt%) = 5.12 emu/g, magnetic remanence (5 wt%) = 0.56 emu/g, and electromagnetic interference shielding effectiveness (5 wt%) = 1.45 dB. This unique combination of physical properties at relatively low Fe₃O₄ loading is attributed to ultrasound-mediated uniform dispersion of the nanofiller in the polymer matrix.

Ultrasound-assisted synthesis of poly(MMA-co-BA)/ZnO nanocomposites with enhanced physical properties

The present study reports synthesis and characterization of poly(MMA-co-BA)/ZnO nanocomposites using ultrasound-assisted in-situ emulsion polymerization. Methyl methacrylate (MMA) was copolymerized with butyl acrylate (BA), for enhanced ductility of copolymer matrix, in presence of nanoscale ZnO particles. Ultrasound generated strong micro-turbulence in reaction mixture, which resulted in higher encapsulation and uniform dispersion of ZnO (in native form - without surface modification) in polymer matrix, as compared to mechanical stirring. The nanocomposites were characterized for physical properties and structural morphology using standard techniques such as XRD, FTIR, particle size analysis, UV-Visible spectroscopy, electrical conductivity, TGA, DSC, FE-SEM and TEM. Copolymerization of MMA and BA (in presence of ZnO) followed second order kinetics. Thermal stability (T_10%=324.9°C) and glass transition temperature (T_g=67.8°C) of poly(MMA-co-BA)/ZnO nanocomposites showed significant enhancement (35.1°C for 1wt% ZnO and 15.7°C for 4wt% ZnO, respectively), as compared to pristine poly(MMA-co-BA). poly(MMA-co-BA)/ZnO (5wt%) nanocomposites possessed the highest electrical conductivity of 0.192μS/cm and peak UV absorptivity of 0.55 at 372nm. Solution rheological study of nanocomposites revealed enhancement in viscosity with increasing ZnO loading. Maximum viscosity of 0.01Pa-s was obtained for 5wt% ZnO loading.

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 (1-5wt% 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 (4wt%), T₅₀=373°C (4wt%), maximum degradation temperature=384°C (4wt%); glass transition temperature=64.8°C (4wt%); tensile strength=20MPa (2wt%), Young's modulus=1.31GPa (2wt%), Percentage elongation=17.5% (1wt%). 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.

Synergistic effect of ultrasonication and phase transfer catalysts in radical polymerization of methyl methacrylate - A kinetic study

Methyl methacrylate (MMA) has been polymerized to poly methyl methacrylate (PMMA) by employing three different phase transfer catalysts (PTC) such as 1,4-bis(dimethylhexyl)ethylenediammoniumbromide (DMHEDAB), 1,4bis(dimethylheptyl)ethylenediammoniumbromide (DMH1EDAB) and 1,4-bis(dimethyloctyl)ethylenediammonium bromide (DMOEDAB) under the influence of ultrasound radiation. The radical polymerization was performed under unstirred condition at a temperature of 60±1°C in an oxygen free atmosphere employing water soluble K₂S₂O₈ as initiator. Various parameters such as role of [Monomer], [Initiator], [PTC], solvent and temperature were investigated on rate of polymerization (Rp) and the synergic efficacy of ultrasound wave variation and phase transfer catalysts were also assessed. It was found that the rate of polymerization (Rp) increased drastically for all the three catalyst under the influence of ultrasound and the order of efficiency was found to be [Formula: see text] This increase may be due to the number of carbon chain attached to the polar group which facilitate and accelerate the rate of polymerization.

Various aspects of ultrasound assisted emulsion polymerization process

In this paper, the effects of ultrasonic (US) power, pulse ratio, probe area and recipe composition were investigated on two process responses namely, monomer (methyl methacrylate, MMA) conversion and electrical energy consumption per mass of product polymer (PMMA). Pulsed mode US is more suitable than continuous mode US for emulsion polymerization. The probe (tip) area has little effect on the yield of polymerization when comparing 19 and 13 mm probes, 13 mm probe performing slightly better for high conversion levels. Meanwhile, large probe area is beneficial for high conversion efficiency of electric energy to US energy as well as for high radical generation yield per energy consumed. The conversion increased slightly and electrical energy consumption decreased substantially by using a recipe with high SDS and monomer concentrations. Conclusions presented in this paper may be useful for scale-up of US assisted emulsion polymerization.

Numerical Simulation and Investigation of System Parameters of Sonochemical Process

This paper presents the effects of various parameters that significantly affect the cavitation. In this study, three types of liquid mediums with different physicochemical properties were considered as the cavitation medium. The effects of various operating parameters such as temperature, pressure, initial bubble radius, dissolved gas content and so forth, were investigated in detail. The simulation results of cavitation bubble dynamics model showed a very interesting link among these parameters for production of oxidizing species. The formation of •OH radical and H2O2 is considered as the results of main effects of sonochemical process. Simulation results of radial motion of cavitation bubble dynamics revealed that bubble with small initial radius gives higher sonochemical effects. This is due to the bubble with small radius can undergo many acoustic cycles before reaching its critical radius when it collapses and produces higher temperature and pressure inside the bubble. On the other hand, due to the low surface tension and high vapor pressure, organic solvents are not suitable for sonochemical reactions.