Shell Polymer Particles Research Articles

Origin of the Acoustic Bandgaps in Hypersonic Colloidal Phononics: The Role of the Elastic Impedance.

How phonons propagate in nanostructures determines the flow of elastic and thermal energy in dielectric materials. However, a reliable theoretical prediction of the phonon dispersion relation requires experimental verification both near to and far from the Brillouin zone of the nanostructure. We report on the experimental hypersonic phonon dispersion of hard (SiO2) and soft (polymer) fcc colloidal crystals infiltrated in liquid polydimethylsiloxane with different elastic impedance contrast using Brillouin light spectroscopy. We discuss the distinct differences with first-principles full elastodynamic calculations involving a multiple-scattering theory. Interparticle contacts strongly impact the long-wavelength speed of sound and the nature of the particle vibration resonance-induced hybridization hypersonic bandgap. The absence of the order-induced Bragg bandgap in SiO2 and its presence in soft opals cannot be fully accounted for by the theory, limiting its predictive power. Bridging the elasticity of the two colloidal crystals with suitable SiO2 core–shell (polymer) particles reveals an unprecedented crossover behavior in the dispersion relation. In view of many conversational parameters, the control tuning of phonon propagation in soft matter-based hypersonic phononics remains challenging.

Synthesis of luminescent core–shell polymer particles carrying amino groups for covalent immobilization of enzymes

Synthesis of luminescent core–shell polymer particles carrying amino groups for covalent immobilization of enzymes

Multi-objective dynamic optimization of seeded suspension polymerization process

The temperature profile of the seeded suspension polymerization process was optimized to maximize molecular weight, shell thickness and monomer conversion ratio of core–shell polymer particles. Extreme learning machine radial basis function neural networks with R2 values greater than 0.93 were developed, to predict polymer properties at any point in time, using data generated by a computational fluid dynamics model. The optimal combination of input parameters for each neural network was selected from a pool of 44 variables, by using a weight-based method that uses a support vector regression model, and a global exhaustive search algorithm, consecutively. The neural networks developed were incorporated into a genetic algorithm that maximizes the molecular weight, monomer conversion ratio and shell thickness. The optimum temperature profile generated by the algorithm satisfactorily maximized all target polymer properties. This study also demonstrates that a support vector machine classifier could be reliably used for imposing nonlinear inequality constraints for solving dynamic optimization problems.

Effects of Reaction Operation Policies on Properties of Core–Shell Polymer Supports Used for Preparation of Highly Active Biocatalysts

AbstractCore–shell polymer supports with different morphological features and compositions are prepared through combined suspension and emulsion polymerizations. It is shown that proper manipulation of the divinylbenzene (DVB) feed content allows for maximization of specific areas, porosities, and mechanical resistances. Additionally, it is shown that feeding of previously prepared miniemulsions leads to core–shell particles with smaller specific areas, due to less efficient coating of the cores. Particularly, the combined manipulation of polymerization times and DVB feed compositions allows for production of particles with pronounced specific area (50 m2 g−1) and porosity (0.30 cm3 g−1). Produced core–shell polymer particles are employed as supports for the immobilization of lipase B from Candida antarctica, and the obtained enzymatic activities for both hydrolysis (A hyd) and esterification (A est) reactions are very high (A hyd = 34.7 ± 3.8 U/g; A est = 3564.6 ± 581 U/g), even when compared to activities obtained using the reference commercial biocatalyst Novozym 435 (A hyd = 7.6 ± 1.8 U/g, A est = 2384.7 ± 307.2 U/g). Finally, biocatalysts prepared with the core–shell supports present higher enzymatic activities than biocatalysts prepared with supports of higher specific area obtained through conventional emulsion polymerizations, indicating that the porous structure of the shell can be beneficial for the immobilization and activity of the enzymes.

Core-Shell Morphology of Redispersible Powders in Polymer-Cement Waterproof Mortars.

Redispersible powders based on soft core-hard shell polymer particles can be used as additives in polymer-cement mortars. The role of this morphology on the spray-drying production of these powders and on the crack-bridging properties of the corresponding cement-based membranes is investigated. Different polymer latexes at high solid content with varied core-shell ratio, shell thickness and chemical composition (hardness) were prepared from styrene and 2-ethylhexyl acrylate monomers via semi-batch emulsion polymerization. The latexes were characterized in terms of size, composition, and glass transition temperature (T), and spray-dried to obtain redispersible polymer powders (RPPs) using poly (vinyl alcohol) and limestone powder as anti-caking agents. The polymer powders were mixed with a mortar mixture and redispersed in water to produce cement-based membranes, which were tested for crack-bridging properties at different temperatures. The results showed that it was not possible to spray-dry a dispersion of homogeneous polymer particles with T of −25 C, unless these particles are protected by much harder (high T) shell. In particular, it was observed that a thicker shell improved the spray-ability, but lowered the crack-bridging properties of the produced membrane. A trade-off between these two was revealed to be the key for the optimal design of the polymer nanoparticles, as proven by the systematic study of the core-shell morphology reported in this work. The best compromise was shown to consist of particles larger than 300 nm, shell thickness of about 5 nm, and core-shell ratio of 97%, with styrene content in the shell not larger than 80% to avoid excessive hydrophobicity.

Core–shell and gradient morphology polymer particles analyzed by X‐ray photoelectron spectroscopy: Effect of monomer feed order

The synthesis of composite latex particles possessing core–shell and gradient morphologies, respectively, using seeded starve-fed semibatch emulsion polymerization of styrene (St) and methyl methacrylate (MMA) is presented. The focus is on the effect of the monomer feed order on the particle morphology development. The particle morphology is assessed using a novel approach which entails comparing the experimental surface composition as a function of polymerization time (particle growth) obtained by X-ray photoelectron spectroscopy with the predicted surface composition using a mass balance mathematical model. Both types of composite latexes (core–shell and gradient) feature changes with polymerization time in the oxygen/carbon surface composition which enables one to track the morphology development. Differential scanning calorimetry is also implemented to analyze the extent of phase separation. The monomer feed order is shown to play a crucial role—under the present conditions, gradient and core–shell particles are obtained if the feed order is St/MMA (St fed first), but not if the feed order is reversed. These findings illustrate that thermodynamic factors are important, given that thermodynamically it is more favorable for MMA-rich chains to occupy the oil–water interface to reduce the interfacial tension. Systems where St is the second stage monomer lead to mixed structures rather than the targeted core–shell or gradient morphology with St-rich chains at the particle surface.

Environmental durability of glass fiber epoxy composites filled with core–shell polymer particles

A manufacturing technique was successfully adopted for incorporating core–shell polymer (CSP) particles into glass fiber reinforced polymer (GFRP) composites. CSP particles were firstly added into inter-ply interfaces during the lamination process. Conventional as well as CSP particle filled GFRP laminates were then cured at 122°C under high pressure while in a vacuum environment. Good adhesion between the particles and the epoxy matrix was achieved during the curing. GFRP laminates with or without particles were immersed in water at 80°C for different durations. These conditioned laminates were later subjected to low-velocity impact tests. It was found that the GFRP laminates with CSP particles absorbed more moisture while had less structural defects formed during the conditioning. The CSP particles significantly improved the impact properties of the GFRP laminates. After hygrothermal aging, the beneficial effects brought about by these particles for effectively resisting impact loads diminished. The underlying mechanisms were identified, studied and explained.

An efficient approach to prepare boronate core–shell polymer nanoparticles for glycoprotein recognition via combined distillation precipitation polymerization and RAFT media precipitation polymerization

Stimuli-responsive core-shell nanoparticles, with 3-acrylamidophenyl boronic acid (APBA) as the functional group, were synthesized via combined distillation precipitation polymerization and RAFT media precipitation polymerization. The well-defined boronic acid-polymer branch on the nanoparticle surface displayed high binding capacity and good selectivity towards cis-diol-containing molecules.

Damage evolution in glass/epoxy composites engineered using core–shell microparticles under impact loading

The overall objective of the investigation presented in this paper was to study the effect of dispersion of core–shell polymer (CSP) particles within the ply interfaces on damage evolution of glass/epoxy laminates under impact loading. These laminates were fabricated with the CSP particle dispersion controlled to 14 % of the total weight of the used prepreg. A series of impact experiments were done with instrumental drop tower device at all probable impact energies within a practical low velocity impact range. The damage phenomena occurring in the internal microstructure of the laminates were analysed with the help of scanning electron microscope and correlated to the structural response of the laminate. The predominant damage modes were dependent on the magnitude of the applied impact energy. The CSP particle incorporation does not change the sequence of the fracture events but it delays and mitigates the damage creation. The deformation of the CSP particles and the tearing of their outer shells absorb most of the impact energy thereby preventing initiation of matrix cracks at lower impact energies and delaying fibre damage at higher energies. The crushed particles along with their nano-size rubber cores impede crack propagation requiring the cracks to follow torturous paths consequently dissipating additional amount of energy. These particles also promote elastic energy absorption of the laminates minimizing their tendency to fracture easily under impact. The ultimate load bearing capability of the modified laminate showed 60 % improvement and the deflection characteristics indicated lower proneness to impact.

Synthesis of well-defined poly(vinyl ether)-based macromonomers having pendant glycerols via living cationic polymerization and their application to the preparation of core−shell polymer particles

A new vinyl ether monomer bearing a glycerol pendant moiety protected with an isopropylidene group (2-(2,2-dimethyl-[1,3]dioxolan-4-ylmethoxy)-ethyl vinyl ether, IpGEVE) was designed as the precursor of a novel type of hydrophilic poly(vinyl ether) containing glycerol pendants. It was found that the polymerization of IpGEVE proceeded in a controlled manner, and the protecting groups of isopropylidene moieties could be cleaved with trifluoroacetic acid. Living cationic polymerization of IpGEVE with an initiator bearing a methacryloyl group (VEM-HCl) and subsequent deprotection of the pendant isopropylidene groups of the resultant precursor afforded a glycerol-substituted hydrophilic macromonomer MA-PGEVE. Nearly monodispersed polymer particles in the submicron size range were successfully obtained via dispersion copolymerization of MA-PGEVE with styrene.© 2013 Society of Chemical Industry

A novel approach for preparation of “cage-like” multihollow polymer microspheres through sulfonated polystyrene particles

A new and effective process has been developed for fabrication of novel cage-like multihollow polymer particles by using sulfonated polystyrene (SP) particles as the templates, with heptane as the phase separation agent, in an ethanol/water medium. The ratio of water/ethanol and the heating temperature play important roles in the formation of these multihollow particles. It was found that the cage-like polymer particles could be obtained when the ratio of ethanol/water is 5:5 (w/w), with a temperature above 50 °C. After a detailed study, the formation mechanism was proposed based on an SP swollen (ethanol and heptane penetrating process) and phase separation process. This new method for fabricating the cage-like multihollow polymer particles has a great meaning not only on confirming the formation mechanism, but also on providing an effective way to prepare the special hollow core/porous shell polymer particles, which could have wide range of potential applications, such as catalysts, sensors, and drug release.

Morphology control of magnetic latex particles prepared from oil in water ferrofluid emulsion

The use of magnetic latex particles as solid support in biomedical applications is favourable when homogeneous and well-defined core–shell polymer particles are used. Accordingly, this paper concerns with the synthesis of magnetic poly(styrene–divinylbenzene) latex particles using emulsion polymerization of styrene (St) and divinylbenzene (DVB) monomers in the presence of preformed oil in water organic ferrofluid emulsion droplets as seed. The key parameters which affect on formation and morphology of the prepared magnetic latexes were investigated, including type of magnetic emulsion, St/DVB monomers ratio, DVB amount, type of initiator and surfactant nature. In this study, two different magnetic emulsions were used, low and high octane content magnetic emulsions. The magnetic emulsions were stabilized using different types of surfactants including AP, Triton X 405 and SDS. In addition, four different initiators, including AIBN, V50, ACPA and KPS were examined. The morphology of the prepared magnetic latexes was investigated using transmission electron microscopy. In addition, particle size and size distribution, magnetic content and magnetic properties of the prepared magnetic latexes were also examined, using various techniques, e.g. dynamic light scattering, thermal gravimetric analysis and vibrating sample magnetometer, respectively. The results showed that the morphology type (Janus like, moon like and/or core–shell) of the prepared magnetic latex particles could be controlled depending mainly on the used formulation. In fact, the use of styrene monomer leads to anisotropic morphology. Whereas, the progressive use of DVB in presence of KPS intiator leads to a well-defined magnetic core and polymer shell structure.

Preparation of titania hollow particles with independently controlled void size and shell thickness by catalytic templating core–shell polymer particles

Organic/inorganic hybrids were prepared by catalytic hydrolysis and subsequent polycondensation of tetra-n-butyl titanate (TnBT) in shell layers grafted on core particles. The core particles were synthesized by emulsifier-free emulsion polymerization of styrene, N-n-butyl-N-2-methacryloyloxyethyl-N,N-dimethylammonium bromide (C4DMAEMA), and 2-chloropropionyloxyethyl methacrylate using 2,2′-azobis(2-amidinopropane) dihydrochloride as an initiator. The core diameters were controlled in the range of 70–550 nm by adjusting a C4DMAEMA feed concentration. The core–shell particles were prepared by surface-initiated activator generated electron transfer–atom transfer radical polymerization of 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA). The sizes of core–shell particles were found to increase monotonically with an increase in a DMAEMA concentration. The hybrid particles were fabricated by adding TnBT into a water/ethanol dispersion of core–shell particles. The amounts of titania deposited increased in proportion to the grafted amounts of poly[2-(N,N-dimethylamino)ethyl methacrylate] on the core particles. The X-ray diffraction measurement revealed that the hollow titania particles obtained by heat treatment of hybrids have an anatase crystallographic phase.

Monomer type emission of perylenediimide derivatives doped polymer particles

This study aims to present the fabrication of colloidal photonic crystals (PCs) doped with perylenediimide (PDI) derivatives. Monodisperse PDI doped core–shell polymer particles have been obtained by employing a soap-free emulsion polymerization process of styrene and 2-hydroxyethylmethacrylate with the chromophore solubilized in the organic phase. The obtained polymer colloids allowed the fabrication of PC films that have been investigated by UV–vis and fluorescence spectroscopy. The hybrid materials have been investigated in comparison with PCs doped by the classical impregnation method. Thus, the doping using soap-free emulsion polymerization resulted in the obtaining of PDI doped core–shell polymer particles exhibiting monomer emission, whereas by employing an impregnation doping method H-type aggregates are formed.

Impact Damage Resistance of CFRP Prepreg Laminates with Dispersed CSP Particles into Ply Interfaces

The effects of incorporating core shell polymer (CSP) particles within interply interfaces on the impact response of CFRP prepreg laminates are investigated. The impact tests were conducted on samples without and with CSP particles into the ply interfaces. The loads versus time curves were examined to determine the impact response and the associated energy absorption by the laminates were studied. The results indicate that both, the peak load of the laminates improved by 41% and damping index (DI) reduced by 90% with the dispersion of 51 g/m2 of CSP particles within the prepreg ply interfaces of the laminates. It was noted that the CSP particles shielded the composites from the initial severity of impact. The energy absorbing mechanisms altered the supercritical response of the laminate to subcritical due to increase in the elastic energy stored within the laminates with CSP particles thereby changing the energy absorption modes. It was observed from macroscopic observations and SEM images of the damage sites that the damage mechanism and patterns changed and the extent of damage reduced with the addition of CSP particles.

Synthesis of zinc oxide-encapsulated poly(methyl methacrylate)–chitosan core–shell hybrid particles and their electrochemical property

The synthesis of hybrid materials possessing zinc oxide nanoparticles encapsulated in core–shell polymer particles having poly(methyl methacrylate) core and chitosan shell (PMMA–CS/ZnO) was carried out via an emulsifier-free emulsion polymerization. The ZnO nanoparticles modified by 3-(trimethoxysilyl)propyl methacrylate (TPMZnO) were first prepared before being charged to the polymerization system. The effects of polymerization time (from 2h to 6h) and the amount of TPMZnO added (0.018g, 0.020g, and 0.030g) were studied. It was found that the polymerization time of 5h yielded colloidally stable hybrid latex with% MMA conversion up to 90%. Moreover, the increase in the amount of TPMZnO resulted in a decrease in% MMA conversion from 90% to 80%. It was also found from TGA analysis that the amount of TPMZnO added affected the percentage of TPMZnO encapsulation. PMMA–CS/ZnO particles with the size ranging from 173 to 245nm were observed by TEM. In addition, the PMMA–CS/ZnO hybrid latexes possessed high positive charges in the range of 40–51mV. The electrochemical property of the electrodes fabricated from PMMA–CS/ZnO nanoparticles was illustrated by cyclic voltammetry.

Production of Core–shell Particles by Combined Semibatch Emulsion/Suspension Polymerizations

AbstractCore–shell polymer particles were produced by combined semibatch emulsion/suspension polymerizations, using different monomers. It is shown that the morphology of the shell depends on the glass transition temperature (Tg) of the emulsified particles and that specific areas can vary considerably (7.9 to 37 m2 · g−1), depending on reaction conditions and used monomers. Particularly, a thin film is formed around the core when the Tg of the polymer that constitutes the shell is lower than the reaction temperature, while a porous shell is formed when the Tg of the polymer material is higher than the reaction temperature. Based on the observed data, a physical model was proposed to explain the formation of core–shell particles by combination of typical suspension and emulsion polymerization recipes.magnified image

Preparation of organic/inorganic composites by deposition of silica onto shell layers of polystyrene (core)/poly[2-( N, N-dimethylamino)ethyl methacrylate] (shell) particles

Organic/inorganic composites were prepared by catalytic hydrolysis and subsequent condensation of tetraethoxysilane (TEOS) in a shell layer of core–shell polymer particles. First, core–shell particles were prepared by emulsifier-free emulsion polymerization of styrene (St) with 2-chloropropionyloxyethyl methacrylate (CPEM) using potassium persulfate as an initiator, followed by surface-initiated activator generated electron transfer–atom transfer radical polymerization (AGET–ATRP) of 2-( N, N-dimethylamino)ethyl methacrylate (DMAEMA). Dynamic light scattering revealed that hydrodynamic diameter of the particle increased from 482 to 931 nm after AGET–ATRP of DMAEMA. The amount of grafted DMAEMA was determined to be ca. 10 mol% with respect to (wrt) St by 1H NMR. Second, the composite particles were prepared by adding TEOS into a water/methanol dispersion of the P(St-CPEM)- g-P(DMAEMA). The P(St-CPEM)- g-P(DMAEMA)–SiO 2 composite particles containing ca. 50 wt.% of silica wrt the total weight were obtained. Hollow silica shell particles were also obtained by extraction of polymer components from the composites with tetrahydrofuran.

Narrow‐disperse or monodisperse crosslinked and functional core–shell polymer particles prepared by two‐stage precipitation polymerization

AbstractNarrow‐disperse and monodisperse cross‐linked core–shell polymer particles containing different functional groups, such as esters, hydroxyls, chloromethyls, carboxylic acids, amides, cyanos, and glycidyls, in the shell layers in the micrometer size range were prepared by a two‐stage precipitation polymerization in the absence of any stabilizer. Commercial divinylbenzene (DVB), containing 80% DVB, was precipitation polymerized in acetonitrile without any stabilizer as the first‐stage polymerization and was used as the core. Several functional monomers, including methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2‐hydroxyethyl methacrylate, glycidyl methacrylate, methyl acrylate, ethyl acrylate, butyl acrylate, t‐butyl acrylate, i‐octyl acrylate, acrylic acid, acrylamide, acrylonitrile, styrene, and p‐chloromethyl styrene, were incorporated into the shells during the second‐stage polymerization. The resulting core–shell polymer particles were characterized with scanning electron microscopy and Fourier transform infrared spectroscopy. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1776–1784, 2006

Modeling of semibatch styrene suspension polymerization processes

AbstractWe developed a mathematical model to describe the behavior of semibatch styrene suspension polymerization processes, where the constituents of a typical emulsion polymerization process are added into the reaction vessel during the course of a typical suspension reaction. This technique was recently described for the production of core–shell polymer particles. The model assumes that the nucleated emulsion particles can agglomerate with the sticky and much bigger suspension particles and that the agglomeration rate constant is a function of the internal states of the suspended droplets. The proposed model presented good agreement with experimental conversion, average molecular weight, and molecular weight distribution data. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 1950–1967, 2005