Monomer Droplets Research Articles

Doubly curved nanofiber-reinforced optically transparent composites.

Doubly curved nanofiber-reinforced optically transparent composites with low thermal expansion of 15 ppm/k are prepared by hot pressing vacuum-filtered Pickering emulsions of hydrophobic acrylic resin monomer, hydrophilic chitin nanofibers and water. The coalescence of acrylic monomer droplets in the emulsion is prevented by the chitin nanofibers network. This transparent composite has 3D shape moldability, making it attractive for optical precision parts.

Synthesis of Spherical Polymer Nanoparticles Reflecting Size of Monomer Droplets Formed by Tandem Acoustic Emulsification

We have successfully synthesized polymer nanoparticles which reflect precisely the size of monomer droplets formed by the tandem acoustic emulsification. This new synthetic method involves sequenti...

Sonication-Aided Formation of Hollow Hybrid Nanoparticles as High-Efficiency Absorbents for Dissolved Toluene in Water.

A surfactant-free emulsion polymerization process was developed to produce hollow hybrid nanoparticles (HHNP thereafter). Ultrasonication was found not only to help the generation of nanosized monomer droplets but also to generate surface active species through mediating the hydrolysis of the monomer, 3-(methacryloyloxy) propyltrimethoxysilane (MPS), thus stabilizing the oil/water interface. The hollow structure was formed based on a soft template approach, where the partially hydrolyzed monomer served as emulsifier and polymerized at the interface to form a hybrid shell. These HHNPs were used to absorb dissolved toluene in water and it was found they could reduce the toluene level down to zero, a level hardly being achieved by other methods. Combined with their good colloidal stability in water, these HHNPs are very promising colloidal collectors for dissolved organic solvents, in order to generate high quality water from contaminated water.

Synthesis of Water-Based Dispersions of Polymer/TiO₂ Hybrid Nanospheres.

We develop a strategy for preparing water-based dispersions of polymer/TiO2 nanospheres that can be used to form composite materials applicable in various fields. The formed hybrid nanospheres are monodisperse and possess a hierarchical structure. It starts with the primary TiO2 nanoparticles of about 5 nm, which first assemble to nanoclusters of about 30 nm and then are integrated into monomer droplets. After emulsion polymerization, one obtains the water-based dispersions of polymer/TiO2 nanospheres. To achieve universal size, it is necessary to have treatments with intense turbulent shear generated in a microchannel device at different stages. In addition, a procedure combining synergistic actions of steric and anionic surfactants has been designed to warrant the colloidal stability of the process. Since the formed polymer/TiO2 nanospheres are stable aqueous dispersions, they can be easily mixed with TiO2-free polymeric nanoparticle dispersions to form new dispersions, where TiO2-containing nanospheres are homogeneously distributed in the dispersions at the nanoscale, thus leading to various applications. As an example, the proposed strategy has been applied to generate polystyrene/TiO2 nanospheres of about 100 nm in diameter.

Effect of living polystyrene costabilizer on styrene miniemulsion polymerization

RAFT miniemulsion polymerizations of styrene with living polystyrene (PSlc) serving as both RAFT reagent and polymer costabilizer were investigated. The miniemulsion upon aging at 25 °C showed satisfactory stability against the Ostwald Ripening process. The rate of polymerization for RAFT miniemulsion polymerization initiated by oil-soluble AIBN is much slower than that for the water-soluble SPS counterpart. In addition to the predominant monomer droplet nucleation, much stronger particle nucleation taking place in the continuous aqueous phase (homogeneous nucleation) for the run with AIBN was observed. It is the different extents of homogeneous nucleation that is responsible for the quite different kinetic behaviors between the RAFT miniemulsion polymerizations initiated by different types of initiator (AIBN versus SPS). Furthermore, increasing initial molar ratio of RAFT reagent to AIBN greatly enhances the characteristics of RAFT polymerization (i.e., better control over polymer chain growth with the progress of polymerization).

Kinetics of reversible addition–fragmentation transfer (RAFT) miniemulsion polymerization of styrene using dibenzyl trithiocarbonate as RAFT reagent and costabilizer

AbstractThe roles of dibenzyl trithiocarbonate (DBTTC) as both costabilizer and reversible addition–fragmentation transfer (RAFT) reagent in RAFT miniemulsion polymerizations of styrene were investigated. The effectiveness of DBTTC costabilizer in retarding Ostwald ripening involved in the storage stability of miniemulsion is comparable to that of conventional low‐molecular‐weight costabilizers such as cetyl alcohol, but inferior to that of hexadecane. The major variables chosen for studying kinetics of RAFT miniemulsion polymerizations include the type of initiators and levels of DBTTC and surfactant. At a constant level of DBTTC, the rate of polymerization for benzoyl peroxide (BPO)‐initiated polymerization is slower than that for sodium persulfate (SPS)‐initiated polymerization. Furthermore, the polymerization rate decreases with increasing level of DBTTC for polymerizations initiated by BPO (or SPS). It is the monomer droplet nucleation that governs BPO‐initiated polymerizations. In contrast, for SPS‐initiated polymerizations, the probability for homogeneous nucleation to take place is greatly increased, especially for polymerizations with lower levels of DBTTC and higher levels of surfactant. © 2015 Society of Chemical Industry

Preparation of size-controlled polymer particles by polymerization of O/W emulsion monomer droplets obtained through phase inversion temperature emulsification using amphiphilic comb-like block polymers

Abstract Polystyrene latex particles with controlled size were prepared by polymerization of oil-in-water (O/W) emulsion styrene droplets obtained through the phase inversion temperature (PIT) emulsification using amphiphilic comb-like block polymers, polystyrene- b -poly[oligo(ethylene glycol) methyl ether methacrylate] (PSt n - b -POEGMA m -Cl). PSt n - b -POEGMA m -Cl block polymers were synthesized by sequential atom transfer radical polymerization (ATRP) of St and OEGMA. The interfacial properties of PSt n - b -POEGMA m -Cl in aqueous media were investigated by means of surface tension measurement, fluorescence probe technique, and transmittance measurement. The length of hydrophobic PSt block chain was found to affect the critical micelle concentration, the micelle aggregation number, and the cloud point. O/W emulsions were obtained through the PIT process using PSt n - b -POEGMA m -Cl as a surfactant by lowering the temperature of emulsions below the PIT in an ice bath. PSt particles with precisely controlled size in a range between 30 and 120 nm were successfully prepared by a free radical polymerization of St droplets initiated by the water- or oil-soluble initiators. FE-SEM observation revealed that the morphology of polystyrene particles was found to depend on the relative PSt chain length of PSt n - b -POEGMA m -Cl.

Reduction in aggregation and energy transfer of quantum dots incorporated in polystyrene beads by kinetic entrapment due to cross-linking during polymerization.

We report the development of barcoded polystyrene microbeads, approximately 50 μm in diameter, which are encoded by incorporating multicolored semiconductor fluorescent nanocrystals (quantum dots or QDs) within the microbeads and using the emission spectrum of the embedded QDs as a spectral label. The polymer/nanocrystal bead composites are formed by polymerizing emulsified liquid droplets of styrene monomer and QDs suspended in an immiscible continuous phase (suspension polymerization). We focus specifically on the effect of divinylbenzene (DVB) added to cross-link the linearly growing styrene polymer chains and the effect of this cross-linking on the state of aggregation of the nanocrystals in the composite. Aggregated states of multicolor QDs give rise to nonradiative resonance energy transfer (RET) which distorts the emission label from a spectrum recorded in a reference solvent in which the nanocrystals are well dispersed and unaggregated. A simple barcode is chosen of a mixture of QDs emitting at 560 (yellow) and 620 nm (red). We find that for linear chain growth (no DVB), the QDs aggregate as is evident from the emission spectrum and the QD distribution as seen from confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM) images. Increasing the extent of cross-linking by the addition of DVB is shown to significantly decrease the aggregation and provide a clear label. We suggest that in the absence of cross-linking, linearly growing polymer chains, through enthalpic and entropic effects, drive the nanocrystals into inclusions, while cross-linking kinetically entraps the particle and prevents their aggregation.

Real time monitoring of the quiescent suspension polymerization of methyl methacrylate in microreactors—Part 1. A kinetic study by Raman spectroscopy and evolution of droplet size

This paper presents an experimental study on the polymerization of droplets of methyl methacrylate (MMA) in quiescent state using microreactors. The reaction kinetics was monitored by Raman spectroscopy, while the images of MMA droplets image were captured by CCD (charge-coupled device) camera within a microcapillary. Different experimental recipes were proposed with commercial initiators in order to compare the system performance with two types of initiators: monofunctional and bifunctional peroxides. It is shown in this paper that the Raman technique is able to monitor the reaction kinetics at different conditions. For the first time in the open literature it was possible to identify the evolution of the monomer droplets during polymerization to high conversions (>90%) in quiescent state. In addition, it was possible to identify three different stages during the polymerization reactions of MMA. Finally, it is shown that the dispersities (M¯w/M¯n) obtained with the bifunctional initiator were lower than 2, while the dispersities obtained with the monofunctional initiator were greater than 2.

(Cryo)-TEM Assessment of Droplet Nucleation Efficiency in Hybrid Acrylic/CeO2 Semibatch Miniemulsion Polymerization

Monomer droplet nucleation has been successfully tracked in a seeded semibatch miniemulsion polymerization with miniemulsion feeding. Taking advantage of the marker capacity of CeO2 nanoparticles two polymerizations were designed. In the first one the seed contained nanoceria while a blank monomer miniemulsion was fed to the reactor and in the second reaction the opposite was done; namely, the seed did not contain any CeO2 and the miniemulsion fed did. In this way, the presence of the CeO2 in either seed or nucleated particles allowed tracking the fraction of droplets that efficiently nucleated during miniemulsion feeding. Conventional TEM and cryo-TEM were used to monitor the nucleation efficiency by analyzing separately the particles that did or did not contain CeO2 nanoparticles.

Preparation of Core-Shell Composite Particles Containing a Dye Powder by a Droplet Coalescence Method

It was attempted to prepare core-shell composite particles containing a hydrophilic dye powder by a droplet coalescence method using liquid-liquid dispersion. Core particles composed of dye powder and oleic acid have been forced to coalesce with styrene monomer droplets, and then suspension polymerization has been performed to form the polystyrene shell. In the experiment, the number and diameter of styrene monomer droplets were mainly changed stepwise to promote coalescence between the core particles and the monomer droplets and to control the shell thickness. It was found that the core shell composite particles could be prepared by increasing the monomer droplet number at the constant impeller speed, because the coalescence frequency between the monomer droplets and the core particles increased with the monomer droplet number at the constant impeller speed. Moreover, the diameter and shell thickness of the core shell composite particles increased with the diameter of monomer droplets.

Encapsulation of submicron particles with polymer

This article presents the results of experimental studies of polymer shell formation on the surface of submicron (including nano-) particles due to mixing of a pair of two-phase gas flows of submicron particles and fine-dispersed liquid monomer droplets. The possibility of changing the polymer shell thickness on the surface of submicron particles by controlling the ratio of charges and particle sizes due to variations of electrical field strength in discharge cameras for charging and the dispersion of submicron particles and fine-dispersed liquid monomer droplets is shown.

Online monitoring of emulsion polymerization using electrical impedance spectroscopy

A frequency-dependent electrical monitoring technique was developed for characterizing emulsion polymerization online. High resolution electrical impedance spectroscopy (EIS) was conducted to study emulsion polymerization of styrene in terms of the key process parameters. Relationships between EIS data and process and product attributes such as monomer conversion and particle size were investigated. Electrical impedance values were measured at frequencies ranging from 1 Hz to 100 kHz. EIS parameters revealed changes in emulsion properties with time for both aqueous and organic phases during polymerization. At relatively higher frequencies (≥1 kHz) EIS data were found to be dominated by events in the continuous phase showing transitions in polymerization rates and intervals, while changes in monomer droplet and polymer particle sizes were dominant at lower frequencies (1 Hz). The EIS data were found to correlate well with polymerization rate, monomer conversion and particle size profiles at the appropriate frequencies in real time. © 2014 Society of Chemical Industry

Cationic Aerosol Photopolymerization

AbstractPhotoinitiated polymerization in aerosols is employed for the preparation of spherical polymer particles via cationic polymerization. The UV irradiation of aerosol monomer droplets starts the cationic curing process without the employment of any solvent or additives such as stabilizers, resulting in highly pure polymers. Crosslinked polymer spheres with a high gel content are obtained by processing vinyl ether and epoxy monomers via this aerosol‐photopolymerization technique, which exhibits great potential for the development of multifunctional materials.

On the Reaction Characteristics of Miniemulsion Polymerization with Aqueous Phase Initiation – Experiments and Modeling

Miniemulsions, consisting of submicron droplets of very hydrophobic lauryl methacrylate or 4‐tert‐butyl styrene, are successfully polymerized using water‐soluble sodium persulfate. Monitoring the calorimetric profile as well as the droplet and particle size distribution with conversion manifests a process of monomer redistribution, droplet disappearance, and narrowing of the particle size distribution. The observed reaction characteristics could be modeled adequately, using thermodynamic principles. The results of the work presented do not only have predicting value, but also enfeeble the idea of a one‐to‐one translation of monomer droplets into polymer particles in miniemulsion polymerization.

Kinetic studies of semibatch emulsion copolymerization of methyl methacrylate and styrene in the presence of high intensity ultrasound and initiator

The present work deals with kinetic studies of copolymerization of methyl methacrylate and styrene using ultrasound assisted semibatch emulsion copolymerization in the presence of sodium dodecyl sulfate (emulsifier) and potassium persulfate (external initiator). The effect of temperature, acoustic intensity, initiator loading, surfactant concentration and monomer concentration on the extent of conversion has been investigated. The extent of polymerization was observed to increase with an increase in the temperature, and concentrations of initiator, monomer and surfactant. Further, the initial polymerization rate increased with an increase in the acoustic intensity from 11.2 to 23.1Wcm−2 and then it was found to decrease with a further increase to 33.80Wcm−2. The novelty of this work lies in the fact that there have been only limited kinetic studies for the approach of ultrasound assisted emulsion copolymerization. It has been also established in the present work that the formation of fine and stable monomer droplets, due to the cavitational activity at/near the interface of immiscible monomer phase and subsequent disruption by micro jets, leads to the smaller final polymer particle size and under optimized conditions, it was found to be about 40nm.

Kinetics and effect of surfactant and cosurfactant on miniemulsion polymerization of acrylate monomers

The effects of the type and amount of the surfactant and cosurfactant on the miniemulsion polymerization of acrylate monomers were studied, and the comparison of the kinetics between miniemulsion polymerization and conventional emulsion polymerization was discussed in the presence of reactive surfactant allyloxy nonylphenol propyl polyoxyethylene (10), ether sulfate (DNS-86), and reactive cosurfactant stearyl methacrylate (SMA). The results showed that the obtained polyacrylate miniemulsion had a high monomer conversion rate and a low coagulum fraction, which were affected little by the surfactant and cosurfactant type. When the surfactant and cosurfactant amounts were all 2 wt%, the contact angle of the prepared polyacrylate miniemulsion with DNS-86/SMA and the water absorption fraction of the latex film were 39° and 8.3 wt%, respectively. FTIR results confirmed that DNS-86 and SMA took part in the polymerization of acrylate monomers. In the miniemulsion polymerization of acrylate monomers with DNS-86/SMA, monomer droplet nucleation was the main nucleation style.

Synthesis and Characterization of Hydrogenated Rosin/Polyacrylate Composite Emulsions by Two-Step Mini-Emulsion Polymerization Method

Hydrogenated rosin/polyacrylate composite emulsions were prepared by a two-step mini-emulsion polymerization method, which included the first step polymerization of mini-emulsion-A (ME-A) without hydrogenated rosin and the second of mini-emulsion-A-R (ME-A-R) with hydrogenated rosin. The effect of the two step polymerization on the particle size and its distribution, molecular mass, gel fraction, swelling ratio and adhesion properties of composite emulsions was studied. The results showed that the two step polymerizations were all monomer droplet nucleation and independent. When ME-A/ME-A-R was 25/75, the initial force, 180° peel strength and shear resistance of composite emulsions were 12 #, 9.4 N/25 mm and 69 h, respectively.

Defined polymer shells on nanoparticles via a continuous aerosol-based process

A continuous aerosol-based process is described for the encapsulation of nanoparticles with a thin polymer shell. The process is essentially based on directed binary collisions between gas-borne core particles and liquid monomer droplets carrying opposite electrical charges, followed by photo-initiated polymerization. Once the two streams are mixed together, the process runs to completion on a time scale of about 2 min or less, required for coagulation and polymerization. Gold, silica, and sodium chloride nanoparticles were successfully coated by this technique with PHDDA [poly(hexanediol diacrylate)] and/or crosslinked PMMA [poly(methyl methacrylate)]. It was found that all core materials as well as agglomerates were wettable at room temperature and that the spreading kinetics of the monomer were fast enough to cover the core particles uniformly within the time scale provided for coagulation. The shell thickness depends on the volume ratio between core particles and monomer droplets. This was demonstrated for a combination of monodisperse silica spheres (d = 241 nm) and polydisperse methyl methacrylate droplets, resulting in a theoretical shell thickness of 18 nm. There was very good agreement between measurements by TEM and electrical mobility spectroscopy. The results revealed that about 90 % or more of the core–shell structures were formed from 1:1 collisions between a core particle and a single monomer droplet.

Single-step microfluidic synthesis of various nonspherical polymer nanoparticles via in situ assembling: dominating role of polyelectrolytes molecules.

In this paper, a microfluidic approach has been used for the synthesis of ellipsoidal, dumbbell, rodlike, and necklacelike polymer nanoparticles. High yields of special types of nonspherical nanoparticles have been achieved by the implementation of an emulsion polymerization into microfluidic arrangement with a micro hole-plate reactor for the formation of monomer droplets. Here, in particular, the formation of nonspherical polymer nanoparticles is dependent on the presence of polyelectrolyte surface active molecules such as poly(4-styrenesulfonic acid-co-maleic acid) sodium salt (PSS-co-PM), poly(sodium-p-styrenesulfonate) (PSSS), and polyanetholesulfonic acid sodium salt (PAES). The shapes and sizes of the interparticle nanoassemblies are precisely controlled by adjusting the concentration of polyelectrolytes in the aqueous phase, and by choosing suitable flow rate ratios (aqueous to monomer phase), respectively. The formation of polymer nanoparticles with different morphologies can be explained by a spontaneous in situ assembling under partial electrostatic repulsive control in the single step synthesis. The effect of particle charge and the competition between thermal motion of particles and electrostatic repulsion on the spontaneous assembling under the condition of a limited polarizability are discussed here as an important factor for the formation process of nonspherical polymer nanoparticles.