Micron-sized Polymer Particles Research Articles

Capturing Acidic CO2 Using Surface-Active Difunctional Core-Shell Composite Polymer Particles via an Aqueous Medium.

Multifunctional surface-active polymeric composites are attractive materials for the adsorption of various small molecules. Herein, dual-functionalized micron-sized surface-active composite polymer particles were prepared by a three-step process for CO2 adsorption. First, polystyrene (PS) seed particles were prepared via the dispersion polymerization of styrene. PS/P(MMA-AAm-EGDMA) composite polymer particles were then synthesized by aqueous seeded copolymerization of methyl methacrylate (MMA) and acrylamide (AAm) in the presence of an ethylene glycol dimethacrylate (EGDMA) cross-linker. Finally, the amide moieties of PS/P(MMA-AAm-EGDMA) composite particles were converted into an amine-functionalized composite by using the Hofmann degradation reaction. The presence of primary amine groups on the surface of aminated composite particles was confirmed by some conventional chemical routes, such as diazotization and Schiff's base formation reactions. The formation and functionality of the PS seed, PS/P(MMA-AAm-EGDMA), and aminated PS/P(MMA-AAm-EGDMA) composite polymer particles were confirmed by Fourier transform infrared (FTIR) spectra analyses. Scanning electron microscopy (SEM) analysis revealed spherical shape, size, and surface morphologies of the PS seed, reference composite, and aminated composites. The elemental surface compositions, surface porosity, pore volume, pore diameter, and surface area of both composite particles were evaluated by energy-dispersive X-ray (EDX) mapping, X-ray photoelectron spectroscopy, and Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) analyses. Dynamic light scattering (DLS) and ζ-potential measurements confirmed the pH-dependent surface properties of the functionalized particles. The amount of the adsorbed anionic emulsifier, sodium dodecyl sulfate (SDS), on the surface of aminated PS/P(MMA-AAm-EGDMA) is higher at pH 4 than that at pH 10. A vice versa result was found in the case of cationic surfactant, hexadecyltrimethylammonium bromide (HTABr), adsorption. Synthesized aminated composite particles were used as an adsorbent for CO2 adsorption via bubbling CO2 in an aqueous medium. The changes in dispersion pH were monitored continuously during the adsorption of CO2 under various conditions. The amount of CO2 adsorption by aminated composite particles was found to be 209 mg/g, which is almost double that of reference composite particles.

Scalable synthesis of methacrylate-based vitrimer powders by suspension polymerization

We describe how methacrylate-based vitrimer powders can be synthesized through a scalable suspension polymerization technique, leading to micron-sized polymer particles with controllable rheological properties.

Fabrication of solid and hollow colloidosomes through self-assembly of micronsized polymer particles and their controlled transition

Colloidal particles self-organize themselves, leading to their highly ordered arrays of superstructure, which are of high interests to understand the fundamental physics of complex colloids and of great potential in catalysts, filters, and optical or photovoltaic materials. Herein highly uniform polystyrene based polymer particles, P(St-TPTA), of 1 μm are first prepared through precipitation polymerization of styrene (St) and trihydroxymethyl propane triacrylate (TPTA) in ethanol. Colloidosomes were prepared by a simple self-assembly of these P(St-TPTA) primary particles in water-ethanol (H2O–EtOH) binary solvent, with a third solvent (ethyl benzene, EB) as organic template. By varying the shaking frequency, assembly time, temperature, EB amount and TPTA amount in P(St-TPTA), spherical and solid colloidosomes of about 15 μm diameter were obtained at H2O/EtOH volume ratio around 30/70. By increasing this ratio to about 80/20, hollow colloidosomes of about the same size were achieved. The formations of these colloidosomes and the transition from one to another form were well interpreted based on the adsorption energy of the primary particles on the interface of EB and H2O–EtOH. This study provides an easy protocol, featured by absence of any additives in the entire process, for fabrication of hollow and solid colloidosomes with clear mechanism.

Shredding of polyethylene terephthalate waste

Methods of recycling polyethylene terephthalate waste are analyzed. Thermoplastic waste has great potential for mechanical recycling. Lack of information on the quality of recycled products and their applicability for specific purposes hinders their use. Shredding is a main process in mechanical recycling. Due to the viscoelastic properties, the cost of grinding polymer waste is several times higher than for most brittle mineral materials. Cutting and impact equipment is often used to shred plastic waste. To obtain micron-sized polymer particles, the technologies of cryogenic grinding and wet grinding in solvents are used, which is followed by high operating costs. The purpose of this work was to develop an economical method for producing fine powders from polyethylene terephthalate waste. The specific surface of the powders has been investigated. To investigate the destruction, differential thermal analysis and infrared spectroscopy were used. The technology of secondary mechanical recycling is proposed: crushing, melting of waste, natural or water cooling of the melt, grinding on equipment typical for brittle materials. A dispersed product with a proportion of micronized fraction of about 50% was obtained for use as filler in composites. The resulting product is more degraded in comparison with the feedstock. Therefore, its use as binders is advisable in applications where a decrease in initial properties is permissible, in products with a long lifecycle, for example, in the production of building materials. The use of waste thermoplastic in applications other than the original one does not always reduce the value of the technology.

Thermal rounding of micron-sized polymer particles in a downer reactor: direct vs indirect heating

Purpose The purpose of this paper is to investigate the effect of different heating approaches during thermal rounding of polymer powders on powder bulk properties such as particle size, shape and flowability, as well as on the yield of process. Design/methodology/approach This study focuses on the rounding of commercial high-density polyethylene polymer particles in two different downer reactor designs using heated walls (indirect heating) and preheated carrier gas (direct heating). Powder bulk properties of the product obtained from both designs are characterized and compared. Findings Particle rounding with direct heating leads to a considerable increase in process yield and a reduction in powder agglomeration compared to the design with indirect heating. This subsequently leads to higher powder flowability. In terms of shape, indirect heating yields not only particles with higher sphericity but also entails substantial agglomeration of the rounded particles. Originality/value Shape modification via thermal rounding is the decisive step for the success of a top-down process chain for selective laser sintering powders with excellent flowability, starting with polymer particles from comminution. This report provides new information on the influence of the heating mode (direct/indirect) on the performance of the rounding process and particle properties.

Flow synthesis of monodisperse micron-sized polymer particles by heterogeneous polymerization using a water-in-oil slug flow with a non-ionic surfactant

Flow synthesis of poly(methyl methacrylate) particles was performed by heterogeneous polymerization of methyl methacrylate using a water-in-oil (W/O) slug flow with or without a non-ionic surfactant in the continuous organic phase. It was found that undesired phenomena in this polymerization system, clogging of the channel and broadening particle size distribution, can occur when growing polymer particles adsorb to the W/O interface during polymerization, and that the addition of non-ionic surfactant to the continuous organic phase prevents the particles from adsorption to the W/O interface and gives monodisperse polymer particles. In addition, it was shown that as the initiator concentration increases, the particle diameter becomes larger, resulting in monodisperse micron-sized polymer particles with 100% monomer conversion at a 120-min reaction time. These results indicated that the heterogeneous polymerization process using a W/O slug flow can be a promising way to continuously prepare monodisperse polymer particles with micron sizes in a short reaction time.

Interfacial Instability of Emulsion Droplets Containing a Polymer and a Fatty Alcohol.

We investigated the interfacial instability of emulsion droplets via in situ measuring the oil/water interfacial tension (IFT) using the capillary suction method. The discrete phase of the oil-in-water emulsion contains a hydrophobic polymer (polystyrene, PS) and a fatty alcohol cosurfactant n-cetyl alcohol (CA) or n-octadecanol (OD), both of which were dissolved in an organic solvent (chloroform). The continuous phase is an aqueous solution of surfactant (sodium dodecyl sulfate, SDS). Upon removal of the organic solvent, the concentrations of CA and PS increase gradually, which induce a continual decrease of the IFT until the occurrence of interfacial instability. Micropipette tensiometry performed on an evaporating emulsion droplet reveals that interfacial instability is triggered when the IFT decreases close to ∼0.17 mN/m. As a result, micron particles with wrinkled surfaces can be obtained after the complete removal of the organic solvent. The effect of the initial concentration and alkyl chain length of the cosurfactant on the interfacial instability and surface roughness of the formed particles was studied. This study provides theoretical guidance for the preparation of micrometer-sized polymer particles with diverse morphologies via the interfacial instability of emulsion droplets.

Contact area measurement of micron-sized metal-coated polymer particles under compression

The contact problem of a sphere under compression by a rigid plate is pertinent to understanding electrical contact formation in anisotropic conductive adhesive (ACA) applications. However, no work has experimentally verified existing contact models for the metal-coated sphere-plate contact problem. Herein, compression tests on metal-coated polymer spheres were performed by flat punch nanoindentation with in-situ scanning electron microscopy (SEM) monitoring, and the resultant contact area was measured using SEM images. The obtained results were compared to Tatara and Abbott-Firestone models, along with finite element analysis (FEA). The measured contact area falls between Tatara and Abbott–Firestone models, indicating a mixture of elastic and plastic deformation. The contact area as a function of force is dominated by the polymer core and independent of the metal coating for the thin metal coatings tested. The work provides guidelines for bonding parameters for ACA assembly.

Pickering emulsion-templated polymers: insights into the relationship between surfactant and interconnecting pores.

Pickering high internal phase emulsions (HIPEs) using micron-size polymeric particles as stabilizer were developed. By adding a small amount of surfactant to the Pickering HIPEs, macroporous polymers with a well-define open-cell structure were synthesized with these HIPEs as templates. Owing to the micron-size of the particles, the particle locations could be observed directly by laser scanning confocal microscopy. It was found that the excess and attached particles aggregated and formed thick particle layers around the droplets when the HIPE was stabilized solely by particles. These thick particle layers were extremely stable, and did not easily rupture during or after polymerization, which caused the resulting polymers to have a closed-cell structure. When a small amount of surfactant was added, it was found that the surfactant disaggregated the particles, leaving them well-dispersed in the continuous phase. Moreover, the surfactant tended to occupy the oil–water interface at the contact point of adjacent droplets, where the interconnecting pores were hence likely to be formed after consolidation of the continuous phase. This observation confirmed experimentally the mechanism of interconnecting pore formation in Pickering-HIPE-templated porous polymers proposed theoretically in previous works.

Resistance Analysis of Spherical Metal Thin Films Combining Van Der Pauw and Electromechanical Nanoindentation Methods

Although micron-sized metal-coated polymer particles are an important conductive filler material in anisotropic conductive adhesives, the resistance of the particles in an adhesive is not well understood. In this study, a van der Pauw method for spherical thin films is developed and applied to determine the resistivity of 30 μm silver-coated poly(methyl methacrylate) (PMMA) particles. The resistivity is used to interpret resistance contributions in single particle electromechanical nanoindentation measurements, which simulate the compression particles undergo in application. The resistivity was found to be coating thickness dependent for thin films in the range 60–270 nm. Estimation of the resistance of the metal shell using the measured resistivity did not account for the total resistance measured in electromechanical nanoindentation. We therefore deduce a significant contribution of contact resistance at the interfaces of the particle. The contact resistance is both coating thickness and particle deformation dependent.

Cu(0)-mediated reversible-deactivation radical polymerization of n-butyl acrylate in suspension

Cu(0)-mediated reversible-deactivation radical polymerization of n-butyl acrylate was performed in suspension without the use of an organic solvent. In all cases, a 5 v% organic phase (monomer, initiator, and ligand) was used with respect to 95 v% aqueous phase. Polyvinyl alcohol (PVA) as a suspension stabilizer has been shown to be able to control the polymerization for the degree of polymerizations of 222 and higher. The polymerization reaction showed linear first-order kinetics for a PVA concentration range of 1–10 wt%, leading to polymers with dispersities from 1.22 to 1.43. Conversions as high as 96% were obtained in 55 min. Scanning electron microscopy analysis of the suspensions confirmed the formation of micron-sized polymer particles dispersed in aqueous media, and that the size of the particles decreased with increasing PVA concentration. Rheometry measurements of the aqueous phase containing PVA before and after polymerization demonstrated the increase in the viscosity of the reaction mixture after polymerization. The difference between the viscosity of the PVA solution in water and the same solution after polymerization decreased as the PVA decreased, which indicates smaller particle sizes formed with increasing PVA content. All suspensions were stable over a period of three months storage at room temperature without any precipitation or sedimentation. The maximum copper species concentration in the reaction medium and water can be as low as 7 ppm. This Cu(0)-mediated reversible-deactivation radical polymerization in suspension has the potential for industrial use, especially for paint and adhesives.

Viscoelastic Behavior of Polymer-Modified Cement Pastes: Insight from Downscaling Short-Term Macroscopic Creep Tests by Means of Multiscale Modeling

Adding polymers to cementitious materials improves their workability and impermeability, but also increases their creep activity. In the present paper, the creep behavior of polymer-modified cement pastes is analyzed based on macroscopic creep tests and a multiscale model. The continuum micromechanics model allows for “downscaling” the results of macroscopic hourly-repeated ultra-short creep experiments to the viscoelastic behavior of micron-sized hydration products and polymer particles. This way, the increased creep activity of polymer-modified cement pastes is traced back to an isochoric power-law-type creep behavior of the polymers. The shear creep modulus of the polymers is found (i) to be two orders of magnitude smaller than that of the hydrates and (ii) to increase considerably with increasing material age. The latter result suggests that the creep activity of the polymers decreases with the self-desiccation-related decrease of the relative humidity inside the air-filled pores of cement paste. Furthermore, its decrease is most likely related to the penetration of cementitious hydrates into compliant polymer agglomerates.

Catalytic Oxidation of Thiols within Cavities of Phthalocyanine Network Polymers

Two three-dimensional (3D) network polymers (1 and 2), in which zinc(II) or cobalt(II) phthalocyanines were interconnected with twisted 9,9′-spirobifluorene linkers, were synthesized in order to investigate their performance as heterogeneous catalysts for thiol oxidations. From the spectroscopic analyses of two dimers (3 and 4) as component units of the network polymers, 3 connected with a short linker revealed electronic interaction between the two phthalocyanine units. Micrometer-sized polymer particles were formed due to the condensation of the twisted 9,9′-spirobifluorene linkers in the presence of zinc or cobalt ions. The dispersed solutions of 1 and 2 had sharp Q-bands, indicating the prevention of stacking among phthalocyanine moieties within the polymers. Powdered X-ray diffraction pattern and N2 adsorption–desorption analyses suggested that 1 created small and rigid cavities as compared with 2 through the regular spatially arrangement of the phthalocyanine moieties in the 3D networks. The photoca...

On determining the Poisson's ratio of viscoelastic polymer microparticles using a flat punch test

Microscopic spherical polymer particles are increasingly used in a wide range of areas, including pharmacy, physics and microelectronics. For most of the applications a precise knowledge of the mechanical properties is crucial. Nanomechanical indentation, often using flat-punch geometry, allows determining the deformation and fracture properties of individual particles. Measurements of the lateral expansion as function of axial compression in the flat-punch test can under certain conditions be used to extract the Poisson's ratio of the particle material. Here, we demonstrate that the models based on linear elasticity break down even at moderate strain values in micron-sized polymer (resorcinol-formaldehyde) particles in flat-punch tests monitored with optical microscopy. Finite element analysis was used to solve the standard linear solid model of viscoelasticity, giving excellent agreement with the experimental data and pin-pointing the short-comings of linear elastic models. We finally present a parameterized equation for the sphere deformation, relating the long-term Poisson's ratio ν to the Young's modulus E and the dimensionless viscoelastic Prony parameters g1 and τ1.

Electrical four-point probing of spherical metallic thin films coated onto micron sized polymer particles

Micron-sized metal-coated polymer spheres are frequently used as filler particles in conductive composites for electronic interconnects. However, the intrinsic electrical resistivity of the spherical thin films has not been attainable due to deficiency in methods that eliminate the effect of contact resistance. In this work, a four-point probing method using vacuum compatible piezo-actuated micro robots was developed to directly investigate the electric properties of individual silver-coated spheres under real-time observation in a scanning electron microscope. Poly(methyl methacrylate) spheres with a diameter of 30 μm and four different film thicknesses (270 nm, 150 nm, 100 nm, and 60 nm) were investigated. By multiplying the experimental results with geometrical correction factors obtained using finite element models, the resistivities of the thin films were estimated for the four thicknesses. These were higher than the resistivity of bulk silver.

Electromechanical characterization of individual micron-sized metal coated polymer particles

Micron-sized polymer particles with nanoscale metal coatings are essential in conductive adhesives for electronics assembly. The particles function in a compressed state in the adhesives. The link between mechanical properties and electrical conductivity is thus of the utmost importance in the formation of good electrical contact. A custom flat punch set-up based on nanoindentation has been developed to simultaneously deform and electrically probe individual particles. The set-up has a sufficiently low internal resistance to allow the measurement of sub-Ohm contact resistances. Additionally, the set-up can capture mechanical failure of the particles. Combining this data yields a fundamental understanding of contact behavior. We demonstrate that this method can clearly distinguish between particles of different sizes, with different thicknesses of metal coating, and different metallization schemes. The technique provides good repeatability and physical insight into the behavior of these particles that can guide adhesive design and the optimization of bonding processes.

Size effect in microcompression of polystyrene micropillars

Abstract Experiments by He et al. [J.Y. He, Z.L. Zhang, M. Midttun, G. Fonnum, G.I. Modahl, H. Kristiansen, and K. Redford. Size effect on mechanical properties of micron-sized PS-DVB polymer particles. Polymer 2008, 49(18), 3993] have indicated that polymers exhibit enhancement of strength at length scales of the order of microns. This is surprising since size effects, widely reported for FCC metals, owe their origin to the presence of crystalline defects, particularly dislocations. On the other hand, polymers being a material of choice in microfabrication, these results assume technological importance. In this work, we conduct controlled experiments on polystyrene (PS) micropillars to ascertain whether they exhibit size effects. The pillars are microfabricated and hence free of beam damage. The experimental load displacement curves obtained from microcompression experiments are matched with computer simulations on similar samples using a well-calibrated constitutive model. Our results demonstrate significant intrinsic size effect on the yield strength, though effects of size on rehardening response turned out to be an experimental artifact.

Aqueous Foams Stabilized with Several Tens of Micrometer-sized Polymer Particles: Effects of Surface Hydrophilic–Hydrophobic Balance on Foamability and Foam Stability

40 micrometer-sized polystyrene particles coated by polymer shells with various hydrophilic–hydrophobic balances were synthesized by seeded dispersion polymerization and used as a foam stabilizer. ...

Microencapsulation of Ascorbic Acid for Cosmetic by Utilizing Self-assembly of Phase Separated Polymer.

Micrometer-sized polymer particles encapsulated ascorbic acid (vitamin C; VC) were successfully prepared by the three types of the self-assembling method, those are, phase separation and self-assembly of added polymer at the oil-water interface in emulsion, microsuspension polymerization utilizing the self-assembling of phase separated polymer (SaPSeP) method, and their hybrid method. In the stability study at 50°C for 2 months, the three kinds of capsule particles exhibited effective protection of VC from the interaction with other components in cosmetic consisting of water-in-oil (W/O) emulsion. The encapsulated VC was easily released from the capsule particles by an excess of water. These encapsulation methods will be useful for the stabilization of water-soluble substances in cosmetic consisting of W/O emulsion.

Spontaneous formation and spin of particle pairs in a single-layer complex plasma crystal

In an experiment with a single-layer plasma crystal, spontaneous pairing of particles was observed upon a sudden reduction of the discharge power. The pairs were oriented vertically with the upper particle above the crystal layer and the lower particle beneath it, the pair size was about 0.2 mm. The pairs were spinning around their vertical axis with the upper particle leading and the lower one following it; the rotation speed was 10–13 Hz. Spinning particle pairs disturbed the plasma crystal through interaction with their neighbors. Upon further reduction of the discharge power, the spinning pairs proliferated in the plasma crystal and eventually it melted. The experiment was performed with micron-size polymer particles suspended in the radio-frequency (rf) argon plasma at a pressure of 157 mtorr. We propose a theoretical model of a spinning particle pair based on the plasma wake effect. Spinning particle pairs can be used as a diagnostic tool for plasma wakes or as a generic model of a 2D system of vortices.