Monodisperse Latex Particles Research Articles

RAFT emulsion polymerization of methyl methacrylate mediated by protonated poly(2‐(dimethylamino)ethyl methacrylate) macromolecular chain transfer agent: A mechanism study

AbstractSurfactant‐free reversible addition‐fragmentation transfer (RAFT)‐mediated emulsion polymerization has been used in the synthesis of latex particles. Although this method has been developed for some time, some detailed mechanisms are not clear. Herein, RAFT emulsion polymerization of methyl methacrylate (MMA) mediated by protonated poly(2‐(dimethylamino)ethyl methacrylate) (H+‐PDMAEMA) macromolecular chain transfer agent (macro‐CTA) is studied. The effects of the molar ratios of MMA/macro‐CTA and initiator/macro‐CTA, and the macro‐CTA chain length on the emulsion polymerizations are investigated. At the nucleation stage, H+‐PDMAEMA‐CTA is chain extended with MMA dissolved in aqueous phase; and when the length of PMMA block is above a critical length, the formed amphiphilic block copolymer (BCP) chains self‐assemble into micellar particles. The nucleation time in the emulsion polymerization is strongly dependent on the chain length of H+‐PDMAEMA‐CTA, and the molar ratio of free radical initiator/macro‐CTA. The emulsion polymerization rate is in direct proportion to the molar ratio of free radical initiator/macro‐CTA. The size and the size distribution of the latex particles can be tuned through control of the macro‐CTA chain length and MMA/macro‐CTA molar ratio. Monodispersed latex particles can be synthesized under proper conditions. It is expected that well‐defined latex particles with a variety of hydrophilic polymers (or biomacromolecules) on the surfaces can be synthesized by this approach.

A single-parameter hygroscopicity model for functionalized insoluble aerosol surfaces

Abstract. The impact of molecular level surface chemistry for aerosol water-uptake and droplet growth is not well understood. In this work, spherical, nonporous, monodisperse polystyrene latex (PSL) particles treated with different surface functional groups are exploited to isolate the effects of aerosol surface chemistry for droplet activation. PSL is effectively water insoluble and changes in the particle surface may be considered a critical factor in the initial water uptake of water-insoluble material. The droplet growth of two surface modified types of PSL (PSL-NH2 and PSL-COOH) along with plain PSL was measured in a supersaturated environment with a Cloud Condensation Nuclei Counter (CCNC). Three droplet growth models – traditional Köhler (TK), Flory–Huggins Köhler (FHK) and the Frenkel–Halsey–Hill adsorption theory (FHH-AT) were compared with experimental data. The experimentally determined single hygroscopicity parameter, κ, was found within the range from 0.002 to 0.04. The traditional Köhler prediction assumes Raoult's law solute dissolution and underestimates the water-uptake ability of the PSL particles. FHK can be applied to polymeric aerosol; however, FHK assumes that the polymer is soluble and hydrophilic. Thus, the FHK model generates a negative result for hydrophobic PSL and predicts non-activation behavior that disagrees with the experimental observation. The FHH-AT model assumes that a particle is water insoluble and can be fit with two empirical parameters (AFHH and BFHH). The FHH-AT prediction agrees with the experimental data and can differentiate the water uptake behavior of the particles owing to surface modification of PSL surface. PSL-NH2 exhibits slightly higher hygroscopicity than the PSL-COOH, whereas plain PSL is the least hygroscopic among the three. This result is consistent with the polarity of surface functional groups and their affinity to water molecules. Thus, changes in AFHH and BFHH can be quantified when surface modification is isolated for the study of water-uptake. The fitted AFHH for PSL-NH2, PSL-COOH, and plain PSL is 0.23, 0.21, and 0.18 when BFHH is unity. To simplify the use of FHH-AT for use in cloud activation models, we also present and test a new single parameter framework for insoluble compounds, κFHH. κFHH is within 5 % agreement of the experimental data and can be applied to describe a single-parameter hygroscopicity for water-insoluble aerosol with surface modified properties.

Surface Wettability Drives the Crystalline Surface Assembly of Monodisperse Spheres in Evaporative Colloidal Lithography

The wettability nature of substrates has been found to profoundly influence the surface assembly of monodisperse spherical particles for colloidal suspensions that are dried by evaporation to spontaneously form either periodic or disordered packing arrangements. The self-assembly of spheres has consequences when preparing surface masks for evaporative colloidal lithography. When a droplet of an aqueous suspension of monodisperse latex particles was dried by evaporation on flat substrates that are hydrophilic, a close-packed arrangement was formed spontaneously. However, when a similar aqueous suspension was deposited and dried on relatively hydrophobic substrates such as silicon and glass, a disordered arrangement was produced, revealing that there were negligible regions of hexagonal packing. The wettability of silicon wafers can be rendered to be hydrophilic by certain surface treatments. For example, after ozone exposure, silicon surfaces became hydrophilic as evidenced by changes measured for water contact angles. For silicon surfaces that were exposed to UV/ozone, crystalline arrangements of monodisperse latex spheres were generated with relatively few defects. Such physical or chemical treatments which tailor the wettability of surfaces can be used to improve reproducibility and to lower the density of defects when preparing surface masks for emerging manufacturing processes based on colloidal lithography.

Synthesis, characterization, and dynamic‐mechanical properties of styrene‐acrylate/nanoclay interpenetrating polymer network

AbstractWaterborne styrene/acrylate latex interpenetrating polymer network (LIPN) with core‐shell structure was synthesized via a three‐stage emulsion polymerization method. A natural montmorillonite (MMt) and an organically modified montmorillonite (OMMt) were used to see their effect on the morphology and damping properties of polymer‐clay nanocomposite LIPN. The samples were characterized by dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), dynamic mechanical thermal analysis (DMTA), and X‐ray diffraction (XRD). The appearance of a single peak in the particle size distribution curve and nearly monodisperse latex particles observed in the SEM images indicated that all LIPN particles were of nanoscale size, without evidence for new nucleation occurrence. TEM images demonstrated that latex particles had clearly core‐shell structures. It also showed that most of the OMMt clay platelets were encapsulated in the polymer latex particles. According to the tan δ‐temperature curve, addition of 0.5 wt% OMMt to the core layer improved the damping properties of the LIPN, while MMt could not affect the damping curve significantly. The results indicated that the diffusion of polymer chains into the OMMt clay galleries has increased the internal friction and so improved the damping properties.

Exploring the upper particle size limit for field flow fractionation online with ICP-MS to address the challenges of water samples from the Taihu Lake

Regular algal blooms are occurring in Taihu lake, which may be triggered by resuspension of sediments containing relevant amounts of phosphorus. Therefore, our study aims at quantification of phosphorus concentrations bound to suspended particulate matter in Taihu water samples to investigate this hypothesis. A field flow fractionation (FFF) method online with ICP-MS detection was developed to achieve an overview on particulate fractions of phosphorus and related elements including Fe, Al and C from the low nanometer to the low micrometer size range. Mass balance of dissolved and particulate elemental contents was established for quality control purpose and indicated low recovery of Fe, Al and P. Complementary determination of volume based particle size distribution by dynamic imaging analysis showed a majority of particle volume and thus mass in particles with size >5 μm. In order to address this challenge, the upper particle size limit of FFF online with ICP-MS was for the first time investigated in detail using well characterised monodisperse latex particles as model for organic matter in the low micrometer size range including microalgae. The effect of pre-filtration of the sample as well as the contribution of sample introduction via three different interfaces including micromist nebuliser/spray chamber, direct injection nebulisation and APEX with heated spray chamber and solvent removal by condensation on the particulate carbon recovery was studied by ICP-MS detection. The same instrumental setup was also applied for the characterisation of particulate elemental contents in the Taihu water samples as far as possible. Significant improvement of the detected particulate fraction in Taihu water samples was achieved by increasing the membrane pore size for pre-filtration and by using the APEX for introduction of the eluate from FFF into ICP-MS.

Interlaboratory comparison of nanoparticle size measurements between NMIJ and NIST using two different types of dynamic light scattering instruments

The question of how to relate particle sizes measured using a fixed-angle dynamic light scattering (DLS) instrument with those measured using a multi-angle DLS instrument is addressed. A series of nearly monodisperse polystyrene latex (PSL) particles with nominal diameters of 100 nm, 70 nm, 50 nm, and 30 nm were measured using two different types of DLS instruments: one owned by the National Metrology Institute of Japan (NMIJ) of the multi-angle type and the other owned by the National Institute of Standards and Technology (NIST) of the fixed-angle type. The mean particle size of the PSL particles was measured using the multi-angle-type instrument at various scattering angles and at various concentrations of particle suspension. These data were used to establish the functional dependence of the measured particle size on the scattering angle and particle concentration through the least-squares fitting method. The established function was then used to predict the mean particle sizes that would have been obtained if the same scattering angle and particle concentrations as those used at NIST had been selected at NMIJ. The mean particle sizes obtained at NIST and at NMIJ agreed quite well for all four PSL particle samples after compensating for the angle and concentration differences. The result of this study clearly demonstrates that consideration for the dependence of measured particle sizes on the scattering angle and particle concentration is crucial in intra-method comparisons of mean particle sizes obtained using DLS.

Modeling of retention and re-entrainment of mono- and poly-disperse particles: Effects of hydrodynamics, particle size and interplay of different-sized particles retention

In this paper, numerical simulations of experimental data were performed with kinetic rate coefficients to characterize the retention and re-entrainment dynamics under different hydrodynamic conditions for monodisperse and polydisperse latex particles (3, 10, 16μm and the mixture). The results show that drastic increase in fluid velocity provokes hardly any remarkable decrease in retention in the presence of large energy barriers (>2000kT). Systematical increases in deposition and re-entrainment dynamic rates were observed with fluid velocity and/or particle size. Increased irreversible deposition rate indicates straining and wedging dominate deposition in this study. Excess retention of 3μm particle in the polydisperse particle suspension was observed. The origins are reckoned that deposited larger particles may hinder the re-entrainment of smaller particles near the grain-to-grain contact and can provide additional sites of attachment.

Surface-collection efficiency of Nuclepore filters for nanoparticles

ABSTRACTThe flat surface of Nuclepore filters is suitable for observing collected particles with a scanning electron microscope (SEM). However, experimental data on surface-collection efficiency are limited because surface-collection efficiencies cannot be measured directly using aerosol measuring instruments. In this study, the surface-collection efficiencies of Nuclepore filters were determined by establishing the ratio of the number of particles deposited on the surface of the filter visually counted with an SEM to the number of inflow particles counted by a condensation particle counter, using monodispersed polystyrene latex particles (30–800 nm) and silver particles (15–30 nm). Because Nuclepore filters with smaller pore sizes would be expected to produce higher minimum surface-collection efficiency and a higher pressure-drop, 0.08 and 0.2 µm Nuclepore filters were chosen as the test filters in view of both collection efficiency and pressure drop. The results showed that the minimum surface-collectio...

P-182: Functional Coatings for Display Applications by a Spray Process

Antiglare coatings were spray coated on plasma treated glass surfaces followed by low temperature curing at 150 °C for 1 hour. The anti-glare coatings with embedded mono-dispersed latex particles can reach a pencil hardness of ≥8H, and a gloss range of 40 to 90 GU. In addition, a novel anti-fingerprint coating was discussed and showed significantly reduced fingerprint visibility and improved easy-to-clean properties.

Synthesis of large-scale, monodisperse latex particles via one-step emulsion polymerization through in situ charge neutralization

Abstract Monodisperse sub −200 nm polystyrene nanoparticles were synthesized by a facile one-step emulsion polymerization technology using sodium dodecyl sulfonate (SDS) and 2, 2′- azobis (2-methylpropionamide) dihydrochloride (AIBA) as the surfactant and initiator, respectively. The in situ neutralization between negatively charged surfactant SDS and positively charged AIBA was used to control the primary particle (or swollen micelle) volume and the extent of the particle coagulation. As the oligomeric radicals with cationic AIBA chain ends were captured by anionic swollen micelles, the electrostatic stability of swollen micelles gradually reduced, further promoting the primary particle coagulation. As a result, the initial particle number decreased with the addition of AIBA. The earlier primary particle coagulation not only enlarged the particle size, but also narrowed the particle size distribution of final the latex particles.

In situ charge neutralization on governing particle coagulation nucleation and size distribution in macroemulsion polymerization

Fabricating monodispersed polymer latex particles with ∼300 nm size at high monomer concentrations by batch macroemulsion polymerization based on in situ charge neutralization mechanism.

Random Copolymer as Polymeric Surfactant in Seed Emulsion Polymerization

AbstractAn amphiphilic random copolymer was synthesized and applied as a surfactant in seed emulsion polymerization. The composition and structure of the copolymer were confirmed by Fourier transforms infrared spectroscopy (FTIR), 1H nuclear magnetic resonance spectroscopy (1H NMR), gel permeation chromatography (GPC) and differential scanning calorimetry (DSC). The effect of the copolymer content on the properties of latexes and their sizing properties was discussed. The average size, size distribution and stability of latexes were measured by quasi-elastic light scattering. The results suggest that the copolymer was a random copolymer, and displayed surface-active properties in water. The copolymer content affected strongly the properties of latex and its sizing performance. Monodisperse and nano-sized latex particles were obtained in the presence of 10.5 % copolymer. The thermal characteristics of latex films could be regulated by controlling the content of the copolymer. Adding an appropriate amount of the copolymer could reduce the surface tension of the latexes and promote their adsorption on the paper surface. Latex-treated paper showed a better water resistance and higher surface strength.

Characterization of a Three Wavelength Photoacoustic Soot Spectrometer (PASS-3) and a Photoacoustic Extinctiometer (PAX)

Laboratory experiments were conducted for characterizing the performance of two commercially available instruments employed for the measurement of light absorption and scattering coefficients of aerosols at λ = 405, 532, and 781 nm (using three-wavelength photoacoustic soot spectrometer; PASS-3) as well as at 375 nm (using photoacoustic extinctiometer; PAX) based on photoacoustic spectroscopy and reciprocal nephelometry, respectively. The calibration factors (conversion factors from the readout to real values) associated with scattering measurements, estimated using gaseous molecules, mono-disperse polystyrene latex and ammonium sulfate particles, and/or poly-disperse ammonium sulfate particles, are in good agreement with one another, typically within 5 %, 5 %, and 10 % at 375, 405, and 781 nm, respectively. In contrast, a significant particle size dependency was observed for the calibration factors at 532 nm, which is possibly because of a combination of differences in the polarization states of the lasers relative to the scattering planes and large truncation angle. Considering the estimated effective truncation angle, the typical uncertainties in calibration factors for scattering when measuring non- or weakly light-absorbing particles, with volume-based geometrical diameters of less than 700 nm, were estimated to be 12 %, 7 %, 34 %, and 17 %, at 375, 405, 532, and 781 nm, respectively. The typical uncertainties in the calibration factors for absorption measurements, which were determined using poly-disperse propane soot particles, were estimated to be 6 %, 4 %, 8 %, and 11 %, at 375, 405, 532, and 781 nm, respectively. The calibration factors for absorption determined by the poly-disperse soot particles at 375 and 405 nm were 48 % and 36 % smaller than those by light absorption of NO2 molecules possibly because of NO2 photolysis, although good agreement was observed at 532 nm. These results suggest that the photolysis effect should be taken into account when light absorption by NO2 is used for calibration at 375 and 405 nm.

Hydrophobe-free miniemulsion polymerization: towards high solid content of fatty acid-based poly(urethane-urea) latexes

High solid content of aqueous fatty acid-based PU latexes.

Synthesis of Latex Particles with Surface Functional Groups and Their Applications for the Fabrication of Porous Materials

In this study, monodisperse latex particles with specific surface functional groups were synthesized by emulsifier-free emulsion polymerization. Amidine or carboxylated polystyrene nanospheres with narrow size distribution were prepared by emulsion polymerization using AIBA (α,α′-zodiisobutyramidine dihydrochloride) as amine-containing initiator or acrylic acid as carboxyl-containing comonomer, respectively. Factors affecting the particle size and distribution were systemically studied by changing the amount of initiator or monomer, the polymerization temperature, and the stirring speed of emulsion polymerization reactor. Monodisperse polymethylmethacrylate beads were also synthesized by soapless emulsion polymerization using methacrylic acid or aminoethylmethacrylate hydrogen hydrochloride as comonomer for the surface functionalization of the particles. As applications of the latex beads, the polymeric particles were adopted as templating materials for the fabrication of macroporous titania film and meso-macroporous silica particles by colloidal templating method.

A Novel Route to Prepare Cationic Polystyrene Latex Particles with Monodispersity

Relatively clean cation-charged polystyrene (PS) latex particles were prepared via a novel and simple route in the absence of steric stabilizers. The reaction system only included medium, styrene, and initiator with quaternary ammonium moiety. The influences of initiator concentration, and medium composition on the diameter and size distribution of PS latex particles were systematically investigated. The particle morphology and size, the surface N content, and the particle size distribution were respectively determined by SEM, XPS, and laser particle size analyzer. The results indicated that monodisperse and cation-charged PS latex particles with diameter of 0.45–0.95 μm could be successfully produced via the simple reaction system, and cationic initiator concentration played a key role in the preparation of uniform PS latex particles. Finally, a plausible mechanism was proposed for explaining nucleation, growth, and stabilization of PS latex particles.

Preparation of amphiphilic glycopolymers with flexible long side chain and their use as stabilizer for emulsion polymerization

A glycomonomer was synthesized from poly(ethylene glycol) methacrylate (PEGMA). The terminal hydroxyl moieties were activated with ester groups and subsequently the glucosamine was incorporated forming urethane linkages. The obtained glycomonomer was copolymerized with methyl acrylate by free radical polymerization varying the initial feed composition to produce different amphiphilic glycopolymers. The glycopolymers were then characterized and compared with the homologous glycopolymers based on 2-{[(d-glucosamin-2-N-yl)carbonyl]oxy}ethyl methacrylate. Both series of glycopolymers were used in emulsion polymerization of methyl acrylate as stabilizers without the addition of any cosurfactant. Although high conversions were not achieved with any of the employed surfactant, the glycopolymers provide good colloidal stability, spherical, monodisperse and small latex particles in comparison with the surfactant-free emulsion polymerization. The latex particles stabilized with the glycosurfactant based on PEGMA, containing a flexible spacer between the backbone and the glucosamine, lead to smooth films whereas the short side chain surfactant from 2-hydroxyethyl methacrylate (HEMA), with higher glass transition temperature, restricts the coalescence of particles and, therefore, the film formation. Moreover, the surface bioactivity of these polymer coatings was examined by analyzing their specific interaction with the lectin, Concanavalin A, Canavalia ensiformis. The specific and successful binding to the Concanavalin A was demonstrated by fluorescence microscopy for both series being more intense with increasing amount of glycounits in the glycopolymer stabilizers. Interestingly, the incorporation of a flexible spacer in the glycopolymer structures enhances the binding activity.

Optimisation and standardisation of an immunoagglutination assay for the diagnosis of Trypanosoma cruzi infection based on latex‐(recombinant antigen) complexes

To determine the conditions under which the immunoagglutination assay to detect Chagas disease, obtained from a novel latex-(chimeric recombinant antigen) complex, shows greater discrimination between the responses of a positive control serum and a negative control serum. The following variables were determined: (i) the sensitisation mechanism, (ii) the emulsifier employed for protein desorption, (iii) the reaction time, (iv) the ionic strength of the reaction medium, (v) the particle concentration, (vi) the presence of blocking agents, (vii) the presence of polyethyleneglycol as potentiator of reaction and (viii) the antigen and antibody concentrations. The search of optimal conditions was investigated by varying one variable at a time. To this effect, monodisperse latex particles sensitised with a recombinant chimeric protein (CP1) were subjected to different conditions. The agglutination reaction was followed by measuring the changes in the optical absorbance by turbidimetry. The maximum discrimination between negative and positive sera was obtained at a reaction time of 5 min, when latex complexes with a concentration of covalently coupled protein of 2.90 mg/m(2) were put in contact with undiluted sera in buffer borate pH 8-20 mm containing glycine (0.1 m) and polyethyleneglycol 8000 (3% w/v). Finally, the latex-protein complex was tested under the obtained optimal conditions, with a panel of Trypanosoma cruzi-positive sera, leishmaniasis-positive sera and -negative sera for both parasites. The immunoagglutination test based on the latex-CP1 complex could be used as a screening method for detecting Chagas disease. This test is rapid, easy to implement and could be used under field conditions; but its results should be confirmed by reference techniques like ELISA, HAI, and IFI.

Novel Synthesis of Multi-Scaled, Surfactant-Free Monodisperse Latexes via Alcoholic Dispersion Polymerization in a Mixed Ionic/Nonionic Initiation System

We propose a new strategy for preparing high solid content, surfactant-free charge stabilized monodisperse latex particles via alcoholic dispersion polymerization by means of a mixed inoic/nonionic initiator system, which produces hundreds of nanometer up to several micrometer sized latex particles with a clean surface in a single batch process. Two criteria should be met to produce these electrostatically stabilized uniform size latexes: (1) The ionic initiator chosen should have a greater or comparable decomposition rate to the nonionic initiator. (2) A relatively small amount of ionic initiator to the nonionic initiator should be employed in the polymerization. The electrostatic stabilization is solely provided by the ionic fragments arising form the ionic initiator in the absence of any stabilizer, and the addition of nonionic initiator has increased the latex uniformity through the enhancement of particle seeds formation at the nucleation stage also the perferred particle phase polymerization after n...

Design and performance of a new device for the study of thermophoresis: The radial flow thermophoretic analyser

A new device to study the thermophoresis of particles is presented in this paper. The instrument, called a radial flow thermophoretic analyser, is based on the geometry of the radial flow differential mobility analyser RF-DMA or SMEC (Spectromètre de Mobilité Electrique Circulaire). The device uses two circular plates, each with hot and cold temperature imposed. The instrument was designed with computational fluid dynamic software in order to check uniformity of the temperature field in the selection area after an establishment length. The transfer function of the instrument is then established and determines the effective thermophoretic velocity of particles selected in the temperature field imposed in the apparatus. For the experimental validation, effective thermophoretic velocities of monodispersed spherical latex particles for diameters ranging from 64nm to 500nm and a temperature gradient equal to 50,750K/m are measured and compared with theoretical values. The results show good repeatability and discrepancies with theoretical values less than 7%.