Core Latex Research Articles

Surface characterization of nanoparticles carrying pH-responsive polymer hair

The surface of near-monodisperse colloidal polystyrene (PS) latex particles carrying pH-responsive poly[2-(diethylamino)ethyl methacrylate] (PDEA) polymer chains as a steric stabilizer has been extensively characterized in dry and wet states. X-ray photoelectron spectroscopy and contact angle measurement studies confirm that PDEA chains are located on the PS latex particle surface. Transmission electron microscopy (TEM) studies reveal that the sterically stabilized PS particles have a core-shell morphology and wet atomic force microscopy data confirm that the pH-responsive PDEA component covers the PS latex core and the thickness of the protonated steric polymer is estimated to be approximately 15 nm. The PS latex particles can be easily dispersed in acidic aqueous media (pH 3.0) whilst they flocculate in basic aqueous media (pH 10.0) due to the pH-responsive PDEA hair. This dispersion–flocculation cycle of the PS latex is fully reversible.

Synthesis of Spherical Polyelectrolyte Brushes by Thermo‐controlled Emulsion Polymerization

A novel method of thermo-controlled emulsion polymerization has been employed to synthesize spherical polyelectrolyte brushes that consist of a solid polystyrene core and a poly (acrylic acid) (PAA) shell covalently attached on the core surface densely by one end. The growth of brushes from the core surface was monitored by dynamic light scattering (DLS). The particle size of PS core latex showed a narrow size distribution when observed by scanning electron microscopy (SEM). The brush size changed significantly upon changing pH value and ionic strength, and displayed similar behavior to brushes prepared by photo-emulsion polymerization. The grafting density of the PAA brush, which was determined by cutting off the PAA chains using alkali hydrolysis, confirmed the formation of PAA brushes.

Hybrid additives for construction applications, fabricated through layer-by-layer adsorption of polycondensate type superplasticizers on latex templates

Novel hybrid admixtures for construction applications were prepared by layer-by-layer deposition technique. Colloidal core templates consisting of styrene/acrylate latex particles were coated with multilayers of polycondensate-based dispersants commonly used in concrete. This way, core–shell particles possessing both dispersing and film-forming properties were achieved. Incorporation of the latex@dispersant hybrid additive into a cement paste results in a slow release of the dispersant which instigates prolonged plastification of the cement slurry. Following disintegration of the shell, the latex core particles are released into the pore solution and coalesce into a polymer film which improves the mechanical properties of the hardened cement. Characterization of the templates and novel additives plus tracking of the layer-by-layer polyelectrolyte adsorption was performed by means of zeta potential measurement, dynamic light scattering and electron microscopy. Our method allows to synthesize multifunctional additives with time-controlled release effect.

Synthesis of Crosslinkable Core-Shell Emulsion and Rheology of the Core-Shell/Amine Crosslinking Process

Starve feed and semi-continuous seed emulsion polymerization were used to control the morphology of core shell latex particles with a vinyl acetate (VAc)/vinyl ester of versatic acid 10(VeoVa10) copolymer core surrounded by a poly(glycidyl methacrylate) (PGMA) shell. Pure core and core-shell structures were confirmed by TEM. The results suggest that core-shell morphology of the two stage emulsion was favoured by higher concentration of emulsifier in the seed latex: the particle size distribution of core-shell latex was broader than that of the core latex, and the average particle size of core-shell latex was larger than that of the core latex. The core-shell structure was not produced using seed emulsion with emulsifier concentration at or below the critical micelle concentration. The core shell emulsion containing epoxy functional group with added ethylene diamine showed an abrupt increase in dynamic shear moduli, G' and G'' and complex viscosity η* (several orders of magnitude) at about 35oC, during temperature ramps, over a wide range of angular frequencies. The time ramps showed that the crosslinking reaction did not occur at 15oC for the core-shell emulsion/amine system. The time for gel formation decreased with increase in temperature.

Preparation of raspberry-like polymer/silica nanocomposite microspheres via emulsifier-free polymerization in water/acetone media

Raspberry-like polymer/silica nanocomposite microspheres were prepared by emulsifier-free copolymerization of styrene (St) with butyl acrylate (BA) in the presence of 20 nm silica nanoparticles in water/acetone media. A cationic monomer, 2-(methacryloyl)ethyltrimethylammonium chloride (MTC), was used as comonomer and nanosilica particles were adsorbed onto the growing latex core via the electrostatic interaction between negatively charged silica particles and positively charged polymer particles. The average particle sizes and the final silica contents of the nanocomposite microspheres ranged from 200 to 500 nm and 20 to 40 wt%, respectively, depending on the reaction conditions. The solid content of the obtained dispersions could be adjusted between 10 and 25 wt%. The influence of some synthetic parameters, for instance, the ratio of acetone/water, initial silica amount, the mass ratio of the St/BA, MTC, and the APS concentration on the polymerization stability, the average particle size, silica content, and morphology of the composite microspheres, were studied here in detail. It was found that the addition of acetone to the continuous phase resulted in smaller particle sizes and for the lower dielectric medium electrostatic repulsion becomes larger; hence coagulative nucleation is reduced compared to that in aqueous media.

Packing Efficiency of Small Silica Particles on Large Latex Particles: A Facile Route to Colloidal Nanocomposites

The adsorption of small silica particles onto large sterically stabilized poly(2-vinylpyridine) [P2VP] latex particles in aqueous solution is assessed as a potential route to nanocomposite particles with a "core-shell" morphology. Geometric considerations allow the packing efficiency, P, to be related to the number of adsorbed silica particles per latex particle, N. Making no assumptions about the packing structure, this approach leads to a theoretical estimate for P of 86 +/- 4%. Experimentally, dynamic light scattering is used to obtain a plot of hydrodynamic diameter against N, which indicates the conditions required for monolayer coverage of the latex by the silica particles. Transmission electron microscopy confirmed that, at approximately monolayer coverage, calcination of these nanocomposite particles led to the formation of well-defined hollow silica shells. This is interpreted as strong evidence for a contiguous monolayer of silica particles surrounding the latex cores. On this basis, an experimental value for P of 69 +/- 4% was estimated for nanocomposite particles prepared by the heteroflocculation of a 20 nm silica sol with near-monodisperse P2VP latexes of either 463 or 616 nm diameter at approximately pH 10. X-ray photoelectron spectroscopy was used to quantify the extent of latex surface coverage by the silica particles. This technique gave good agreement with the silica packing efficiencies estimated from calcination studies.

Synthesis of PVAc/SiO 2 latices stabilized by silica nanoparticles

This paper presents a method for the preparation of raspberry-like organic–inorganic composite spheres with poly(vinyl acetate) (PVAc) as core and nanosilica particles as shell. A small amount of anionic reactive surfactant, 3-allyloxy-2-hydroxy-1-propanesulfonic acid sodium salt (HAPS), was used as co-stabilizer and nanosilica particles were adsorbed onto the growing latex core in aqueous medium via the formation of hydrogen bonds between nanosilica particles and PVAc particles. TEM indicated that the hydrogen bonds between nanosilica particles and PVAc were strong enough for the formation of long-stable composite spheres with raspberry-like morphology. Influences of some synthetic parameters, for instance, type of silica sol, initial silica amount, and different kinds of low-molecular-weight surfactant, on the morphology of the composite spheres and properties of the latex films were studied in detail. A possible formation mechanism of the composite spheres was also proposed.

Deposition of core latex particles encapsulated in polyelectrolyte shells at modified mica surfaces

We used an oblique impinging jet (OIJ) cell to determine the initial deposition rates of model microcapsules at bare and modified by multilayer polyelectrolyte (PE) film mica surfaces. The transport conditions in the cell were quantitatively established by studying the kinetics of deposition of negatively charged latex at mica surfaces converted to positively charged by adsorption of (3-aminoprolyl)triethoxysilane. The dependence of reduced particle flux on the Reynolds number of the flow in the OIJ cell was determined by a direct counting of particles deposited on the mica surface. The results are described in terms of convective-diffusion theory taking into account hydrodynamic, dispersive, and electrostatic interactions, between the charged particles/capsules and the mica plate. In this way, transport conditions in the cell were characterized and they were used to interpret the results concerning the deposition of microcapsules with PE shells of various thickness obtained by layer-by-layer polyelectrolyte adsorption on colloidal cores. We demonstrated that the initial deposition rate of capsules is governed by the charge of the solid/liquid interface and the outermost layer of the capsule shell, and is largely independent of the thickness of the capsule shell or the number of PE layers at the mica surface. The deposition rates were in good agreement with theoretical predictions derived from the convective-diffusion theory.

Preparation and Electrochemical Characterization of Ferrocenyl-coated Polystyrene Monodispersed Latex Particle

Abstract The mono dispersed redox-active latex particle with 0.90 μm in diameter was prepared by immobilizing ferrocenylmethanol acrylate on a surface of a polystyrene latex core through the emulsion copolymerization reaction. The aqueous suspensions exhibited stable voltammetric waves at 0.271/0.207 V vs Ag|AgCl. The anodic and the cathodic peak currents were diffusion-controlled, as if it were huge redox molecules with 3.8 × 107 electrons.

Dual Latex/Surfactant Templating of Hollow Spherical Silica Particles with Ordered Mesoporous Shells

Hollow spherical silica particles with hexagonally ordered mesoporous shells are synthesized with the dual use of cetyltrimethylammonium bromide (CTAB) and unmodified polystyrene latex microspheres as templates in concentrated aqueous ammonia. In most of the hollow mesoporous particles, cylindrical pores run parallel to the hollow core due to interactions of CTAB/silica aggregates with the latices. Effects on the product structure of the CTAB:latex ratio, the amount of aqueous ammonia, and the latex size are studied. Hollow particles with hexagonally patterned mesoporous shells are obtained at moderate CTAB:latex ratios. Too little CTAB causes silica shell growth without surfactant templating, and too much induces nucleation of new mesoporous silica particles without latex cores. The concentration of ammonia must be large to induce co-assembly of CTAB, silica, and latex into dispersed particles. The results are consistent with the formation of particles by addition of CTAB/silica aggregates to the surface of latex microspheres. When the size and number density of the latex microspheres are changed, the size of the hollow core and the shell thickness can be controlled. However, if the microspheres are too small (50 nm in this case), agglomerated particles with many hollow voids are obtained, most likely due to colloidal instability.

Submicron Sized Hollow Polymer Particles: Preparation and Properties

AbstractThe considered method for obtaining hollow polymer particles is based on the following pathway: (1) preparation of a carboxylated core latex by emulsion copolymerization of acrylic monomers with methacrylic acid, (2) synthesis of a core‐shell latex comprising a styrene (co)polymer shell, (3) neutralization of the core carboxylic groups with a base followed by the core ionization and hydration to a high degree, shell expansion and formation of water‐filled hollows. A number of approaches to improve the hydrophilic core – hydrophobic shell compatibility and enlarge the hollow volume are considered. The synthesized hollow particles are of a submicron size with the relative hollow volume Vhol : Vpart.= 0.43 – 0.64. Methods for cationic hollow particle latex preparation by anionic latex recharging with a cationic surfactant or acidic melamine resin are discussed. Recharging with a melamine resin is shown to afford hollow particles with an external polymer shell providing a high thermal stability of the particles.

Density changes of aerosol particles as a result of chemical reaction

Abstract. This paper introduces the capability to study simultaneously changes in the density, the chemical composition, the mobility diameter, the aerodynamic diameter, and the layer thickness of multi-layered aerosol particles as they are being altered by heterogeneous chemical reactions. A vaporization-condensation method is used to generate aerosol particles composed of oleic acid outer layers of 2 to 30nm on 101-nm polystyrene latex cores. The layer density is modified by reaction of oleic acid with ozone for variable exposure times. For increasing ozone exposure, the mobility diameter decreases while the vacuum aerodynamic diameter increases, which, for spherical particles, implies that particle density increases. The aerosol particles are confirmed as spherical based upon the small divergence of the particle beam in the aerosol mass spectrometer. The particle and layer densities are calculated by two independent methods, namely one based on the measured aerodynamic and mobility diameters and the other based on the measured mobility diameter and particle mass. The uncertainty estimates for density calculated by the second method are two to three times greater than those of the first method. Both methods indicate that the layer density increases from 0.89 to 1.12g·cm-3 with increasing ozone exposure. Aerosol mass spectrometry shows that, concomitant with the increase in the layer density, the oxygen content of the reacted layer increases. Even after all of the oleic acid has reacted, the layer density and the oxygen content continue to increase slowly with prolonged ozone exposure, a finding which indicates continued chemical reactions of the organic products either with ozone or with themselves. The results of this paper provide new insights into the complex changes occurring for atmospheric particles during the aging processes caused by gas-phase oxidants.

Gold Nanoshells on Polystyrene Cores for Control of Surface Plasmon Resonance

A method is presented for synthesizing core-shell structures consisting of monodisperse polystyrene latex nanospheres as cores and gold nanoparticles as shells. Use of polystyrene spheres as the core in these structures is advantageous because they are readily available commercially in a wide range of sizes, and with dyes or other molecules doped into them. Gold nanoparticles, ranging in size from 1 to 20 nm, are prepared by reduction of a gold precursor with sodium citrate or tetrakis(hydroxymethyl)phosphonium chloride (THPC). Carboxylate-terminated polystyrene spheres are functionalized with 2-aminoethanethiol hydrochloride (AET), which forms a peptide bond with carboxylic acid groups on their surface, resulting in a thiol-terminated surface. Gold nanoparticles then bind to the thiol groups to provide up to about 50% coverage of the surface. These nanoparticles serve as seeds for growth of a continuous gold shell by reduction of additional gold precursor. The shell thickness and roughness can be controlled by the size of the nanoparticle seeds as well as by the process of their growth into a continuous shell. By variation of the relative sizes of the latex core and the thickness of the gold overlayer, the plasmon resonance of the nanoshell can be tuned to specific wavelengths across the visible and infrared range of the electromagnetic spectrum, for applications ranging from the construction of photonic crystals to biophotonics. The position and width of the plasmon resonance extinction peak are well-predicted by extended Mie scattering theory.

Fabrication of Hollow Spheres and Thin Films of Nickel Hydroxide and Nickel Oxide with Hierarchical Structures

Hollow spheres and thin films of Ni(OH)(2) and NiO with unusual form and hierarchical structures have been synthesized by a simple solution chemistry method. First, in situ formed Ni(OH)(2) nanoflakelets organized on the surface of styrene-acrylic acid copolymer (PSA) latex particles to form core/shell structures. Ni(OH)(2) hollow shells built up with nanoflakelets were obtained after subsequent removal of the core latex particles by dissolving PSA latex in toluene; the removal of the cores by calcinations would result in NiO hollow shells, also with hierarchical structures. BET calculation showed the surface area of the NiO hollow spheres was 156 m(2)/g. The nanoflakelets could also organize themselves into thin films with hierarchical structures. It is anticipated that these novel structures will have some unique applications in Ni-based batteries and other potentials.

Silicone–polyacrylate composite latex particles. Particles formation and film properties

Composite latex particles with a polydimethylsiloxane PDMS core and a poly(methyl methacrylate- co- n-butyl acrylate) P(MMA-BA) copolymer shell were synthesized by seeded emulsion polymerization using the PDMS latex as the seed. The compatibility between the two polymer phases was changed by introducing vinyl groups in the latex core. Monomer conversions and particle size evolution were monitored to see the influence of the nature of the core functionality on the polymerization kinetics and on the extent of secondary nucleation. Particle morphology was characterized by cryo-transmission electron microscopy. The P(MMA-BA) copolymer formed a regular shell around the PDMS seed, whereas nonuniform coatings were formed when vinyl functionalities were introduced into the seed. Films were produced from the latexes, and their surface property was analyzed by X-ray photoelectron spectroscopy and contact angle measurements. It was shown that the PDMS component segregated to the polymer/air interface and that the extent of segregation depended on the original particles structure. Because PDMS has a very low glass transition temperature, it can easily diffuse throughout the film material. However, protected by an acrylic shell, polymer diffusion is significantly hindered and the film then displays all the characteristic properties of the acrylic copolymer. The surface composition of the films formed by the structured particles which PDMS core was not totally covered by the polyacrylate, was found to be intermediate between the composition of the films issued from the core–shell latexes and that of the films produced from blends of pure polyacrylate and PDMS latexes.

Laser-Light-Scattering Study of Internal Motions of Polymer Chains Grafted on Spherical Latex Particles

Using atom-transfer radical polymerization, we have prepared core−shell particles by grafting thermally sensitive poly(N-isopropylacrylamide) (PNIPAM) chains on a spherical polystyrene latex core (...

Products and Mechanisms of Ozone Reactions with Oleic Acid for Aerosol Particles Having Core−Shell Morphologies

Heterogeneous reactions of oleic acid aerosol particles with ozone are studied below 1% relative humidity. The particles have inert polystyrene latex cores (101-nm diameter) coated by oleic acid layers of 2 to 30 nm. The chemical content of the organic layer is monitored with increasing ozone exposure by using an aerosol mass spectrometer. The carbon-normalized percent yields of particle-phase reaction products are 20−35% 9-oxononanoic acid, 1−3% azelaic acid, 1−3% nonanoic acid, and 35−50% other organic molecules (designated as CHOT). There is approximately 25% evaporation, presumably as 1-nonanal. To explain the formation of CHOT molecules and the low yields of azelaic and nonanoic acids, we suggest a chemical mechanism in which the Criegee biradical precursors to azelaic acid and nonanoic acid are scavenged by oleic acid to form CHOT molecules. These chemical reactions increase the carbon-normalized oxygen content (z/x) of the CxHyOz layer from 0.1 for unreacted oleic acid to 0.25 after high ozone exposure. Under the assumption that oxygen content is a predictor of hygroscopicity, our results suggest an increased cloud condensation nuclei activity of atmospherically aged organic particles that initially have alkene functionalities.

Nanostructured hybrid materials from aqueous polymer dispersions

Organic–inorganic (O–I) hybrids with well-defined morphology and structure controlled at the nanometric scale represent a very interesting class of materials both for their use as biomimetic composites and because of their potential use in a wide range of technologically advanced as well as more conventional application fields. Their unique features can be exploited or their role envisaged as components of electronic and optoelectronic devices, in controlled release and bioencapsulation, as active substrates for chromatographic separation and catalysis, as nanofillers for composite films in packaging and coating, in nanowriting and nanolithography, etc. A synergistic combination or totally new properties with respect to the two components of the hybrid can arise from nanostructuration, achieved by surface modification of nanostructures, self-assembling or simply heterophase dispersion. In fact, owing to the extremely large total surface area associated with the resulting morphologies, the interfacial interactions can deeply modify the bulk properties of each component. A wide range of starting materials and of production processes have been studied in recent years for the controlled synthesis and characterization of hybrid nanostructures, from nanoparticle or lamellar dispersions to mesoporous materials obtained from templating nanoparticle dispersions in a continuous, e.g. ceramic precursor, matrix. This review is aimed at giving some basic definitions of what is intended as a hybrid (O–I) material and what are the main synthetic routes available. The various methods for preparing hybrid nanostructures and, among them, inorganic–organic or O–I core–shell nanoparticles, are critically analyzed and classified based on the reaction medium (aqueous, non-aqueous), and on the role it plays in directing the final morphology. Particular attention is devoted to aqueous systems and water-borne dispersions which, in addition to being environmentally more acceptable or even a mandatory choice for any future development of large output applications (e.g. in paint, ink and coating industry), can provide the thermodynamic drive for self-assembling of amphiphilics, adsorption onto colloidal particles or partitioning of the hybrid's precursors between dispersed nanosized reaction loci, as in emulsion or miniemulsion free-radical polymerization. While nanoencapsulation and self-assembling processes are already exploited as commercially viable fabrication methods, a newly developed technique based on two-stage sol–gel and free-radical emulsion polymerization is described, which can grant a versatile synthetic approach to hybrid O–I nanoparticles with tailor-made composition of both the organic core and the silica or organosilica shell, and good control on morphology, size and heterophase structure in the 50–500 nm range. Styrene or acrylate homo- and copolymer core latex particles need to be modified with a reactive comonomer, such as trimethoxysilylpropyl methacrylate, to achieve efficient interfacial coupling with the inorganic shell. Accurate control over pH and process conditions is required to avoid latex coagulation or, in case of organic particles with uniform composition, incipient intraparticle crosslinking.

Single particle light-scattering photometry—some fields of application

Present developments in the field of bioscience will profit from the fabrication of multilayer films of polyelectrolytes on colloids as well as of nano- and microsized capsules. The single particle light-scattering technique is suitable for process control. This paper describes the mode of operation and efficiency of a laboratory-built single particle light-scattering photometer, which opens up new possibilities in applications, especially in the field of bioscience. This has been achieved by improving the measurement capabilities of organic particle sizes near 100 nm and precision of thickness changes of about 0.5 nm. Besides the classic applications, such as particle size distribution measurements at high resolution and the coagulation kinetics of colloids, the measurement of the layer-by-layer polyelectrolyte adsorption at colloid particle surfaces and the fabrication of colloidal carriers is introduced. The described method is also a precise method for controlling the removal of the latex core to obtain multilayer microcapsules.

Nanostructured hybrid materials from aqueous polymer dispersions

Organic–inorganic (O–I) hybrids with well-defined morphology and structure controlled at the nanometric scale represent a very interesting class of materials both for their use as biomimetic composites and because of their potential use in a wide range of technologically advanced as well as more conventional application fields. Their unique features can be exploited or their role envisaged as components of electronic and optoelectronic devices, in controlled release and bioencapsulation, as active substrates for chromatographic separation and catalysis, as nanofillers for composite films in packaging and coating, in nanowriting and nanolithography, etc. A synergistic combination or totally new properties with respect to the two components of the hybrid can arise from nanostructuration, achieved by surface modification of nanostructures, self-assembling or simply heterophase dispersion. In fact, owing to the extremely large total surface area associated with the resulting morphologies, the interfacial interactions can deeply modify the bulk properties of each component. A wide range of starting materials and of production processes have been studied in recent years for the controlled synthesis and characterization of hybrid nanostructures, from nanoparticle or lamellar dispersions to mesoporous materials obtained from templating nanoparticle dispersions in a continuous, e.g. ceramic precursor, matrix. This review is aimed at giving some basic definitions of what is intended as a hybrid (O–I) material and what are the main synthetic routes available. The various methods for preparing hybrid nanostructures and, among them, inorganic–organic or O–I core–shell nanoparticles, are critically analyzed and classified based on the reaction medium (aqueous, non-aqueous), and on the role it plays in directing the final morphology. Particular attention is devoted to aqueous systems and water-borne dispersions which, in addition to being environmentally more acceptable or even a mandatory choice for any future development of large output applications (e.g. in paint, ink and coating industry), can provide the thermodynamic drive for self-assembling of amphiphilics, adsorption onto colloidal particles or partitioning of the hybrid's precursors between dispersed nanosized reaction loci, as in emulsion or miniemulsion free-radical polymerization. While nanoencapsulation and self-assembling processes are already exploited as commercially viable fabrication methods, a newly developed technique based on two-stage sol–gel and free-radical emulsion polymerization is described, which can grant a versatile synthetic approach to hybrid O–I nanoparticles with tailor-made composition of both the organic core and the silica or organosilica shell, and good control on morphology, size and heterophase structure in the 50–500 nm range. Styrene or acrylate homo- and copolymer core latex particles need to be modified with a reactive comonomer, such as trimethoxysilylpropyl methacrylate, to achieve efficient interfacial coupling with the inorganic shell. Accurate control over pH and process conditions is required to avoid latex coagulation or, in case of organic particles with uniform composition, incipient intraparticle crosslinking.