Core-shell Latex Particles Research Articles

Novel synthesis and electrophoretic response of low density TiO–TiO 2–carbon black composite

Novel low density TiO–TiO 2–carbon black composite was synthesized, which involved the deposition of inorganic coating on the surface of core–shell latex particles and subsequent removal of latex particles by calcination in high-purity nitrogen. The morphology and interior structure were characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The images exhibited the composite had spherical shape and smooth surface, and the interior structure was hollow or porous. X-ray diffraction peaks (XRD) were mostly in agreement with the standard diffraction patterns of rutile TiO 2. In addition, the observed peaks at 2 θ of 43.5°, 50.6° and 74.4° can be indexed to (1 1 1), (2 0 0) and (2 2 0) planes of cubic phase TiO. The X-ray photoelectron spectroscopy (XPS) results indicated that composite consisted of carbon black, TiO and TiO 2. The apparent density of the composite was suitable to 1.62 g cm −3, due to density matching with suspending media. Glutin–arabic gum microcapsules containing TiO–TiO 2–carbon black composite electrophoretic liquid were prepared via complex coacervation. The particles in the microcapsules showed excellent electrophoretic mobility under a DC field.

Formation of nanostructured composites with environmentally-dependent electrical properties based on poly(vinylidene fluoride)–polyaniline core–shell latex system

Submicron poly(vinylidene fluoride) (PVDF)/polyaniline (PANI) core–shell latex particles are synthesized and examined as an active component in a simple conductometric chemical sensor. The structure and physical properties of these particles and nanostructured composite PVDF–PANI polymer films built of them are characterized with transmission electron, atomic force, and helium ion microscopy techniques, differential scanning calorimetry, and conductivity measurements. The nanostructured composite films with conductivity of about 4 × 10−4 S/cm suitable for sensor applications are prepared by casting from the core–shell particles dispersions on glass substrates patterned with silver electrodes followed by annealing at 180 °C, i.e. above Tm of the PVDF component. Sensor properties of these films are tested by measuring current–voltage (I–V) characteristics in response to varying concentration of NH3 or HCl vapors. The developed thin film sensor heterostructures with electrically conductive percolation network of PANI as an active component and employing the conductometric detection scheme show high sensitivity to both analytes. However, the polymer material is especially efficient for application to NH3 sensing with the detection limit as low as 100 ppb, and good reproducible recovery behavior upon repeated exposure to NH3 at ambient conditions.

Characterisation of the dispersion stability of a stimulus responsive core–shell colloidal latex

Light scattering, electrokinetic measurements and flow rheology have been used to characterise the dispersion behaviour a responsive core–shell latex particle system. The system of choice is polystyrene latex which has a stimulus responsive steric polymeric layer at its surface: the responsive polymer used here is a block copolymer of poly(N,N-dimethylaminoethyl methacrylate)- b-poly(methylmethacrylate) [pDMAEMA- b-pMMA], where the pMMA block acts as an anchor to the latex particle and the pDMAEMA block projects into solution. pDMAEMA is a weakly basic polymer and its solubility is therefore dependent upon the pH, it also has a lower critical solution temperature (LCST) of around 40–50 °C in water. Zeta potential measurements showed an iso-electric point (iep) at between pH 7.5 and 8.2, dependent on the background salt concentration, with the core–shell particles having a positive charge at low pH as a result of the strong protonation of the weakly basic pDMAEMA shell. The dimensions of the pDMAEMA shell as a function of pH were measured using dynamic light scattering. At low pH, the steric pDMAEMA shell was seen to extend strongly from the surface of the core PS latex as a result of charge repulsions within this layer. Near to the iep, the steric polymer shell was seen to shrink as a result of the discharging of the weakly basic amine functionalities, finally collapsing back to the latex particle surface close to the iep. Flow rheology data indicated a significant shear-thinning behaviour at all measured particle volume fractions and at all pH. High shear rate data of the viscosity as a function of pH correlated directly with changes in the hydrodynamic volume of the particles; the measured viscosity decreasing as the apparent size of the core–shell particles decreased due to shell collapse. Evidence for the aggregation of the dispersion at high pH near to and above the iep were also seen.

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 and Characterization of Hollow TiO<sub>X</sub> Nano-Spheres for Electrophoretic Displays

Hollow TiOX nano-spheres have been successfully prepared using hollow core-shell latex particles as template, which involves the deposition of inorganic coating on the surface of hollow core-shell latex particles and subsequent removal of the latex particles by calcinations in air or ammonia gas. The formation route of hollow core-shell polymer particles is presented as follows: Firstly, poly-methyl methacrylate (PMMA) seed emulsions are prepared as the 'core'. Subsequently, the outer shell poly(styrene-co-methyl methacrylate) (PS-co-MMA) particles wrap on the surface of the core, the microspheres with core-shell have been prepared. Finally, Ti(OBu)4 is used as precursor for the preparation of hollow TiOX nanospheres. Transmission electron microscopy (TEM) and atom force microscopy (AFM) images of seed emulsions show they have the uniform size of about 470 nm. TEM of hollow core-shell polymers particles show they have an average diameter of about 500 nm. X-ray diffraction (XRD) analysis of TiO2 sample calcined presents that the strong absorptions is coordinated with the standard chart of rutile TiO2. TEM of TiO2 and TiO show hollow spheres well-dispersed with the diameter range of 300-400 nm and 350-400 nm, respectively. The density (in the atmospheric pressure, 20 °C) of TiO2 and TiO hollow spheres was 2.49 and 2.37 g∙mL-1, respectively. The Zeta potentials were 6.20 mV and 20.39 mV, respectively. Uniform hollow spheres show low density and good electrophoretic displays. The electrophoretic mobilities of white TiO2 and black TiO hollow spheres in tetrachloroethylene show they are suitable for electronic paper as background and display particles, respectively. It is anticipated that this method would present a potential toward the road of large-scale industrial production of TiOx hollow spheres.

Polymer-induced generation and characterization of electrophoretic properties of hollow TiOX nanospheres for electronic paper

Hollow TiOX nanospheres have been successfully prepared using hollow core–double shell latex particles (poly(styrene-co-methyl methacrylate-co-butyl acrylate-co-methacrylic acid) (abbreviated in poly(St-co-MMA-co-BA-co-MAA)) as template, which involves the deposition of inorganic coating on the surface of hollow core–shell latex particles and subsequent removal of the latex by calcinations in air or ammonia gas. Ti(OBu)4 was used as precursor for the preparation of hollow TiOX nanospheres. TEM of white hollow core–double shell polymers particles with an aperture of approximately 225nm displays the perfect characteristic hollow nanospheres structure of primary core–double shell particles. The formation of TiOX was confirmed by XRD analysis and hollow structure of the particles was revealed by transmission electron microscopy (TEM). When the calcined temperature was at 800°C, hollow TiO2 nanospheres were arranged regularly with the diameter range of 130–170nm. The electrophoretic properties were characterized by JS94J micro-electrophoresis apparatus. The electrophoretic mobility of white TiO2 and black TiO hollow spheres in tetrachloroethylene were 1.09×10−5 and 3.12×10−5cm2/Vs, and the zeta potentials were 7.10 and 20.24mV, respectively. The results show that white TiO2 particles and black TiO hollow nanoparticles are suitable as electrophoretic particles and possess the application potential in the future electrophoretic display.

Effect of acrylic core–shell rubber particles on the particulate flow and toughening of PVC

AbstractDifferent types of acrylic core–shell rubber particles with a poly(butyl acrylate) (PBA) core and a grafted poly(methyl methacrylate) (PMMA) shell were synthesized. The average size of acrylic core–shell latex particles ranged from 100 to 170 nm in diameter, having the core gel content in the range of 35–80%. The melt blending behavior of the poly(vinyl chloride) (PVC) and the acrylic core–shell rubber materials having different average particle sizes and gel contents was investigated in a batch mixing process. Although the torque curves showed that the particulate flow of the PVC in the blends was dominant, some differences were observed when the size and gel content of the particles varied. This behavior can be attributed to differences in the plasticizing effect and dispersion state of various types of core–shell rubber particles, which can vary the gelatin process of the PVC in the mixing tool. On the other hand, the highest toughening efficiency was obtained using core–shell rubber particles with the smallest particle size (i.e., 100 nm). The results showed that increasing the gel content of the core–shell impact modifiers with the same particle size improved the particle dispersion state in the PVC matrix. The toughening efficiency decreased for the blends containing 100 and 170 nm rubber particles as the gel content increased. Nevertheless, unexpected behavior was observed for the blends containing 140 nm rubber particles. It was found that a high level of toughness could be achieved if the acrylic core–shell rubber particles as small as 100 nm had a lower gel content. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Simple route to get very hydrophobic surfaces of fibrous materials with core–shell latex particles

AbstractThe aim of this article is to report the creation of artificial, robust, and very hydrophobic materials with core–shell polyurethane–polydimethylsiloxane or polyurethane–poly(n‐butyl acrylate) polymer microparticles. These latexes were prepared by polyaddition in cyclohexane with commercial or synthetic steric stabilizers. An easy one‐step method based on the filtration of the colloidal particles was developed to obtain water‐repellent fibrous materials such as paper or textiles that maintain stable properties even after several washing/drying cycles. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008

Core-shell and other multiphase latex particles—confirming their morphologies and relating those to synthesis variables

Composite latex particles made from sequential processing steps may have a wide range of morphologies. The particular structure achieved is the result of a number of complex interactions between the chemical and physical aspects of the emulsion polymerization process. The intention is often to produce a core-shell particle structure, but in reality this is often a nontrivial task. In addition, it is challenging to develop confident conclusions about the detailed morphology of such particles, even when the two-component polymers are well phase-separated. This paper reports on an inter-laboratory study of acrylic-styrene copolymer latices in which the two-component polymers were not well phase-separated—a common result when attempting to make core-shell latex particles. Six different organizations each performed a number of analytical measurements to characterize two different latex systems. Their collective results were presented at a workshop in which the group strived to reach consensus on the detailed structures of the particles. Their conclusions were that multiple, complementary analytical results are required to reach a sound decision. While electron microscope results were always judged to be necessary, considered by themselves, it is often found that one can be led to false conclusions, especially for systems that are not well phase-separated. Given the results of this study it is clearly inappropriate to assume that the polymer formed in the second stage of a semibatch latex polymerization process forms a shell, giving rise to a core-shell morphology.

Preparation and Characterization of Polymer Core Shell Latex Particles

Stable core‐shell latex was synthesized by semicontinuous seeded emulsion polymerization with core monomers consisting of styrene (St), butyl acrylate (BA), and shell monomers consisting of methyl methacrylate (MMA), eutyl acrylate (EA), and methacrylic acid (MAA). The effects of compound emulsifier amount, mass ratio of anionic/nonionic emulsifier, and initiator amount on latex performance were investigated. By particle size analysis and transmission electron microscopy (TEM) observation, results suggest that final latex particles have clearly core shell structures.

EFFECT OF THE PHASE STRUCTURE EVOLUTION ON THE PROPERTIES OF FILMS FORMED FROM PBA/P(ST-co-MMA) COMPOSITE LATEX

A group of heterogeneous latexes poly(butyl acrylate)/poly(styrene-co-methyl methacrylate) (PBA/P(St-co-MMA)) were prepared by a semi-continuous seeded emulsion polymerization process under monomer starved conditions. The glass transition temperature (Tg) and the mechanical properties of the film formed from the composite latex changed with the evolution of the particle morphology. A photon transmission method was used to monitor the phase structure evolution of films which were prepared from core-shell PBA/P(St-co-MMA) latex at room temperature and annealed at 383 K above Tg of the polymers. In addition, the changes of the surface of the film formed from the composite latex with time at 383 K were observed by AFM. The evidence illustrated that the film formed from the core-shell latex particles was metastable. The rearrangement of the phases could occur under proper conditions.

Preparation of the stable core–shell latex particles containing organic-siloxane in the shell

In this study, the latex particles with a polyacrylate core and a polydimethylsiloxane shell via 3-(methacryloxypropyl)-trimethoxysilane as the space arm to link the core and shell have been prepared by semi continuous seeded emulsion polymerization. And several key polymerization reaction conditions such as the emulsifier concentration, 3-(methacryloxypropyl)-trimethoxysilane dosages, feeding sequence and the acrylates/siloxanes ratio were detailedly discussed. Then, the optimal condition to prepare stable core/shell particles was selected and a proper preparation process has been established. The as-synthesized particles were characterized by TEM and XPS. The clear core/shell structure of the particles could be observed through analysis TEM. In addition, the results of XPS analyses manifested that siloxanes had been grafted on the surface of the polyacrylate particles and they distributed on the outmost layer of the particles. Finally, the surface hydrophobicity of the film formed by latex particles was investigated by the water absorption ratio measurement. The results indicated the developed latex particle provided with a fair water-repellency property.

Tracer diffusion properties of core–shell latex films studied by photoinduced grating relaxation

AbstractThis article reports the application of the Photo‐Induced Grating Relaxation technique (also known as Forced Rayleigh Scattering) to investigate the dynamics of films prepared from structured core–shell latex particles via the transport property of the photochromic tracer molecule Aberchrome 540®. The core–shell particles were prepared with a fluoropolymer core (immiscible and impenetrable to the tracer) and a poly(butyl methacrylate) shell. The incompletely dried films (with residual water) manifest their spatial heterogeneity via non‐Fickian behavior (spatial scale‐ dependent apparent diffusion coefficient). The diffusion data was interpreted using the two‐state diffusion model, previously developed to describe the tracer diffusion in latex films without any core–shell structure. In contrast to dry latex films made from homogeneous particles, where one observes Fickian diffusion indicative of a homogeneous polymer film, we find that the lattice of fluoropolymer cores leads to a length scale dependent diffusion coefficient for the tracer. This effect can be interpreted as microscopic evidence for a strain hardening effect due to the presence of a hardened layer of matrix polymer (= shell) surrounding the core, which act as nanofillers. This strain hardening effect could be quantified within the two‐state diffusion model in terms of tracer diffusion coefficients and root mean squared displacements. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 2823–2834, 2007

The application of distance distribution functions to structural analysis of core–shell particles

The structure of core–shell latex particles of polymethylmethacrylate (the core) and polyurethane (the shell) have been investigated by methods of small-angle X-ray scattering (SAXS) and atom-force microscopy. A set of SAXS patterns has been obtained using contrast variation method. Indirect methods have been used to follow the evolution of distance distribution functions from SAXS for lattices in various sucrose solutions over a range of solution density, yielding structural parameters of the particles such as core size, shell thickness and density of the polymers including density deviations within the particle's core and shell. A model for an ensemble of core–shell particles with a normal distribution of average electron density of both the core and the shell has been developed to fit the distance distribution functions using a random search algorithm. The effects of nanophase separation in the polyurethane is estimated using Monte Carlo simulations of the distance distribution functions where the phase-separated polyurethane is represented by spherical truncated cones in a shell simulating the location of hard and soft polyurethane blocks, respectively.

Synthesis and characterization of core-shell particles containing a perfluoroacrylate copolymer rich in the shell

A simple synthetic method for preparing the core-shell latex particles containing fluorinated shell was presented. Polymerization was achieved by a low-sheer monomer-starved emulsion polymerization process, thus facilitating mobility and subsequent polymerization of perfluoroacrylate (FA) along with methyl methacrylate (MMA) and n-butyl acrylate (nBA) monomers. The structure and thermal behavior of the resulting perfluoroacrylate copolymer were investigated by FTIR, NMR, and DSC. Furthermore, PCS, TEM as well as SFM, were carried out to characterize the surface morphology of the particles. These studies illustrated that the incorporation of FA into MMA/nBA particle morphologies facilitated surface phase separation during coalescence, resulted in F-containing film-air interfaces. Thus, surface properties with a significant increase in the contact angles could be produced. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007

The morphology of submicronsized core–shell latex particles: An electron microscopy study

The core–shell structure of a range of acrylic–acrylic latexes has been investigated by combining different specimen preparation methods with transmission electron microscopy (TEM), dark-field scanning transmission electron microscopy (DSTEM) and low-voltage scanning electron microscopy (LV-SEM), including the first reported use of LV-SEM to observe composite latex particles at ambient and subambient temperatures. Spin-coating of liquid latex dispersions directly onto TEM grids or SEM stubs is shown to be a relatively straightforward mean of avoiding film formation during specimen preparation. In conjunction with double staining techniques, it has been found to be particularly convenient for characterizing the fine structure of particles with diameters down to below 100 nm.

Design and use of macromonomers as steric stabilizers for the synthesis of novel functional particles in dispersed media

AbstractThe synthesis of core–shell latex particles is discussed in this paper. Various macromonomers have been engineered and used as steric reactive stabilizers to render these particles surface active. Latexes of polystyrene, polynorbornene and polyurethane have been obtained in aqueous, organic and supercritical CO2 dispersant media. The fields of application of these original materials are also discussed. Copyright © 2005 Society of Chemical Industry

New Possibilities for Controlling the Morphology of Core-Shell Latex Particles During Emulsion Polymerization

A simple technology is described for preparing latexes with core-shell particles, in which the composition of the shell copolymer regularly varies from the inner layers of the shell to the particle periphery. Equations are suggested for calculating the instantaneous and integrated compositions of the shell copolymer and for analyzing how the composition of the copolymer varies along the particle radius. Specific examples of synthesis of emulsion copolymers intended for preparing plastisols and latexes with hollow particles demonstrate the benefits from application of the technology suggested.

Effect of initiator on morphology in poly(vinyl acetate)/polystyrene and poly(butyl acrylate)/polystyrene composite latexes

A simple method of related sensitivity range to predict thermodynamic equilibrium morphology of a core-shell latex particle (J Appl Polym Sci. 2004, 92, 3144), is recently explored. The article proposed that it is necessary to classify core-shell latex systems as sensitivity and no-sensitivity by their equilibrium morphology sensitivity to initiator and emulsifier. As for the sensitivity system, the final morphology may change by adjusting initiator and emulsifier, whereas, for the no-sensitivity system, it is hard to change its final morphology in this way. Equilibrium morphologies in system poly(vinyl acetate) (PVAc)/polystyrene (PSt) and poly(butyl acrylate) (PBA)/ PSt composite latexes particles were observed by changing initiator. Composite latexes of the two systems were synthesized by two-stage semi-continuous emulsion polymerization. The types or/and concentration of initiator changed in two stages in which the oil-soluble initiator 2,2-azobis(isobutyronitrile) (AIBN) and the water-soluble initiator potassium persulfate (KPS) were used respectively, the concentration of which was 0.5% or 2% based on the weight of monomer. The results showed that the two systems had different characteristics. At different experiment conditions designed, the same equilibrium morphologies with PSt as core and PVAc as shell were obtained in system PVAc/PSt, whereas, three different equilibrium morphologies, core-shell, inverted core-shell and hemisphere, were obtained in system PBA/PSt. The equilibrium morphology in system PVAc/PSt is no-sensitive to initiator, and the equilibrium morphology in system PBA/PSt is sensitive to initiator.

Synthesis of cationic core-shell latex particles

Surfactant-free seeded (core-shell) polymerization of cationic polymer colloids is presented. Polystyrene core particles with sizes between 200 nm and 500 nm were synthesized. The number average diameter of the colloidal core particles increased with increasing monomer concentration. Cationic shells were introduced by co-polymerizing styrene with the cationic monomers (vinylbenzyl)trimethylammonium chloride (VBTMAC), [(2-methacryloyloxy)ethyl] trimethylammonium chloride (METMAC) and [(2-(acryloyloxy)ethyl] trimethylammonium chloride (AETMAC) onto the polystyrene cores. The cationic monomer AETMAC, undocumented to our knowledge in colloid synthesis, produced the best cationic shells and could be incorporated at much higher concentrations in the shell compared to the commonly used VBTMAC and METMAC, which yielded undesired polyelectrolyte side products already at relatively low cationic monomer concentrations. In shell formation, feed concentrations of AETMAC between 1.3 mol% (2.4 wt%) and 10.7 mol% (20 wt%) in styrene could be employed, allowing us to control colloid surface charge density over a wide range. The influence of various polymerization parameters (initiator concentration, cross-linking agent, and ionic strength) on the co-polymerization process with AETMAC is discussed. Core-shell particles were characterized using HR-SEM, potentiometric titration and zeta potential measurements.