Polystyrene Core Particles Research Articles

Poly(4-vinylpyridine) and Poly(methacrylic acid) Particle Architectures for pH-Responsive and Mechanochromic Opal Films.

While stimuli-responsive structural colors are commonly found in nature, mimicking these in artificial materials is challenging. Dynamically switchable and tunable coloration, however, is in high demand in widespread fields of applications, including advanced display and monitoring technologies, smart sensing, and anticounterfeiting. This work reports a scalable protocol for the synthesis of tailor-made core-shell particles and subsequent processing to opal films with iridescent, pH-responsive, and mechanochromic structural color. Novel monodisperse core-shell architectures based on hard polystyrene core particles are synthesized via stepwise emulsion polymerization in a starved-feed mode. The incorporation of 4-vinylpyridine and methacrylic acid as functional comonomers in the soft particle shell facilitates pH-responsive swelling and deswelling. Mechanically stable and well-ordered colloidal crystal films are obtained by the self-assembly of the particles during processing with the powerful melt-shear organization technique. Thereby obtained opal films show Bragg-scattering at the colloidal crystalline structure and exhibit brilliant green-turquoise to blue-violet reflection colors, dependent on the angle of view and illumination. Upon changes in the pH value or mechanical deformation, the reflected wavelength shifts by more than 100 nm, leading to intriguing changes in the visible structural color. Excellent reversibility is achieved by the subsequent application of a convenient UV cross-linking strategy, corroborating the high application potential of these advanced functional materials.

Continuous flow synthesis of plasmonic gold patches and nearly-complete nanoshells on polystyrene core particles

We describe the development of a T-mixer based continuous flow process for the coating of 86–500 nm diameter spherical polystyrene particles with thin gold patches by heterogeneous nucleation and growth. After establishing a suitable flow rate for good mixing and sufficiently uniform product morphology we systematically investigate the main reaction parameters. This reveals a considerable tunability of the patch morphology and, by virtue of the localized surface plasmon resonance of gold, the optical properties of the product dispersions. In order to further widen the range of nanostructures accessible by our process, a second T-mixer was added. This introduced new gold precursor, leading to further growth of the patches that were formed after the first mixer. By this approach, nearly-complete gold nanoshells could be produced in high yield on both small and large core particles, without the unwanted production of free-standing gold nanoparticles. Due to the pronounced optical properties of nearly-complete gold nanoshells on small core particles, we could estimate from electrodynamic simulations the equivalent shell thickness to be as low as 8.6 nm. This is significantly thinner than can be routinely achieved using the standard seeded growth approach to synthesise gold nanoshells. Our results are therefore highly promising for the gram-scale synthesis of plasmon resonant nanostructures with designed optical properties.

Decomposing Oil-Soluble Initiators in Particles: A Template-Free Method for the Preparation of Hollow Polymer and Silica Particles.

Nanovoids contained in hollow particles render them potential drug carriers. However, conventional methods for the synthesis of these particlhes involve complex processes. In this study, we developed a template-free method for the synthesis of hollow polymer and silica particles by initially preparing polystyrene core particles containing 2,2′-azobis(2-methylbutyronitrile) (V-59) through soap-free emulsion polymerization. The subsequent generation of nitrogen gas inside these particles upon the decomposition of V-59 at 70 °C led to the formation of voids. In addition, silica shells were synthesized on the surfaces of the V-59-containing polystyrene core particles through a sol–gel reaction at 40 °C, following which voids were formed by the decomposition of V-59 at 70 °C. The developed method involves straightforward steps and is environmentally friendly, as it does not require the use of surfactants, organic solvents, or templates.

Making hollows using nitrogen gas emitted by the decomposition of VAm-110 in polystyrene particles

Due to the useful features of hollow particles, such as the presence of nanovoids and their large specific surface areas, they have potential for use as drug carriers. Unfortunately, conventional methods for the synthesis of hollow particles involve complicated processes. In this study, we developed a template-free method for the production of hollow polymer particles. Polystyrene core particles containing 2,2′-azobis(N-butyl-2-methylpropionamide) (VAm-110) were initially formed via soap-free emulsion polymerization, after which shells were constructed using divinylbenzene. Nitrogen gas was then generated inside the particles by the decomposition of VAm-110 at 100 °C, which led to the formation of hollows. Consequently, this method involves three easy steps and is environmentally friendly, as it does not require the use of a surfactant or organic solvent. Furthermore, the morphology and size of the particle hollows can be controlled by varying the concentration of VAm-110.

Hybrid Nanoparticle Platform for Nanoscale Scintillation Proximity Assay.

β-particle emitting radionuclides, such as 3H, 14C, 32P, 33P, and 35S, are important molecular labels due to their small size and the prevalence of these atoms in biomolecules but are challenging to selectively detect and quantify within aqueous biological samples and systems. Here, we present a core-shell nanoparticle-based scintillation proximity assay platform (nanoSPA) for the separation-free, selective detection of radiolabeled analytes. nanoSPA is prepared by incorporating scintillant fluorophores into polystyrene core particles and encapsulating the scintillant-doped cores within functionalized silica shells. The functionalized surface enables covalent attachment of specific binding moieties such as small molecules, proteins, or DNA that can be used for analyte-specific detection. nanoSPA was demonstrated for detection of 3H-labeled analytes, the most difficult biologically relevant β-emitter to measure due to the low energy β-particle emission, using three model assays that represent covalent and non-covalent binding systems that necessitate selectivity over competing 3H-labeled species. In each model, nmol quantities of target were detected directly in aqueous solution without separation from unbound 3H-labeled analyte. The nanoSPA platform facilitated measurement of 3H-labeled analytes directly in bulk aqueous samples without surfactants or other agents used to aid particle dispersal. Selectivity for bound 3H-analytes over unbound 3H analytes was enhanced up to 30-fold when the labeled species was covalently bound to nanoSPA, and 4- and 8-fold for two non-covalent binding assays using nanoSPA. The small size and enhanced selectivity of nanoSPA should enable new applications compared to the commonly used microSPA platform, including the potential for separation-free, analyte-specific cellular or intracellular detection.

Electrostatic formation of polymer particle stabilised liquid marbles and metastable droplets – Effect of latex shell conductivity

HypothesisParticle cohesion and conductivity affects the electrostatically driven transport of particles to a suspended water droplet. The conditions at which liquid marbles and particle stabilised liquid droplets form are a function of these parameters. ExperimentParticle beds placed below an earthed pendent water drop had a negative potential applied, thus inducing an opposing positive charge on the liquid, which results in particle transfer and eventual coating of the liquid drop. Experiments where both the particle bed was constantly moved slowly toward the droplet, and the particle bed remained at a fixed, small separation distance were completed. These enabled the investigation of a number of variables that influence successful aggregate formation, including separation distance between the droplet and particle bed, coating mechanism and kinetics of the transfer process. FindingsMonodisperse polystyrene core particles with polypyrrole shells of various cohesiveness and conductivity were observed to behave differently in the presence of the applied potential, where the least cohesive and conductive sample (polystyrene) required the smallest separation distance, i.e. the greatest field strength for particle transfer. Increasing conductivity of the particle shell decreases the field strength required for particle transfer, and thus an increase was observed in separation distance at which particles were observed to move to the air-water interface. The transfer kinetics followed the same trend where the least conductive and cohesive sample was the slowest to coat the air-water interface, and vice-versa. Since an increase in cohesion hinders particle transfer, it is concluded that particle conductivity is of greater importance in the electrostatic aggregation process.

Preparation of pH-Responsive Hollow Capsules via Layer-by-Layer Assembly of Exfoliated Layered Double Hydroxide Nanosheets and Polyelectrolytes.

pH-Responsive smart capsules were developed by the layer-by-layer assembly with a colloidtemplating technique. Polystyrene (PS) particles were employed as core templates. Acid-soluble inorganic nanosheets were prepared from Mg-Al layered double hydroxide (LDH) by an exfoliation technique. LDH nanosheets and anionic polyelectrolytes were alternatively deposited on PS core particles by the layer-by-layer assembly using electrostatic interaction. Hollow capsules were obtained by the removal of the PS core particles. The hollow capsules obtained thus were collapsed at acidic conditions by dissolution of LDH nanosheets in the hollow shells. The dissolution rate, i.e., the responsiveness of capsule, is tunable according to the strength of acids.

TSEM-based contour analysis as a tool for the quantification of the profile roughness of silica shells on polystyrene core particles

Core-shell (CS) particles with a polymeric core and a silica shell play an important role in the materials and (bio)analytical sciences. Besides the establishment of reliable synthesis procedures, comprehensive particle characterization is essential for batch-to-batch reproducibility and objective performance assessment across architectures, protocols, and laboratories. Particle characterization with respect to size, size distribution, shell thickness and texture, surface area and roughness or materials composition is commonly conducted with different analytical methods, often on different samples. Our approach uses a dual-mode TSEM/SEM set-up with an EDX detector to obtain a complementary data set with sufficient statistical confidence of one and the same sample on a single instrument. Our protocol reveals information about size, size distribution and shell thickness of the various particles employed from overview images, while an increased field of view (FOV) and high-resolution EDX analysis yields detailed information on shell texture and elemental composition. An image analysis tool was developed to derive and quantify the profile roughness of CS particles from individual beads. Comparison with surface roughness data from AFM showed a similar trend in roughness across the series of particles. Reliable classification into smooth and rough is proposed and roughness changes within different particle batches were tracked systematically.

Synthesis of adenosine-imprinted microspheres for the recognition of ADP-ribosylated proteins

Core-shell structural adenosine-imprinted microspheres were prepared via a two-step procedure. Polystyrene core particles (CP) were firstly prepared via a reversible addition-fragmentation chain transfer (RAFT) polymerization leaving the iniferter on the surface of the cores, then a molecularly imprinted polymer (MIP) shell was synthesized on the surface of the cores by using acrylamide (AAm) as the functional monomer and ethylene glycol dimethacrylate (EGDMA) as the cross-linker. The formation and growth of the MIP layer were seen dependent on the initiator (AIBN), AAm and the polymerization time used within the polymerization. SEM/TEM images showed that the dimensions of the cores and shells were 2μM and 44nm, respectively. The MIP microspheres exhibited a fast rebinding rate within 2h and a maximum adsorption capacity of 177μg per gram for adenosine. The adsorption fitted a Langmuir-Freundlich (LF) isotherm model with a KLF value of 41mL/μg and a qm value of 177μg/g for the MIP microspheres. The values were larger than those for a non-molecularly imprinted polymer (NIP) particles (5mL/μg and 88μg/g) indicating a better adsorption ability towards adenosine. The MIP microspheres showed a good selectivity for adenosine with a higher adsorption (683nmol/g) for adenosine than that (91nmol/g, 24nmol/g and 54nmol/g) for guanosine, cytidine and uridine respectively. Further experiment proved that the adenosine-imprinted polymer microspheres also had a good selectivity for ADP-ribosylated proteins that the MIP could extract the ADP-ribosylated proteins from the cell extract samples.

Protein immobilization and separation using anionic/cationic spherical polyelectrolyte brushes based on charge anisotropy

Interactions between bovine serum albumin (BSA)/β-lactoglobulin (BLG) and spherical polyelectrolyte brushes (SPBs) were investigated by a combination of turbidimetric titration, dynamic light scattering (DLS), zeta potential measurement, and small angle X-ray scattering (SAXS) which revealed different behaviors, architectures, and phase states of pH dependent protein–SPB interactions. Binding energetics, affinity, and stoichiometry between BSA–BLG and SPBs were determined by isothermal titration calorimetry (ITC) to get further information concerning the interaction difference. The SPBs consist of narrowly distributed polystyrene core particles (ca. 80 nm in diameter) onto which linear chains of polyelectrolytes, either weak anionic poly(acrylic acid) (PAA) or weak cationic poly(2-aminoethyl methacrylate hydrochloride) (PAEMH), are grafted. For a particular protein (BSA or BLG), the binding stoichiometry, affinity, architecture, and phase state between proteins and anionic SPBs were significantly different from those for cationic SPBs. Significantly larger binding affinity and adsorbed amount were observed for BSA in anionic SPBs versus cationic SPBs, while opposite for BLG, which were explained in terms of different charge anisotropy of proteins. These findings lay the foundation for SPB applications in the separation and immobilization of different proteins.

Controllable fabrication of PS/Ag core-shell-shaped nanostructures

In this paper, based on the previous steps, a facile in situ reduction method was developed to controllably prepare polystyrene/Ag (PS/Ag) core-shell-shaped nanostructures. The crucial procedure includes surface treatment of polystyrene core particles by cationic polyelectrolyte polyethyleneimine, in situ formation of Ag nanoparticles, and immobilization of the Ag nanoparticles onto the surface of the polystyrene colloids via functional group NH from the polyethyleneimine. The experimental parameters, such as the reaction temperature, the reaction time, and the silver precursors were optimized for improvement of dispersion and Ag coat coverage of the core-shell-shaped nanostructures. Ultimately, the optimum parameters were obtained through a series of experiments, and well-dispersed, uniformly coated PS/Ag core-shell-shaped nanostructures were successfully fabricated. The formation mechanism of the PS/Ag core-shell-shaped nanostructures was also explained.

Preparation of polymer core–shell particles supporting gold nanoparticles

The organic/inorganic composites were fabricated by catalytic reduction of tetrachloroaurate ions in poly[2-( N, N-dimethylamino)ethyl methacrylate] shell layers on polystyrene core particles. The core–shell particles were prepared by emulsifier-free emulsion polymerization of styrene (St) with 2-chloropropionyloxyethyl methacrylate (CPEM) using potassium persulfate as an initiator, followed by surface-initiated activator generated electron transfer-atom transfer radical polymerization (AGET-ATRP) of 2-( N, N-dimethylamino)ethyl methacrylate (DMAEMA) on core particles dispersed in aqueous media. The concentration effect of both DMAEMA ( x) and copper complex ( y) on a shell thickness of P(St-CPEM)- g-PDMAEMA x/ y core–shell particles was investigated by light scattering technique. The amount of grafted DMAEMA units with respect to (wrt) St was determined by 1H NMR spectra measurement. The P(St-CPEM)- g-PDMAEMA x/ y /Au z hybrid particles were successfully obtained by loading with hydrogen tetrachloroaurate (HAuCl 4) into the P(St-CPEM)- g-PDMAEMA aqueous dispersions. The particle size and shape of gold nanoparticles (NPs) generated by catalytic reduction in the poly[2-( N, N-dimethylamino)ethyl methacrylate] (PDMAEMA) shell layers were evaluated by both UV/vis absorption spectra measurement and TEM observation. The size and the number of gold NPs increased with increasing HAuCl 4 concentration ( z) below 75 mM. Interestingly, 60–80 nm sized, trigonal or polygonal, plate-like gold NPs were generated in the PDMAEMA shell by adding HAuCl 4 of 100 mM.

Synthesis and characterization of dual‐responsive micrometer‐sized core‐shell composite polymer particles

AbstractDual‐responsive micrometer‐sized core‐shell composite polymer particles were prepared by dispersion polymerization followed by seeded copolymerization. Polystyrene (PS) particles prepared by dispersion polymerization were used as core particles. N‐isopropyl acrylamide (NIPAM) and methacrylic acid (MAA) were used to induce dual‐responsive that is thermo‐ and pH‐responsive properties in the shell layer of composite polymer particles, prepared by seeded copolymerization with PS core particles. Temperature‐ and pH‐dependent adsorption behaviors of some macromolecules on composite polymer particles indicate that produced composite polymer particles exhibit dual‐responsive surface properties. Copyright © 2007 John Wiley & Sons, Ltd.

Chemical bath deposition synthesis of sub-micron ZnS-coated polystyrene

The synthesis of ZnS-coated polystyrene composite colloids by the decomposition of thioacetamide in the presence of polystyrene seed particles and metal salt is presented. The chemical bath deposition technique incorporates poly(vinyl pyrrolidone) to inhibit particle aggregation during the synthesis so that core–shell particles with sizes in the low sub-micron range were achieved. The shell thickness was well controlled through the reaction time and core size. ZnS shells were composed of primary crystallites, approximately 5 nm in diameter, which had the zinc blend crystal structure. The porosity of the shells was between 12 and 19%. Accordingly, the effective refractive index of the particles varied between 1.73 and 1.98 at wavelengths above the optical absorption edge of ZnS. Ordered colloidal crystals were produced by convective assembly of the poly(sodium 4-styrenesulfonate) stabilized core–shell particles. Assemblies of ZnS shell–polystyrene core particles are photonic crystal materials which may have applications in optical computing and communications environments.

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.