Polystyrene Colloidal Particles Research Articles

Preparation of PS-Cores/Au Nanoparticles and Polyaniline-Shells Sub-Microspheres via Layer-by-Layer Method

Functional multi-layers containing polyaniline (PANI) /gold nanoparticles have been successfully decorated on the substrate of polystyrene (PS) latex spheres via layer-by-layer method. Gold nanoparticles were assembled on the surface of PS latex spheres via their consecutive electrostatic adsorption from solution, followed by the formation of polyaniline layer to obtain the PS-cores/ conductive polymer and Au-shells multi-layer spheres. FTIR spectroscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) confirmed the growth of gold nanoparticles and PANI layer on the PS colloidal particles.

Colloid dynamics in semiflexible polymer solutions

We investigate the dynamics of monodisperse colloidal polystyrene particles suspended in solutions of the semiflexible polymer filamentous actin, over a range of filament lengths that either exceed or are substantially less than the particle radius. The filament length is controlled by the capping protein gelsolin, and particle surface chemistries that minimize the adsorption of filaments are used. The particle dynamics are measured on short time scales using diffusing wave spectroscopy. A sharp transition in the initial particle diffusivity marks the expected shift from a dilute to a tightly entangled polymer network as the filament average length increases. In both the dilute and entangled regimes, the measured particle dynamics are compared with the theories of rodlike and semiflexible polymer solution rheology using the generalized Stokes-Einstein relationship. In the dilute limit, the particle dynamics are in good agreement with theory. However, in the tightly entangled regime, the particle response is consistent with polymer depleted near the surfaces of the particles. The magnitude of the depletion layer thickness depends strongly on particle size and weakly on filament length. This behavior is in agreement with nonlocal entropic repulsions and the loss of conformational entropy associated with rodlike molecules near impenetrable particles. These results illustrate the use of microrheology as a method to investigate local structure and dynamics in colloid-polymer solutions.

Polymerization of pyrrole on a polyelectrolyte hollow-capsule microreactor

‘Caved-in’ and spherical polypyrrole (PPy) capsules were successfully prepared by direct polymerization of pyrrole on polyelectrolyte hollow-capsule microreactors at different conditions. This microreactor was formed by alternate layer-by-layer (LbL) adsorption of chitosan (CS) and poly(sodium 4-styrenesulfonate) (PSS) on polystyrene (PS) colloidal particle and followed by removing the PS core with tetrahydrofuran (THF). The integrity and self-sustaining of the microreactor could be ensured through the chemical cross-linking of CS in multilayers with glutaraldehyde before the removing of PS. The direct polymerization of pyrrole on the microreactor, either polycations or polyanions at the outmost layer, can be achieved according to hydrogen bonding effect or electrostatic interaction. Participation of inorganic salts plays a significant role on morphology controllable of intact hollow polypyrrole capsules.

Nanofabrication of Polymer Surfaces Utilizing Colloidal Lithography and Ion Etching

In this paper, we utilize colloidal lithography based on electrostatic self-assembly of polystyrene colloidal particles onto a polymer surface as a nanoscale mask. The pattern is then transferred to the surface by ion beam etching. Each particle acts as an individual mask, resulting in an array of identical structure. Ion beam exposure etches away the unmasked surface between the particles, so the particle mask pattern can be transferred into the polymer surface. This method allows to nanofabricate bulk polymeric surfaces with systematic variation in relief, structure sizes, and aspect ratios. It is a fast, simple, and reliable method to fabricated different polymeric surfaces even on large area samples (> 1 cm2). The structural variation is achieved by use of different conditions during the self-assembly of the mask (e.g., different particles sizes) or different ion etching conditions during the pattern transfer (e.g., ion energy, ion flux, ion incident angle, etching time, gas environment).

Effect of the ionic surfactant concentration on the stabilization/destabilization of polystyrene colloidal particles

One of the most interesting properties of the surfactants is that they are able to alter the stability of colloidal dispersions. Despite its great industrial relevance, only a few works analyze the colloidal stability of these systems at high surfactant concentrations (well above the critical micelle concentration (CMC)). In the present work, the colloidal stability of polystyrene particles is studied under a wide range of ionic surfactant concentrations. The effects of the surface charge of the latex particles (evaluating both sign and value), and surfactant type (cationic or anionic) have been examined. Colloidal stability data have been gathered by monitoring aggregation using a nephelometric technique. As will be shown, it is possible to reach different stability regimes using the same colloidal system just by changing the surfactant concentration. Independently of the sign of both the surfactant and the surface, the destabilization of the system consistently takes place above certain surfactant concentration due to a depletion effect from non-adsorbed micelles. This destabilization can be predicted by adding to the DLVO interaction energy a new contribution addressing the force between two spherical particles in the presence of non-adsorbing spherical macromolecules.

Formation of nanoimprinting mould through use of nanosphere lithography

Two-dimensional (2D) photonic crystal (PC) fabrication is generally carried out by electron beam lithography (EBL). This technique is very expensive and has a low throughput because it works serially. In this paper, we report an inexpensive, fast and simple nano-fabrication technique for creating nanostructures based on nanoimprint lithography (NIL) and nanosphere lithography (NSL) techniques. A monolayer of self-assembled polystyrene colloidal particle is used as a mask for dry etching of SiO 2 to create periodic ordered nano-plates on glass. Then the nanopatterns are transferred by imprinting onto a polymer film or poly (methyl methacrylate) (PMMA)-coated Si substrate. Preliminary results show that this technique is a promising way to fabricate 2D photonic crystals.

Sculpted substrates for SERS

Sculpted SERS-active substrates are prepared by assembling a closed packed monolayer of uniform polystyrene colloidal particles (diameter 350 to 800 nm) onto an evaporated gold surface and then electrodepositing gold through this template to produce films with controlled thicknesses, measured as fractions of the sphere diameter, d. The resulting surfaces consist of a regular hexagonal array of interconnected spherical cross-section dishes. The role of localised plasmons in determining the SERS enhancement factor obtained for benzene thiol adsorbed onto the surfaces is then investigated by correlation of the UV-visible reflectance spectra, 400 to 900 nm, measured at the same positions on the substrate surfaces, with the SERS spectra. The results are interpreted in terms of the relative contributions of plasmons that are free to propagate across the top surface and those trapped within the dishes of the sculpted surface.

The Effects of Surfactants on the Morphology of Colloidal Crystals in Self-assembly

AbstractIn this research, sodium dodecyl sulfates (SDS) and N-cetyl-n,n,n-trimethyammonium bromide (CTAB) surfactant solutions are used as solvents of polystyrene (PS) colloidal suspension during the fabrication of colloidal crystals. The effects of the surfactant on the quality and the morphology of the colloidal crystals are studied. It was found that surfactants not only change the charge of PS colloidal particles, but also significantly changed the surface tension and the 3 phase contact angle of the suspension with respect to the glass substrate, in turn they change the thickness of the formed crystal as well as the crystal structure. The derived knowledge will be potentially useful in clarifying the mechanisms involved in the formation of colloidal crystals.

Microphase separation during binary electrophoretic deposition of particles with dissimilar polarizabilities

We describe a two-dimensional, microphase separation in a binary mixture of yeast cells and colloidal polystyrene particles driven by the electrophoretic deposition (EPD) process. Self-organized core-shell clusters with predominantly yeast cores surrounded by shells of polystyrene (PS) particles were observed after applying uniform 5 Hz, 10 V/cm ac electric fields to initially randomly mixed monolayers adjacent to an ITO electrode. Depending on the type, size and ζ-potential of the colloids, the interplay between an aggregative electrohydrodynamic (EH) force and a repulsive induced-dipole–induced-dipole (ID) force produced either particle separation, aggregation or a combination of both in single component experiments conducted at 5Hz, 10 V/cm. In binary systems, the PS particle size and ζ-potential had only a secondary effect on the microphase structure, and the yeast–PS binary cluster morphology was frequency dependent. Differences in the particle dielectric response, characterized by the induced-dipole strength for PS and yeast, and in their relative vertical displacements during an alternating field cycle gave rise to the different self-organized morphologies observed in binary systems, while differences in the vertical motions of the assembling particles were directly observed to play a critical role in the binary sorting process.

Optical properties of single droplet of photonic crystal assembled by ink-jet printing

An array of droplets of photonic crystal with polystyrene colloidal particles was assembled on silicon using ink-jet printing. A microreflectance spectrum from a single droplet was collected using an optical microscope and a spectrometer. It was observed that the photonic band gap of these droplets shifts as a function of the size of the colloidal particle. The reflectance peak position predicted from the model based on Bruggeman and Maxwell–Garnett effective medium approximations agrees well with those of the experimentally observed peak.

Colloid Surface Engineering via Deposition of Multilayered Thin Films from Polyelectrolyte Blend Solutions

Multilayer thin films were constructed on polystyrene colloidal particles by depositing alternating layers of poly(allylamine hydrochloride) (PAH) at pH 7.5 and varying composition blends of poly(acrylic acid) (PAA) and poly(styrenesulfonate) (PSS) at pH 3.5. Following the deposition of each layer, microelectrophoresis experiments showed alternating zeta-potentials, suggesting the formation of multilayered films on the particles. Scanning and transmission electron microscopy were used to examine the surface morphology of the colloidal particles, with homogeneous surface coatings apparent for films deposited from PAA/PSS blend solutions containing up to 90 wt % PAA. The colloidal stability of these particles is greater than those coated with individual PAH and PAA layers. In the case of the blend PAA/PSS = 25:75 wt %, up to 20 layers were assembled without compromising the colloidal stability of the dispersion. The results demonstrate that the deposition of layers from PE blend solutions containing a strong and weak PE can be used as a facile method for controlling the surface properties and hence the colloidal stability of core-shell particles, as well as the thickness and morphology of the coatings. Control of these parameters is important for subsequent processing and application of these particles in controlled delivery, photonics, catalytic, and separation applications.

Reflectance spectroscopy of single photonic crystal island fabricated by ink-jet printing

AbstractA micro-reflectance spectroscopy was performed on a single island of photonic crystal array. An array of islands of photonic crystal with colloidal polystyrene beads was assembled on Si using ink-jet printing. The polystyrene colloids with three different sizes (190 nm, 210 nm, and 270 nm in diameter) were used and the polystyrene colloidal particles were self-assembled to form fcc lattices with three different lattice spacing. It was observed from the reflectance spectra that the position of the optical stop band shifts as the size of the colloidal particle changes. Effective medium approximations were used to model the dielectric properties of the colloid/air composite. The theoretically expected reflectance peak position agrees well with those of the experimentally observed peaks. The effect of finite size of the photonic crystal island on its reflectance spectroscopy was investigated by comparing the reflectance spectra collected from four different photonic crystal islands assembled from the same polystyrene colloidal particles, but with different lateral size for each island. It was found that the primary reflection peak was broadened and its intensity was reduced when the lateral size of the island was decreased.

Lateral separation of colloids or cells by dielectrophoresis augmented by AC electroosmosis

Colloidal particles and biological cells are patterned and separated laterally adjacent to a micropatterned electrode array by applying AC electric fields that are principally oriented normally to the electrode array. This is demonstrated for yeast cells, red blood cells, and colloidal polystyrene particles of different sizes and ζ-potentials. The separation mechanism is observed experimentally to depend on the applied field frequency and voltage. At high frequencies, particles position themselves in a manner that is consistent with dielectrophoresis, while at low frequencies, the positioning is explained in terms of a strong coupling between gravity, the vertical component of the dielectrophoretic force, and the Stokes drag on particles induced by AC electroosmotic flow. Compared to high frequency dielectrophoretic separations, the low frequency separations are faster and require lower applied voltages. Furthermore, the AC electroosmosis coupling with dielectrophoresis may enable cell separations that are not feasible based on dielectrophoresis alone.

Electrodeposition of Nanostructured Films Using Self-Organizing Templates

Over the last eight years, together with colleagues in Southampton, we have been interested in the templated electrodeposition of regularly structured nanoporous materials and their properties and applications. Over this time we have worked extensively with two different types of self-organizing template: lyotropic liquid crystalline phases and close-packed arrays of spherical colloidal polystyrene particles.

Silica Honeycomb-Crystal Structure Prepared by Fabrication of Silica-Coated Particles

Polystyrene (PS) colloidal particles have been used as templates to produce well-ordered macroporous silica structure. The silica-films on the PS surface were grown from ethanol solution containing acidic water and tetraethyl orthosilicate (TEOS). The films were measured using transmission electron microscopy (TEM), and scanning electron microscopy (SEM). The thickness of the silica film reached a maximum film thickness that varied from 40 to 15 nm, at pHl.5 and pH3. Ordered macro-honeycomb-crystal structures were formed by centrifugation and calcination of silica-coated PS particles. A continuous silica matrix was consisted of a three dimensional well-ordered network like honeycomb.

On the Role of Block Copolymers in Self-Assembly of Dense Colloidal Polymeric Systems

In the present work, we discuss the role of block copolymers in the self-assembly of diblock copolymers and monodisperse colloidal polymeric particles. Experiments for this type of system were carried out on colloidal dispersions of polystyrene (PS) colloidal particles and polystyrene−poly(2-vinylpyridine) (PS−PVP) block copolymers in ethanol. After complete solvent evaporation and upon annealing at temperatures above the glass transition temperature of both PS and PVP, the system self-assembles into closely packed PS polyhedrons surrounded by a PVP phase. A three-step mechanism is suggested for the rearrangement of the system, based on the segregation of block copolymers at the colloidal surface, penetration of PS blocks into the PS colloids, and frustration and relaxation of the PVP chains with subsequent relaxation of the colloid. A simple mathematical model is proposed for the packing frustration of the PS−PVP block copolymers, which allows a direct benchmark of the suggested mechanism with the experimental evidence for the colloidal system investigated.

Self-Assembly and Characterization of Polyaniline and Sulfonated Polystyrene Multilayer-Coated Colloidal Particles and Hollow Shells

Conductive core-shell particles were prepared by the deposition of polyaniline (PANI) and poly(sodium 4-styrenesulfonate) (PSS) multilayers onto polystyrene (PS) colloidal particles via the alternate electrostatic layer-by-layer (LbL) assembly technique. PSS was used as a polymeric counterion for multilayer formation as well as a stabilizer and codopant for PANI. Electrophoresis, FT-IR spectroscopy, and transmission electron microscopy (TEM) confirmed the regular growth of PSS/PANI multilayers on PS colloidal particles. It was found that the PSS/PANI-coated particle is oxidatively more stable due to stabilization of the partially oxidized emeraldine salt by PSS. The conductivity of (PSS/PANI)5-coated PS particles was 0.003 S/cm and increased to 0.1 S/cm after additional dopant exposure with HCl vapor. Furthermore, hollow shells made up of PSS/PANI layers were produced by dissolution of the PS core from PSS/PANI-coated particles. Cyclic voltammetry (CV) showed that PSS/PANI multilayers maintained their oxi...

Lacunary Keggin-type polyoxometalates-based macroporous composite films: preparation and photocatalytic activity

A simple method for the fabrication of highly ordered macroporous composite films, [X n+ W 11O 39] (12− n)− –MO 2 (abbreviated XW 11–MO 2, X: P, Si, and Ge; M: Si and Ti), is described. That is, mono-dispersed colloidal polystyrene (PS) particles were first assembled on quartz slides by utilizing capillary force. Then XW 11–MO 2 sol infiltrated into the voids between these template PS spheres on the slides by a spin-coating technique. After the composite films were dried at room temperature, PS spheres were removed by extraction in ultrasound. Highly ordered macroporous composite films formed; the surface morphology of these films was characterized by scanning electron microscopy (SEM). The surfaces of these films are highly uniform, and the size of the pores is in the range of 300–450 nm. The photocatalytic performances of different macroporous composite films were compared via the degradation of aqueous dyes Rhodamine B (RB), Erythrosine BS (E-BS), Methyl Orange (MO) and Congo Red (CR) under UV irradiation. The composite PW 11–TiO 2 film showed higher photoactivity than did the PW 11–SiO 2 film. This difference is attributed to a synergistic effect of the combination of polyoxometalates (POMs) and titanium dioxide.

Coated polystyrene particles as templates for ordered macroporous silica structures with controlled wall thickness

Polystyrene (PS) colloidal particles have been used as templates to produce ordered macroporous silica structures. The silica films were deposited from ethanol solution containing acidic water and tetraethyl orthosilicate. The silica-coated PS spheres were characterized using transmission electron microscopy, and the film thickness determined by scanning electron microscopy and calculated from the relative weight of silica remaining after calcination. We found that the thickness of the silica film increased rapidly with time and reached a maximum that varied from 40 to 15 nm at pH 1.5 and 3, respectively. The data could be fitted to a simple first-order equation and the reaction rate and maximum thickness were related to the hydrolysis and condensation rate, respectively. Ordered macroporous structures were formed by centrifuging silica-coated PS spheres. Calcination of the close-packed spheres yielded a continuous silica matrix consisting of a three-dimensional well-ordered network of monodisperse pores.

Reactivity of Pt/ceria and Pt/alumina planar model catalysts prepared by colloidal lithography

Abstract We report on the structure, chemical state, and catalytic activity of nanofabricated, planar Pt/ceria and Pt/alumina model catalysts prepared by colloidal lithography. Employing extended etching times, catalyst particles are fabricated that are much smaller than the size of the polystyrene colloidal particle mask. Using CO oxidation as a probe reaction, the influence of various pretreatments has been studied. We find that the H 2 /O 2 pretreatment deteriorates the reactivity on Pt/alumina, which is accompanied by blocking of the high-temperature CO adsorption sites as seen by TPD. After prolonged reactions the Pt/ceria particles show pronounced restructuring, indicating a low-temperature, reaction-induced, strong metal–support interaction, where ceria is decorating the Pt particles. In contrast, after an identical reaction history the Pt/alumina particles become facetted. The nanofabrication approach allows us to attribute the structural changes on individual particles to the integrated, macroscopic catalytic response.