Polystyrene Microparticles Research Articles

Hierarchical Porous Carbon Cathode for Lithium–Sulfur Batteries Using Carbon Derived from Hybrid Materials Synthesized by Twin Polymerization

AbstractA new route of fabrication of cathodes for lithium–sulfur (Li–S) batteries with high cycle stability is reported. The cathodes are fabricated using porous carbon materials obtained from hybrid materials synthesized by twin polymerization on sulfonated polystyrene microparticles. The sulfonic acid groups act as room temperature catalyst for twin polymerization resulting in the formation of nanostructured phenolic resin/silica hybrid materials on the surface of sulfonated polystyrene particles. The shell formed by phenolic resin is transformed into carbon by simple pyrolysis and the polystyrene core is decomposed simultaneously at the pyrolysis temperature yielding porous carbon/silica nanocomposite hollow spheres. After silica removal, a hierarchical, highly porous carbon is obtained. Melt mixing of the carbon with sulfur is used for the fabrication of cathodes for Li–S batteries. The presence of silica on one hand imposes strength to the sphere wall during the carbonization and depolymerization of polystyrene, and on the other hand generates microporous carbon material for lithium–sulfur batteries. The nanostructured hybrid cathode allows very high capacity of 800–1000 mAh gsulfur −1 and remarkable reversible cycling stability and rate capability over 200 cycles at 0.1C rate and over 440 cycles at 1C rate for Li–S batteries.

Nanospikes-mediated Anomalous Dispersities of Hydropobic Micro-objects and their Application for Oil Emulsion Cleaning

Many fields of applications require dispersion of hydrophobic particles in water, which is traditionally achieved by using surfactants or amphiphilic molecules to modify particle surfaces. However, surfactants or amphiphilic molecules may disturb the native solution or particles’ surface hydrophobicity, limiting extended applications such as oil emulsion cleaning. Recently one example of 2 μm-size polystyrene microparticles covered with ZnO nanospikes has been shown to exhibit excellent dispersity in water in spite of surface hydrophobicity. Whether this anomalous dispersion phenomenon was applicable to other hydrophobic microparticle systems was still unclear and its application scope was limited. Here the anomalous dispersities of different hydrophobic spiky micro-objects were systematically explored. The results show that the anomalous dispersion phenomenon was universally observed on different hydrophobic spiky micro-objects including different hydrophobic coating, particle sizes, material compositions and core particle morphologies. In addition, the spiky micro-objects displayed anomalous dispersity in water without compromising surface hydrophobicity, and their applications for oil spills absorption and oil emulsion cleaning were demonstrated. This work offers unique insight on the nanospikes-mediated anomalous dispersion phenomenon of hydrophobic micro-object and potentially extends its applicability and application scopes.

Microfluidic single-particle chemical analyzer with dual-comb coherent Raman spectroscopy.

Label-free particle analysis is a powerful tool in chemical, pharmaceutical, and cosmetic industries as well as in basic sciences, but its throughput is significantly lower than that of fluorescence-based counterparts. Here we present a label-free single-particle analyzer based on broadband dual-comb coherent Raman scattering spectroscopy operating at a spectroscopic scan rate of 10kHz. As a proof-of-concept demonstration, we perform broadband coherent anti-Stokes Raman scattering measurements of polystyrene microparticles flowing on an acoustofluidic chip at a high throughput of >1000 particles per second. This high-throughput label-free particle analyzer has the potential for high-precision statistical analysis of a large number of microparticles including biological cells.

Random lasing from dyed polystyrene spheres in disordered environments

Advance designs of random lasers toward the development of miniature laser systems are in demand. Random lasing from Rhodamine-B dye doped polystyrene microparticles was demonstrated. Bare polystyrene spheres were used as scatterers, and these provided optical feedback to the gain. Random lasing was successfully demonstrated in two different disordered environments: in binary colloidal solution and in photonic glass. Incoherent feedback occurred in both the cases, and laser emission was obtained with a spectral line width of ∼10 nm. Optimized number densities of bare and dye doped polystyrene microparticles required for random lasing action in such systems were evaluated. Although both disordered media showed random lasing with similar number densities of the microparticles, the lasing threshold in the case of photonic glass was lower in comparison to binary colloidal solution. This was because of higher index contrast and larger filling fraction of microparticles in the case of photonic glass. Lasing results obtained for photonic glass were compared with their previous results of Bloch lasing in photonic crystal synthesized using similar dye doped polystyrene microparticles.

Lysozyme Monolayers at Polymer Microparticles: Electrokinetic Characteristics and Modeling

Adsorption of hen egg-white lysozyme (HEWL) molecules at negatively charged polystyrene microparticles was studied using dynamic light scattering (DLS), electrophoresis (LDV), solution depletion te...

Gold Nanoparticle Layers on Polystyrene Microspheres of Controlled Structure and Electrokinetic Properties.

Formation of positively charged gold nanoparticle layers on polystyrene microparticles (PSMs600) was studied using the electrokinetic and the concentration depletion methods based on atomic force microscopy (AFM) and scanning electron microscopy (SEM) imaging. Primarily, the dependence of electrophoretic mobility of microparticles on the gold nanoparticle concentration in the suspension was measured. These results were quantitatively interpreted in terms of the three-dimensional electrokinetic model. This allowed to derive a formula for calculating the coverage of nanoparticles under in situ conditions whose validity was confirmed by direct SEM imaging of deposited gold nanoparticles (AuNPs). Additionally, the maximum coverage of gold nanoparticles for various ionic strengths was determined using a concentration depletion method based on AFM imaging of residual particles deposited on the silica substrate. The maximum coverage increased with ionic strength attaining a value of 0.35 for the ionic strength of 3 × 10-3 M. This effect was attributed to the decreasing range of lateral electrostatic interactions among deposited particles. The electrokinetic properties of the gold nanoparticle layers were also evaluated in pH cycling experiments that confirmed their stability. Beyond significance to basic science, the new data acquired in this work confirm the feasibility of preparing gold nanoparticle layers on polymer microparticles characterized by a controlled structure, coverage, and electrokinetic properties.

Formation, properties and stability of silver nanoparticle monolayers at PDADMAC modified polystyrene microparticles

A facile self-assembly procedure was developed for the preparation of silver nanoparticle shells at polystyrene microparticles (PSMPs) modified by poly(diallyldimethylammonium chloride) (PDADMAC). Initially, physicochemical properties of microparticles, silver particles and (PDADMAC) were determined for various ionic strength and pHs. Then, PDADAMAC adsorption on the PSMPs was studied in situ via electrokinetic measurements. The influence of polyelectrolyte bulk concentration on electrokinetic properties of PDADMAC-coated microparticles for different ionic strength was investigated. The coverage of PDADMAC monolayer was estimated applying an electrokinetic model. The stability of PDADMAC-modified microparticles under controlled conditions of pH and ionic strength was also evaluated. It was confirmed that under acidic conditions (pH 4–5.6) the microparticles were stable for at least two weeks. The modified microparticles were used as substrate for silver nanoparticle immobilization carried out under a diffusion controlled self-assembly process. The coverage of nanoparticles was precisely determined using electrophoretic mobility measurements, the concentration depletion method involving atomic force microscopy and via direct scanning electron microscopy imaging of particles. A large stability of the silver particle monolayers was confirmed. These monolayers of well-defined coverage and acid-base properties can be used for controlled delivery of silver nanoparticles.

Inertial focusing of microparticles in curvilinear microchannels with different curvature angles

Inertial microfluidics has become one of the emerging topics due to potential applications such as particle separation, particle enrichment, rapid detection and diagnosis of circulating tumor cells. To realize its integration to such applications, underlying physics should be well understood. This study focuses on particle dynamics in curvilinear channels with different curvature angles (280°, 230°, and 180°) and different channel heights (90, 75, and 60 µm) where the advantages of hydrodynamic forces were exploited. We presented the cruciality of the three-dimensional particle position with respect to inertial lift forces and Dean drag force by examining the focusing behavior of 20 µm (large), 15 µm (medium) and 10 µm (small) fluorescent polystyrene microparticles for a wide range of flow rates (400–2700 µL/min) and corresponding channel Reynolds numbers. Migration of the particles in lateral direction and their equilibrium positions were investigated in detail. In addition, in the light of our findings, we described two different regions: transition region, where the inner wall becomes the outer wall and vice versa, and the outlet region. The maximum distance between the tight particle stream of 20 and 15 µm particles was obtained in the 90 high channel with curvature angle of 280° at Reynolds number of 144 in the transition region (intersection of the turns), which was the optimum condition/configuration for focusing.

Impact behaviour of microparticles with microstructured surfaces: Experimental study and DEM simulation

The surface topography of a component influences lots of important macroscopic phenomena, for example friction, fatigue and wear behaviour. This study is focused on the effect of surface topography on the collision behaviour of fine particles. To obtain this behaviour an experimental study of the single particle impact with a microstructured substrate was performed. A novel experimental setup was developed to capture collisions of small particles with the surface three-dimensionally. The particle-wall collisions were performed with spherical polystyrene microparticles. As contact partners a polished and a microstructured stainless steel substrate were used. The surface microstructure was produced by a cold spray process with spherical stainless steel particles. The measured restitution coefficient significantly decreased after the microstructuring showing an additional energy dissipation due to topography. The particle impact was simulated using the Discrete Element Method. The surface topography was implemented in the model by reverse engineering and meshed with two different resolutions. The simulations were compared with the experiments regarding the energy dissipation and rebound behaviour. The calculated restitution coefficient was in good agreement with the experiments for a fine meshed surface, but deviated significantly with the coarsened mesh.

Manipulation of micro-objects using acoustically oscillating bubbles based on the gas permeability of PDMS.

This paper presents a novel manipulation method for micro-objects using acoustically oscillating bubbles with a controllable position based on the gas permeability of polydimethylsiloxane. The oscillating bubble trapped within the side channel attracts the neighboring micro-objects, and the position of the air-liquid interface is controlled by generating temporary pressure difference between the side channel and the air channel. To demonstrate the feasibility of the method in technological applications, polystyrene microparticles of 10 μm in diameter were successfully captured, transported, and released. The influence of pressure difference on the movement speed of the air-liquid interface was demonstrated in our experiments, and the manipulation performance was also characterized by varying the frequency of the acoustic excitation and the pressure difference. Since the bubble generation and the air-liquid interface movement in our manipulation method do not need any electrochemical reaction and any high temperature, this on-chip manipulation method provides a controllable, efficient, and noninvasive tool for handling micro-objects such as particles, cells, and other entities. The whole manipulation process, including capturing, transporting, and releasing of particles, spent less than 1 min. It can be used to select the cells and particles in the microfluidic device or change the cell culture medium.

Heterophase polymer dispersion: A green approach to the synthesis of functional hollow polymer microparticles

Hollow nanostructured polymer microspheres have various potential applications; however, the development of a facile method to synthesize such particles has proved challenging. In the current work, an easy-to-use, green and low-cost method adopting a heterophase polymer dispersion strategy was developed to produce monodisperse hollow microparticles with well-defined nanostructures. When polystyrene (PS) seed microparticles prepared using modified dispersion polymerization were dispersed in an ethanol-water mixture at 70 °C, they transformed into hollow PS microparticles as a result of uptake of the continuous phase by the particles. Via consecutive heterophase polymer dispersion processes involving the addition of metal precursors, hollow PS microparticles covered with bimetallic nanocrystals were obtained. That is, metal nanocrystals were produced in situ from metal precursors on the polymer particles. Based on our results and observations, we propose plausible mechanisms for the formation of these hollow microparticles. The hollow PS microparticles covered with bimetallic nanocrystals exhibited high catalytic activity at a low concentration and excellent reusability when used as catalysts for the reduction of 4-nitrophenol to 4-aminophenol using sodium borohydride as the reducing agent.

Computational Sensing of Staphylococcus aureus on Contact Lenses Using 3D Imaging of Curved Surfaces and Machine Learning.

We present a cost-effective and portable platform based on contact lenses for noninvasively detecting Staphylococcus aureus, which is part of the human ocular microbiome and resides on the cornea and conjunctiva. Using S. aureus-specific antibodies and a surface chemistry protocol that is compatible with human tears, contact lenses are designed to specifically capture S. aureus. After the bacteria capture on the lens and right before its imaging, the captured bacteria are tagged with surface-functionalized polystyrene microparticles. These microbeads provide sufficient signal-to-noise ratio for the quantification of the captured bacteria on the contact lens, without any fluorescent labels, by 3D imaging of the curved surface of each lens using only one hologram taken with a lens-free on-chip microscope. After the 3D surface of the contact lens is computationally reconstructed using rotational field transformations and holographic digital focusing, a machine learning algorithm is employed to automatically count the number of beads on the lens surface, revealing the count of the captured bacteria. To demonstrate its proof-of-concept, we created a field-portable and cost-effective holographic microscope, which weighs 77 g, controlled by a laptop. Using daily contact lenses that are spiked with bacteria, we demonstrated that this computational sensing platform provides a detection limit of ∼16 bacteria/μL. This contact-lens-based wearable sensor can be broadly applicable to detect various bacteria, viruses, and analytes in tears using a cost-effective and portable computational imager that might be used even at home by consumers.

Separating large microscale particles by exploiting charge differences with dielectrophoresis

Dielectrophoresis (DEP), the migration of particles due to polarization effects under the influence of a nonuniform electric field, was employed for characterizing the behavior and achieving the separation of larger (diameter >5 μm) microparticles by exploiting differences in electrical charge. Usually, electrophoresis (EP) is the method of choice for separating particles based on differences in electrical charge; however, larger particles, which have low electrophoretic mobilities, cannot be easily separated with EP-based techniques. This study presents an alternative for the characterization, assessment, and separation of larger microparticles, where charge differences are exploited with DEP instead of EP. Polystyrene microparticles with sizes varying from 5 to 10 μm were characterized employing microdevices for insulator-based dielectrophoresis (iDEP). Particles within an iDEP microchannel were exposed simultaneously to DEP, EP, and electroosmotic (EO) forces. The electrokinetic behavior of four distinct types of microparticles was carefully characterized by means of velocimetry and dielectrophoretic capture assessments. As a final step, a dielectropherogram separation of two distinct types of 10 μm particles was devised by first characterizing the particles and then performing the separation. The two types of 10 μm particles were eluted from the iDEP device as two separate peaks of enriched particles in less than 80 s. It was demonstrated that particles with the same size, shape, surface functionalization, and made from the same bulk material can be separated with iDEP by exploiting slight differences in the magnitude of particle charge. The results from this study open the possibility for iDEP to be used as a technique for the assessment and separation of biological cells that have very similar characteristics (shape, size, similar make-up), but slight variance in surface electrical charge.

Quantification of colloidal filtration of polystyrene micro-particles on glass substrate using a microfluidic device.

A microfluidic device was designed to investigate filtration of particles in an electrolyte in the presence of liquid flow. Polystyrene spheres in potassium chloride solution at concentrations of 3-100 mM were allowed to settle and adhere to a glass substrate. A particle free solution at the same concentration was then flushed through the microfluidic channel at 0.03-4.0 mL/h. As the hydrodynamic drag on the adhered particles exceeded the intersurface interaction with the substrate, "pull-off" occurred and the particles detached. Filtration efficiency, α, was shown to a function of both ionic concentration of the liquid medium and flow speed, consistent with a phenomenological model based on the classical DLVO theory. The results elucidates the underlying physics of filtration.

Dielectrophoresis‐based microfluidic devices for field‐flow fractionation

AbstractIn this communication, dynamic model for analysing micro‐objects’ path in dielectrophoresis (DEP)‐based microfluidic devices for executing field‐flow fractionation is formulated and subsequently employed for parametric study. Electrodes of finite length, that pass along the full width of the microchannel, are placed on the microchannel's upper and lower walls; each upper electrode and electrode gap aligns with a lower electrode gap and electrode, respectively. The model accounts for forces associated with inertia, sedimentation, DEP, drag and virtual mass. The model indicates that micro‐objects’ trajectory depends on actuation voltage, volumetric flow rate, micro‐object radius, electrode and gap dimensions, and microchannel height. The steady‐state levitation height is found to be independent of radius of micro‐object and volumetric flow rate while being dependent on electrode and gap dimensions, microchannel height and actuation voltage. The model predicts that there exists an optimal value of electrode and gap dimensions for which the steady‐state levitation height is maximum when all other parameters are kept constant. The efficacy of the device is demonstrated by separating a heterogeneous mixture of silica and polystyrene microparticles into homogeneous samples.

Zeptomole Detection Scheme Based on Levitation Coordinate Measurements of a Single Microparticle in a Coupled Acoustic-Gravitational Field

We present a novel analytical principle in which an analyte (according to its concentration) induces a change in the density of a microparticle, which is measured as a vertical coordinate in a coupled acoustic-gravitational (CAG) field. The density change is caused by the binding of gold nanoparticles (AuNP's) on a polystyrene (PS) microparticle through avidin-biotin association. The density of a 10-μm PS particle increases by 2% when 500 100-nm AuNP's are bound to the PS. The CAG can detect this density change as a 5-10 μm shift of the levitation coordinate of the PS. This approach, which allows us to detect 700 AuNP's bound to a PS particle, is utilized to detect biotin in solution. Biotin is detectable at a picomolar level. The reaction kinetics plays a significant role in the entire process. The kinetic aspects are also quantitatively discussed based on the levitation behavior of the PS particles in the CAG field.

2DEP cytometry: distributed dielectrophoretic cytometry for live cell dielectric signature measurement on population level.

In this work, a novel force equilibrium method called distributed dielectrophoretic cytometry (2DEP cytometry) was developed. It uses a dielectrophoresis (DEP)-induced vertical translation of live cells in conjunction with particle image velocimetry (PIV) in order to measure probabilistic distribution of DEP forces acting on an entire cell population. The method is integrated in a microfluidic device. The bottom of the microfluidic channel is lined with an interdigitated electrode array. Cells passing through the micro-channel are acted on by sedimentation forces, while DEP forces either oppose sedimentation, support sedimentation, or neither, depending on the dielectric (DE) signatures of the cells. The heights at which cells stabilize correspond to their DE signature and are measured indirectly using PIV, which enables simultaneous and high-throughput collection of hundreds of single-cell responses in a single PIV frame. The system was validated using polystyrene micro-particles. Preliminary experimental data quantify the DE signatures of immortalized myelogenous leukemia cell lines K562 and KG1. We show DEP-induced cell translation along the parabolic velocity profile can be measured by PIV with sub-micron precision, enabling identification of individual cell DE signatures. DE signatures of the selected cell lines are distinguishable. Throughput of the method enables measurement of DE signatures at 10 different frequencies in almost real time.

ESI MS for Microsized Bioparticles.

An ESI ion trap mass spectrometer was designed for high-throughput and rapid mass analysis of large bioparticles. Mass calibration of the instrument was performed using commercially available polystyrene (PS) microparticles with a size comparable to cancer cells. Different sizes of MCF-7 breast cancer cells (8 to 15 μm) were used in this study. The masses of different cancer cells were measured. This system allows for the analysis of all types of particles.

Acoustic Wave-Driven Functionalized Particles for Aptamer-Based Target Biomolecule Separation.

We developed a hybrid microfluidic device that utilized acoustic waves to drive functionalized microparticles inside a continuous flow microchannel and to separate particle-conjugated target proteins from a complex fluid. The acoustofluidic device is composed of an interdigitated transducer that produces high-frequency surface acoustic waves (SAW) and a polydimethylsiloxane (PDMS) microfluidic channel. The SAW interacted with the sample fluid inside the microchannel and deflected particles from their original streamlines to achieve separation. Streptavidin-functionalized polystyrene (PS) microparticles were used to capture aptamer (single-stranded DNA) labeled at one end with a biotin molecule. The free end of the customized aptamer15 (apt15), which was attached to the microparticles via streptavidin-biotin linkage to form the PS-apt15 conjugate, was used to capture the model target protein, thrombin (th), by binding at exosite I to form the PS-apt15-th complex. We demonstrated that the PS-apt15 conjugate selectively captured thrombin molecules in a complex fluid. After the PS-apt15-th complex was formed, the sample fluid was pumped through a PDMS microchannel along with two buffer sheath flows that hydrodynamically focused the sample flow prior to SAW exposure for PS-apt15-th separation from the non-target proteins. We successfully separated thrombin from mCardinal2 and human serum using the proposed acoustofluidic device.

In-droplet microparticle separation using travelling surface acoustic wave.

Droplets in microfluidic systems can contain microscale objects such as cells and microparticles. The control of the positions of microscale objects within a microchannel is crucial for practical applications in not only continuous-flow-based but also droplet-based systems. This paper proposes an active method for the separation of microparticles inside moving droplets which uses travelling surface acoustic waves (TSAWs). We demonstrate the preconcentration and separation of 5 and 10 μm polystyrene microparticles in moving water-in-oil droplets through the application of TSAWs with two different frequencies. The microparticles inside the droplets are affected by the acoustic radiation force induced by the TSAWs to move laterally in the direction of the TSAW propagation and are thereby separated according to their size. In-droplet separation is then demonstrated through droplet splitting at a Y-junction. Compared to our previous studies, this acoustic approach offers the label-free and on-demand separation of different-sized micro-objects in moving droplets. The present method has potential uses such as in-droplet sample purification and enrichment.