Polystyrene Colloidal Particles Research Articles

Underwater Structurally‐Colored Adhesives for Visualized Adhesion Monitoring in Aqueous Media

AbstractAssessment of the local strain/stress changes of adhesives is highly desirable for their service to avoid premature failure. However, monitoring local strain/stress variations in adhesives in practical settings remains challenging, especially in aqueous media. Here, an underwater structurally‐colored adhesive for visualized local strain/stress monitoring in aqueous media is reported. The structurally‐colored adhesive is obtained by shearing composites of poly(butyl acrylate‐co‐acrylic acid) copolymer and carboxylated polystyrene colloidal particles. The resultant structurally‐colored adhesive exhibits underwater adhesive strength (i.e., 238 kPa for stainless steel substrates) to various substrates (e.g., metals and plastics) thanks to hydrophobic segments and carboxyl groups. Notably, they can shift color in response to external force, enabling real‐time visual monitoring of localized strain/stress changes. As a proof of concept, the structurally‐colored adhesive can be used to seal a leaking hole on a bottle or tube, and it can precisely visualize the localized pressure distribution, providing critical information on the adhesion performance and the local pressure. These distinctive properties make the structurally‐colored adhesive suitable for application in wet environments as a real‐time visual pressure tracking device.

Thin photonic crystal templates for enhancing the SERS signal: a case study using very low concentrations of dye molecules

A single monolayer photonic crystal (PhC) of polystyrene(PS) colloidal particles with gold nanoparticles drop-casted on the surface have been employed as templates for the detection of dye molecules (methylene blue is taken as analyte for the case study) at very low concentrations using the surface-enhanced Raman scattering (SERS) technique. Results obtained from the SERS investigations clearly reveal that PhC templates significantly enhance the Raman peak, lowering the detection limits of dye molecules (viz., Methylene Blue, Rhodamine 6G, and Malachite Green) to ∼50 nM. The results are understood by performing finite element method (FEM) based electromagnetic numerical simulations. Simulations have shown that the electric field locally gets redistributed, and significant enhancement occurs at wedge regions formed by touching PS spheres, which gets further enhanced in the presence of a gold nanoparticle at the wedge region. Gold nanoparticles sitting at the wedge regions serve as hot spots and are responsible for enhanced SERS signals.

The effects of selectively blocking the electron transport layer of n-i-p perovskite solar cells with polymer particles on device performance

We use insulating polystyrene colloid particles to selectively cover the electron transport layer of n-i-p perovskite solar cells and investigate the effects of the coverage and lateral blocking distance on device performance.

In-Plane Rotation of Prolate Colloids Adhered to a Planar Substrate in the Presence of Flow.

Micron-size spherical polystyrene colloidal particles are mechanically stretched to a prolate geometry with desirable aspect ratios. The particles in an aqueous medium with specific ionic concentration are then introduced into a microchannel and allowed to settle on a glass substrate. In the presence of unidirectional flow, the loosely adhered particles in the secondary minimum of surface interaction potential are easily washed off, but the remnant in the strong primary minimum preferentially aligns with the flow direction and exercises in-plane rotation. A rigorous theoretical model is constructed to account for filtration efficiency in terms of hydrodynamic drag, intersurface forces, reorientation of prolate particles, and their dependence on flowrate and ionic concentration.

Pinning and Depinning Dynamics of an Evaporating Sessile Droplet Containing Mono- and Bidispersed Colloidal Particles on a Nonheated/Heated Hydrophobic Substrate

The present study is primarily focused on the coupled effects of substrate heating, colloidal dispersion, and particle size variation on the contact line (CL) pinning-depinning dynamics of evaporating droplets containing mono- (3/4.5 μm) and bidispersed (3 and 4.5 μm) polystyrene colloidal particles on poly(dimethylsiloxane) (PDMS) substrates. Experimental techniques such as high-speed visualization, optical microscopy, infrared thermography, and scanning electron microscopy are implemented to discover the plausible causes dictating the underlying physics. In the case of the nonheated substrate, there exists a significant delay in the CL depinning for the evaporating droplets containing bidispersed particles, as opposed to the monodispersed cases. A first-order model is illustrated for the determination of the net horizontal force acting on the particles near the CL. Interestingly, the model's findings revealed that due to the difference of particle size in the case of the bidispersed suspension, the interparticle contact force gets modified, thus enhancing the CL pinning. For the heated substrate cases, droplets with monodispersed particles (3 μm) exhibit a substantial delay in the CL depinning, whereas a nearly complete pinning of the CL is witnessed for the case of bidispersed colloidal suspension droplets. It is mainly due to the augmentation of particle deposition near the CL because of the circulatory thermal Marangoni and outward capillary flows. Thus, the mobility of the CL is inhibited, which is further reinforced by the presence of different-sized particles. Eventually, a ring-like deposition is observed, as opposed to an inner deposit commonly observed from the evaporation of colloidal droplets on hydrophobic substrates.

Frequency-responsive cooperativity of graphene oxide complexes under a low AC bulk electric field

Graphene oxide (GO) is a promising material for the construction of biological functional surfaces and corresponding biomedical applications. The physical properties of sheets of GO are determined by its conductivity, flexibility (being just a few atomic carbon layers thick), and hydrophilicity/hydrophobicity. In order to exploiting multitask surfaces, however, controlling reliable tunability of the complex formation with other macromolecules in aqueous environments is highly non-trivial due to the hydrophobic nature of GO. Thus, one effective way of complicated physical process of dealing with aqueous systems of GO is to perform the complex formation under in-situ external fields. In this paper, we report the response of GO-sheets, complexed with spherical colloidal polystyrene particles, nafion, and long and thin DNA-viruses (fd), in alternating electric fields, probed by means of novel experimental methods of image-time correlation spectroscopy and small-angle dynamic light scattering. Here, the frequency-responsive reorientations of a GO-sheet are interpreted by random orientations of particles. As results, we have found that GO carries overall local reorientations with feedback oscillations, as well in the GO-complexes (of a colloidal sphere polymerized polystyrene (PPs) and nafion solution). However, such oscillations are absent, as overdamped Brownian motion, in the mixture of DNA-virus suspension (with GO-PPs). This indicates that Brownian fluctuations of GO can be effectively stabilized, and cooperated in the membrane-based, isotropic rod-mesh network of DNA-virus (fd) suspension. We hope then the results are useful to foster better designs of processing GO-sheets in the controls of accessible biological and biomedical applications.

Synthesis of anisotropic colloids with concave and convex structures.

Anisotropic colloidal particles with concave and convex structures are useful in both theoretical studies and applications. In this work, we mass-produced polystyrene (PS) colloidal particles with multiple concavities through dispersion polymerization techniques. By increasing the delayed feeding time td of the cross-linker divinylbenzene (DVB), the morphological evolution of particles can be classified into two stages, during which the formation of different concavities is consistent with either the buckling mechanism or phase separation mechanism. By varying the DVB dosage, we found that the size of the big chamber formed on the particle surfaces decreases as the DVB dosage increases. Then, using these concave particles as seeds, 2-5 μm anisotropic colloids with various shapes, including spherical, ellipsoidal, snowman and multi-protrusion, were synthesized by seeded emulsion polymerization. Moreover, our results show that both the chambers and long narrow ditches on the surface of seeds can be the active sites for monomers to gather and polymerize, but monomers in the big chamber have a priority to polymerize first when big and small concavities both exist on seeds. The results of this study could mean great potential in synthesizing a variety of anisotropic particles with well-controlled concave morphologies.

Effect of electrolyte concentration on effective surface charge of colloidal particles

The effective surface charge of colloid particles is an important parameter that determines the colloidal properties. However, it is still unclear whether the solvent environment (such as the electrolyte concentration) can affect the effective surface charge. Due to complicated effects relevant to the effective surface charge, such as the exchange of dissociable ions between the electrolyte and surface groups of polystyrene particles, the coupling effect of incomplete ionization of the surface groups of the particles and the adsorption of ions by colloidal particles, etc., it is rather difficult to accurately measure the surface charge and understand the mechanism of charge variation with solvent environment. To solve this problem, we measure the conductivities of polystyrene colloidal particles of carboxyl groups and sulfonic acid groups at various particle number densities and HCl concentrations. Since the cations generated from the two kinds of particles and HCl solution are all H<sup>+</sup> cations, the surface charge can be obtained by the conductivity-number density method (migrant method), no matter whether the cation exchanges occur between ionized positive ions of the electrolyte and colloidal particles. Based on the experimental results, the influences of HCl concentration and particle number density on the surface charge of colloidal particles are detected, and the reasons of the influence are analyzed. It is found that the change of the surface charge of the particles of carboxyl group with HCl concentration is faster than that of sulfonic acid group with the HCl concentration. For the same electrolyte concentration, the effective surface charge of carboxyl modified colloidal particles is related to the particle number density, while the charge of sulfonic modified particles is not. Considering the fact that the sulfonic acid group and carboxyl group are strong and weak acid groups respectively, the ionization of H<sup>+</sup> cations of the two different groups have profound influences on the cation replacement process, and affect the trend of the curve of the conductivity-particle number density. This effect further results in different change tendencies of effective surface charge with HCl concentration and particle number density. According to the theoretical model as described in this study, all experimental results are well explained. The mechanisms described in this article will be useful for stating the influencing factors of the surface effective charge, and the application of the effective charge to different phenomena relating to interparticle interactions with different parameters of solutions.

Perfusion Chamber for Observing a Liposome-Based Cell Model Prepared by a Water-in-Oil Emulsion Transfer Method.

For the construction of a chemical model of contemporary living cells, the so-called water-in-oil emulsion transfer (WOET) method has drawn much attention as one of the promising preparation protocols for cell-sized liposomes encapsulating macromolecules and even micrometer-sized colloidal particles in high yields. Combining the throughput and accuracy of the observation is the key to developing a synthetic approach based on the liposomes prepared by the WOET method. Recent advances in microfluidic technology can provide a solution. By means of surface modification of a poly(dimethylsiloxane)-type microfluidic device integrating size-sorting and trapping modules, here, we enabled a simultaneous direct observation of the liposomes with a narrow size distribution, which were prepared by the WOET method. As a demonstration, we evaluated the variance of encapsulation of polystyrene colloidal particles and water permeability of the cell-sized liposomes prepared by the WOET method in the device. Since the liposomes prepared by the WOET method are useful for constructing cell models with an easy protocol, the current system will lead to a critical development of not only supramolecular chemistry and soft matter physics but also synthetic biology.

Decimating Spatial Frequency Components in Periodically Modulated Nanoscale Surface Structures for Sensing of Ambient Refractive Index Changes.

In our previous study, we developed an array of unique porous structures (an array of barnacle-like porous structures) to apply to biosensing chips. The porous structure was formed by an internal swelling phenomenon of a polystyrene colloidal particle monolayer, which was surrounded by a poly(vinyl alcohol) layer, for the duration of the monolayer’s immersion in a toluene bath. Barnacle-like porous structures were formed when polystyrene particles that had rapidly swelled broke the outer layer around the top of the particles. However, after the surface was coated with a thin Ag layer, the porous structure showed a relatively broad extinction spectrum that was undesirable for sensing chips based on both surface plasmon extinction and grating coupling. In this paper, we propose an approach to obtain relatively sharp extinction spectra based on the decimation of the spatial frequencies of the porous structures. This study also investigates formation properties in more detail to control the structural features of the resultant porous structures. A relatively sharp peak in the extinction spectrum was ultimately obtained.

Robust hydrophobic veova10-based colloidal photonic crystals towards fluorescence enhancement of quantum dots.

Hydrophobic photonic crystals (PCs) has been increasingly appreciated as a promising functional material due to their distinct surface characteristic of structural color and hydrophobicity. However, it remains a challenge to fabricate hydrophobic PCs via a one-step process. Inspired by the development of high-performance waterborne coatings, we propose an easy-to-perform and high-efficiency strategy to construct hydrophobic building blocks (diameter of 221, 247, 276 and 305 nm), where the umbelli-form hydrophobic long chain (veova10 Cn > 9) was loaded onto polystyrene (PS) colloidal particles in situ. Taking advantage of the hydrophobic driving force between the colloidal particles, large-scale colloidal photonic crystals (CPCs) film with crack-free morphology was obtained efficiently. The derived CPCs exhibit robust mechanical stability, prominent hydrophobicity and excellent optical properties. In addition, the colloidal latex holds great potential toward PCs coatings on a variety of substrates (glass, plastic and steel) with excellent adhesiveness. Furthermore, we contrive to construct angle-independent structural color films and supraballs, and explore their application in quantum dots (QDs) fluorescence enhancement, which achieved an enhancement effect by more than eight times. From the standpoint of practical applications, we achieved the flexible high-brightness wearable light-emitting diode (LED) displays. This work will lay a foundation for the development of high-efficiency PCs building blocks, and indicate the direction for the meaningful application of CPCs.

Signature of jamming under steady shear in dense particulate suspensions

Under an increasing applied shear stress (), the viscosity of many dense particulate suspensions increases drastically beyond a stress onset (), a phenomenon known as discontinuous shear-thickening. Recent studies point out that some suspensions can transform into a stress induced solid-like shear jammed (SJ) state at high particle volume fraction (). SJ state develops a finite yield stress and hence is distinct from a shear-thickened state. Here, we study the steady state shear-thickening behaviour of dense suspensions formed by dispersing colloidal polystyrene particles (PS) in polyethylene glycol (PEG). We find that for small values the viscosity of the suspensions as a function of can be well described by Krieger–Dougherty (KD) relation. However, for higher values of (), KD relation systematically overestimates the measured viscosity, particularly for higher values. This systematic deviation can be rationalized by the weakening of the sample due to flow induced failures of the solid-like SJ state. Using Wyart–Cates model, we propose a method to predict the SJ onset from the steady state rheology measurements. Our results are further supported by in situ optical imaging of the sample boundary under shear.

A Photochemical Approach toward High‐Fidelity Programmable Transfer Printing

AbstractTransfer printing is a critically important process toward assembling a wide range of materials and fabricating high‐performance flexible and stretchable electronics. It is still challenging to directly integrate transfer printing techniques into current semiconductor processing technologies via a low‐cost, scalable, and programmable manner. Here, a photochemical approach is proposed to transfer microelectronic components and functional materials onto soft substrates. This approach relies on the photoinduced modulation of the adhesive strength of stamps, leading to faithfully pick up and release inks upon UV irradiation. Moreover, by coupling with a photomask, this method could be further utilized to print inks via a spatially selective manner which is difficult to realize in conventional approaches. Micrometer‐sized Si inks, thin‐film metal electrodes, and polystyrene colloidal particles are transferred from their corresponding donor substrates to polydimethylsiloxane substrates to demonstrate the potential of this versatile approach. Considering that UV light is widely used in current semiconductor industry (e.g., photolithography), this method could be potentially compatible with large‐area, high‐throughput manufacturing processes. This newly developed photochemical approach toward programmable transfer printing provides a promising solution for high‐volume production of flexible and stretchable electronics in the near future.

Analysis of profile and morphology of colloidal deposits obtained from evaporating sessile droplets

We experimentally investigate the profile and morphology of the ring-like deposits obtained after evaporation of a sessile water droplet containing polystyrene colloidal particles on a hydrophilic glass substrate. In particular, the coupled effect of particle size and concentration are studied. The deposits were qualitatively visualized under an optical microscope and profile of the ring was measured by an optical profilometer. The profile of the ring resembles a partial torus-like shape for all cases of particles size and concentration. The cracks on the surface of the ring were found to occur only at smaller particle size and larger concentration. We plot a regime map to classify three deposit types - discontinuous monolayer ring, continuous monolayer ring, and multiple layers ring - on particles concentration - particle size plane. Our data shows a possible existence of a critical concentration (particle size) for a given particle size (concentration) at which the monolayer ring forms. For the larger particle sizes, the immersion capillary forces between the particles dominate, aiding the formation of a monolayer ring of the particles. We measure the width and height of the ring and show that they scale with particle concentration by a power law for the multiple layers ring. This scaling corroborates with an existing continuum based theoretical model. We briefly discuss the effect of the interaction of growing deposit with shrinking free surface on the ring dimensions and profile. The present results aid understanding of the ring formation process and will be useful in guiding the design of self-assemblies of the colloidal particles formed by the evaporating droplets.

Efficient Removal of Lead, Copper and Cadmium Ions from Water by a Porous Calcium Alginate/Graphene Oxide Composite Aerogel.

In this study, we fabricated a porous calcium alginate/graphene oxide composite aerogel by using polystyrene colloidal particles as sacrificial template and graphene oxide as a reinforcing filler. Owing to the excellent metal chelation ability of calcium alginate and controlled nanosized pore structure, the as-prepared calcium alginate/graphene oxide composite aerogel (mp-CA/GO) can reach the adsorption equilibrium in 40 min, and the maximum adsorption capacity for Pb2+, Cu2+ and Cd2+ is 368.2, 98.1 and 183.6 mg/g, respectively. This is higher than most of the reported heavy metal ion sorbents. Moreover, the mp-CA/GO can be regenerated through simple acid-washing and be used repeatedly with little loss in performance. The adsorption mechanism analysis indicates that the mp-CA/GO adsorb the heavy metal ions mainly through the ion exchange and chemical coordination effects.

Surface-enhanced Raman scattering from metal and transition metal nano-caped arrays

The metal and transition metal cap-shaped arrays on polystyrene colloidal particle (PSCP) templates were fabricated to study the surface-enhanced Raman scattering (SERS) effect. We obtained the Ag and Fe complex film by a co-sputtering deposition method. The size of the deposited Fe particle was changed by the sputtering power. We also study the SERS enhancement mechanism by decorating the PATP probe molecule on the different films. The SERS signals increased firstly, and then decreased as the size of Fe particles grows gradually. The finite-difference time domain (FDTD) simulation and experimental Raman results manifest that SERS enhancement was mainly attributed to surface plasma resonance (SPR) between Ag and Ag nanoparticles. The SERS signals of PATP molecule were enhanced to reach a lowest detectable concentration of 10−8 mol/L. The research demonstrates that the SERS substrates with Ag-Fe cap-shaped arrays have a high sensitivity.

Reduced graphene oxide/2D colloidal array composite membrane fabricated layer-by-layer

Photonic crystal (PhC) presents unique optical properties and functionality, and are used widely as detectors, modulators, plasmonics and light generating devices. However, the low electrical conductivity and mechanical strength limit its applications. We introduced here a layer-by-layer composite membrane based on reduced graphene oxide (RGO) and two-dimensional (2D) colloidal crystal array (CCA). The 2D CCA was fabricated by an air/water interface deposition technique using polystyrene (PS) and polymethyl methacrylate (PMMA) colloidal particles. The composite membrane were characterized by SEM, Debye diffraction, reflectance spectra and electrical resistance measurement. The results indicated that layer-by-layer composite membrane have highly periodicity, and the monolayer of RGO and 2D CCA combined tightly. The Debye diffraction rings of the layer-by-layer heterostructure composite are the superimposition of the individual monolayers of 2D CCA. The reflection spectrum of the layer-by-layer heterostructure composite membrane showed that two peaks of reflection curve located in near ultraviolet region and visible region respectively, and the RGO sheet have no influence on the peak position and shape of reflection curve of the PhC. The RGO improved the electrical conductivity of the layer-by-layer heterostructure composite. The layer-by-layer heterostructure composite showed promising potential for the applications as sensors and optoelectronic devices.

Iron layer-dependent surface-enhanced raman scattering of hierarchical nanocap arrays

In this report, we fabricated the multi-layer Ag/Fe/Ag sandwich cap-shaped films on monolayer non-closed packed (ncp) polystyrene colloidal particle (PSCP) templates through a layer-by-layer (LBL) depositing method. This research focused on the surface-enhanced Raman scattering (SERS) effect of the thickness of the deposited Fe film which was controlled by the sputtering time. The SERS intensities were increased firstly, and then decreased as the thickness of Fe layer grows gradually, which is attributed to the charge transition from the Fermi level of the Ag NPs to Fe layer. The use of multi-layer Ag/Fe/Ag sandwich cap-shaped films enables us to evaluate the contribution of surface plasmon resonance and charge distribution between Ag and Fe to SERS enhancement. Our work introduced a novel system (Ag/Fe/Ag) for high performance SERS and extended the SERS application of Fe. Furthermore, we have designed the Ag/Fe/Ag SERS-active substrate as the immunoassay chip for quantitative determination of AFP-L3 which is the biomarker of hepatocellular carcinoma (HCC). The proposed research demonstrates that the SERS substrates with Ag/Fe/Ag sandwich cap-shaped arrays have a high sensitivity for bioassay.

Induced Attraction between Polystyrene Colloidal Particles in a Binary Mixture with PNIPAM Colloidal Microgels.

We investigate the phase behaviors of binary mixtures of polystyrene (PS) hard-sphere and poly(N-isopropylacrylamide-co-acrylic acid) (PNIPAM) soft-sphere colloidal particles as a function of temperature. As the temperature increases, apparent attractions arise between the PS particles, to the point of clustering at the highest temperature. This attractive force is found to be due to the change in pH caused by the acrylic acid co-polymerized with the temperature-sensitive PNIPAM particles, which in turn collapses the sterical stabilizing surface layers on the PS particles. Our experiments provide a new way to tune colloidal interactions with temperature for particles that are otherwise insensitive to temperature variations.

Temperature-Induced, Selective Assembly of Supramolecular Colloids in Water.

In this article, we report the synthesis and physical characterization of colloidal polystyrene particles that carry water-soluble supramolecular N,N′,N″,-trialkyl-benzene-1,3,5-tricarboxamides (BTAs) on their surface. These molecules are known to assemble into one-dimensional supramolecular polymers via noncovalent interactions. By tethering the BTAs to charge-stabilized particles, the clustering behavior of the resulting colloids was dictated by a balance between interparticle electrostatic repulsion and the BTA-mediated attractions. Through careful tuning of the dispersing medium’s ionic strength, a regime was found in which particle aggregation could be reversibly induced upon heating the dispersion. These findings clearly indicate that hydrophobic interactions, which become stronger upon heating, play an important role during the clustering process. Besides the thermoreversible nature of the generated hydrophobic interparticle attractions, we found the clustering to be selective, that is, the BTA-functionalized colloids do not interact with nonfunctionalized hydrophobic polystyrene particles. This selectivity in the association process can be rationalized by the preferred stacking of the surface-tethered BTAs. These selective intermolecular/particle bonds are likely stabilized by the formation of hydrogen bonds, as previously observed for analogous molecular BTA assemblies. The resulting driving force responsible for particle clustering is therefore dual in nature and depends on both hydrophobic attractions and hydrogen bonding.