Spherical Polyelectrolyte Brushes Research Articles

Advances and Prospects in the Study of Spherical Polyelectrolyte Brushes as a Dopant for Conducting Polymers.

Owing to their special structure and excellent physical and chemical properties, conducting polymers have attracted increasing attention in materials science. In recent years, tremendous efforts have been devoted to improving the comprehensive performance of conducting polymers by using the technique of "doping." Spherical polyelectrolyte brushes (SPBs) bearing polyelectrolyte chains grafted densely to the surface of core particles have the potential to be novel dopant of conducting polymers not only because of their spherical structure, high grafting density and high charge density, but also due to the possibility of their being applied in printed electronics. This review first presents a summary of the general dopants of conducting polymers. Meanwhile, conducting polymers doped with spherical polyelectrolyte brushes (SPBs) is highlighted, including the preparation, characterization, performance and doping mechanism. It is demonstrated that comprehensive performance of conducting polymers has improved with the addition of SPBs, which act as template and dopant in the synthesis of composites. Furthermore, the applications and future developments of conductive composites are also briefly reviewed and proposed, which would draw more attention to this field.

Spherical Polyelectrolyte Brushes as Flocculants and Retention Aids in Wet-End Papermaking.

As the criteria of energy conservation, emission reduction, and environmental protection become more important, and with the development of wet-end papermaking, developing excellent retention aids is of great significance. Spherical polyelectrolyte brushes (SPBs) bearing polyelectrolyte chains grafted densely to the surface of core particle have the potential to be novel retention aids in wet-end papermaking not only because of their spherical structure, but also due to controllable grafting density and molecular weight. Such characteristics are crucial in order to design multi-functional retention aids in sophisticated papermaking systems. This review presents some important recent advances with respect to retention aids, including single-component system and dual-component systems. Then, basic theory in papermaking is also briefly reviewed. Based on these advances, it emphatically describes spherical polyelectrolyte brushes, focused on their preparation methods, characterization, conformation, and applications in papermaking. This work is expected to contribute to improve a comprehensive understanding on the composition, properties, and function mechanisms of retention aids, which helps in the further investigation on the design of novel retention aids with excellent performance.

Continuous Synthesis of Spherical Polyelectrolyte Brushes by Photo-Emulsion Polymerization in a Microreactor.

Nanosized spherical polyelectrolyte brushes (SPBs) are ideal candidates for the preparation of nanometal catalysts, protein separation, and medical diagnostics. Until now, SPBs have been synthesized by photo-emulsion polymerization in a batch reactor, which remains challenging to scale up. This paper reports a successful continuous preparation of SPBs by photo-emulsion polymerization in a self-made microreactor. The effects of residence time, monomer concentration, and feed ratios on the conversion of monomers and SPB structures are systematically investigated by dynamic lighting scattering and transmission electron microscopy. Poly(acrylic acid) (PAA) SPBs obtained in a microreactor exhibiting a narrow size distribution with a short reaction time are very effective in inhibiting the calcium carbonate scale and are comparable to those produced in a batch reactor. This work confirms the feasibility of continuous preparation and scaled-up production of SPBs.

Colloidal Polymer-Templated Formation of Inorganic Nanocrystals and their Emerging Applications.

Inorganic nanocrystals possess unique physicochemical properties compared to their bulk counterparts. Stabilizing agents are commonly used for the preparation of inorganic nanocrystals with controllable properties. Particularly, colloidal polymers have emerged as general and robust templates for in situ formation and confinement of inorganic nanocrystals. In addition to templating and stabilizing inorganic nanocrystals, colloidal polymers can tailor their physicochemical properties such as size, shape, structure, composition, surface chemistry, and so on. By incorporating functional groups into colloidal polymers, desired functions can be integrated with inorganic nanocrystals, advancing their potential applications. Here, recent advances in the colloidal polymer-templated formation of inorganic nanocrystals are reviewed. Seven types of colloidal polymers, including dendrimer, polymer micelle, stare-like block polymer, bottlebrush polymer, spherical polyelectrolyte brush, microgel, and single-chain nanoparticle, have been extensively applied for the synthesis of inorganic nanocrystals. Different strategies for the development of these colloidal polymer-templated inorganic nanocrystals are summarized. Then, their emerging applications in the fields of catalysis, biomedicine, solar cells, sensing, light-emitting diodes, and lithium-ion batteries are highlighted. Last, the remaining issues and future directions are discussed. This review will stimulate the development and application of colloidal polymer-templated inorganic nanocrystals.

A brushed magnetic microbeads carrier with host-guest structures for enhancing bio-detection performance in beads-based flow cytometry

Here we report a brushed magnetic microbeads (BMBs) carrier with host-guest structures for enhancing bio-detection performance in beads-based flow cytometry (FCM). The micro-sized MBs are employed as host spheres and the nano-sized spherical polyelectrolyte brushes (SPBs) are utilized as guest particles to achieve the covalent assembly of SPBs on MBs (that is BMBs). Our proposed BMBs carrier exhibits a remarkable signal to noise improvement of approximately 8–9 times in beads-based immunoassay on FCM compared to conventional MBs via preserving capture antibodies’ activity and reducing detection antibodies’ nonspecific adsorption. This study demonstrates the promising potential of our developed BMBs carrier for beads-based flow cytometry.

Effects of electrostatic coupling and surface polarization on polyelectrolyte brush structure.

In this work, we perform molecular dynamics simulations to study a spherical polyelectrolyte brush. We explore the effects of surface polarization and electrostatic coupling on brush size and distribution of counterions. The method of image charges is considered to take into account surface polarization, considering a metallic, an unpolarizable, and a dielectric nano-core. It is observed that, for all cases, a moderate shrinking-swelling effect appears with an increase in the electrostatic coupling parameter. This effect occurs under high Manning ratios. The curves relating the average size of polyelectrolyte brush as a function of coupling show a minimum. The results show that the grafting density of polyelectrolytes on the nano-core surface plays an important role in the polarization effect. We consider a modified Poisson-Boltzmann theory to describe the counterion profiles around the brush in the case of unpolarizable nano-cores and weak electrostatic coupling.

Photosensitive Spherical Polymer Brushes: Light-Triggered Process of Particle Repulsion

We report on a light-triggered process at which repulsive interactions between microparticles with a polyelectrolyte (PE) brush coating can be remotely controlled. The spherical polyelectrolyte brushes are loaded with photosensitive azobenzene containing surfactant which can undergo reversible photo-isomerization from trans to cis state. The surfactant hydrophilicity is altered by illumination with light of an appropriate wavelength, at which a dynamic exchange of the more surface-active trans isomer in comparison to the more water soluble cis isomer with the PE brush generates a concentration gradient of the cis isomers near a solid surface where the particle is sedimented. In this way, each spherical brush produces its local lateral diffusioosmotic flow pointing outside in a radial direction resulting in mutual long-range repulsive interactions. We demonstrate that a PE layer has a higher tendency to absorb surfactant in comparison to plain silica particles, yielding a larger flow strength. This correlation holds true up to a critical intensity, where the dynamic exchange is adsorption limited with respect to trans isomers and especially pronounced for the PE-coated particles.

Ultrasmall Pt Nanozymes Immobilized on Spherical Polyelectrolyte Brushes with Robust Peroxidase-like Activity for Highly Sensitive Detection of Cysteine.

Distinct platinum (Pt) nanozymes as peroxidase mimics have received extensive interest owing to their outstanding catalytic activity, high environmental tolerance, lower consumption, and great potential in replacing natural enzymes. However, easy agglomeration of Pt nanoparticles (Pt NPs) resulting from the high surface free energy significantly decrease their peroxidase-like activity. Herein, spherical polyelectrolyte brush (SPB)-stabilized ultrasmall Pt NPs (SPB@Pt NPs) were prepared by a novel synthetic strategy where the SPB not only performed as a nanoreactor for the synthesis of ultrasmall Pt NPs but also greatly stabilized Pt NPs against aggregation. The well-defined SPB@Pt NP nanozymes exhibited outstanding peroxidase-like activity for the catalytic oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) to blue oxidized TMB and were then used to establish a colorimetric sensor for rapid detection of cysteine, giving a limit of detection of 0.11 μM. Moreover, the colorimetric detection system was demonstrated with outstanding performance in sensitive and selective detection of cysteine in the presence of several interference molecules. From these results, SPB@Pt NPs have been regarded as promising peroxidase mimics for a large number of applications such as in biosensing, biomedicine, the food industry, and environmental chemistry.

Electric double layer of spherical pH-responsive polyelectrolyte brushes in an electrolyte solution: A strong stretching theory accounting for excluded volume interaction and mass action law

In this paper, we study the electrostatics of pH-responsive polyelectrolyte-grafted spherical particles by using a strong stretching theory that takes into account the excluded volume interaction and the density of chargeable sites on the polyelectrolyte molecules. Based on free energy formalism, we obtain self-consistent field equations for determining the structure and electrostatics of spherical polyelectrolyte brushes. First, we find that the smaller the radius of the inner core, the longer the height of the polyelectrolyte brush. Then, we also prove that an increase in the excluded volume interaction yields a swelling of the polyelectrolyte brush height. In addition, we demonstrate how the effect of pH, bulk ionic concentration, and lateral separation between adjacent polyelectrolyte chains on the electrostatic properties of a spherical polyelectrolyte brush is affected by the radius of the inner core, the excluded volume interaction, and the chargeable site density.

Preparation and performance of retention and drainage aid made of cationic spherical polyelectrolyte brushes

Abstract Spherical polymer brushes were synthesized by grafting acrylamide from the surface of γ-methacryloxypropyl trimethoxy-silane-modified SiO2 nanoparticles. Then, cationic spherical polyacrylamide (CSPAM) brushes were obtained by a manniched polyacrylamide (PAM). Fourier-transform infrared spectroscopy, transmission electron microscopy, thermogravimetric analysis, and gel permeation chromatography were introduced to analyze the structure, morphology, and molecular weight of CSPAM, respectively. The effects of pH and the dosage of CSPAM on the flocculation of fine pulp and precipitated calcium carbonate were studied. Furthermore, the optimal drainage performance could be achieved when the beating degree (°SR) decreased by about 14.42% with the dosage of CSPAM of 2 mg·g−1. The retention effect of CSPAM revealed that the highest first-pass retention was 71.1% when the dosage of CSPAM was 3.5 mg·g−1. In addition, the mechanism of retention and drainage of CSPAM was discussed.

Comprehensive demetallization of crude oil using spherical polyelectrolyte brushes with submicron polybutadiene latex as a core

AbstractStable oil‐soluble metals complexes in crude oil bring various problems to the oil processing. In the previous work, four spherical polymer brushes with SiO2 as a core showed high nickel and calcium removal efficiency, but SiO2 has high density and smaller specific surface area, greatly limiting the demetallization efficiency. In the present work, spherical polyelectrolyte brushes (PAA@PB) were synthesized by emulsion grafting polymerization. DLS and TEM show that PAA@PB exhibits a uniform spherical core‐shell structure with a diameter of 526.3 nm, and TGA exhibits that the grafting rate is 20.6%. The demetallization rate and selectivity of PAA@PB were investigated with varying concentration, electrical desalination conditions, pH value, and NaCl concentration. In contrast, the demetallization efficiency of PAA@PB is much greater than that of PAA@SiO2‐G. Notably, PAA@PB exhibits excellent nickel removal efficiency, but a little more selective for iron. The optimal removal rate for calcium, nickel, and iron are 55.3%, 52.6%, and 46.1%, respectively. Compared with P4VP@SiO2‐G, which possesses the highest demetallization efficiency among four polymer brushes with SiO2, to achieve the same nickel removal rate, the concentration of PAA@PB is almost eight times less than that of P4VP@SiO2‐G. Consequently, PAA@PB has great potential as an excellent comprehensive demetallization agent.

Spherical Polyelectrolyte Brushes Templated Hollow C@MnO Nanospheres as Sulfur Host Materials for Li−S Batteries

AbstractLi−S battery has been considered as the next‐generation energy storage device, which still suffers from the shuttle effect of lithium polysulfides (LiPSs). In this work, mesoporous hollow carbon‐coated MnO nanospheres (C@MnO) have been designed and synthesized using spherical polyelectrolyte brushes (SPB) as template, KMnO4 as MnO precursor, and polydopamine as carbon source to improve the electrochemical performance of Li−S battery. The hollow C@MnO nanospheres enable the combination of physical confinement and chemical adsorption of the LiPSs. The thin carbon coating layer can provide good electrical conductivity and additional physical confinement to polysulfides. Moreover, the encapsulated MnO inside the carbon shell exhibits strong chemical adsorption to polysulfides. The constructed C@MnO/S cathode shows the discharge capacity of 1026 mAh g−1 at 0.1 C with 79% capacity retention after 80 cycles. The synthesized hollow C@MnO nanoparticles can work as highly efficient sulfur host materials, providing an effective solution to suppress the shuttle effect in Li−S battery.

Catalytic Activity Comparison of Gold Nanoparticles in Annealed and Quenched Spherical Polyelectrolyte Brushes

Abstract Two kinds of cationic spherical polyelectrolyte brushes (SPB), quenched poly(methacryloxyethyltrimethyl ammonium chloride) brush and annealed poly(2-aminoethyl methacrylate hydrochloride) brush with polystyrene cores (PS-PMETAC and PS-PAEMH), were synthesized by photo-emulsion polymerization. The small and uniform gold nanoparticles (AuNPs) were successfully immobilized in these two SPBs. The chain layer extension of the quenched SPB loaded with AuNPs (SPB-Au) was more complete than that of the annealed SPB-Au in alkaline system. Compared the catalysis of the prepared AuNPs onto the two SPBs, it was found that the catalytic activity of AuNPs in quenched SPB is higher than that in annealed SPB.

Exploration on the Application of Nano-Sized Spherical Polyelectrolyte Brush as Membrane Antiscalants for Wastewater Treatment

Exploration on the Application of Nano-Sized Spherical Polyelectrolyte Brush as Membrane Antiscalants for Wastewater Treatment

Ultrafast Water Transport in Two‐Dimensional Channels Enabled by Spherical Polyelectrolyte Brushes with Controllable Flexibility

AbstractFast water transport channels are crucial for water‐related membrane separation processes. However, overcoming the trade‐off between flux and selectivity is still a major challenge. To address this, we constructed spherical polyelectrolyte brush (SPB) structures with a highly hydrophilic polyelectrolyte brush layer, and introduced them into GO laminates, which increased both the flux and the separation factor. At 70 °C, the flux reached 5.23 kg m−2 h−1, and the separation factor of butanol/water increased to ≈8000, which places it among the most selective separation membranes reported to date. Interestingly, further studies demonstrated that the enhancement of water transport was not only dependent on the hydrophilicity of the polyelectrolyte chains, but also influenced by their flexibility in the solvent. Quartz crystal microbalance with dissipation and molecular dynamics simulations revealed the structure‐performance correlations between water molecule migration and the flexibility of the ordered polymer chains in the 2D confined space.

Effect of Counterions on the Interaction among Concentrated Spherical Polyelectrolyte Brushes.

The effect of counterions on interactions among spherical polyelectrolyte brushes (SPBs) was systematically investigated by rheology, small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS). The SPB particles consist of a solid polystyrene (PS) core with a diameter of ca.100 nm and a chemically grafted poly-(acrylic acid) (PAA) brush layer. Metal ions of different valences (Na+, Mg2+ and Al3+) were used as counterions to study the interactions among concentrated SPBs. The so-called “structure factor peak” in SAXS, the “local ordered structure peak” in WAXS and rheological properties indicated the interactions among concentrated SPBs. Combining SAXS, WAXS and rheology, the formation mechanism of the local ordered structure among PAA chains in the overlapped area of adjacent SPB, which was generated due to the bridge function of counterions, was confirmed. In contrast, excessive counterions shielded the electrostatic interaction among PAA chains and destroyed the local ordered structure. This work enriches our understanding of the polyelectrolyte assembly in concentrated SPBs under the effect of counterions and lays the foundations for SPB applications.

Coacervation of Spherical Polyelectrolyte Brushes with Additional Polyelectrolytes Bearing Positive or Negative Charges.

By combining small-angle X-ray scattering, wide-angle X-ray scattering, and rheology, the effect of additional polyelectrolyte chains on interactions among spherical polyelectrolyte brushes (SPB) was systematically investigated both on microscopic and macroscopic levels. The negatively charged poly(acrylic acid) (PAA) chains and positively charged poly(dimethyl diallyl ammonium chloride) (PDDA) chains were used as additional polyelectrolyte chains to investigate the local ordered structure and the "polyelectrolyte peak" among SPB. Interestingly, coacervation appeared in the SPB emulsion while introducing additional free polyelectrolyte chains. The addition of excess positively charged PDDA chains would lead to the transformation of the SPB emulsion from the coacervation to the aggregation, while it has not been observed in the case of PAA chains. Moreover, it was further confirmed that the specific local ordered structure was caused by the electrostatic interaction among polyelectrolyte chains of adjacent SPB. This work could enrich our understanding of polyelectrolyte assembly in concentrated SPB, thereby greatly broadening the application fields of SPB.

Morphologies of a spherical bimodal polyelectrolyte brush induced by polydispersity and solvent selectivity* *Project supported by the Fundamental Research Funds for the Central Universities of China (Grant No. 3122020080).

It is commonly realized that polydispersity may significantly affect the surface modification properties of polymer brush systems. In light of this, we systematically study morphologies of bidisperse polyelectrolyte brush grafted onto a spherical nanocolloid in the presence of trivalent counterions using molecular dynamics simulations. Via varying polydispersity, grafting density, and solvent selectivity, the effects of electrostatic correlation and excluded volume are focused, and rich phase behaviors of binary mixed polyelectrolyte brush are predicted, including a variety of pinned-patch morphologies at low grafting density and micelle-like structures at high grafting density. To pinpoint the mechanism of surface structure formation, the shape factor of two species of polyelectrolyte chains and the pair correlation function between monomers from different polyelectrolyte ligands are analyzed carefully. Also, electrostatic correlations, manifested as the bridging through trivalent counterions, are examined by identifying four states of trivalent counterions. Our simulation results may be useful for designing smart stimuli-responsive materials based on mixed polyelectrolyte coated surfaces.

Selective uptake of different proteins by annealed and quenched cationic spherical polyelectrolyte brushes

AbstractThe selective uptake of bovine serum albumin (BSA) and β‐glucosidase (β‐G) by annealed and quenched cationic spherical polyelectrolyte brushes (SPB) was systematically studied by combining turbidimetric titration, dynamic light scattering and small angle X‐ray scattering (SAXS). These two kinds of SPB consist of a same polystyrene core and a dense shell of poly (2‐aminoethyl methacrylate hydrochloride) (PAEMH) and poly [2‐(methacryloyloxy) ethyl] trimethylammonium chloride (PMAETA), respectively. Results reveal that the adsorption/desorption of proteins on SPB can be easily controlled by changing external conditions (pH and ionic strength). For a particular annealed or quenched SPB, there is a significant difference of the interaction pH regions between the brush and the two proteins, and this difference can be tuned by ionic strength. At low ionic strength, quenched brushes were more suitable for selective adsorption of BSA and β‐G, while annealed brushes performed better at high ionic strength. SAXS analysis demonstrated that volume exclusion effect played a remarkable role in protein uptake by both SPB, and larger proteins were more likely to be adsorbed on the outer layer of the brush. The unique core‐shell structure and controllable chain types make SPB an excellent candidate in selective adsorption/separation of proteins of different sizes.

CO2-Responsive Spherical Polyelectrolyte Brush with Multi-Stimulation for Reversible Protein Immobilization and Release

Multi-responsive materials have received extensive interest in many areas due to their smart characteristics. This paper presents rationally designed multi-responsive spherical polyelectolyte brushes composed of a solid polystyrene (PS) core and a poly (2-(dimethylamino) ethyl methacrylate) (PDMAEMA) shell synthesized by photoemulsion polymerization. Based on dynamic light scattering, Zeta potential, turbidity measurements, isothermal titration calorimetry, and UV-vis spectroscopy, PS-PDMAEMA works as a good potential adsorbent for bovine serum albumin (BSA) for which the maximum adsorption capability could reach up to 5190mg g−1. Moreover, the immobilization and release of protein on the polymer brush could be adjusted with different triggers, including the pH, ionic strength, and temperature. Furthermore, the green gas triggers, CO2 and N2, could be employed in the BSA@ PS-PDMAEMA system by easily bubbling over many cycles without any salt accumulation. The main reason for the observed actions is the brushes could be switched alternately between extended and collapsed states with different stimulations. Upon comparing the circular dichroism spectra of original and released BSA after many cycles of adsorption and release, it’s clear that the protein can retain its initial biological activity after release from the PS-PDMAEMA. This work provides an effective and green way to immobilize and release proteins in biotechnology.