Spherical Polyelectrolyte Brushes Research Articles

Preparation of Au/Ag multilayers via layer-by-layer self-assembly in spherical polyelectrolyte brushes and their catalytic activity

Spherical polyelectrolyte brushes (SPBs) consisting of polystyrene (PS) core and poly(2-aminoethyl methacrylate hydrochloride) (PAEMH) shell were prepared by photo-emulsion polymerization. Au nanoparticles (Au-NPs) with controlled size and size distribution were synthesized in situ using SPBs as nanoreactors. Via layer-by-layer deposition technique on the surface of SPBs, nano-composite particles with Au/Ag-NPs bilayer and Au/Ag/Au-NPs trilayer were prepared. The structures of the as-prepared Au/Ag multilayer SPBs were characterized by UV-Vis spectroscopy, TEM, ICP-AES and DLS. The charge reversal of the nano-composite particles observed by zeta potential confirmed the success of layer-by-layer assembly. The Au/Ag-NPs bilayer nano-composite particles showed high catalytic efficiency with an apparent activation energy of about 41.2 kJ/mol in the reduction reaction of 4-nitrophenol to 4-aminophenol in the existence of sodium borohydride monitored. The catalytic activity of Au/Ag-NPs multilayer SPBs close to Au-NPs SPBs and much higher than Ag-NPs SPBs reveals its potential applications in cost-effective catalysts with high-performance.

Simple synthesis of high-quality CdTe QDs in spherical polyelectrolyte brushes with stable and reversible photoluminescence

A facile method of high-quality CdTe quantum dots (QDs) synthesis in spherical polyelectrolyte brushes (SPBs) was reported in this work. The size of CdTe QDs, with emission color from green to red, could be tuned by adjusting the duration of nucleation, feed ratio of reductants (NaBH4/N2H4), and pH of precursor (SPB solution). Short duration of nucleation and low ratio of NaBH4/N2H4 could promote the growth rate of QDs to form big-sized CdTe QDs. The pH of SPB solution, in the range of 7–9, was optimal condition for formation of high-quality QDs. The SPB@CdTe exhibited high photochemical stability as the pH of mixture was above 10, which could be stored in the visible light for several months without aggregation and optical deterioration. The photoluminescence emission of SPB@CdTe could be reversibly quenched and restored with shrinkage and swollen shell if employed pH as a regulator.

An anionic spherical polyelectrolyte brushes-driven approach to synthesize conductive composites

The composites of anionic spherical polyelectrolyte brushes/conducing polymer (ASPB/CP) have been successfully prepared by chemical oxidative polymerization of aniline and pyrrole monomers in an acidic medium containing anionic spherical polyelectrolyte brushes. These composites were characterized by field emission scanning electron microscopy, transmission electron microscopy, Fourier-transform infrared spectrometry, zeta potentials, X-ray photoelectron spectroscopy, and four probe methods. It was found that the poly(aniline-co-pyrrole) was uniformly coated on the surface of ASPB. Besides, the ASPB/CP composites had higher doping level than the pure copolymer after doping with ASPB. Moreover, these composites also showed better solubility and storage stability than pure copolymer. The electrical conductivity of the ASPB/CP composites at room temperature was 7.2 S/cm, while it was 2.4 S/cm for the pure copolymer under the same circumstances.

Dielectric Relaxation of Spherical Polyelectrolyte Brushes: Movement of Counterions and Electrical Properties of the Brush Layer.

Dielectric behaviors of spherical polyelectrolyte brush (SPB) suspensions under various mass fractions of SPB and the pH of solution were investigated in a frequency range of 40 Hz to 110 MHz. The SPB consists of a polystyrene (PS) core grafted with poly(acrylic acid) (PAA) chains. Two unique relaxations were found at either about 10 kHz or 1-10 MHz, respectively, with the former due to the diffusion of counterions and the latter resulting from the interfacial polarization. Using dielectric parameters of two relaxations, we obtained information about the migration of counterion and the conformation of polyelectrolyte chains. The PAA chains are fully stretched when pH is about 8 under the domination of the equilibrium between the penetration and diffusion of counterions in the brushes. A dielectric model is proposed to describe the high-frequency relaxation, and the permittivity and conductivity of SPB and its volume fraction were also calculated on the basis of the model. The surface conductivity of SPB, the Donnan potential, and the fixed charge density in the brush layer were derived from these paramaters. The distribution of the Donnan potential was also simulated by using Poisson-Boltzmann equations, and the result is in accordance with these obtained on the basis of the dielectric model.

Improving Electrical Conductivity, Thermal Stability, and Solubility of Polyaniline-Polypyrrole Nanocomposite by Doping with Anionic Spherical Polyelectrolyte Brushes.

The extent to which anionic spherical polyelectrolyte brushes (ASPB) as dopant improved the performance of polyaniline-polypyrrole (PANI-PPy) nanocomposite was investigated. Different characterization and analytical methods including Fourier transform infrared spectroscopy (FTIR), thermo-gravimetric analysis (TGA), scanning electron microscopy (SEM), and X-ray diffraction (XRD) confirmed that ASPB serving as dopant could improve the comprehensive properties of PANI-PPy nanocomposite. It was different from dopants such as SiO2, poly(sodium-p-styrenesulfonate) (PSS), and canonic spherical polyelectrolyte brushes (CSPB) which only enhanced the performance of PANI-PPy nanocomposite on one or two sides. The electrical conductivity of (PANI-PPy)/ASPB nanocomposite at room temperature was 8.3 S/cm, which was higher than that of PANI-PPy (2.1 S/cm), (PANI-PPy)/PSS (6.8 S/cm), (PANI-PPy)/SiO2 (7.2 S/cm), and (PANI-PPy)/CSPB (2.2 S/cm). Meanwhile, (PANI-PPy)/ASPB nanocomposite possessed enhanced thermal stability and good solubility. In addition, the effects of polymerization temperature, the molecular weight of grafted polyelectrolyte brushes, and storage time on electrical conductivity were discussed.

Viscosity Modulation by Magnetic Field for Colloidal Polyelectrolyte Brushes

Aqueous dispersions of magnetic spherical polyelectrolyte brushes (MSPB) are prepared by mini‐emulsion followed by photo‐emulsion polymerization. Their viscosity increases dramatically upon increasing the intensity of an external magnetic field, showing the “magnetoviscous effect.” Unlike general magnetic nano‐particles, the increase in viscosity of MSPB cannot be described by Shliomis's theory, probably due to the covering of a spherical polyelectrolyte brush layer. MSPB rheology is also tunable by pH, and the brushes can stay in atmospheric conditions for months without changes in particle size and size distribution, which should make them ideal candidates for a broad range of industrial applications. The future applications of our multifunctional magnetic responsive system are promising.

Synthesis and application of cationic spherical polyelectrolyte brushes as retention and drainage aid in bleached eucalyptus kraft pulp

In the present study, a series of cationic spherical polyelectrolyte brushes (CSPB), consisting of a silica core and a shell of copolymer of acrylamide (AM) and [2-(methacryloyloxy)ethyl] trimethylammonium chloride (METAC), were synthesized. Then a dual-component system which was composed of CSPB and anionic polyacrylamide (APAM) was used to improve the retention and drainage properties of bleached eucalyptus kraft pulp and precipitated calcium carbonate (PCC). Comparative researches about retention and drainage properties between CSPB/APAM system and cationic starch/APAM system were undertaken as well. Results showed that further improvement in first-pass retention (FPR) of pulp, FPR of PCC and drainage time could be achieved by CSPB/APAM system. It was also found that increase of shear intensity led to a decrease in retention efficiency, while it had no significant influence on drainage time of pulp. However, due to the symmetrical or quasi-symmetrical spherical brush structure, CSPB still showed better retention efficiency than cationic starch under different turbulent conditions. Furthermore, the flocculation mechanism of the CSPB/APAM dual-component system was proposed in the paper.

Tunable immobilization of protein in anionic spherical polyelectrolyte brushes as observed by small-angle X-ray scattering

Tunable immobilization of bovine serum albumins (BSA) onto anionic spherical polyelectrolyte brushes (SPB) by changing BSA concentration, pH, and ionic strength was mainly observed by small-angle X-ray scattering (SAXS). Change of the BSA amount immobilized in SPB can be determined by SAXS which was confirmed by UV spectroscopy, and SAXS is the unique method to “see” the distribution of BSA in SPB. More BSA entered into brush layer upon increasing the protein concentration or decreasing the ionic strength of solutions. When pH increased from 3 to 5 (around the isoelectric point of BSA 4.9), more BSA came into the brush inner layer, while the proteins partly moved to the outer layer when pH continued to increase. After pH was higher than 7, most of BSA were desorbed from SPB. SAXS is proved to be a powerful tool to monitor the tunable immobilization and distribution of proteins in SPB.

Preparation and properties of polyaniline–anionic spherical polyelectrolyte brushes nanocomposite

A novel polyaniline–anionic spherical polyelectrolyte brushes (PANI/ASPB) nanocomposite was synthesised by means of chemical oxidative polymerisation. Different characterisation and analytical methods involving scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction and thermo-gravimetric analysis confirmed that anionic spherical polyelectrolyte brushes served both as a dopant and as a template. While polyaniline (PANI) nanocomposites have a ‘rod-like’ or fibrillar morphology, the PANI/ASPB nanocomposite displayed a sphere-like structure. The room temperature electrical conductivity of the PANI/ASPB nanocomposite was 26.3 S/cm, which is higher than that of PANI (7.1 S/cm). In addition, PANI/ASPB nanocomposites possessed enhanced thermal stability and good solubility properties.

Stable and efficient loading of silver nanoparticles in spherical polyelectrolyte brushes and the antibacterial effects

A more efficient and convenient strategy was demonstrated to immobilize silver nanoparticles (NPs) with a crystalline structure into the spherical polyelectrolyte brushes (SPB) as an antibacterial material. The SPB used for surface coating (Ag immobilized PVK–PAA SPB) consists of a poly(N-vinylcarbazole) (PVK) core and poly(acrylic acid) (PAA) chain layers which are anchored onto the surface of PVK core at one end. Well-dispersed silver nanoparticles (diameter∼3.5nm) then formed and were electrostatically confined in the brush layer. Ag content is controlled by a repeated loading process. Thin film coatings were then constructed by layer-by-layer depositions of positive charged poly(diallyldimethylammonium chloride) (PDDA) and SPB. The multilayer composites display excellent stability as well as antibacterial performance but not for simple PVK–PAA coated surface. The results show that almost complete bacteria growth including both dispersed bacterial cells and biofilms was inhibited over a period of 24h. This approach opens a novel strategy for stable and efficient immobilization of Ag NPs in fabrication of antibacterial materials.

Kinetic analysis of the reduction of 4-nitrophenol catalyzed by Au/Pd nanoalloys immobilized in spherical polyelectrolyte brushes.

We present a detailed study of the catalytic activity of Au/Pd nanoalloys with Au : Pd molar ratio 75 : 25 synthesized using spherical polyelectrolyte brushes (SPB) as carrier system. The reduction of 4-nitrophenol (Nip) by sodium borohydride (BH4(-)) has been used as a model reaction. This reaction proceeds in two steps: 4-nitrophenol is first reduced to 4-hydroxylaminophenol which in a second step is reduced to the final product 4-aminophenol. Both steps of the reaction proceed on the surface of the nanoparticles (Langmuir-Hinshelwood-mechanism). We use this model to analyze the experimental data obtained by catalysis with the Au/Pd-nanoalloys. Good agreements between theory and experiments were found up to 30% conversion of Nip. The kinetic parameters were compared with the data derived from neat Au and Pd nanoparticles immobilized in the same SPB carrier system. The addition of 25% molar ratio of Pd to the nanoalloys increases the reaction rate of the first step nearly 10 times compared with that of SPB-Au and 60 times compared with that of SPB-Pd. Analysis of the nanoalloy by high-resolution transmission electron microscopy suggests that the surface defects of the nanoalloys play an important role for the enhanced catalytic activity.

Preparation of conductive polypyrrole composite particles based on spherical polyelectrolyte brushes

Preparation of conductive polypyrrole composite particles based on spherical polyelectrolyte brushes

Preparation and Characterization of Poly(Dimethyl Diallyl Ammonium Chloride)/Modified SiO<sub>2</sub> Spherical Brushes

Novel cationic spherical polyelectrolyte brushes (CSPB) consisting of γ-methacryloxypropyl trimethoxy-silane (KH-570) modified SiO2cores and poly (Dimethyl diallyl ammonium chloride) (PDMDAAC) brushes were prepared by conventional free radical polymerization. The resulting CSPB were characterized by Fourier transform infrared spectroscopy (FTIR), Transmission electron microscopy (TEM), Scanning electron microscopy (SEM), and Thermo-gravimetric analysis (TGA). After cleaving the polyelectrolyte chains from the anchoring surface, the molecular weight of brushes was 1.824×103gmol-1from Gel Permeation Chromatography (GPC) measurements.

Synthesis and Characterization of Polyaniline Dopd with Anionic Spherical Polyelectrolyte Brushes

The synthesis of polyaniline (PANI) doped with anionic spherical polyelectrolyte brushes (ASPB) (PANI/ASPB nanocomposite) by means of in situ chemical oxidative polymerization were presented. The PANI/ASPB nanocomposite was characterized by Fourier trans-form infrared spectroscopy (FTIR), Scanning electron microscopy (SEM), Energy dispersive x-ray detector (EDX), and Thermo-gravimetric analysis (TGA). Results showed that PANI/ASPB nanocomposite was successfully fabricated with regular morphology. Investigation of the electrical conductivity at room temperature showed that the electrical conductivity of PANI/ASPB nanocomposite was 9.03 S/cm, which was higher than that of PANI (2.7 S/cm). The measurement of dispersity demonstrated that PANI/ASPB nanocomposite had enhanced dispersity in water.

A numerical study of spherical polyelectrolyte brushes by the self-consistent field theory

The self-consistent field theory (SCFT) is employed to numerically study the scaling laws of brush height and the amount of counter-ions trapped inside a spherical polyelectrolyte (PE) brush immersed in a good solvent with no added salt ions. In particular, the curvature effect of the grafting substrate on the brush height and the amount of counter-ions trapped inside the PE brush is carefully examined. It is found that the brush height shows a non-trivial dependence on the radius of the grafting substrate. The numerical result reveals that the brush height scales linearly with respect to the grafting density and the average degree of ionization of PE chains in the planar surface limit, but not in the opposite limit. The numerical results show that, in a salt-free solution, about 96% of the counter-ions are trapped within the range of extension of grafted PE chains in the planar surface limit, irrespective of other system parameters. On the contrary, for the grafting substrate with high curvature, i.e., the radius of the grafting substrate is much smaller than the brush height, the amount of counter-ions trapped inside the PE brush approaches zero in the large system size limit. The underlining mechanisms governing the curvature effect of the grafting substrate on the brush height and the amount of counter-ions trapped inside PE brushes are elucidated.

Enhancement of enzymatic activity by magnetic spherical polyelectrolyte brushes: a potential recycling strategy for enzymes.

Interactions between amyloglucosidase and magnetic spherical polyelectrolyte brushes (MSPB) were studied by turbidimetric titration, which reveals reversible and tunable behaviors of pH-dependent enzyme-SPB binding. Quantitative thermodyanmic parameters including binding affinity and stoichiometry between enzyme and SPBs were further measured by isothermal titration calorimetry (ITC). A large amount of enzyme can be loaded in MSPB without loss of MSPB stability. We demonstrated that the enzymatic activity of amyloglucosidase bound in MSPB could be greatly enhanced (catalytic reaction rate, k(bound) = 1.36k(free)) compared to free enzyme acitivity in solution. This is tremendous improvement from other carrier systems that usually lead to a significant decrease of enzymatic activity. Both the high enzyme loading capacity and the enhancement of the catalytic activity probably arise from the Coulombic interactions between the enzyme and MSPB. These findings provide a practical strategy for enhancement of enzyme activity and enzyme recycling by MSPB.

Distribution of magnetic nanoparticles in spherical polyelectrolyte brushes as observed by small‐angle X‐ray scattering

ABSTRACTMagnetic nanoparticles (MNPs) with a size of about 2 nm are prepared in nanoreactors of spherical polyelectrolyte brushes (SPBs) consisting of a solid polystyrene (PS) core and a shell of linear poly(acrylic acid) (PAA) chains densely grafted onto the core by one end. The synthesized MNP are strongly adhered to PAA chains due to the intense interaction of chemical coordination with the carboxyl groups. The generation of MNP in SPB layer is legibly revealed by small‐angle X‐ray scattering (SAXS) due to the significant increase in electron density. The radial distribution of MNP in SPB is built by fitting SAXS data. Most of MNP are found to locate nearby the surface of PS core. Compared to dynamic light scattering and transmission electron microscopy, SAXS can observe the generation and distribution of MNP in SPB as well as the changes upon changing pH and salt concentration in real time. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014, 52, 1681–1688

Encapsulation of Quantum Dot Clusters in Stimuli-Responsive Spherical Polyelectrolyte Brushes

Novel fluorescence-labeled spherical polyelectrolyte brushes consisting of a fluorescent polystyrene (PS) nanocomposite core and a poly(acylic acid) (PAA) brush shell were successfully prepared. Quantum dots (QDs) were well confined in the PS core through hybrid emulsion polymerization. PAA chains were then grafted onto the surface of the fluorescent PS core to form a brush structure through photoemulsion polymerization. The obtained fluorescent spherical polyelectrolyte brushes are highly pH sensitive in addition to their excellent dispersibility in water. Fluorescent nanoclusters were introduced into spherical polyelectrolyte brushes to acquire high sensitive detection in the applications of spherical polyelectrolyte brushes as catalyst tracer, as biosensor, and in protein coding.

Surface modification and characterization of carbon spheres by grafting polyelectrolyte brushes.

Modified carbon spheres (CSPBs) were obtained by grafting poly(diallyl dimethyl ammonium chloride) (p-DMDAAC) on the surface of carbon spheres (CSs). It can be viewed as a kind of cation spherical polyelectrolyte brushes (CSPBs), which consist of carbon spheres as core and polyelectrolytes as shell. The method of synthesizing carbon spheres was hydrothermal reaction. Before the polyelectrolyte brushes were grafted, azo initiator [4,4′-Azobis(4-cyanovaleric acyl chloride)] was attached to the carbon spheres' surface through hydroxyl groups. CSPBs were characterized by scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), conductivity meter, and system zeta potential. The results showed that compared with carbon spheres, the conductivity and zeta potential on CSPBs increased from 9.98 to 49.24 μS/cm and 11.6 to 42.5 mV, respectively, after the polyelectrolyte brushes were grafted. The colloidal stability in water was enhanced, and at the same time, the average diameter of the CSPBs was found to be 173 nm, and the average molecular weight and grafted density of the grafted polyelectrolyte brushes were 780,138 g/mol and 4.026 × 109/nm2, respectively.

Analysis of spherical polyelectrolyte brushes by small angle X-ray scattering

Spherical polyelectrolyte brushes (SPBs) with PS core and poly(acrylic acid) (PAA) brushes were prepared and analyzed by SAXS in this article. A radial electron density profile of SPB was brought up, which fits well with the SAXS result and shows a core-shell structure. The effect of pH on SPB form was represented by SAXS and it proves that the chains of SPB will stretch in response to increased pH owning to the increased electrostatic repulsion. SPBs immobilized with magnetic nanoparticles or bovine serum albumin (BSA) were prepared and analyzed by SAXS as well. SAXS could characterize the changes of electron density inside brushes of SPBs due to the immobilization of magnetic nanoparticles or BSA. This provides significant supports for further application of immobilized metal nanoparticles or proteins.