Cationic Spherical Polyelectrolyte Brushes Research Articles

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.

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.

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.

Preparation of hollow silica nanoparticles using cationic spherical polyelectrolyte brushes as catalytic template

This paper presents a facile procedure to fabricate uniform-sized hollow silica nanoparticles (SNP) under a mild condition by using cationic spherical polyelectrolyte brushes (SPB) with a polystyrene (PS) core and densely grafted poly(2-aminoethyl methacrylate hydrochloride) (PAEMH) brush shell as a catalytic template. By changing the brush layer thickness of SPB, hollow SNP with different silica shell thickness could be easily obtained. This method provides a new way for the preparation of hollow SNP without additional catalyst. The obtained hollow SNP exhibited a high-drug encapsulation efficiency (80%) for doxorubicin hydrochloride (DOX), should be of significance in the fields of drug delivery, cancer therapy, and bioimaging.

Protein Immobilization onto Cationic Spherical Polyelectrolyte Brushes Studied by Small Angle X-ray Scattering.

The immobilization of bovine serum albumins (BSA) onto cationic spherical polyelectrolyte brushes (SPB) consisting of a solid polystyrene (PS) core and a densely grafted poly(2-aminoethyl methacrylate hydrochloride) (PAEMH) shell was studied by small-angle X-ray scattering (SAXS). The observed dynamics of adsorption of BSA onto SPB by time-resolved SAXS can be divided into two stages. In the first stage (tens of milliseconds), the added proteins as in-between bridge instantaneously caused the aggregation of SPB. Then BSA penetrated into the brush layer driven by electrostatic attractions, and reached equilibrium in the second stage (tens of seconds). The amount of BSA immobilized onto brush layer reached the maximum when pH was increased to about 6.1 and BSA concentration to 10 g/L. The cationic SPB were confirmed to provide stronger adsorption capacity for BSA compared to anionic ones.

Preparation and performance of cationic flocculant for papermaking based on the graft polymerization of cationic chains from colloidal silica particles

Abstract The cationic spherical polyelectrolyte brushes (CSPB), with poly(2-(acryloyloxy) ethyltrimethylammonium chloride) chains grafted from the surfaces of colloidal silica particles were prepared and evaluated. The CSPB was characterized by Fourier-transform infrared spectrometry, thermo gravimetric analysis, colloid titration, gel permeation chromatography, transmission electron microscopy and X-ray photoelectron spectroscopy. The results show that CSPB with 1.8 × 10−3 mmol/g surface grafting density was successfully fabricated. The CSPB was investigated as flocculation and retention-aids for bleached eucalyptus kraft pulp and kaolin/pulp particles using relative turbidity, zeta potential, Focused beam reflectance measurement (FBRM), dynamic drainage jar and field emission scanning electron microscopy methods. The results showed that the zeta potential of pulp suspension gradually changed from negative to zero and then to positive, maximum flocculation occurred when the zeta potential was still negative. The data also suggested that the efficiency of both flocculation and retention-aid were increased and then demonstrated a gradual downward trend as the concentration of the CSPB increased. FBRM showed that flocs of CSPB had low re-flocculate ability. Bridging flocculation model may be the mainly mechanism for CSPB on flocculation of pulp.

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.

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.

Tunable adsorption of bovine serum albumin by annealed cationic spherical polyelectrolyte brushes

By combining turbidimetric titration, dynamic light scattering (DLS), and zeta potential methods, we demonstrated that the adsorption of bovine serum albumin (BSA) in annealed cationic spherical polyelectrolyte brushes (SPB) can be controlled by modulating the pH, ionic strength, BSA concentration of the mixed solution, and SPB thickness. The SPB consist of a polystyrene core with a diameter around 80nm and a dense shell of poly (2-aminoethylmethacrylate hydrochloride) (PAEMH) with a thickness from 10 to 60nm covalently attached on the core surface. Results revealed the existence of three pH regions, corresponding to (1) adsorption of BSA in SPB, (2) aggregation of SPB induced by BSA adsorption, and (3) desorption of BSA from SPB. The extent of the pH regions can be modulated by ionic strength, BSA concentration, or SPB thickness. Adsorption measurements demonstrated that the adsorbed amount of BSA in SPB was affected by pH, ionic strength, and SPB thickness. These findings lay the foundation for protein separation by SPB.

Binding between Proteins and Cationic Spherical Polyelectrolyte Brushes: Effect of pH, Ionic Strength, and Stoichiometry

Cationic spherical polyelectrolyte brushes (SPBs) were synthesized by photoemulsion polymerization, consisting of a polystyrene core with a diameter around 80 nm and a poly(2-aminoethylmethacrylate hydrochloride) (PAEMH) shell with a thickness from 10 to 50 nm densely grafted on the core surface. The binding of various proteins onto SPBs was observed by turbidimetric titration, dynamic light scattering (DLS), zeta potential, and isothermal titration calorimetry (ITC). The binding, aggregation, and releasing of proteins by SPB can be tuned by modulating pH. The pH regions of binding for bovine serum albumin (BSA), β-lactoglobulin (BLG), and papain onto SPBs are markedly different and tunable by ionic strength and stoichiometry between protein and SPB. Binding energetics, affinity, and amount of various proteins onto cationic SPBs were determined by ITC. These findings lay the foundation for SPB applications in the protein purification and selective immobilization of different proteins, enzymes, and antibodies.

Structural analysis of colloidal MnO x composites

We report on the detailed structure of MnOx nanoparticles (MnOxNP) which are either stabilized by cationic spherical polyelectrolyte brushes or by star-shaped cationic polyelectrolyte chains. In both cases, the polycation is composed of 2-(trimethylammonium)ethyl methacrylate chloride (TMAEMC). The analysis by transmission electron microscopy (TEM), cryogenic transmission electron microscopy (cryoTEM), and powder X-ray diffraction leads to the conclusion that the MnOx nanoparticles in aqueous dispersed state are composed of only a few or even single lamellae of c-disordered potassium birnessite (birnessite). Using star-shaped pTMAEMC homopolymer for the synthesis of composite particles, we obtain MnOxNP with an average diameter of about 5 nm. MnOxNP immobilized on cationic spherical polyelectrolyte brush have a length of about 20 nm and a width of 1.6 nm. Comparison of the extended X-ray absorption fine structure (EXAFS) spectra of the MnOx composites with reference spectra leads to the conclusion that all materials include c-disordered birnessite-type nanoparticles. A comparison of the energy shift of the Mn K-edge absorption peak of the X-ray absorption near-edge structure spectra of different manganese oxide reference materials with the different MnOxNP revealed an average oxidation state of about 3.5–3.7 for synthesized compounds. No distinct structural difference is found when comparing the dried samples to samples dispersed in water. A comparison of the EXAFS data of the birnessite nanoparticles with the crystal structure of macroscopic systems showed a compression along the c direction accompanied by a slight elongation within the ab plane of the layered material.

Catalytic activity of nanoalloys from gold and palladium

We present a quantitative study of the catalytic activity of well-defined faceted gold-palladium nanoalloys which are immobilized on cationic spherical polyelectrolyte brushes. The spherical polyelectrolyte brush particles used as carriers for the nanoalloys consist of a solid polystyrene core onto which cationic polyelectrolyte chains of 2-aminoethyl methacrylate are attached. Au/Pd nanoalloy particles with sizes in the range from 1 to 3 nm have been generated which are homogeneously distributed on the surface of the spherical polyelectrolyte brushes. The reduction of 4-nitrophenol has been chosen as a well-controlled model reaction allowing us to determine the catalytic activity of the nanoalloys as a function of the Au/Pd composition. The adsorption behavior was studied by Langmuir-Hinshelwood kinetics. We find a pronounced maximum of the catalytic activity at 75 molar % Au. A comparison of gold, platinum, palladium and gold-palladium alloy nanoparticles is made in terms of Langmuir-Hinshelwood kinetics. Density functional calculations for Au/Pd clusters with up to 38 atoms show that the density of states at the Fermi level increases with increasing Pd content, and that the highest occupied orbitals are associated with Pd atoms. The calculations confirm that small changes in the atomic arrangement can lead to pronounced changes in the particles' electronic properties, indicating that the known importance of surface effects is further enhanced in nanoalloys.

Platinum nanoparticles generated in spherical polyelectrolyte brushes and their high catalytic activity

ABSTRACTNano‐sized cationic spherical polyelectrolyte brushes (SPBs) consisting of a solid core of polystyrene and a shell of poly(aminoethyl methacrylate hydrochloride) grafted densely on the core were prepared by photo‐emulsion polymerization. They were found to be ideal nanoreactors to generate platinum (Pt) nanoparticles. Because of Donnan equilibrium, SPBs can concentrate and confine the divalent PtCl62− ions as counterions within the brush layer. The PtCl62− ions were reduced into Pt particles with an average size of 3 nm by sodium borohydride (NaBH4) in situ. The prepared Pt nanoparticles were stably immobilized in SPB and showed high catalytic activity in the reduction of p‐nitrophenol to p‐aminophenol by NaBH4. The results reported here suggest that spherical polyelectrolyte brushes are ideal nanoreactors for the preparation of Pt nanoparticles. © 2011 Curtin University of Technology and John Wiley & Sons, Ltd.

Preparation and Performance of Cationic Spherical Polyelectrolyte Brushes as Retention and Drainage Aid in Papermaking

Novel cationic spherical polyelectrolyte brushes (CSPBs) were prepared by photoemulsion polymerization. Dimethyl diallyl ammonium chloride was grafted onto the surface of polystyrene particles bearing a thin layer of photoinitiator that was prepared by Schotten-Baumann reaction of Darocur 1173 and Methacryloyl chloride. Transmission electron microscopy (TEM) was used to analyze the size and shape of CSPBs, the average diameter of these particles with uniform spherical structure was ca.170nm. A link to the use of this system as a model for retention and drainage aid in the papermaking process was described. Dynamic drainage experiment indicated that the shortest drainage time was 23.2s when the percentage of the aid was 0.04%(wt). The retention effect of the aid was tested that the highest of the first-pass retention was 70.89% when the percentage of aid was 0.035%(wt).

Adhesion of Spherical Polyelectrolyte Brushes on Mica: An in Situ AFM Investigation

We demonstrate that the adsorption of cationic spherical polyelectrolyte brushes (SPB) on negatively charged mica substrates can be controlled in situ by the ionic strength of the suspension. The SPB used in our experiments consist of colloidal core particles made of polystyrene. Long cationic polyelectrolyte chains are grafted onto these cores that have diameters in the range of 100 nm. These particles are suspended in aqueous solution with a fixed ionic strength. Atomic force microscopy (AFM) in suspension as well as in air was used for surface characterization. In pure water the polymer particles exhibit a strong adhesion to the mica surface. AFM investigations of the dry samples show that the particles occupy the identical positions as they did in liquid. They were not removed by the capillary forces within the receding water front during the drying process. The strong interaction between the particles and the mica surface is corroborated by testing the adhesion of individual particles on the dried surface by means of the AFM tip: after a stepwise increase of the force applied to the surface by the AFM tip, the polymer particles still were not removed from the surface, but they were cut through and remained on the substrate. Moreover, in situ AFM measurements showed that particles which adsorb under liquid in a stable manner are easily desorbed from the surface after electrolyte is added to the suspension. This finding is explained by a decreasing attractive particle-substrate interaction, and the removal of the particles from the surface is due to the significant reduction of the activation barrier of the particle desorption. All findings can be explained in terms of the counterion release force.