Abstract: The effects of charge density on weak polyelectrolyte multilayer growth were investigated by assembling several strong polyelectrolytes with either poly(allylamine hydrochloride) (PAH) or poly(acrylic acid) (PAA) to keep one polymer fully charged while varying the degree of ionization of the other. The degree of ionization of the weak polyelectrolytes in solution and in a multilayer film was controlled by pH adjustment and quantified by Fourier transform infrared spectroscopy analyses. In all cases, the bilayer thickness exhibited a dramatic change from molecularly thin bilayers (case of two fully charged polymers) to much thicker bilayers when the degree of ionization of the weak polyelectrolyte decreased below 70−90% charged units. We also confirmed and quantified earlier observations that both the charge density and the effective pKa of a weak polyelectrolyte can change substantially from solution-state values when the polymer is incorporated into a multilayer film. In addition, it was found that the d...

Abstract: Laser mediated remote release of encapsulated fluorescently labeled polymers from nanoengineered polyelectrolyte multilayer capsules containing gold sulfide core/gold shell nanoparticles in their walls is observed in real time on a single capsule level. We have developed a method for measuring the temperature increase and have quantitatively investigated the influence of absorption, size, and surface density of metal nanoparticles using an analytical model. Experimental measurements and numerical simulations agree with the model. The treatment presented in this work is of general nature, and it is applicable to any system where nanoparticles are used as absorbing centers. Potential biomedical applications are highlighted.

Abstract: An efficient pH-responsive carrier system has been constructed by oppositely charged ionic interaction between carboxylic acid modified SBA-15 silica rods and polyelectrolyte. Active molecules such as vancomycin can be stored and released from the pore voids of SBA-15 by changing pH values at will. The amount of vancomycin stored in the pores of sample based on carboxylic acid modified SBA-15 rods and poly(dimethyldiallylammonium chloride) is up to 36.4 wt % at pH 6.8. When the pH is at mild acidity, vancomycin is steadily released from the pores of SBA-15. Both nitrogen adsorption−desorption isothems and X-ray diffraction patterns show that this system possesses stable mesostructure, which will be considered an interesting alternative to a polymeric delivery system.

Abstract: The versatile layer-by-layer (LbL) approach has been used for the synthesis of polyelectrolyte-coated gold nanorods. The simple process first involves the synthesis of gold nanorods by our previously published three-step seed-mediated protocol. The presence of a bilayer of the surfactant cetyltrimethylammonium bromide (CTAB) on the gold nanorod surface imparts a net positive charge to the nanorods. Alternate adsorption of anionic and cationic polyelectrolytes on these positively charged gold nanorods leads to the formation of polyelectrolyte multilayers around the nanorods. These coated gold nanorods have been characterized by UV−vis spectroscopy, zeta potential measurements, and transmission electron microscopy (TEM). Depending on the surface chemical functionality of the coated gold nanorods, they have been selectively immobilized onto either cationic or anionic surfaces. Scanning electron microscopy (SEM) has been used to visualize the immobilized nanorods and to determine the nanorod density on flat s...

Abstract: Poor solubility of single-walled and multiwalled carbon nanotubes (NTs) in water and organic solvents presents a considerable challenge for their purification and applications. Macromolecules can be convenient solubilizing agents for NTs and a structural element of composite materials for them. Several block copolymers with different chemical functionalities of the side groups were tested for the preparation of aqueous NT dispersions. Poly(N-cetyl-4-vinylpyridinium bromide-co-N-ethyl-4-vinylpyridinium bromide-co-4-vinylpyridine) was found to form exceptionally stable NT dispersions. It is suggested that the efficiency of macromolecular dispersion agents for NT solubilization correlates with the topological and electronic similarity of polymer-NT and NT-NT interactions in the nanotube bundles. Raman spectroscopy and atomic force and transmission electron microcopies data indicate that the polycations are wrapped around NTs forming a uniform coating 1.0-1.5 nm thick. The ability to wind around the NT originates in the hydrophobic attraction of the polymer backbone to the graphene surface and topological matching. Tetraalkylammonium functional groups in the side chains of the macromolecule create a cloud of positive charge around NTs, which makes them hydrophilic. The prepared dispersions could facilitate the processing of the nanotubes into composites with high nanotube loading for electronic materials and sensing. Positive charge on their surface is particularly important for biological and biomedical applications because it strengthens interactions with negatively charged cell membranes. A high degree of spontaneous bundle separation afforded by the polymer coating can also be beneficial for NT sorting.

Abstract: We present a study on the catalytic activity of platinum nanoparticles immobilized on spherical polyelectrolyte brushes that act as carriers. The spherical polyelectrolyte brushes consist of a solid core of poly(styrene) onto which long chains of poly(2-methylpropenoyloxyethyl) trimethylammonium chloride are grafted. These positively charged chains form a dense layer of polyelectrolytes on the surface of the core particles ("spherical polyelectrolyte brush") that tightly binds divalent PtCl6-(2) ions. The reduction of these ions within the brush layer leads to nearly monodisperse nanoparticles of metallic platinum. The average size of the particles is approximately 2 nm. The composite particles exhibit excellent colloidal stability. The catalytic activity is investigated by photometrically monitoring the reduction of p-nitrophenol by an excess of NaBH4 in the presence of the nanoparticles. The kinetic data could be explained by the assumption of a pseudo-first-order reaction with regard to p-nitrophenol. In all cases, a delay time t0 has been observed, after which the reactions start. This time is shorter when the catalyst has already been used. All data demonstrate that spherical polyelectrolyte brushes present an ideal carrier system for metallic nanoparticles.

Abstract: We explored using a magnetic field to modulate the permeability of polyelectrolyte microcapsules prepared by layer-by-layer self-assembly. Ferromagnetic gold-coated cobalt (Co@Au) nanoparticles (3 nm diameter) were embedded inside the capsule walls. The final 5 mum diameter microcapsules had wall structures consisting of 4 bilayers of poly(sodium styrene sulfonate)/poly(allylamine hydrochloride) (PSS/PAH), 1 layer of Co@Au, and 5 bilayers of PSS/PAH. External alternating magnetic fields of 100-300 Hz and 1200 Oe were applied to rotate the embedded Co@Au nanoparticles, which subsequently disturbed and distorted the capsule wall and drastically increased its permeability to macromolecules like FITC-labeled dextran. The capsule permeability change was estimated by taking the capsule interior and exterior fluorescent intensity ratio using confocal laser scanning microscopy. Capsules with 1 layer of Co@Au nanoparticles and 10 polyelectrolyte bilayers are optimal for magnetically controlling permeability. A theoretical explanation was proposed for the permeability control mechanisms. "Switching on" of these microcapsules using a magnetic field makes this method a good candidate for controlled drug delivery in biomedical applications.

Abstract: Reactive zero valent iron nanoparticles can degrade toxic nonaqueous phase liquids (NAPL) rapidly in contaminated groundwater to nontoxic products in situ, provided they can be delivered preferentially to the NAPL/water (oil/water) interface. This study demonstrates the ability of novel triblock copolymers to modify the nanoiron surface chemistry in a way that both promotes their colloidal stability in aqueous suspension and drives their adsorption to the oil/water interface. The ability of the copolymers to drive adsorption is demonstrated by the ability of copolymer-modified iron nanoparticles, but not the unmodified iron nanoparticles, to stabilize oil-in-water emulsions.

Abstract: Tannic acid (TA) was assembled in alternation with two different polycations, strong poly(dimethyldiallylamide) (PDDA) and weak poly(allylamine) (PAH), using a layer-by-layer technique. Their deposition at different pH was confirmed by QCM, UV−vis spectroscopy, and surface charge measurements. TA/polyelectrolyte multilayer films and capsules have pH-dependent structural properties different from those of commonly used poly(styrenesulfonate)/poly(allylamine) (PSS/PAH) compositions. The lowest speed of TA/polycation multilayer dissolution was found at the conditions close to those used for film preparation. Permeability for fluorescein-labeled dextrans into tannic acid/polycation capsules with a five bilayer wall composition was investigated as a function of pH using confocal microscopy. It was found that minimal permeability occurs at pH 5−7 and maximal permeability at very high and very low pH, providing new opportunities for capsule loading as compared with an established procedure for PSS/PAH microcapsu...

Abstract: Layer-by-layer deposition of anionic and cationic polyelectrolytes readily converts polymeric ultrafiltration membranes into materials capable of nanofiltration. ATR-FTIR spectra confirm that layer-by-layer deposition occurs on the ultrafiltration substrates, and adsorption of as few as 2.5 bilayers of poly(styrenesulfonate) (PSS)/protonated poly(allylamine) (PAH) or 3.5 bilayers of PSS/poly(diallyldimethylammonium chloride) (PDADMAC) reduces the molecular weight cutoff of polyethersulfone ultrafiltration supports from 50 kDa to <500 Da. Deposition of multilayer polyelectrolyte films on 300 and 500 kDa membranes also decreases molecular weight cutoffs, but solute rejections are significantly lower when using these supports, suggesting that the polyelectrolyte films do not completely cover large (0.2−0.4 μm in diameter) pores. On the 50 kDa substrates, PSS/PDADMAC films containing 3.5 bilayers exhibit a 95% rejection of SO42- and a chloride/sulfate selectivity of 27, whereas 4.5-bilayer PSS/PAH coatings sh...

Abstract: We exploit a precipitation−redispersion mechanism for complexation of short chain polyelectrolytes with cerium oxide nanoparticles to extend their stability ranges. As synthesized, cerium oxide sols at pH 1.4 consist of monodisperse cationic nanocrystalline particles having a hydrodynamic diameter of 10 nm and a molecular weight of 400 000 g mol-1. We show that short chain uncharged poly(acrylic acid) at low pH when added to a cerium oxide sols leads to macroscopic precipitation. As the pH is increased, the solution spontaneously redisperses into a clear solution of single particles with an anionic poly(acrylic acid) corona. The structure and dynamics of cerium oxide nanosols and their hybrid polymer−inorganic complexes in solution are investigated by static and dynamic light scattering, X-ray scattering, and chemical analysis. Quantitative analysis of the redispersed sol gives rise to an estimate of 40−50 polymer chains per particle for stable suspension. This amount represents 20% of the mass of the pol...

Abstract: Polyelectrolyte multilayers were constructed from poly(styrenesulfonate), PSS, and poly(diallyldimethylammonium) with regularly interspersed layers of deuterated PSS. Annealing, by salt, of the fuz...

Abstract: The review surveys the thermodynamics, kinetics and reaction mechanisms of oppositely charged polyelectrolytes in aqueous solutions giving rise to insoluble stoichiometric or soluble non-stoichiometric interpolyelectrolyte complexes. The mechanisms of polyelectrolyte exchange reactions are discussed. Equilibrated non-stoichiometric interpolyelectrolyte complexes show a dual behaviour in aqueous solutions. On the one hand, they behave as usual linear polyelectrolytes and, on the other hand, they exhibit properties of amphiphilic block copolymers. The addition of low-molecular-weight salts to solutions of interpolyelectrolyte complexes usually leads to redistribution of electrostatically bound chains and phase separation. Analysis of these processes is of key importance in assigning these complexes to a special family of polymeric materials. Selected data on the conformations of polyions in solid interpolyelectrolyte complexes are given and their thermomechanical properties in the swollen state are considered.

Abstract: Fully sulfonated poly(styrenesulfonate) brushes were grown from the surface of colloidal silica particles and used to prepare stable trichloroethylene-in-water and heptane-in-water Pickering emulsions. These particles were highly charged and colloidally stable in water but could not be dispersed in trichloroethylene or heptane. Both two-phase (emulsion plus neat water) and three-phase (emulsion separating neat oil and water phases) systems were observed, with water-continuous emulsion phases in all cases. Emulsion phases containing as much as 83% (v/v) oil were stable for over six months. Poly(styrenesulfonate)-grafted particles were very efficient emulsifiers; stable emulsion phases were prepared when using as little as 0.04 wt% particles. The emulsifying effectiveness of the poly(styrenesulfonate)-grafted silica particles can be attributed to the hydrophobicity of the vinylic polymer backbone that makes this highly charged polyelectrolyte unusually surface active at the oil/water interface.

Abstract: Alternating adsorption of polycations and polyanions on porous supports yields a variety of size-selective membranes whose swelling and transport properties depend on constituent polyelectrolytes, capping layer choice (polycation or polyanion), and deposition conditions. This report shows that in aqueous experiments, ellipsometrically determined swelling percentages correlate well with nanofiltration (NF) rejections and diffusion dialysis fluxes. For example, hyaluronic acid (HA)/chitosan films swell 4 times more than poly(styrene sulfonate) (PSS)/poly(allylamine hydrochloride) coatings, and in NF experiments, the HA/chitosan membranes permit a 250-fold greater fractional passage of sucrose. In general, films prepared from polyelectrolytes with a high charge density show low swelling and slow solute transport, presumably because of a high degree of ionic cross-linking. In the case of PSS/poly(diallyldimethylammonium chloride) (PDADMAC), PDADMAC-capped films can swell 4-fold more than their PSS-terminated ...

Abstract: Catalytic Pd nanoparticles in multilayer polyelectrolyte films can be easily prepared by alternating immersions of a substrate in PdCl42- and polyethylenimine (PEI) solutions followed by chemical reduction of Pd(II) with NaBH4. Transmission electron microscopy confirms that reduced [PdCl42-/PEI]3 films contain nanoparticles with diameters of 1−4 nm, and X-ray photoelectron spectroscopy indicates that ∼70% of the Pd in these films is Pd(0). Atomic emission analysis shows that little Pd is removed from PdCl42-/PEI films during deposition of PEI or rinsing, but about 60% of the Pd in the film is leached during reduction by NaBH4. In a system in which Pd(II) is deposited as a PEI complex, poly(acrylic acid) (PAA)/PEI−Pd(II) films, minimal leaching occurs during either reduction or deposition of PAA. Encapsulated nanoparticles in both [PAA/PEI−Pd(0)]nPAA and reduced [PdCl42-/PEI]n films exhibit selective catalysis, as shown by the fact that Pd-catalyzed hydrogenation of allyl alcohol can occur an order of magn...

Abstract: In this work, we report the synthesis of a great variety of polycations with varying counter-anions. These new polymers were obtained by a simple anion exchange reaction facilitated by the phase separation of the resulting products. This strategy has been successfully applied to three different polycations, poly(1-vinyl-3-ethylimidazolium bromide) poly(ViEtIm+Br-), poly(1-ethyl-4-vinylpyridinium bromide) poly(ViEtPy + Br - ), and poly(methacryloyloxyethyltrimethylammonium chloride) poly(EMTMA + Cl - ), with seven counter-anions such as PF - 6 , CF 3 SO - 3 , (CF 3 SO 2 ) 2 N - , (CF 3 CF 2 SO 2 ) 2 N - , dodecylbenzenesulfonate, toluene-4-sulfonate, and bis(2-ethylhexyl) hydrogen phosphate. The solubility range of the new polymeric ionic liquids becomes very broad, including apolar organic solvents and ionic liquids, depending on the nature of the counter-anion. Thermogravimmetric experiments showed that the thermalstability of the PILs also depends on the nature of the counter-anion improving in the order CF 3 SO - 3 > (CF 3 CF 2 SO 2 ) 2 N - > C 12 H 25 C 6 H 4 SO - 3 > PF - 6 > Br - > C 16 H 34 PO - 4 .

Abstract: lution of 512 pixels × 512 pixels. The SFM images in Figure S2 were taken with an Autoprobe CP research microscope (Thermomicroscope, Veeco, Santa Barbara, California, USA) operating at room temperature in air. Images with scan lengths ranging from 5 lm down to 0.5 lm have been recorded with a resolution of 512 pixels × 512 pixels using the 5 lm scanner and non-contact Si ultralevers with a spring constant (k) in the range 2.1–17.0 N m.

Abstract: In this review we present an overview of the developments of (self-)assembly of linear block copolymers containing one or more polyelectrolyte blocks in aqueous solution. Different micellar structures and phase behaviour are described. The role of inter- and intramolecular complex coacervation is emphasised. Recent developments in applications of assembly of polyelectrolyte-containing copolymers are presented.