Sequential Adsorption Of Polyelectrolytes Research Articles

Two Sides of the Same Coin: A Unified Theoretical Treatment of Polyelectrolyte Complexation in Solution and Layer-by-Layer Films

Polyelectrolyte coacervates, obtained by mixing solutions of oppositely charged polyions, and layer-by-layer films, produced by sequential adsorption of polyelectrolytes on a surface, are two types of closely related soft materials. While both types of materials are produced by polyelectrolyte complexation, their theoretical description had so far followed divergent paths. This work reports a unifying theoretical treatment of polyelectrolyte complexation in solution and layer-by-layer self-assembled thin films using a molecular theory that describes polyelectrolyte complexation by using a chemical-equilibrium formalism. The theory is shown to predict both the phase diagrams of polyelectrolyte mixtures in solution and the formation of layer-by-layer thin films in good agreement with experimental evidence. In the latter case, the theory correctly captures the effects of solution pH and ionic strength on the mass of the deposited films as well as the possibility of layer-by-layer deposition without full charge reversal at extreme pHs. The theory is then used to revisit the “universal curve” for the effect of salt concentration on layer-by-layer deposition previously proposed on experimental grounds by Salehi et al. [Macromolecules 2015, 48, 400–409]. This universal curve makes predictions about the growth rate of a layer-by-layer film for a given polyanion/polycation pair by using only information obtained from a mixture of the same polyelectrolytes in solution, thereby linking both phenomena. Our theoretical results confirm the validity of the curve. This achievement demonstrates the practical importance of describing polyelectrolyte coacervates and multilayer films within a unified theoretical framework.

Catalytic antioxidant nanocomposites based on sequential adsorption of redox active metal complexes and polyelectrolytes on nanoclay particles.

An antioxidant nanocomposite was prepared by successive adsorption of redox active metal complexes (copper(ii)-bipyridyl and iron(iii)-citrate) and polyelectrolytes (poly(styrene sulfonate) and poly(diallyldimethyl ammonium)) on layered double hydroxide nanoclay. The experimental conditions were optimized in each preparation step and thus, the final composite formed highly stable colloids, i.e., excellent resistance against salt-induced aggregation was achieved. Due to the synergistic effect of the metal complexes, the developed composite showed remarkable activity in the dismutation of superoxide radicals, close to the one determined for the native superoxide dismutase enzyme. The obtained composite is highly selective for superoxide radical dismutation, while its activity in other antioxidant tests was close to negligible. Structural characterization of the composite revealed that the excellent superoxide radical scavenging ability originated from the advantageous coordination geometry around the copper(ii) center formed upon immobilization. The structure formed around the metal centers led to optimal redox features and consequently, to an improved superoxide dismutase-like activity. The catalytic antioxidant composite is a promising candidate to reduce oxidative stress in industrial manufacturing processes, where natural enzymes quickly lose their activity due to the harsh environmental conditions.

Effect of Polyelectrolyte Mono- and Bilayer Formation on the Colloidal Stability of Layered Double Hydroxide Nanoparticles.

Sequential adsorption of polyelectrolytes on nanoparticles is a popular method to obtain thin films after deposition. However, the effect of polyelectrolyte multilayer formation on the colloidal stability of the nanoparticles has not been studied in detail. In the present work, layered double hydroxides (LDH) were synthesized and interaction with oppositely and like-charged polyelectrolytes was investigated. Electrophoretic and light scattering measurements revealed that colloidal stability of LDH can be tuned by adsorption of poly(styrene sulfonate) (PSS) on the oppositely charged LDH surface in appropriate doses and thus, unstable or stable dispersions can be designed. Negatively charged LDH of adsorbed PSS monolayer was obtained and a poly(diallyldimethyl ammonium chloride) (PDADMAC) second layer was systematically built on the particles. The obtained polyelectrolyte bilayer provided high colloidal stability for the LDH-PSS-PDADMAC dispersions due to the presence of repulsive interparticle forces of electrostatic and steric origin. The results provide crucial quantitative information on designing highly stable particle-polyelectrolyte systems for the preparation of thin films or immobilization of guest substances between the layers for delivery processes.

Biocompatible Polymeric Nanoparticles as Promising Candidates for Drug Delivery.

The use of polymeric nanoparticles (NPs) in pharmacology provides many benefits because this approach can increase the efficacy and selectivity of active compounds. However, development of new nanocarriers requires better understanding of the interactions between NPs and the immune system, allowing for the optimization of NP properties for effective drug delivery. Therefore, in the present study, we focused on the investigation of the interactions between biocompatible polymeric NPs and a murine macrophage cell line (RAW 264.7) and a human monocytic leukemia cell line (THP-1). NPs based on a liquid core with polyelectrolyte shells were prepared by sequential adsorption of polyelectrolytes (LbL) using AOT (docusate sodium salt) as the emulsifier and the biocompatible polyelectrolytes polyanion PGA (poly-l-glutamic acid sodium salt) and polycation PLL (poly l-lysine). The average size of the obtained NPs was 80 nm. Pegylated external layers were prepared using PGA-g-PEG (PGA grafted by PEG poly(ethylene glycol)). The influence of the physicochemical properties of the NPs (charge, size, surface modification) on viability, phagocytosis potential, and endocytosis was studied. Internalization of NPs was determined by flow cytometry and confocal microscopy. Moreover, we evaluated whether addition of PEG chains downregulates particle uptake by phagocytic cells. The presented results confirm that the obtained PEG-grafted NPs are promising candidates for drug delivery.

Cytotoxic activity of paclitaxel incorporated into polyelectrolyte nanocapsules

Nanoencapsulation is a promising solution for the delivery of chemotherapeutics to tumors. A method of preparation of drug-loaded nanocapsules based on the liquid core encapsulation by a sequential adsorption of a polyelectrolyte is described. An easily evaporative solvent, chloroform, was used as an oil phase. An interfacial complex formed with an oil-soluble, Food and Drug Administration-approved surfactant, and polycation poly-l-lysine (PLL) was used as a microemulsion stabilizer. A polyelectrolyte multilayer shell was constructed by a sequential adsorption of polyelectrolytes using biocompatible polyelectrolytes (PLL as a polycation and poly-l-glutamic acid as a polyanion). A hydrophobic anticancer agent, paclitaxel, was successfully encapsulated in the nanocarriers with the average size of 100 nm. In vitro analysis of the effects of nanoformulations was performed using a mouse colon carcinoma cell line CT26-CEA. Biocompatibility of the nanocapsules was evaluated using various biochemical assays. The results indicate that the cell viability was diminished by positively but not by negatively charged nanocarriers. Analysis of the cellular uptake of nanocapsules determined by flow cytometry and confocal microscopy confirmed their accumulation inside the cells. Encapsulated paclitaxel retains its cytotoxic/cytostatic activity; although its effects were weaker than those of the corresponding concentrations of the free drug. The generated nanocapsules seem to be a valuable vehicle for tumor drug delivery; although further work is needed to increase their overall activity.

Albumin–furcellaran complexes as cores for nanoencapsulation

The possibility of using protein–polysaccharide complexes as cores for nanocapsules formation by sequential adsorption of polyelectrolytes were investigated. We selected the globular protein bovine serum albumin (BSA) and the natural anionic polysaccharide–furcellaran (FUR) and studied their complexation in the broad range of their concentration ratio and pH of the solutions. Analysing the zeta potential dependencies on these parameters, we selected optimal conditions for the core formation. The capsule shells were formed by the layer-by-layer adsorption of polyelectrolytes; polycation PDADMAC (polydiallyl dimethyl ammonium chloride) and polyanion PSS poly(sodium-4-styrene sulfonate). Depending on the shell thickness the size of the capsules was in the range of 60–80nm.

Formation of oil filled nanocapsules with silica shells modified by sequential adsorption of polyelectrolytes

The aim of our work was to develop a novel method of encapsulation of emulsion droplets by silica shells modified by polyelectrolyte multilayers. Dimethyloctadecyl[3-(trimethoxysilyl) propyl]ammonium chloride (DTSACl) was used as the silane for silica shell formation as well as emulsion stabilizer. The silica nanocapsules were subsequently modified by sequential adsorption of polyelectrolytes. Polyelectrolyte multilayers were formed using the saturation method from the various pairs of polyelectrolytes. The average size of nanocapsules with polyelectrolyte shell was 100–120nm. To demonstrate the possibility of encapsulation of hydrophobic substance we enclosed oil-soluble dye Coumarine-6. The obtained capsules’ suspensions were stable for the period of several weeks.

Nucleation and Growth of Zinc Sulfide Nanoparticles in Ultrathin Polymer Films by Layer-by-Layer Polyionic Assemblies

In this work, zinc sulfide (ZnS) nanoparticles were formed by nucleation and growth in ultrathin films of polydiallyldi-methylammonium chloride (PDDA)–polystyrenesulfonate sodium salt (PSS) film produced by the Layer-by-Layer (LbL) deposition technique. Multilayer thin film assemblies, fabricated by sequential adsorption of polyelectrolytes on a quartz substrate, were used as a supramolecular reaction template to study the in-situ nucleation and growth of ZnS nanoparticles. ZnS nanoparticles were nucleated within the polymeric supramolecular structure through cyclic expo-sure to the solutions of Zn(NO3)2 and thiourea. The growth and nucleation of nanoparticles were accomplished by a cyclic repetition of reductive hydrolysis reactions. The growth of a thin film on a flat substrate via LbL was monitored by ultraviolet-visible (UV-Vis) spectroscopy. Analysis of the UV-visible absorption spectra of the films revealed that the nanoparticles grew with increasing number of cycles. The presence of ZnS nanoparticles were verified by transmission electron microscopy (TEM). Selected area electron diffraction (SAED) showed that the ZnS has a cubic spheralite structure.

Liquid crystal-in-water emulsion stabilized by layer-by-layer adsorption of polyelectrolytes and magnetite nanoparticles

We propose a method for stabilizing and modifying the dispersed phase of a liquid crystal-in-water (LC/water) emulsion using the sequential adsorption of polyelectrolytes and magnetite nanoparticles, which leads to the formation of LC-filled nanocomposite microcapsules. The obtained samples were studied by optical microscopy and Raman spectroscopy. It is established that the LC-filled nanocomposite microcapsules can move under the action of an external magnetic field.

Polyelectrolyte Multilayer Films as Templates for the In Situ Photochemical Synthesis of Silver Nanoparticles

Multilayer films formed by the sequential adsorption of polyelectrolytes (PEs) from aqueous solution were used as templates for the in situ growth of silver nanoparticles. When films consisting of ...

Encapsulation of liquid cores by layer-by-layer adsorption of polyelectrolytes

The aim of this work was to develop the method of preparation of loaded, submicron nanocapsules based on the liquid core encapsulation by polyelectrolyte (PE) multilayer adsorption. The procedure of PE adsorption on the emulsion droplets requires a specific selection of surfactants, which have good properties as emulsifiers and provide a stable surface charge for sequential adsorption of PE without losing stability of emulsion. Using AOT as emulsifier this study obtained droplets, stabilized by AOT/PDADMAC surface complexes. These positively charged liquid cores were then modified by sequential adsorption of polyelectrolytes to obtain nanocapsules with the average size of 200 nm, with various combinations of polyelectrolytes (PDADMAC, CHIT, PAH, PSS, ALG). This study demonstrated the formation of consecutive layers of PE shells by measuring zeta potential of capsules after adsorption of each layer. It visualized the cores by dissolving fluorescent dye Coumarine6 in oil phase and multilayer shells by using FITC labelled polycation.

The effect of support material and conditioning on wettability of PAH/PSS multilayer films

An efficient method for characterizing wetting properties of heterogeneous surfaces produced by sequential adsorption of polyelectrolytes was developed. Three types of polyelectrolytes were used: polyallylamine hydrochloride (PAH), polyethyleneimine (PEI), both of a cationic type, and polysodium 4-styrenesulfonate (PSS), of an anionic type. Multilayer films were prepared by ‘layer-by-layer’ (LbL) deposition technique. Natural ruby mica, glass, titanium foil and silicon wafers were used as the support material for PE films. Wetting of polyelectrolyte films was determined experimentally by contact angle measurements, using technique of direct image analysis of shape of sessile drops. Periodic oscillations in contact angle values were observed for multilayers terminated by polycation and polyanion, respectively, and the variations in contact angle values strongly depended on the conditions of adsorption and multilayer treatment after deposition. Therefore, the influence of ionic strength of polyelectrolyte solution used for deposition on wetting of multilayer films was considered and also the effect of conditioning in different environments was investigated. It is usually assumed that film properties and stability strongly depend on the first layer which is used to anchor a multilayer at the surface of support material. To investigate influence of the first layer, PAH/PSS films were compared with more complex ones having PEI as the first layer with a sequence of PSS/PAH deposited on top of it.

Thin Multilayer Films of Weak Polyelectrolytes on Colloid Particles

We report the formation of poly(acrylic acid) (sodium salt) (PAA) and poly(allylamine hydrochloride) (PAH) multilayers on polystyrene (PS) and melamine formaldehyde (MF) colloid particles by the layer-by-layer (LbL) assembly technique. The use of different solution processing conditions (e.g., pH and ionic strength) was found to have a pronounced effect on film growth, with the degree of dissociation of both polyelectrolytes (PEs) playing an important role for regular PAA/PAH multilayer growth. To retain colloidal stability during the sequential adsorption of PEs, it was essential to deposit the PE layers from adsorption solutions where the PEs are in a highly charged state, the degree of which was regulated by varying the pH. Thicker PAA/PAH coatings were obtained when the pH value of the PAA deposition solution was close to the pKa value of PAA in solution. The presence of salt in the deposition and rinsing solutions also promoted the formation of thicker PAA/PAH coatings. The ζ-potential of the particl...

Nucleation and Growth of Lead Sulfide Nano- and Microcrystallites in Supramolecular Polymer Assemblies.

Multilayer thin film assemblies fabricated by the sequential adsorption of polyelectrolytes on a quartz substrate were used as a supramolecular reaction template to study the in situ nucleation and growth of PbS nano- and microparticles. Chemical reaction within the polymer film was initiated by absorbing Pb2+ from an aqueous solution of Pb(NO3)2 followed by exposing the film to H2S gas. Electron microscopic examination of the films revealed that while nanoparticles are formed in films that were subject to one or two reaction cycles, large crystallites were formed when these films were exposed to a large number (10) of reaction cycles. In the latter case, a broad distribution of particle sizes is observed and may be attributed to Ostwald ripening. Detailed studies show the nucleation and growth of the PbS particles into crystallites of different shapes. UV−vis absorption studies reveal that the absorption spectral profiles of the films are dependent on the size of the PbS crystallites. The broadened absor...

Nano-scale control of composite polymer films by mass-controlled layer-by-layer sequential adsorption of polyelectrolytes

The mass of polyelectrolyte films adsorbed onto a surface during the deposition of a thin polymer film by a layer-by-layer sequential adsorption process was systematically controlled using a feedback system with a computer. For the deposition process, a quartz crystal microbalance (QCM) with an integrated oscillation circuit was attached to the arm of an automatic slide stainer and the frequency shift during adsorption or rinsing of the polyelectrolytes was monitored by a computer attached to a frequency counter. By feeding back the data acquired by the in situ QCM measurement, the mass of material deposited was controlled and a high quality self-assembly film was produced. This method is termed mass-controlled layer-by-layer sequential adsorption. The accuracy of the layer thickness in the multiplayer film was found to be approximately 1 nm. Copyright © 2000 John Wiley & Sons, Ltd.

Thin polymer films for the filter of an air cleaner fabricated by mass-controlled layer-by-layer adsorption of polyelectrolytes

An extremely high performance of tobacco smoke filter for air cleaner was established by forming the polymer thin films on the surface of fiberglass by layer-by-layer sequential adsorption of polyelectrolytes. The mass controlled automatic dipping machine was used for the deposition process of the polyelectrolytes and it was easy to optimize the adsorption characteristics of the filter to smoke. The newly developed filter showed remarkably high performance because it adsorbed large amount of smoke without supplying electric power. It was also found that the polyelectrolytes filters can be cleaned just by rinsing in a hot water at 90 °C. Consequently, a remarkable high performance of the polymer filter for air cleaner can be produced by the mass-controlled layer-by-layer adsorption method of polyelectrolytes. Copyright © 2000 John Wiley & Sons, Ltd.

Photoinduced Charge Separation in Multilayer Thin Films Grown by Sequential Adsorption of Polyelectrolytes

Photoinduced Charge Separation in Multilayer Thin Films Grown by Sequential Adsorption of Polyelectrolytes