Polyelectrolyte Adsorption Research Articles

Adsorption and encapsulation of flexible polyelectrolytes in charged spherical vesicles.

We present a theory of adsorption of flexible polyelectrolytes on the interior and exterior surfaces of a charged vesicle in an electrolyte solution. The criteria for adsorption and the density profiles of the adsorbed polymer chain are derived in terms of various characteristics of the polymer, vesicle, and medium, such as the charge density and length of the polymer, charge density and size of the vesicle, electrolyte concentration and dielectric constant of the medium. For adsorption inside the vesicle, the competition between the loss of conformational entropy and gain in adsorption energy results in two kinds of encapsulated states, depending on the strength of the polymer-vesicle interaction. By considering also the adsorption from outside the vesicle, we derive the entropic and energy contributions to the free energy change to transfer an adsorbed chain in the interior to an adsorbed chain on the exterior. In this paper, we have used the Wentzel-Kramers-Brillouin (WKB) method to solve the equation for the probability distribution function of the chain. The present WKB results are compared with the previous results based on variational methods. The WKB and variational results are in good agreement for both the interior and exterior states of adsorption, except in the zero-salt limit for adsorption in the exterior region. The adsorption criteria and density profiles for both the interior and exterior states are presented in terms of various experimentally controllable variables. Calculation of the dependencies of free energy change to transfer an adsorbed chain from the interior to the exterior surface on salt concentration and vesicle radius shows that the free energy penalty to expel a chain from a vesicle is only of the order of thermal energy.

Characterization and application of self-assembled thin films of polyelectrolytes/TiO2/CdSe for hydrogen production

Photocatalysis of water to produce hydrogen gas over titanium dioxide or other semiconductor films, known as water splitting, is a promising alternative using solar energy to obtain a clean fuel. Self-assembled thin films (SATFs) from the physical adsorption of polyelectrolytes and inorganic semiconductor nanoparticles are created by an inexpensive and non-polluting process that gives films with high molecular organization. The aim of this work was to fabricate and characterize SATFs via the layer-by-layer technique using the polyelectrolytes polyallylamine hydrochloride (PAH), poly(acrylic acid) and poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) in combination with titanium dioxide and CdSe nanoparticles and evaluate the application potential of these systems to produce hydrogen gas by solar radiation. The characterization of the SATFs showed that films with positive surface charge present favourable conditions for incorporation of negatively charged CdSe nanoparticles and that alkaline condition favour agglomeration of TiO2 nanoparticles. The best system was composed of (PAH + CdSe) and (PEDOT:PSS + TiO2 100% anatase) in alkaline medium. With a hydrogen gas average production rate of 0.350 μmol h−1 cm−2, the maximum number of layers was optimized at 120 layers, beyond which there was a decrease in photocatalytic activity, reducing the average production rate to 0.07 with the SATF of 160 layers. Moreover, the presence of CdSe increased the hydrogen gas production by 75% when compared to the film containing only titanium dioxide.

Adsorption of polyelectrolyte multilayers imparts high monovalent/divalent cation selectivity to aliphatic polyamide cation-exchange membranes

Nafion membranes coated with polyelectrolyte multilayers (PEMs) exhibit outstanding monovalent/divalent cation electrodialysis selectivity in a single-membrane cell. Nevertheless, the high cost of Nafion and the extensive pretreatments required for polyelectrolyte adsorption on this surface may preclude the use of these membranes in many applications. This work reports that native aliphatic polyamide Fujifilm type 1 cation-exchange membranes modified with protonated poly(allylamine) (PAH)/poly (4-styrenesulfonate) (PSS) films also show extremely high K+/Mg2+ cation selectivities in ED with a single-membrane cell. Even with 0.1M salt in the source phase, the K+/Mg2+ selectivity is >1000. The very low transfer of divalent cations implies that the PEM forms a complete, continuous coating on the smooth Fujifilm surface. Moreover, for a membrane coated on both sides, the PEM on the anode side is responsible for most of the selectivity. However, the current efficiency is only ~0.6 for PAH/PSS-modified Fujifilm or Nafion membranes. Adsorption of highly water-swollen (PDADMAC/PSS)n films on Nafion membranes leads to high K+/Mg2+ and Li+/Co2+ selectivities in ED, and the monovalent cation current efficiency reaches 0.8.

Nanoscale monolayer adsorption of polyelectrolytes at the solid/liquid interface observed by quartz crystal microbalance

The adsorption properties of cationic polyelectrolytes (poly (diallyl dimethylammonium chloride) (PDDA) and poly (allylamine hydrochloride) (PAH)) on solid surfaces were observed using quartz crystal microbalance. The response of adsorption was different with the change of polyelectrolyte solution concentration and pH value. The influence of pH value on the PDDA adsorption process is inconspicuous, while PAH shows strong dependence on the pH value. Furthermore, the change of molecular conformation of polyelectrolyte molecule is the main factor that affects the adsorption properties and structures.

Competitive Adsorption of Polyelectrolytes onto and into Pellicle-Coated Hydroxyapatite Investigated by QCM-D and Force Spectroscopy

A current effort in preventive dentistry is to inhibit surface attachment of bacteria using antibacterial polymer coatings on the tooth surface. For the antibacterial coatings, the physisorption of anionic and cationic polymers directly onto hydroxyapatite (HA) and saliva-treated HA surfaces was studied using quartz crystal microbalance, force spectroscopy, and atomic force microscopy. First, single species adsorption is shown to be stronger on HA surfaces than on silicon oxide surfaces for all polymers (i.e., Gantrez, sodium hyaluronate (NaHa), and poly(allylamine-co-allylguanidinium) (PAA-G75)). It is observed through pH dependence of Gantrez, NaHa, and PAA-G75 adsorption on HA surfaces that anionic polymers swell at high pH and collapse at low pH, whereas cationic polymers behave in the opposite fashion. Thicknesses of Gantrez, NaHa, and PAA-G75 are 52 nm (46 nm), 35 nm (11 nm), and 6 nm (54 nm) at pH 7 (3.5), respectively. Second, absorption of charged polymer is followed by absorption of the oppositely charged polymer. Upon exposure of the anionic polymer layers, Gantrez and NaHa, to the cationic polymer, PAA-G75, films collapse from 52 to 8 nm and 35 to 11 nm, respectively. This decrease in film thickness is attributed to the electrostatic cross-linking between anionic and cationic polymers. Third, for HA surfaces pretreated with artificial saliva (AS), the total thickness decreases from 25 to 16 nm upon exposure to PAA-G75. Force spectroscopy is used to further investigate the PAA-G75/AS coating. The results show that the interaction between a negatively charged colloidal bead and the AS surface is strongly repulsive, whereas PAA-G75/AS is attractive but varies across the surface. Additionally, AFM studies show that AS/HA is smooth with a RMS roughness of 1.7 nm, and PAA-G75-treated AS/HA is rough (RMS roughness of 5.4 nm) with patches of polymer distributed across the surface with an underlying coating. The high roughness of PAA-G75 treated AS/HA is attributed to the strong adsorption of the relatively small PAA-G75 onto the heterogeneously distributed negatively charged AS surface. In addition, uptake of PAA-G75 by pellicle layer (saliva-treated HA surface) is observed, and the adsorbed amount of PAA-G75 on/into pellicle layer is ∼2 times more than that on/into AS layer. These studies show that polymer adsorption onto HA and saliva-coated HA depends strongly on the polymer type and size and that there is an electrostatic interaction between polymer and saliva and/or oppositely charged polymers that stabilizes the coatings on HA. Lastly, assessing the viability of the adherent bacteria collected from the PAA-G75-coated surfaces showed a significant reduction (∼93%) in bacterial viability when compared to bacteria collected from untreated and Gantrez-coated HA. These results suggest the potential antimicrobial activity of PAA-G75.

The influence of a silicon substrate conductivity type on the efficiency of photostimulated polyelectrolyte adsorption

Changes in the work function of silicon substrates of different conductivity types under illumination and after deposition of a polyethylenimine layer by the method of photostimulated adsorption were examined. It is revealed that photostimulated adsorption of polyethylenimine results in the electrical passivation of silicon and its correlates with a value of the work function change under illumination.

Photo-assisted adsorption of gold nanoparticles onto a silicon substrate

We report on a photo-assisted adsorption of gold nanoparticles on a silicon substrate studied using atomic-force microscopy and secondary ion mass-spectrometry. Depending on a silicon conductivity type (n-Si or p-Si), the amount of photo-assisted adsorbed gold nanoparticles either increases (n-Si) or decreases (p-Si) on irradiation. In addition, the impacts of a cationic polyelectrolyte monolayer and adsorption time were also revealed. The polyelectrolyte layer enhances the adsorption of the gold nanoparticles but decreases the influence of light. The results of the photo-assisted adsorption on two types of silicon wafer were explained by electron processes at the substrate/solution interface.

Effect of carboxymethylcellulose on potassium bitartrate crystallization on model solution and white wine

Instability in bottled wines refer to tartaric salts crystallization such as potassium bitartrate (KHT). It is not desirable as consumers see the settled salts as an evidence of a poor quality control. In some cases, it causes excessive gushing in sparkling wine. We investigate the effect of two oenological carboxymethylcellulose (CMC) for KHT inhibition in a model solution of white wine by studying the impact of some properties of CMC such as the degree of polymerization, the degree of substitution, and the apparent dissociation constant determined by potentiometric titration. Polyelectrolyte adsorption is used for determining the surface and total charge and for providing information about the availability of CMC charged groups for interacting with KHT crystal faces. The inhibitory efficiency of CMC on model solution is evaluated by measuring the induction time with the help of conductimetric methods. Crystals growth with and without CMC are studied by observation with MEB and by thermal analysis using DSC. The results confirm the effectiveness of CMC as an inhibitor of KHT crystallization in a model solution. The main hypothesis of the mechanism lies in the interaction of dissociated anionic carboxymethyl groups along the cellulose backbone with positively charged layers on KHT faces like the {010} face. Key factors such as pH, CMC chain length and total charge are discusses.

Facile Synthesis of SiO2–Ni Raspberry Composites by Electroless Plating and Polyelectrolyte Adsorption

Facile Synthesis of SiO₂–Ni Raspberry Composites by Electroless Plating and Polyelectrolyte Adsorption

Mapping Infrared Enhancement around Gold Nanoparticles Using Polyelectrolytes

Enhancement of infrared signals from polyelectrolyte adsorbed on gold nanoparticles (GNPs) was studied in situ by attenuated total reflection infrared spectroscopy. Nanoparticles and polyelectrolytes were deposited using layer-by-layer techniques, and the infrared signal was studied as a function of particle size, particle density, and distance from particle surface. It was observed that enhancement is more pronounced for larger nanoparticles and it decreases with increasing distance from the particle surface. Furthermore, at high GNP coverage, the signal from the first polyelectrolyte layer is particularly enhanced, and the signal increases slowly with time, in contrast to subsequent layers. We assign this to polyelectrolyte adsorption within narrow gaps between nanoparticles, where the electric field is enhanced. Furthermore, enhanced absorption was observed in the gap between the GNPs and the germanium internal reflection element, which was confirmed by polarized measurements. This enhancement is more ...

Novel multilayer microcapsules based on soy protein isolate fibrils and high methoxyl pectin: Production, characterization and release modeling

In this study, novel microcapsules were produced through the layer by layer adsorption of food-grade and plant-based polyelectrolytes, soy protein isolate (SPI) fibrils and high methoxyl pectin (HMP). The physical properties of the fibrils were investigated by TEM and AFM and the properties of the microcapsules such as size, uniformity, zeta potential, morphology, functional groups, modeling and the release kinetics of limonene were examined. The results revealed that SPI-fibrils had a thickness varying from 1 to 10nm and strand like structure. SEM images showed that the microcapsules were spherical and the thickness increased by the number of layers which led to the improvement of shell strength. The FTIR results confirmed that HMP and SPI-fibrils were adsorbed layer by layer as the walls of microcapsules and presence of limonene was stable into microcapsules. By increasing the number of layers of the shell from 2 to 6, the release rate of limonene decreased significantly. The index n in Rigter–Peppas model indicates that the release mechanism of limonene from multilayer microcapsules followed a non-Fick law. This method of microcapsule production is very simple and could be readily industrialized, especially for the manufacture of food products for vegetarians.

Interfacial adsorption of pH-responsive polymers and nanoparticles.

Using dissipative particle dynamics (DPD), we model the interfacial adsorption of pH-responsive polyelectrolytes and polyelectrolyte-grafted nanoparticles (PNPs) at a planar water-oil interface. The electrostatic interactions in the presence of the dielectric discontinuity across the interface are modeled by exploiting the Groot method, which uses an iterative method to solve the Poisson equation on a uniform grid with distributed charge. We reveal the effects of the pH and salinity of the aqueous solution and the length of the polyelectrolyte on the adsorption behavior of weak polyelectrolytes. The adsorption kinetics is monitored via the trajectory of the center of mass of the polyelectrolyte in the direction normal to the interface. The residence time at the interface and the pair correlation function between the polyelectrolyte and the oil are measured to quantitatively characterize the adsorption. Similar to the weak polyelectrolytes, the influences of pH, salinity and grafted chain length on the adsorption of an individual PNP are explored. Our results show that by grafting polyelectrolytes, the interfacial behavior of the nanoparticles can be tuned by changing the pH and salinity of the solution, which is dictated by the contact angle, the pair correlation function between the particles and the oil, the desorption energy, and the particle morphology at the interface. We also observe that the electrostatic-driven variations in the interfacial activity and morphology of the PNPs are not sensitive to the length of the grafted polyelectrolytes.

Critical adsorption of periodic and random polyampholytes onto charged surfaces.

How different are the properties of critical adsorption of polyampholytes and polyelectrolytes onto charged surfaces? How important are the details of polyampholyte charge distribution on the onset of critical adsorption transition? What are the scaling relations governing the dependence of critical surface charge density on salt concentration in the surrounding solution? Here, we employ Metropolis Monte Carlo simulations and uncover the scaling relations for critical adsorption for quenched periodic and random charge distributions along the polyampholyte chains. We also evaluate and discuss the dependence of the adsorbed layer width on solution salinity and details of the charge distribution. We contrast our findings to the known results for polyelectrolyte adsorption onto oppositely charged surfaces, in particular, their dependence on electrolyte concentration.

Electrophoretic Deposition of Ni(OH)2 Nanoplatelets Modified by Polyelectrolyte Multilayers: Study of the Coatings Formation in a Laminar Flow Cell

The electrophoretic deposition (EPD) of semiconductor ceramic nanoplatelets functionalized by self-assembled polyelectrolyte multilayers has been investigated. The influence of particle surface modification in the packing of the nanostructured film on a nickel cathode has been determined for different electrical conditions. A polymer multilayer shell has been fashioned onto β-Ni(OH)2 nanoplatelets surfaces by alternating the adsorption of Polyethylenimine (PEI) and Polyacrylic Acid (PAA). Two different core-shell systems with 1, 3 and 5 layers were considered using either linear or branched PEI as polycation to alternate with the anionic polyelectrolyte (PAA). The Layer by Layer, (LbL) build-up of polyanions and polycations was characterized both in terms of particle zeta potential measurements and in situ measurements of polyelectrolyte adsorption onto a flat substrate by optical fixed-angle reflectometry. The amount of polyelectrolyte required to build up each layer was determined from zeta potential measurements. Both data allowed the design of the in situ formation of the core-shell nanostructures as well as the shaping of the particulated coatings following the one-pot procedure, avoiding intermediate steps of drying or washing. The movement of the core-shell particles, their aggregation state and the coating growth during electrophoretic deposition were studied in situ using a laminar flow cell coupled to an optical microscope. The particle flux was calculated from the surface coverage of the cathode and compared to the values estimated by the EPD electrokinetic model, demonstrating the strong impact of the steric interactions between the core-shell particles in both the deposition rate of nanoplatelets and the coating morphology.

Microfibrilated cellulose as a model for soft colloid flocculation with polyelectrolytes

The effect of polyelectrolyte molecular weight, charge density and dose on the flocculation of Microfibrillated Cellulose (MFC) was investigated. Four types of cationic polyelectrolyte commonly used in industry were chosen: Cationic Polyacrylamide (CPAM), Polyethylenimine (PEI), Polydadmac (PDADMAC) and Poly-aluminium Chloride (PAC). Adsorption isotherm and zeta potential measurements of MFC-polyelectrolyte suspensions quantified polyelectrolyte adsorption behaviour. The flocculation mechanisms, size, strength and type of flocs formed were quantified using static conditions, driven by gravity sedimentation through gel point measurements and dynamic conditions through Focussed Beam Reflectance Measurements (FBRM). Four distinct flocculation behaviours were observed. The first of which was that of a polysalt, PAC. Based on the gel point curve, PAC is unable to create a self-supporting network. FBRM reveals that PAC induces the formation of small and dense flocs, corresponding to an aggregation caused by charge screening. Second, charge neutralisation was observed for PEI with total reflocculation and maximum flocculation occurring at the isoelectric point and corresponding to 85% polymer surface coverage. Third, MFC-PDADMAC flocs presented a total reflocculation and maximum flocculation occurring at 50% coverage and a colloid charge of –10mV or −15mV; this agrees with the formation of polymer patches on MFC. Lastly, low reflocculation and maximum flocculation occurred at half polymer surface coverage for CPAM-MFC flocs, corresponding to a bridging mechanism. Polyelectrolyte maximum surface coverage was found to scale inversely to polymer charge density and was mostly independent of polymer molecular weight and morphology. Finally MFC flocs properties were used as model of soft colloids and analysed for specific industrial applications.

Adsorption and interlayer diffusion controlled growth and unique surface patterned growth of polyelectrolyte multilayers

In this work, extremely high molecular weight (Mw) poly(allylamine hydrochloride) (PAH, 900K g/mol) and poly(acrylic acid) (PAA, 225 K g/mol) were selected to amplify the difference in the growth of multilayers in comparison with low Mw PAA (15K g/mol) and PAH (15K g/mol). By varying the pH conditions, the PAH/PAA multilayers were fabricated via the layer-by-layer (LbL) assembly in both linear and exponential growth regimes. In the linear growth regime with interlayer diffusion suppressed, high Mw polyelectrolytes with low charge density could slow down the adsorption step, leading to the decrease of thickness compared to low Mw polyelectrolytes when the deposition time was limited. However, the effect of Mw could be reversed by increasing the deposition time, for the adsorption of low Mw polyelectrolyte reached equilibrium, while the adsorption of high Mw polyelectrolyte continued. The larger coil size of high Mw polyelectrolyte could enable the surpassing of multilayer thickness compared with low Mw polyelectrolyte. In the exponential growth regime, besides the slow adsorption, the application of high Mw polyelectrolytes further suppressed the interlayer diffusion, leading to the decrease of multilayer thickness regardless of deposition time. We further studied the effects of deposition time, Mw of polyelectrolytes, and the number of bilayers on the surface morphology in the exponential growth regime. Surface roughness significantly increased with the application of high Mw PAA and the increase in deposition time. For the first time, the unique LbL film growth patterns of islet, ring and cantaloupe skin-like structures that consecutively formed on the surface of polyelectrolyte multilayers were reported by tuning the above parameters.

Simulations of Polyelectrolyte Adsorption to a Dielectric Like-Charged Surface.

We explore, using the recently developed efficient Monte Carlo simulation method, the interaction of an anionic polyelectrolyte solution with a like-charged dielectric surface. In addition to polyions, the solution also contains salt with either monovalent, divalent, or trivalent counterions. In agreement with recent experimental observations, we find that multivalent counterions can lead to strong adsorption of polyions onto the surface. On the other hand, addition of a 1:1 electrolyte diminishes the adsorption induced by the multivalent counterions. Dielectric discontinuity at the interface is found to play only a marginal role in polyion adsorption.

Hybrid Polyelectrolyte/Fe3O4 Nanocapsules for Hyperthermia Applications.

We validated here the applicability to hyperthermia treatment of magnetic nanocapsules prepared by the sequential layer-by-layer adsorption of polyelectrolytes and magnetic, Fe3O4 nanoparticles. For the shell preparation around a nanodroplet liquid core, biocompatible polyelectrolytes were used: poly l-lysine as the polycation and poly glutamic acid as the polyanion. The hyperthermia effect was demonstrated by applying the radio frequency (rf) magnetic field with maximum fields H up to 0.025 T and frequencies up to 430 kHz; we found sizable heating effects, with a heating rate up to 0.46 °C/min. We also found effects of irradiation on capsules' morphology that indicated their disruption, thus suggesting their potential use as nanocarriers of drugs that can be locally released on demand. Therefore, these magnetically responsive nanocapsules could be a promising platform for multifunctional biomedical applications such as the controlled release of pharmaceuticals in combination with hyperthermia treatment.

Co-adsorption of polyanions and esterquat surfactants; effect on formation and stability of micellar core nanocapsules

We investigated the co-adsorption at water/air interface of soft cationic surfactants of the esterquat-type, fatty acid quaternary ammonium esters with hydrocarbon chain containing eleven carbons and the amino acid betaine esters with twelve carbons in the chain with polyanions: polysodium 4–styrenesulfonate (PSS), poly-l-glutamic acid sodium salt (PGA), alginic acid sodium salt (ALG) and λ-carrageenan (CAR). The effect of surfactants basic hydrolysis on formation of surfactant/polymer complexes in bulk and at interface was taken into account. We found that the surface charge of the water/air interface originating from the adsorption of fatty acid quaternary ammonium esters decreased as the result of hydrolysis that led to lower co-adsorption of polyanions than in the case of amino acid betaine esters. The optimal conditions for formation of surfactant micelles/polyelectrolyte aggregates were established. These negatively charged aggregates were further used as nanocores for encapsulation by the layer-by-layer (LbL) adsorption of synthetic and natural polyelectrolytes. The average size of nanocapsules was in range 100–200nm. We observed that stability of micellar cores were dependent on the rate of esterquat hydrolysis, ones formed with fast hydrolysable surfactant were stable under acidic but unstable under basic conditions.

Critical adsorption of polyelectrolytes onto planar and convex highly charged surfaces: the nonlinear Poisson–Boltzmann approach

We study the adsorption–desorption transition of polyelectrolyte chains onto planar, cylindrical and spherical surfaces with arbitrarily high surface charge densities by massive Monte Carlo computer simulations. We examine in detail how the well known scaling relations for the threshold transition—demarcating the adsorbed and desorbed domains of a polyelectrolyte near weakly charged surfaces—are altered for highly charged interfaces. In virtue of high surface potentials and large surface charge densities, the Debye–Hückel approximation is often not feasible and the nonlinear Poisson–Boltzmann approach should be implemented. At low salt conditions, for instance, the electrostatic potential from the nonlinear Poisson–Boltzmann equation is smaller than the Debye–Hückel result, such that the required critical surface charge density for polyelectrolyte adsorption increases. The nonlinear relation between the surface charge density and electrostatic potential leads to a sharply increasing critical surface charge density with growing ionic strength, imposing an additional limit to the critical salt concentration above which no polyelectrolyte adsorption occurs at all. We contrast our simulations findings with the known scaling results for weak critical polyelectrolyte adsorption onto oppositely charged surfaces for the three standard geometries. Finally, we discuss some applications of our results for some physical–chemical and biophysical systems.