Ion transport through polyelectrolyte multilayers under steady-state conditions (original) (raw)
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Ion transport through electrolyte/polyelectrolyte multi-layers
Scientific Reports, 2015
Ion transport of multi-ionic solutions through layered electrolyte and polyelectrolyte structures are relevant in a large variety of technical systems such as micro and nanofluidic devices, sensors, batteries and large desalination process systems. We report a new direct numerical simulation model coined E n PE n : it allows to solve a set of first principle equations to predict for multiple ions their concentration and electrical potential profiles in electro-chemically complex architectures of n layered electrolytes E and n polyelectrolytes PE. E n PE n can robustly capture ion transport in submillimeter architectures with submicron polyelectrolyte layers. We proof the strength of E n PE n for three yet unsolved architectures: (a) selective Na over Ca transport in surface modified ion selective membranes, (b) ion transport and water splitting in bipolar membranes and (c) transport of weak electrolytes.
Journal of Electroanalytical Chemistry, 2017
The layer by layer (LbL) sequential adsorption of oppositely charged polyelectrolytes is a simple tool to form ultrathin multilayer membranes with highly controlled properties. In our studies we have focused on the formation of multilayer films from the pair of synthetic, model polyelectrolytes: poly(allylamine hydrochloride) (PAH)/poly(4-styrenesulfonate) (PSS) and poly(diallyldimethylammonium chloride) (PDADMAC)/poly(4-styrenesulfonate) (PSS) in the presence of monovalent (NaCl) and divalent (MgCl 2) ions solution with the same ionic strength. Quartz crystal microbalance (QCM) was used to determine the film mass. To examine barrier properties of the multilayers two electroactive probes were selected: positively charged hexaammineruthenium (III) chloride and equimolar solution of potassium hexacyanoferrate (II) and potassium hexacyanoferrate (III) of negative charge. We demonstrated that the mass/thickness of the film was larger when the polyelectrolytes were deposited in the presence of divalent ions. On the other hand, the permeability of the polymer films depended not only on the ionic strength, but also on the valence of the ions in the polyelectrolyte solution as well as the charge of the chosen electroactive probe.
Materials Science and Engineering: C, 2002
The transport of aqueous salts containing mono-, di-and trivalent metal and tetravalent metal complex ions across ultrathin polyvinylammonium/polyvinylsulphate (PVA/PVS) membranes is described. The membranes were prepared by electrostatic layer-by-layer (LBL) assembly of the two polyelectrolytes. Using spectroscopic measurements and permeability studies, it is demonstrated that the transport of copper(II) chloride, lanthanum(III) chloride, barium chloride and potassium hexacyanoferrate(II) is accompanied by the permanent incorporation of the metal and metal complex ions in the membrane. Upon the uptake of copper, lanthanum and hexacyanoferrate ions, the membranes become cross-linked so that the permeation rates of other salts not taken up by the membrane, e.g. sodium chloride, potassium chloride and magnesium chloride, are decreased. The uptake of barium ions leads to a decrease of the cross-linking density of the membrane so that the permeation rate of NaCl is increased. Possible mechanisms for the ion uptake are discussed. D
Annealing of Polyelectrolyte Multilayers for Control over Ion Permeation
Advanced Materials Interfaces, 2018
Polyelectrolyte multilayer based membranes are highly promising systems to create stable and versatile nanofiltration membranes. One very popular and well‐studied polyelectrolyte pair, is the polycation poly(diallyldimethylammonium chloride) (PDADMAC) and polyanion poly(sodium 4‐styrenesulfonate) (PSS), due to its excellent separation properties and high chemical and physical stability. Membrane charge can be easily controlled by simply terminating the multilayer by either PDADMAC or PSS. Unfortunately, a phenomenon that occurs during multilayer coating, is overcompensation by PDADMAC. In this study, it is shown that overcompensation of PDADMAC results in a positive surface charge even when the multilayer is PSS‐terminated. In addition, it is shown that this leads to poorer membrane separation properties with sulfate retention decreasing from 94 to 39%. At the same time, it is demonstrated that a so‐called annealing cycle with a high salt concentration leads to recovery of the negat...
Specific Ion versus Electrostatic Effects on the Construction of Polyelectrolyte Multilayers †
Langmuir, 2009
Self-assembled multilayers of a strong polyanion, poly(sodium 4-styrenesulfonate) (PSS), and a strong polycation, poly[(diallyl-dimethyl-ammonium chloride)-stat-(N-methyl-N-vinyl acetamide)] (P(DADMAC-stat-NMVA)), are fabricated on silicon substrates. This article addresses the effect of electrostatics versus ion specificity. Therefore, multilayer formation and growth are investigated as a function of the charge density of the polycation, the type of salt in the polyelectrolyte dipping solution, and its ionic strength. This study focuses on monovalent ions (Li + , Na + , K + , Cs + , Rb + , F -, Cl -, Br -, and ClO 3 -). Ellipsometry and X-ray reflectometry data indicate that anions have a significantly larger effect on the thickness of the multilayer, but contrary to other studies on ion-specific effects, the influence of the type of cation is not negligible at higher salt concentrations. Larger ions, with smaller hydration shells, are highly polarizable and consequently interact strongly with charged polyelectrolytes, resulting in thicker and rougher multilayers. AFM studies confirm a higher roughness of the multilayer prepared from larger anions. The substrate can mask ion-specific effects over a distance of about 10 nm. Ion-specific effects become important above an ionic strength of 0.1 M in the case of anions and above an ionic strength of 0.25 M for cations. At lower ionic strengths, electrostatic interactions between and within the polyelectrolyte chains are dominating. Reducing the degree of polymer charge down to 75% does not shift this threshold of ionic strength. It is shown that a combination of ionic strength, polymer charge, and type of ion is a suitable tool for tuning the mobility and stability of polyelectrolyte multilayers.
Langmuir, 2003
Polyelectrolyte/gold nanoparticle multilayers composed of poly(L-lysine) (pLys) and mercaptosuccinic acid (MSA) stabilized gold nanoparticles (Au NPs) were built up using the electrostatic layer-by-layer self-assembly technique upon a gold electrode modified with a first layer of MSA. The assemblies were characterized using UV-vis absorption spectroscopy, cyclic and square-wave voltammetry, electrochemical impedance spectroscopy, and atomic force microscopy. Charge transport through the multilayer was studied experimentally as well as theoretically by using two different redox pairs [Fe(CN) 6 ] 3-/4and [Ru(NH 3 ) 6 ] 3+/2+ . This paper reports a large sensitivity to the charge of the outermost layer for the permeability of these assemblies to the probe ions. With the former redox pair, dramatic changes in the impedance response were obtained for thin multilayers each time a new layer was deposited. In the latter case, the multilayer behaves as a conductor exhibiting a strikingly lower impedance response, the electric current being enhanced as more layers are added for Au NP terminated multilayers. These results are interpreted quite satisfactorily by means of a capillary membrane model that encompasses the wide variety of behaviors observed. It is concluded that nonlinear slow diffusion through defects (pinholes) in the multilayer is the governing mechanism for the [Fe(CN) 6 ] 3-/4species, whereas electron transfer through the Au NPs is the dominant mechanism in the case of the [Ru(NH 3 ) 6 ] 3+/2+ pair.
Ion Dispositions in Polyelectrolyte Multilayer Films
Macromolecules, 2012
Polyelectrolyte multilayers (PEMs) fabricated through layer-by-layer (LbL) assembly from sodium chloride-containing solutions of poly(diallyldimethylammonium chloride) (PDDA) and poly(styrene sulfonate) (PSS) were examined by quartz crystal microbalance (QCM), QCM with dissipation (QCM-D), UV−vis spectroscopy, and X-ray photoelectron spectroscopy (XPS) to determine the dispositions of polyelectrolytes and counterions across the PEM thickness. The key experiment was dry film QCM, which by quantifying the incremental mass depositions during LbL assembly uncovered excess polyelectrolyte charge and excess polyelectrolyte charge density as functions of deposition number. Counterion dispositions depended strongly on salt concentration, and trends in the two PEM charge parameters established three salt concentration regimes: zero to near zero salt ([NaCl] ≲ 0.1 M), low salt (0.1 M ≲ [NaCl] ≲ 0.75 M), and high salt ([NaCl] ≳ 1.5 M]). The first two are associated with linear LbL growth while the latter is associated with exponential LbL growth. At zero salt, no counterions are present in the PEM bulk (middle), while at low salt, an excess of PDDA charge across the bulk coincides with an excess of counteranions. Differently, at high salt, deposited PSS permeates the PEM bulk, conveying an excess of countercations. At all salt concentrations, the PEM surface charge alternates according to the capping polyelectrolyte's identity. Accumulations of small ions in the PEM bulk can be ascribed to property asymmetries between the two deposited polyelectrolytes, but the roles played by different chain properties remain incompletely understood.
Molecular mobility and transport in polymer membranes and polyelectrolyte multilayers
Magnetic Resonance Imaging, 2007
Polyelectrolyte multilayers prepared by the layer-by-layer technique provide an efficient way to generate planar structures of tailored surface charge and hydrophobicity, which are used as membranes for pervaporation. The use of polyelectrolyte multilayers to form the membrane permits tailoring the surface charge of the membrane and, thus, selectivity; at the same time, it reduces fouling of the membrane by adsorption of organic matter. Pulsed field gradient (PFG) nuclear magnetic resonance has been used to investigate the diffusion of probe molecules into polymer systems. Evaluation of the apparent diffusion coefficient in porous poly(amide) results in a pore size of 4 Am, as found in electron micrographs. For the pore size obtained for polyelectrolyte multilayers, no equivalent pores could be found in microscopy. Propagators for the diffusion of propanol and propanol-water mixture into multilayers reveal that there might be selective interaction of probe molecules with the polyelectrolyte system. D
Charge-Dependent Transport Switching of Single Molecular Ions in a Weak Polyelectrolyte Multilayer
Langmuir, 2014
The tunable nature of weak polyelectrolyte multilayers makes them ideal candidates for drug loading and delivery, water filtration, and separations, yet the lateral transport of charged molecules in these systems remains largely unexplored at the single molecule level. We report the direct measurement of the charge-dependent, pH-tunable, multimodal interaction of single charged molecules with a weak polyelectrolyte multilayer thin film, a 10 bilayer film of poly(acrylic acid) and poly(allylamine hydrochloride) PAA/PAH. Using fluorescence microscopy and single-molecule tracking, two modes of interaction were detected: (1) adsorption, characterized by the molecule remaining immobilized in a subresolution region and (2) diffusion trajectories characteristic of hopping (D ∼ 10 −9 cm 2 /s). Radius of gyration evolution analysis and comparison with simulated trajectories confirmed the coexistence of the two transport modes in the same single molecule trajectories. A mechanistic explanation for the probe and condition mediated dynamics is proposed based on a combination of electrostatics and a reversible, pH-induced alteration of the nanoscopic structure of the film. Our results are in good agreement with ensemble studies conducted on similar films, confirm a previously-unobserved hopping mechanism for charged molecules in polyelectrolyte multilayers, and demonstrate that single molecule spectroscopy can offer mechanistic insight into the role of electrostatics and nanoscale tunability of transport in weak polyelectrolyte multilayers.