Swelling Of Polyelectrolyte Multilayers Research Articles

A Perspective on the Glass Transition and the Dynamics of Polyelectrolyte Multilayers and Complexes.

Polyelectrolyte multilayers (PEMs) or polyelectrolyte complexes (PECs), formed by layer-by-layer assembly or the mixing of oppositely charged polyelectrolytes (PEs) in aqueous solution, respectively, have potential applications in health, energy, and the environment. PEMs and PECs are very tunable because their structure and properties are influenced by factors such as pH, ionic strength, salt type, humidity, and temperature. Therefore, it is increasingly important to understand how these factors affect PECs and PEMs on a molecular level. In this Feature Article, we summarize our contributions to the field in the development of approaches to quantify the swelling, thermal properties, and dynamic mechanical properties of PEMs and PECs. First, the role of water as a plasticizer and in the glass-transition temperature (Tg) in both strong poly(diallyldimethylammonium)/poly(sodium 4-styrenesulfonate) (PDADMA/PSS) and weak poly(allylamine hydrochloride)/poly(acrylic acid) (PAH/PAA) systems is presented. Then, factors influencing the dynamics of PECs and PEMs are discussed. We also reflect on the swelling of PEMs in response to different salts and solvent additives. Last, the nature of water's microenvironment in PEMs/PECs is discussed. A special emphasis is placed on experimental techniques, along with molecular simulations. Taken together, this review presents an outlook and offers recommendations for future research directions, such as studying the additional effects of hydrogen-bonding hydrophobic interactions.

Monitoring the salt stability and solvent swelling behavior of PAH‐based polyelectrolyte multilayers by quartz crystal microbalance with dissipation

AbstractThis contribution is aimed to examine the layer stability and solvent swelling behavior of polyelectrolyte multilayers (PEMs) obtained from poly(allylamine hydrochloride) (PAH), poly(styrene sulfonic acid sodium salt) (PSS), and poly(acrylic acid) against different salt solutions using Quartz Crystal Microbalance with Dissipation in terms of the solution concentration, charge type of the top layer, and PEM structure. In general, all multilayers remain stable against MgCl2 and NaCl, phosphate buffer saline, ionic liquid, and solvents, namely methanol and heptane, while 4.5‐bilayered PAH‐PSS film displays partial layer decomposition against 1 M NaOCl. Additionally, it is found that the stability of Layer‐by‐Layer (LbL) films remains unaffected by the surface charge type, although variations in the adsorbed and desorbed amounts, as well as the viscoelastic properties, occur during the salt passage and rinsing steps. Along the salt exposure, changes in dissipation (ΔD) significantly increase because of the fast diffusion of ions through the multilayers but return to their initial value after washing. Especially high and reversible ΔD values of the PEMs against methanol are evaluated as swelling in methanol without chemical disintegration. This behavior can be attractive for solvent‐induced release behavior for the LbL‐assembled films or microcapsules.Highlights Multilayer stability and solvent swelling of PEMs are discussed using QCM‐D. PAH‐PSS films have the highest stability against salt solutions. PAH‐PAA films exhibited significant changes in dissipation values. PEMs did not show multilayer stability against NaOCl solution. (PAH‐PSS)5 film was stable and had swelling/de‐swelling capability against methanol.

Quantifying and controlling the cation uptake upon hydrated ionic liquid-induced swelling of polyelectrolyte multilayers.

Controlling the uptake of specific ions in polyelectrolyte multilayers is of interest for various fields of application. Here, we quantify the amount of cation of an ionic liquid, namely 1,3-bis(cyanomethyl)imidazolium chloride, incorporated into polyelectrolyte multilayers upon contact with an ionic liquid solution. The ion partition equilibrium is determined depending on concentration in solution, employing attenuated total reflection infrared spectroscopy. Generating an excess charge in multilayers by post-preparative manipulation of their charge balance, one can control the incorporated amount. Three multilayer systems are assembled for this purpose, i.e., PSS/PDADMAC, PSS/PAH and PAA/PDADMAC, employing poly(styrene sulfonate) (PSS), poly(diallyldimethylammonium chloride) (PDADMAC), poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA). The charge balance of the latter two films is manipulated by an external pH stimulus generating an excess positive or negative internal charge, respectively. The concentration of cations in PEM amounts to 30% to 100% of the bulk concentration and scales as PAA/PDADMAC > PSS/PDADMAC > PSS/PAH. Thus, post-preparative pH treatment may be a future tool to create ion-conductive polymer gel films with a desired concentration of small cations.

Swelling of Polyelectrolyte Multilayers: The Relation Between, Surface and Bulk Characteristics.

The odd-even effect, i.e., the influence of the outermost layer of polyelectrolyte multilayers (PEMs) on their swelling behavior, is investigated. For that purpose poly(styrene sodium sulfonate) (PSS)/poly(diallyl-dimethylammonium chloride) (PDADMAC) polyelectrolyte multilayers are studied in air with 1% relative humidity (RH), 30% RH, 95% RH, and in liquid water by ellipsometry, atomic force microscopy (AFM), and X-ray reflectometry (XRR). Since the total amount of water uptake in swollen PEMs is divided into two fractions, the void water and the swelling water, a correct evaluation of the odd-even effect is only possible if both fractions are examined separately. In order to allow measuring samples over a larger thickness regime the investigation of a larger amount of samples is required. Therefore, the concept of separating void water from swelling water using neutron reflectometry is for the first time transferred to ellipsometry. The subsequent analysis of swelling water, void water, and roughness revealed the existence of two types of odd-even effects: an odd-even effect which addresses only the surface of the PEM (surface-odd-even effect) and an odd-even effect which addresses also the bulk of the PEM (bulk-odd-even effect). The appearance of both effects is dependent on the environment; the surface-odd-even effect is only detectable in humid air while the bulk-odd-even effect is only detectable in liquid water. The bulk-odd-even effect is related to the osmotic pressure between the PEM and the surrounding water. A correlation between the amount of void water and both odd-even effects is not found. The amount of void water is independent of the terminated layer and the thickness of PEMs.

Swelling and Stability of Polyelectrolyte Multilayers in Ionic Liquid Solutions

Swelling of polyelectrolyte multilayers with aqueous solution of ionic liquid (IL) is examined with a dissipative quartz crystal microbalance. Multilayers are prepared with different combinations of polyelectrolyte, employing PEI(PSS/PAH)4PSS and PEI(PSS/PDADMAC)4PSS. An enhancement of mass coverage and dissipation is found for films in contact with aqueous solution of IL, i.e., 1-hexyl-3-methylimidazolium chloride and 1-methyl-3-methylimidazolium chloride, suggesting incorporation of IL, accompanied by film swelling. Swelling increases with increasing IL concentration. It is strictly reversible up to a stability limit of IL concentration, above which irreversible layer decomposition starts. Each swelling step can be divided into a fast and a slow process, resulting from IL uptake and chain reorganization or layer decomposition, respectively. While absolute IL uptake and swelling limits differ, the concentration dependence is similar in all systems investigated. The swelling is attributed to hydrophobic interactions, since we find a correlation of the swelling with hydrophobicity of IL.

Effect of Ionic Strength and Layer Number on Swelling of Polyelectrolyte Multilayers in Water Vapour

The swelling behavior of polyelectrolyte multilayers (PEMs) of poly(sodium-4 styrene sulfonate) (PSS) and poly(diallyl dimethyl ammonium chloride) (PDADMAC) prepared from aqueous solution of 0.1 M and 0.5 M NaCl are investigated by ellipsometry and Atomic Force Microscopy (AFM). From 1 double-layer up to 4 double-layers of 0.1 M NaCl, the amount of swelling water in the PEMs decreases with increasing number of adsorbed double layers due to an increase in polyelectrolyte density as a result of the attraction between the positively charged outermost PDADMAC layer and the Si substrate. From 6 double layers to 30 double layers, the attraction is reduced due to a much larger distance between substrate and outermost layer leading to a much lower polyelectrolyte density and higher swelling water. In PEMs prepared from aqueous solution of 0.5 M NaCl, the amount of water constantly increases which is related to a monotonically decreasing polyelectrolyte density with increasing number of polyelectrolyte layers. Studies of the surface topology also indicate a transition from a more substrate affected interphase behavior to a continuum properties of the polyelectrolyte multilayers. The threshold for the transition from interphase to continuum behavior depends on the preparation conditions of the PEM.

Gold nanorods as nanotransducers to monitor the growth and swelling of ultrathin polymer films

In this work, we demonstrate that plasmonic nanostructures can be employed as nanoscale transducers to monitor the growth and phase transitions in ultrathin polymer films. In particular, gold nanorods with high refractive index sensitivity (∼150 nm/refractive index unit (RIU)) were employed to probe the growth and swelling of polyelectrolyte multilayers (PEM). By comparing the wavelength shift and extinction intensity increase of the localized surface plasmon resonance (LSPR) of the gold nanorods coated with PEM in air and water, the swelling of PEM was estimated to be 26% ± 6%. The swelling was quantitatively confirmed with independent thickness measurement of PEM in dry and swollen states using AFM. The deployment of shape-controlled metal nanostructures with high refractive index sensitivity represents a novel and facile approach for monitoring the phase transition in polymers with nanoscale resolution.

Specific Anion Effect in Swelling of Polyelectrolyte Multilayers

The well-known strong polyelectrolytes poly(diallyldimethylammonium) cation (PDADMA) and poly(4-styrenesulfonate) anion (PSS) form multilayers (PEMs) where formally the small counterions do not participate in any way. Previously, we have shown that by replacing the conventional chloride as the counteranion of PDADMA by other small anions occupying different positions in the Hofmeister series the resulting PEMs had widely different thicknesses in the dry state [Langmuir 2004, 20, 3679] and widely different stiffnesses in the wet state [Macromolecules 2004, 37, 9585]. In this work we show that even more striking differences are observed in the swelling behavior when comparing PSS/PDADMA multilayers made in the presence of fluoride or bromide. PSS/PDADMA-F shows nearly no swelling at different concentrations of NaF whereas PSS/PDADMA-Br shows strong swelling, especially at low concentrations of NaBr. The similar difference appears also when using the solutions of NaF, HCOONa, NaBrO3, NaCl, NaClO3, NaNO3, and NaBr as swelling agents. Again swelling of PSS/PDADMA-F is negligible but PSS/PDADMA-Br swells, the extent of swelling having some correlation with the hydration entropy of anion; i.e., the more negative is the entropy, the stronger is swelling.