Branched Poly(ethylenimine) as Barrier Layer for Polyelectrolyte Diffusion in Multilayer Films (original) (raw)
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Macromolecules
Polyelectrolyte multilayers are usually prepared from polydisperse polyelectrolytes. It is desirable to measure and control multilayer composition when it deviates from the deposition solution. With neutron reflectivity, multilayers prepared from PDADMA and binary mixtures of long deuterated PSSd long (80.8 kDa) and short protonated PSS short (10.6 kDa) were investigated. A small amount of PSS long in the deposition solution led to a disproportionate increase of PSS long in the film, and completely suppressed the exponential growth regime. Adsorption kinetics were studied with in situ ellipsometry: (i) During adsorption of a PSS layer, the PSS long fraction increased with adsorption time; PSS short could desorb, while PSS long adsorbed irreversibly. (ii) During adsorption of a PDADMA layer, a fast thickness increase was followed by a slow thickness decrease. This was attributed to the formation of PDADMA/PSS short complexes, which eventually desorbed. The desorbed thickness depended on the number of layers deposited. The mechanism of layer formation is attributed to the asymmetric growth of PDADMA/PSS multilayers, as supported by the adsorption kinetics of multilayers prepared from one kind of PSS.
Salt-Induced Polyelectrolyte Interdiffusion in Multilayered Films: A Neutron Reflectivity Study
Macromolecules, 2005
Polyelectrolyte multilayers were constructed from poly(styrenesulfonate), PSS, and poly-(diallyldimethylammonium) with regularly interspersed layers of deuterated PSS. Annealing, by salt, of the fuzzy internal layering within this multilayer was followed using neutron reflectometry. A "limited source" diffusion model fit the data well and showed that polyelectrolyte migrates much more slowly within the bulk of a multilayer than at the surface. Enhanced surface mobility and a nonlinear increase in diffusion rate with salt concentration were explained by a salt doping model, where correlated short lengths of polyelectrolyte move by exchange with counterions ("extrinsic charge") doped into the ultrathin film of polyelectrolyte complex on exposure to solutions of high ionic strength.
Macromolecules, 1998
Using neutron reflectometry we have resolvedsto high resolutionsthe internal structure of self-assembled polyelectrolyte multilayer films and have developed a detailed molecular picture of such systems by analyzing the data with a composition-space refinement technique. We show that such surface films consist of stratified structures in which polyanions and polycations of individual layers interdigitate one another intimately. Nevertheless, the deposition technique leads to results that are predictable, if well-defined and constant environmental conditions are maintained during the preparation. For alternating layers of poly(styrenesulfonate) (PSS) and poly(allylamine hydrochloride) (PAH), adsorbed onto atomically flat surfaces, a roughening of successively deposited layers leads to a progressively larger number of adsorption sites for consecutive generations of adsorbed polymer, and thus to an increase in layer thicknesses with an increasing number of deposited layers. Because of the interpenetration of adjacent polyelectrolyte species, however, this increase settles quickly into an equilibrium thickness. In fully hydrated films (100% relative humidity), water occupies g40% of the volume within the films. About twice as much water (by volume) is associated with PSS as with PAH. Incorporated inorganic salt plays a minor role only, if any. The equilibrium thickness of the deposited layer structure may be fine-tuned via the ionic strength, I, of the solutions used for the preparation. We show that the dependence of the thickness d lp per layer pair on I is linear, with a sensitivity, ∆dlp/∆I ) 16 Å × L/mol. Concurrently with the layer thickness the interface roughness σ between adjacent layers increases: σ ∼ 0.4 × dlp. In contrast to the ionic strength of the deposition solutions, the degree of polymerization of the polyanions used in the preparation plays a minor role only in determining the overall structure of the deposited films. The results reported here are quantitatively consistent with those of a recent study (Tarabia et al. J. Appl. Phys. 1998, 83, 725-732), if one assumes that the hydration of the polyelectrolyte molecules in the sample films investigated in the two studies is similar.
Macromolecules, 2011
Using a series of polycations synthesized by atom transfer radical polymerization (ATRP), we investigate the effects of the polymer charge density and hydrophobicity on salt-induced interdiffusion of polymer layers within polyelectrolyte multilayer (PEM) films. Polycations with two distinct hydrophobicities and various quaternization degrees (QPDMA and QPDEA) were derived from parent polymers of matched molecular weights-poly(2-(dimethylamino)ethyl methacrylate) (PDMA) and poly(2-(diethylamino)ethyl methacrylate) (PDEA)by quaternization with either methyl or ethyl sulfate. Multilayers of these polycations with polystyrenesulfonate (PSS) were assembled in low-salt conditions and annealed in NaCl solutions to induce layer intermixing. As revealed by neutron reflectometry (NR), polycations with lower charge density resulted in a faster decay of film structure with distance from the substrate. Interestingly, when comparing polymer mobility in QPDEA/PSS and QPDMA/PSS films, layer intermixing was faster in the case of more hydrophobic QPDEA as compared to QPDMA because of the weaker ionic pairing (due to the presence of a bulky ethyl spacer) between QPDEA and PSS. B dx.
Anisotropic Diffusion of Polyelectrolyte Chains within Multilayer Films
ACS Macro Letters, 2012
We have found diffusion of polyelectrolyte chains within multilayer films to be highly anisotropic, with the preferential chain motion parallel to the substrate. The degree of anisotropy was quantified by a combination of fluorescence recovery after photobleaching and neutron reflectometry, probing chain diffusion in directions parallel and perpendicular to the substrate, respectively. Chain mobility was controlled by ionic strength of annealing solutions and steric hindrance to ionic pairing of interacting polyelectrolytes.
Physical Chemistry Chemical Physics, 2006
As-deposited films of multilayered polyelectrolytes are considered to be non-equilibrium structures. Due to the strong attraction between oppositely charged polyions, polyelectrolyte interdiffusion is thought to be suppressed during the adsorption process. Equilibration is promoted by a decrease of the electrostatic attraction between polyion pairs. We have used neutral impact collision ion scattering spectroscopy to investigate the influence of polyelectrolyte multilayer annealing in water and aqueous 1 M NaCl solutions at different temperatures (20 and 70 1C) on the increase in interpenetration of a single polyelectrolyte layer throughout the whole film. The multilayers were composed of poly(4-vinylpyridinium) and poly(4-styrenesulfonate). Contrast between neighboring layers was established by labelling the layer in question with the heavy atom ruthenium. It is found that both temperature and salt increase layer interpenetration, whereas salt has a stronger influence than temperature. From numerical simulations polyelectrolyte diffusion coefficients were evaluated for the different annealing conditions. The influence of temperature and salt on the equilibration of the film is interpreted in terms of increased screening of polyion charges and binding of small counterions to polyion monomeric units.
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.
Colloids and Surfaces A: Physicochemical and Engineering Aspects, 2011
a b s t r a c t X-ray reflectivity and adsorption kinetics of two different polyelectrolyte multilayers have been studied for polyelectrolyte multilayers (PEMs) composed of poly(diallyldimethyl ammonium chloride) (PDADMAC) and poly(sodium 4-styrenesulfonate) (PSS) polyelectrolyte pair and of poly(allylamine hydrochloride) (PAH) and PSS. The two characteristic times that describe the adsorption kinetics were found to be related to the X-ray reflectivity results, and their dependence on the number of adsorbed layers depends on the growth mechanisms (linear or superlinear) of the films. Therefore, it has been concluded that there is a correlation between the adsorption kinetics and the internal structure of the films. The time allowed for the adsorption of each polyelectrolyte controls the extension of the interdiffusion within the multilayer, and therefore whether the film is formed by stratified layers or it has a uniform structure except for the first and last layers. While the roughness of the (PDADMAC + PSS) n films strongly depends on the adsorption time, it is almost independent of it for the (PAH + PSS) n multilayer. This behavior correlates with that of the longest characteristic time of the adsorption kinetics.
Langmuir, 2008
The alternate adsorption of polycation poly(allylamine hydrochloride)(PAH) and the sodium salt of the polymeric dye poly{1-[p-(3′-carboxy-4′-hydroxyphenylazo)benzenesulfonamido]-1,2-ethandiyl}(PCBS) on quartz crystals coated with silica was studied to understand the structural properties and adsorption kinetics of these films using a combination of quartz crystal microbalance with dissipation monitoring (QCM-D), absorbance, and ellipsometry measurements. In-situ deposition of the polycation PAH on QCM crystals was monitored, followed by rinsing with water and then deposition of the polyanion PCBS. The effects of polymer concentration and pH on film structure, composition and adsorption kinetics were probed. The polymers were adsorbed at neutral pH conditions and at elevated pH conditions where PAH was essentially uncharged to obtain much thicker films. The change in the resonant frequency, ∆f, of the QCM-D showed a linear decrease with the number of bilayers, a finding consistent with absorbance and ellipsometric thickness measurements which showed linear growth of film thickness. By using the ∆f ratios of PCBS to PAH, the molar ratios of repeat units of PCBS to PAH in the bilayer films as determined by QCM-D were ∼1:1 at polyelectrolyte concentrations 5-10 mM repeat unit, indicating complete dissociation of the ionic groups. The frequency and dissipation data from the QCM-D experiments were analyzed with the Voigt model to estimate the thickness of the hydrated films which were then compared with thicknesses of dry films measured by ellipsometry. This led to estimates of the water content of the films to be ∼45 wt %. In addition to the QCM-D, some films were also characterized by a QCM which measures only the first harmonic without dissipation monitoring. For the deposition conditions studied, the deposited mass values measured by the QCM's first harmonic were similar to the results obtained using higher harmonics from QCM-D, indicating that the self-assembled polyelectrolyte films were rigid.