Influence of Salt and Rinsing Protocol on the Structure of PAH/PSS Polyelectrolyte Multilayers

Abstract

A quartz crystal microbalance (QCM) and dual polarization interferometry (DPI) have been utilized to study how the structure of poly(allylamine hydrochloride) (PAH)/poly(styrene sulfonate) (PSS) multilayers is affected by the rinsing method (i.e., the termination of polyelectrolyte adsorption). The effect of the type of counterions used in the deposition solution was also investigated, and the polyelectrolyte multilayers were formed in a 0.5 M electrolyte solution (NaCl and KBr). From the measurements, it was observed that thicker layers were obtained when using KBr in the deposition solution than when using NaCl. Three different rinsing protocols have been studied: (i) the same electrolyte solution as used during multilayer formation, (ii) pure water, and (iii) first a salt solution (0.5 M) and then pure water. When the multilayer with PAH as the outermost layer was exposed to pure water, an interesting phenomenon was discovered: a large change in the energy dissipation was measured with the QCM. This could be attributed to the swelling of the layer, and from both QCM and DPI it is obvious that only the outermost PAH layer swells (to a thickness of 25-30 nm) because of a decrease in ionic strength and hence an increase in intra- and interchain repulsion, whereas the underlying layers retain a very rigid and compact structure with a low water content. Interestingly, the outermost PAH layer seems to obtain very similar thicknesses in water independent of the electrolyte used for the multilayer buildup. Another interesting aspect was that the measured thickness with the DPI evaluated by a single-layer model did not correlate with the estimated thickness from the model calculations performed on the QCM-D data. Thus, we applied a two-layer model to evaluate the DPI data and the results were in excellent agreement with the QCM-D results. To our knowledge, this evaluation of DPI data has not been done previously.

Biomimmetic surfaces effectively inhibiting coagulation process dedicated for cardiovascular devices

“…PEM films in the cited article have been used to study boost progenitor cells behaviour [52][53][54]. Preliminary studies for this work were carried out under the attempt to create microenvironment for cells in the form of wells, made by laser ablation [55] and the in the form of wrinkles [56].…”

‘Up-scaling’ potential for polyelectrolyte multilayer membranes

“…Kovacevic et al [57] and Saarinen et al [58] also reported that rinsing doesn't have a significant role in the multilayer layer build-up. The different rinsing methods previously studied, either as in pure water, or with a PE solution similar to which is used for multilayer formation or in a salt solution, all showed only a minor effect on the overall multilayer build-up [59]. Thus, the PEMM preparation without rinsing step in-between the addition of oppositely charged PEs helps to reduce the overall multilayer build-up time without compromising membrane performance.…”

Nanoplasmonic Sensing using Metal Nanoparticles

“…These are two of the most frequently used polyelectrolytes for LBL formation and their properties have been comprehensively examined by others. [109][110][111][112] One bilayer of PAH/PSS results in a thickness in air of about 3 nm (Figure 4.3), which was determined using null ellipsometry. However, the thickness of the polymer film significantly depends on the ionic strength in the deposition solution, since an increase of the electrolyte concentration results in a more effective screening of the polyelectrolyte charges, which changes the conformation of the polymers.…”

“…However, the thickness of the polymer film significantly depends on the ionic strength in the deposition solution, since an increase of the electrolyte concentration results in a more effective screening of the polyelectrolyte charges, which changes the conformation of the polymers. 111,112 Also, polyelectrolytes multilayers are known to swell and increase in thickness when exposed to water. A swelling of ~30% for a polymer film composed of PAH/PSS has been reported by others.…”