Influence of the degree of ionization on the growth mechanism of poly(diallyldimethylammonium)/poly(acrylic acid) multilayers

Abstract

pH‐dependent growth laws of the mass coverage Γ(n) of poly(diallyldimethylammonium) chloride and poly(acrylic acid) (PAA) layer‐by‐layer films are analyzed by Quartz Crystal Microbalance‐D. (Attenuated Total Reflection)‐FTIR spectroscopy shows a degree of dissociation of acrylic acid groups in the films identical to that in solution. Apart from pH‐regimes of differently pronounced exponential and linear growth, the corresponding kinetics indicate pH‐dependent adsorption, reorganization, and diffusion processes. As the thickest films form with almost uncharged PAA (low pH), the results can only partly be explained by the dissociation degree of PAA in the film. For intermediate and high pH values chain interdiffusion as a mechanism for nonlinear growth is strongly dependent on the charge density of the PAA chains. However, at low pH other types of interactions, most likely ion–dipole interactions, play a major role in the multilayer growth. Furthermore, a change in the symmetry of growth can be observed in the low to intermediate pH range. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 425–434

Influence of pH on the Growth and the Local Dynamics of Polyelectrolyte Multilayers

“…The LbL technique is driven by electrostatic forces and entropy which is due to the release of water and low-molecular-weight ions into the solution and was further established, inter alia, by Möhwald . The formation of the PEMs mainly depends on the properties of the solutions from which the layers are formed, such as ionic strength, pH value, temperature, and salt concentration. , Different research groups showed that with the increase of the salt concentration, the layers get much thicker due to the screening of the charges, followed by a coiling of the polymer chains before the adsorption process. − Currently, the LbL technique is used to investigate different possibilities of applications such as coatings for water purification and separation membranes, − drug delivery systems, and PEM capsules used as optical sensors or for applications in biological systems. − A great deal of research is already published for polyelectrolyte systems such as poly­(diallyldimethylammonium chloride) (PDADMAC) and poly­(styrene sulfonate). − In this study, we focus on the PEM system of PDADMAC and poly­(ethylene- alt -maleic acid) [P­(E- alt -MA), p K a1 = 3.8, p K a2 = 6.1] which combines a strong and a weak polyelectrolyte. Within the range of pH 3–6 in this study, the degree of dissociation of the polyanion changes and therefore leads to a different growth behavior due to its pH dependence.…”

“…Within the range of pH 3–6 in this study, the degree of dissociation of the polyanion changes and therefore leads to a different growth behavior due to its pH dependence. Here, we expect the buildup of thick layers around pH 4 where the degree of ionization is relatively low and the polyanion is highly protonated . Within this environment, the polymers tend to coil; thus, as a result, thicker layers should be monitored.…”

Polyelectrolyte Multilayers on Silica Surfaces: Effect of Ionic Strength and Sodium Salt Type

“…[20] The influence of different salts (phosphates, chlorides and nitrates) and polyelectrolyte molecular weight on formation and erosion of multilayers on silica surfaces was investigated by means of optical reflectometry method. [8] It was shown that at very low ionic strength (1 mM) regular build-up of multilayers is observed independent of the salt used.…”

Viscoelastic Properties of Polyelectrolyte Multilayers Swollen with Ionic Liquid Solutions

“…The thickness and mechanical strength of PEMs can be varied within a wide range, and typically vary between nm to several µm and between a few kPa to several MPa [2,3,4,5,6], respectively. This is possible by simply varying the number of deposited polyelectrolyte layers and/or intrinsic properties of polyelectrolytes, such as the charge density, molecular weight and structure [7,8,9,10,11,12,13]. Other factors can be employed to even induce post-preparative changes of the film properties: For example, the ionic strength and charge-to-size ratio of specific ions [14,15,16], pH stimulation [17,18,19], organic solvent [20] or inorganic/organic ions exposed to PEMs [21,22] have been shown to influence the thickness and mechanical strength of PEMs.…”