Self-Exchange of Polyelectrolyte in Multilayers: Diffusion as a Function of Salt Concentration and Temperature

Abstract

Polymer chain diffusion within a hydrated polyelectrolyte complex, PEC, has been measured using an ultrathin film format prepared by the layer-by-layer method. Isotopically labeled self-exchange of deuterated poly(styrene sulfonate), dPSS, with undeuterated PSS of the same narrow molecular weight distribution permitted reliable estimates of whole-molecule diffusion coefficients, D . N a r r o w m o l e c u l a r w e i g h t d i s t r i b u t i o n p o l y -(diallyldimethylammonium), PDADMA, was used as the polycation for the PEC. Extensive pretreatment of starting films was undertaken to remove residual stress, anisotropy, and layering. PSS/PDADMA "multilayers," PEMUs, thin enough to provide substantial exchange of polyelectrolyte, even with diffusion coefficients as low as 10 −16 cm 2 s −1 , as a function of salt concentration and temperature were measured for this PEC, which has a glass-transition temperature, T g , close to room temperature. Two molecular weights of dPSS, about 15 and 100 kDa, presumed to be below and above the entanglement molecular weight, respectively, both diffused faster at higher temperatures with respective activation energies, E a , of about 21 and 53 kJ mol −1 , the latter about the same as E a for the place exchange between two pairs of PSS:PDADMA. Studies of the linear viscoelastic response of macroscopic PECs showed a difference of about 8 °C in the T g of the two lengths of PSS complexed with the same PDADMA. Increasing concentrations of NaCl influenced D of 100 kDa PSS but not 15 kDa PSS at room temperature. D was faster in the region of the film near the solution interface, again attributed to a lower T g caused by greater water content at this interface.

Suppressing the Hofmeister Anion Effect by Thermal Annealing of Thin-Film Multilayers Made of Weak Polyelectrolytes

“…Therefore, in our opinion, the main origin of the observed heating effect is interdiffusion and reorientation of polyelectrolyte molecules present at the multilayer–air interface. The diffusion process within the LbL assemblies was extensively studied for the past two decades by the Schlenoff group. − They concluded that there are at least three types of diffusing species within PEM: ions, polymer chains, and extrinsic polyelectrolyte–counterion sites. We are convinced that in our experiments, the amount of energy that was brought to multilayer systems by heating was enough to overcome the energy barriers needed for the migration of all three diffusing species.…”

“…Because polymer diffusion demands massive transport of a material, it is usually too slow to allow access of the polymer to an entire film (even at higher temperatures) . As a result, this migration of macroion chains takes place only in the interface region and thus causes morphological changes in the surface that were directly visualized here by AFM imaging (Figure ).…”

“…Because polymer diffusion demands massive transport of a material, it is usually too slow to allow access of the polymer to an entire film (even at higher temperatures). 88 As a result, this migration of macroion chains takes place only in the interface region and thus causes morphological changes in the surface that were directly visualized here by AFM imaging (Figure 4). In another AFM study, Ghostine et al 89 showed that exposing PEMs to a salt solution ("salt annealing") frees polyelectrolyte segments and allows polymer interdiffusion, leading to the smoothing of the surface.…”

Polyelectrolyte Coacervate Coatings That Dramatically Improve Oxygen Barrier of Paper

“…Polyelectrolytes can be utilized through electrospinning, layer-by-layer assembly, solution complexation, and coacervate deposition. Polyelectrolyte deposition is well-known for its ambient processing, and utilization of environmentally benign materials in aqueous-based solutions, to generate functional thin films. − There is little environmental concern in regard to these films due to lack of harmful solvents and materials that are often used to impart barrier properties on cellulosic substrates using more traditional approaches. Furthermore, these coatings are typically ionically cross-linked and can be expected to exhibit recyclable and self-healing behaviors due to the dynamic/reversible nature of ionic bonds. − Coatings prepared with these charged polymers have been utilized for their flame retardant, dielectric, heat shielding, antifouling, and gas barrier properties. − In the present study, the oxygen transmission rate (OTR) of polyethylenimine (PEI)-poly­(acrylic acid) [PAA] coacervates, prepared with and without clay nanoplatelets, on paper substrates is investigated.…”

Heteroaggregation between particles modified by polyelectrolyte multilayers

“…Numerous studies have already been carried out to understand the kinetics of formation of these multilayers, the organization between the polymers or the ionic distribution within these multilayers [13,14,15,16,17,18]. However, to our knowledge, few studies have been performed on the possibility of using these multilayers to control the behavior of inorganic colloidal suspensions.…”