Polyelectrolyte spin assembly: Influence of ionic strength on the growth of multilayered thin films

Abstract

Layer-by-layer (LbL) assembly of polymer electrolyte multilayers is now a well-established method for the fabrication of thin films by sequential adsorption of alternating layers of oppositely charged polyelectrolytes. Most commonly, such adsorptions have been from quiescent solutions of varying ionic strength and pH. Here, we report results on an alternative processing route for the achievement of polymeric multilayer assemblies of poly(sodium-4-styrene sulfonate) and poly(allylamine hydrochloride) that utilizes conventional spin coating. We investigated and describe herein the dependence of multilayer film buildup on solution ionic strength for comparison with similar dependence in quiescent adsorption. Using UV-Vis spectroscopy we monitored the growth of the multilayered films, while with Atomic Force Microscopy (AFM) we examined the surface features and measured coating thicknesses at different salt concentrations. AFM and UV-Vis data reveal two regimes of behavior with increasing salt: strong salt-dependence at low salt contents, and weak salt-dependence for high salt contents. To explain this observation, we introduce the relevance of the dimensionless group De ϭ ␥, the local Deborah Number, to the problem. As ionic strength increases, increases so that spin-assembly flow influences adsorbed conformation, and thus LbL growth rate. Our results indicate the ability to design and control polyelectrolyte multilayered structures prepared via spin assembly by varying solution properties that influence the conformation of deposited polymer chains. Additionally, our studies reveal the need for study of the fundamental mechanisms of polyelectrolyte adsorption within complex flow fields.

Theory and simulations of charged polymers: From solution properties to polymeric nanomaterials

“…The formation of ionic pairs between polyelectrolyte chains forming multilayers was recently taken into account by Park et al [141] and by Lefaux et al [142]. These models show promising results by predicting the correct salt concentration dependence of multilayer growth by sequential adsorption and by spin coating methods.…”

Brownian dynamics simulations of polyelectrolyte adsorption in shear flow: Effects of solvent quality and charge patterning

“…Experimental 14,16 and theoretical 16,27,28 studies on polyelectrolyte adsorption suggest that an increase in shear rate increases desorption. It should be noted that shear-induced desorption has also been reported in prior experimental 17,[29][30][31][32][33][34][35] and theoretical [35][36][37][38][39][40][41][42][43][44][45][46][47][48] studies on neutral polymers.…”

Spin-Assembled Layer-by-Layer Films of Weakly Charged Polyelectrolyte Multilayer

“…[5][6][7] In particular, the spinassisted LbL assembly using a highly applied shear force has been extensively investigated due to its advantages in alleviating surface roughness and interpenetration, as compared to the dipping-based LbL assembly. [7][8][9] Another notable aspect of the LbL self-assembly is that it usually leads to a linear growth in film thickness as exemplified in the case of many strongly charged polyelectrolyte multilayer systems. Strong charge binding between ion pairs yields an ionically crosslinked network, from which an identical increase in stepwise film thickness can be obtained (linear growth).…”