(354e) Spatiotemporal Evolution of Structure in Layer-By-Layer Assembled Thin Films Composed of Oppositely Charged Polyelectrolytes

Despite the numerous applications of polyelectrolyte (PE) multilayer films and coatings, a framework to model the dynamics of this process quantitatively is still lacking. We here deploy a stress-diffusion multi-fluid framework to integrate transient unidirectional migration of strongly-dissociating PE chains in the presence of gradients of electrochemical potential as well as of elastic stress with previously reported quasi-equilibrium descriptions of PE Layer-by-Layer (LbL) assembly. The significant role of chemical specificity of PE functional groups is accounted for by explicitly tracking the formation of the mean-field density of ionic pairs between the two segment types. Ionic pairs alter the local diffusion driving force, slow down mutual diffusion of chains and control the relaxation of elastic stress generated by the ingress of solvent. The film structure and the interface between PE multilayer and external solution is tracked continuously by numerically solving a set of coupled and nonlinear equations, namely the Poisson equation, Maxwell constitutive equation, solvent osmotic pressure equilibrium, flux equations derived from multi-fluid model as well as material conservation equations. Additionally, the Landau-Ginzburg non-local free energy density functional employed here allows for the structure of diffuse interfaces in the system to be resolved dynamically. The proposed model could drastically accelerate engineering of the structure and properties of multilayered coatings.