(588g) Oppositely Charged Polyelectrolyte Assembly in Solution and in Multilayer Films

Multilayered thin films have been the focus of intense research because of their vast array of applications.  We investigate here the relationship between polyelectrolyte multilayer growth and the phase behavior of the corresponding polyelectrolyte complexes in solution. We examine the growth and disassembly under different pH conditions of layer-by-layer (LbL) films composed of (strong or weak) oppositely charged polyelectrolytes (including poly(diallyldimethylammonium chloride) (PDDA), poly(styrene sulfonate) (PSS), and poly(acrylic acid) (PAA)) and we compare these to the formation and dissolution of the complexes in solution. We monitor the assembly growth by UV-vis spectroscopy, estimate the assembly thickness by scanning electron microscopy (SEM) cross-section images and the surface roughness by atomic force microscopy (AFM). We further examine the charge density of films by Fourier transform infrared (FTIR) spectroscopy. Our results demonstrate that in films different assembly regimes are attained by manipulating the deposition pH of the weak polyelectrolyte solution.  The results are correlated with the phase behavior of the polyelectrolyte complexes in solution. Our findings provide insights into the sensitivity and response of films or complexes to external stimuli during various applications.