(578d) Structure and Properties of Polyelectrolyte Multilayers in the Exponential and Linear Growth Regimes

Multilayered thin films have been the focus of intense research because of their vast array of applications.  We investigate the growth and disassembly under different pH conditions of layer-by-layer (LbL) films composed of oppositely charged polyelectrolytes (including poly(diallyldimethylammonium chloride) (PDDA), poly(styrene sulfonate) (PSS), and poly(acrylic acid) (PAA)) and synthetic clays.  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, we determine the layer spacing by X-Ray diffraction (XRD), and we evaluate the organic-inorganic content by thermogravimetric analysis (TGA). Our results demonstrate that PDDA-PAA-PDDA-Laponite multilayers display exponential growth aided by internal diffusion of PAA molecules, whereas PDDA-PSS-PDDA-Laponite and PDDALaponite multilayers display linear growth by sequential molecular level deposition. We also illustrate that different assembly regimes are attained by manipulating the deposition pH of PAA solution.  The results on the structural characteristics and properties of multilayers formed under different conditions can provide insights into their behavior and sensitivity to external stimuli during various applications.