Controlled exponential growth in layer-by-layer multilayers using high gravity fields†
The high gravity technique is a strongly intensified process used for rapid mass and heat transfer, which has rarely been applied for the construction of layer-by-layer (LbL) self-assembled films. Herein, we used a poly(acrylic acid) (PAA)/poly(allylamine hydrochloride)–porphine complex (PAH–Por) multilayer to investigate the assembly behaviors between exponential and linear growth, and introduced strong shear stress using a high gravity field to reduce the accumulated surface roughness in exponentially growing films. The results demonstrated that strong shear stress in a high gravity field could transform film growth from exponential to linear. This phenomenon is thought to be the result of reducing surface roughness through shear forces, which was supported by stepwise characterization of ultraviolet-visible spectra and atomic force microscopy. Moreover, the intensified LbL deposition to achieve a transformation from exponential to linear growth could be applied to other systems, including PAH–PAA complex/poly(sodium-p-styrenesulfonate) (PSS) and PAH/PSS multilayers.