Spin-speed independent thickness and molecular adsorption behaviour of polyelectrolyte multilayers

Abstract

The science behind the build-up mechanism of polyelectrolyte multilayers is important for developing devices for various engineering applications. Here we, study the dependency of thickness of polyelectrolyte multilayer films, fabricated using spin-assisted layer-by-layer self-assembly of polyelectrolytes technique, with respect to varying spin-speed while keeping all other parameters of the fabrication process-window constant. The thickness measurements were performed using variable angle spectroscopic ellipsometry and atomic force microscopy. The experimentally observed results were validated mathematically using a Flory type theory. In addition, the bio-molecular adsorption studies on these polyelectrolyte multilayer films fabricated at various spin-speeds, were also quantitatively analyzed using fluorescence microscopy studies. It was seen that the effect of spin-speed on the thickness of polyelectrolyte multilayers was negligible. In addition, it was also observed that the bio-molecular adsorption modalities onto these substrates were also independent of the spin-speed. This finding prompts to develop low-cost alternative technologies for various biomedical engineering applications, like functionalized substrates for centrifugal assay for fluorescence-based cell adhesion, wherein stability of films against strong mechanical forces generated during spinning can play an important role.