Elucidation of Titanium Dioxide Nucleation and Growth on a Polydopamine-Modified Nanoporous Polyvinylidene Fluoride Substrate via Low-Temperature Atomic Layer Deposition.

Abstract

Interfaces combining polydopamine (PDA) and nanoparticles have been widely utilized for fabricating hybrid colloidal particles, thin films, and membranes for applications spanning biosensing, drug delivery, heavy metal detection, antifouling membranes, and lithium ion batteries. However, fundamental understanding of the interaction between PDA and nanoparticles is still limited, especially the impact of PDA on nanoparticle nucleation and growth. In this work, PDA is used to generate functional bonding sites for depositing titanium dioxide (TiO2) via atomic layer deposition (ALD) onto a nanoporous polymer substrate for a range of ALD cycles (<100). The resulting hybrid membranes are systematically characterized using water contact angle, scanning electron microscopy, atomic force microscopy, nitrogen adsorption and desorption, and X-ray photoelectron spectroscopy (XPS). An intriguing nonlinear relationship was observed between the number of ALD cycles and changes in surface properties (water contact angle and surface roughness). Together with XPS study, those changes in surface properties were exploited to probe the nanoparticle nucleation and growth process on complex PDA-coated porous polymer substrates. Molecular level understanding of inorganic and polymer material interfaces will shed light on fine-tuning nanoparticle-modified polymeric membrane materials.