Construction of ‘smart’ surfaces with polymer functionalized silica nanoparticles

Silica nanoparticles (SiNPs) coated with the pH responsive poly(2-(diethylamino)ethyl methacrylate) (PDEAEMA) shells have been synthesized in different sizes using surface-initiated atom transfer radical polymerization (ATRP). A mixture of the PDEAEMA functionalized SiNPs (20 and 128 nm) was found to efficiently change the surface property of a substrate. The surface properties were investigated at different ratios of functionalized SiNPs. Moreover, fluorescent-doped SiNPs with PDEAEMA were also prepared to study the adsorption/desorption behavior of the SiNPs on the substrates at different pHs. A Surface Forces Apparatus (SFA) was used to measure the interactions between PDEAEMA surfaces in aqueous solutions of different pHs, and the force–distance profiles directly indicate that the intermolecular interactions of PDEAEMA are pH sensitive. At pH < pKa (∼7.3) steric repulsion dominates while at pH ≥ pKa the hydrophobic attraction between PDEAEMA molecules plays a critical role in their molecular behaviors in solutions and on surfaces. Our results provide a new insight into the fundamental understanding and development of environmentally responsive and multifunctional surfaces and nanomaterials.