Simple Coating with pH-Responsive Polymer-Functionalized Silica Nanoparticles of Mixed Sizes for Controlled Surface Properties

Different-sized silica nanoparticles (SiNPs) were functionalized by pH-responsive poly­(2-(diisopropylamino)­ethyl methacrylate) (PDP) via surface-initiated atom transfer radical polymerization (ATRP). The functionalized PDP-SiNPs were used to coat glass surfaces, polymeric nanofibers, and paper via simple coating methods such as dip, cast, and spray coating. A PDP-SiNPs mixture having different sizes was found to change the surface properties of the substrates remarkably, compared to one containing PDP-SiNPs with uniform sizes. High surface roughness was achieved with very little coating materials, which is beneficial from an economical point of view. Moreover, adsorption/desorption of PDP-SiNPs onto/from the substrates could be controlled by changing solution pH due to the protonation/deprotonation of the PDP. The surface properties of the coated substrates were analyzed by contact angle (CA) measurement, scanning electron microscopy (SEM), and transmission electron microscopy (TEM). This inexpensive system provides a simple, quick, and effective approach to changing the surface properties of substrates that could be exploited for large-scale surface modification.