Υβριδικά janus σωματίδια που αποκρίνονται σε αλλαγές του pH
pH -responsive hybrid janus nanoparticles
Janus particles are named after the two-faced ancient Roman god Janus, based on the chemical and physical anisotropy that these particles exhibit. Soft Janus particles represent a fascinating group of polymeric materials, which open new ways in academia and industry.
In this study we present the characterization of silica nanoparticles with asymmetric grafting of polymer chains from their surface. Hybrid Janus nanoparticles consist of an inorganic silica core and grafted polymer chains. The multistep reaction commenced with the stabilization of a styrene/methanol Pickering emulsion using amine-functionalized silica nanoparticles (D = 100 nm) as stabilizers. The solvent exposed surface of the silica nanoparticles was modified with an atom transfer radical polymerization (ATRP) initiator. After the functionalization, polystyrene was dissolved yielding Janus nanoparticles bearing ATRP initiating sites. Next, surface-initiated ATRP of t-BuA was carried out from the initiator-functionalized hemisphere of the silica nanoparticles followed by the removal of the bromide end groups to obtain halogen free P(t-BuA) polymer chains. Subsequently, functionalization of the second hemisphere with the ATRP initiator was performed. Acid hydrolysis of P(t-BuA) led to oppositely charged Janus particles decorated with PAA polymer chains on the one hemisphere and an amine-functionalized hemisphere.
The amount of grafted polymer chains from the surface of the particles was determined by Thermogravimetric Analysis (TGA), while the molecular weights and molecular weight distributions of the polymers formed in solution were determined by Gel Permeation Chromatography (GPC). The morphology of the polymer-silica Janus particles was studied with Scanning Electron Microscopy (SEM).
The successful hydrolysis of the P(t-BuA) chains was investigated with Fourier Transform Infrared (FT-IR) Spectroscopy. The pH-responsive behaviour of the particles in an aqueous solution was studied using potentiometric titration and dynamic light scattering.