Σύνθεση λειτουργικών "Janus" σωματιδίων από υβριδικά κολλοειδοσώματα

Janus particles are named after the two-faced ancient Roman god, Janus, based on the chemical and physical anisotropy that these particles exhibit. This work focuses on the synthesis of sub-micron silica particles with asymmetric grafting of polymer chains from their surface. High demand of such particles is in contrast to their usually small-scale production. In response to that, this work takes advantage of the large surface area provided by spherical latex particles to immobilize silica particles at the latex-solvent interphase and thus provide shielding to one hemisphere of the colloidal silica particles buried in the latex particles, whereas the exposed silica surface can be chemically modified as required. Here, the exposed surface of the silica particles was functionalized with atom transfer radical polymerization initiating sites. The successful transformation of the particles into Janus precursor initiators was verified by means of transmittance electron microscopy (TEM) and fluorescence microscopy. These Janus initiator particles were used for the preparation of hybrid polymer-silica Janus particles. In order to successfully grow well-defined polymer chains from the surface of the particles, the atom transfer radical polymerization conditions were optimized for each monomer used. In each case, the polymerization kinetic studies provided information on the reaction time and the control of the polymer molecular weight and molecular weight distribution. The results show that high polymer molecular weight and narrow molecular weight distributions are achieved, indicating the good control of the polymerization reactions. The Janus particles synthesized comprised an amine-functionalized hemisphere and a polymer-grafted one. Three different polymers were grown from the particle surface: a hydrophobic poly(methyl methacrylate) (PMMA) leading to amphiphilic Janus particles, a hydrophobic poly(tert-butyl acrylate) (PtBuA) to give polyampholyte particles that can be hydrolyzed to form an anionic and pH-responsive derivative poly(acrylic acid) (PAA) and a hydrophilic cationic and pH- and temperature-responsive polymer; poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA), leading to fully hydrophilic cationic particles. For comparison, fullycoated particles of the same polymers were also synthesized employing the same polymerization conditions. The successful grafting of the polymers from the surface of the silica particles was verified by TGA while the high polymer molecular weight and narrow molecular weight distributions were measured by GPC verifying the control of the surfaceinitiated polymerization reactions. Based on the results derived from these techniques the number of polymer chains grafted per particle was calculated, finding that for the polymer-silica Janus particles this number was significantly lower than for the corresponding fully polymer-coated particles. Observation by SEM provided insight on the topology of the polymer-silica Janus particles, indicating the formation of acorn-like and snowman-like particles. The pH-depended size of the Janus PDMAEMA particles was shown by DLS measurements verifying the pH-responsive behavior of the Janus particles. Although a temperature-induced precipitation of the particles was observed by turbidimetry, the size of the particles measured by DLS was not found to decrease before the LCST of the polymer, as was the case for the fully-coated PDMAEMA particles. Instead, an increase of the size of the particles was found attributed to the formation of controlled aggregates