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Preparation of Janus Particles with Different Stabilizers and Formation of Colloidal Chains

 

SpeakerProf. Hideto Minami

Date: Monday, 11th April 2016

Time: 3:00-4:30 PM

Venue: Yifu Conference Centre for academic report

Sponsor: Beijing University of Chemical Technology, Beijing Engineering Research Center of Synthesis and Application of Waterborne Polymer

Abstract: Janus particles comprising two surfaces with different chemical compositions have attracted considerable attention from an academic perspective owing to their anisotropic properties as well as their potential applications. Janus particles have been prepared by various techniques such as macrophase separation induced by seeded polymerization, microfluidic methods, toposelective surface modification based on the particle monolayer, and Pickering emulsions. Using these techniques, Janus particles responding to external stimuli such as electric and magnetic fields, pH, and temperature have been prepared.  Moreover, one-dimensional (1D) colloidal chain composed of Janus particles that have been produced via anisotropic interactions among the particles because of their anisotropic morphology. Colloidal chains having electronic, photonic, and energy transfer are expected to become innovative products. Hydrogen bonding interactions between hydrogen bond donors and hydrogen bond acceptor often induce the formation of precipitates in aqueous solutions of water-soluble polymers. Recently, we demonstrated a facile preparation and development of raspberry-like particles by mixing large and small polystyrene (PS) particles stabilized by the hydrogen bond donor polymer (poly(acrylic acid) (PAA)) and hydrogen bond acceptor polymer (poly(vinyl pyrrolidone) (PVP)), respectively. Herein, we describe the preparation of Janus particles with two hemispheres having different stabilizers, PS phase stabilized by PAA and a poly(methyl methacrylate) (PMMA) phase stabilized by PVP using the Solvent-Absorbing/Releasing Method (SARM) of PS/PMMA composite particles with a core–shell structure. The core-shell PS/PMMA composite particles were prepared by seeded dispersion polymerization of MMA using PVP as stabilizer in the presence of PS seed particles stabilized by PAA at pH 6.0. A TEM image of ultrathin cross sections of the composite particles demonstrated that the morphology was changed from core–shell (Fig. 1a) to a structure with completely different hemispheres (Fig. 1b) after the SARM.  We also demonstrated the facile formation of the colloidal chains via hydrogen bonding interaction between different stabilizers. At pH 4.0, the core–shell particles were aggregated in a disorderly fashion. However, the Janus particles exhibited the formation of colloidal chains (Fig.1c) indicating that PS/PMMA Janus particles with different stabilizers on different parts of their surfaces were successfully prepared. The behavior of the Janus particles during structuralization of the particle chain does indeed look similar to that of the monomers during step-growth polymerization.

 

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