Confinement Assembly

a) Emulsification of a polymer/oil-phase; b) evaporation of the oil (e.g. CHCl3); c) microparticles with inner morphology
© Elsevier

The self-assembly of block copolymers in confining spaces has emerged as a powerful tool to create multicompartment microparticles. In case of 3D confinement, the block copolymer dries inside of emulsion droplets leaving behind solid microparticles with inner structure according to the combined effect of microphase separation and curvature. We study the confinement-assembly of special polymer architectures and polymer chemistries, e.g., ABC triblock terpolymers, polymer brushes, miktoarm stars, biodegradable or crystalline polymers. ABC triblock terpolymers further give access to new Janus nanoparticle shapes including nanorings, cups, and perforated discs.

  • Comparison of a SBM terpolymer in bulk and in 3D confinement
    © A.Gröschel

    Multicompartment Microparticles

    ABC triblock terpolymers spontaneously form a large variety of nanostructures in the solid state (bulk, thin films) simply by drying from a good solvent for all blocks. Due to five independent parameters (two volume fractions and three interaction parameters), these morphologies can become very complex. A relatively simple lamellar-cylinder morphology of SBM is shown above. We study to formation of terpolymer morphologies in spherical confinement where the additional curved polymer/water interface imposes boundary conditions that directs the morphology into structures difficult to obtain otherwise. For instance, the lamellar-cylinder morphology is deflected at the interface to form an axially-stacked disc-ring morphology. Colloidal rings or toroids are a comparably rare shape in self-assembly, but show interesting physical properties.

  • Microparticles of SBM terpolymer emulsified with a 0.6 µm SPG membrane
    © A.Gröschel

    Shirasu Porous Glass (SPG) Membrane

    A more recent method for microparticle formation is the high-pressure homogenization through SPG membranes. The polymer/oil phase is pressed through the porous glass membrane and into the continuous water/surfactant phase. With this method, microparticles are produced with surprisingly narrow size distribution. The average particle diameter can be controlled in the range of 0.2 µm - 5.0 µm by choice of membrane pore size.

  • Janus nanodiscs with constant thickness (ca. 50 nm) but varying diameter of 0.19, 0.41 and 1.13 µm
    © Wiley 2021

    Narrowly dispersed Janus nanoparticles

    Janus nanoparticles have two faces with different physical properties and require special synthesic methods. While ABC triblock terpolymers are intrinsically asymmetric and have been used to form polymeric Janus nanoparticles, their formation through cross-linked lamella-lamella bulk morphologies requires post sonication treatments to mechanically tear larger sheets apart into smaller fragments. While these fragments have identical thickness (originating from the block length), they can be irregular shaped and have a broad size distribution. Combining microphase separation with the method of SPG membrane emulsification ultimately yields Janus nanoparticles with controllable size. As exemplified on Janus nanodiscs, the SPG membrane considerably narrows this size-distribution, while allowing to control the overall aspect ratio (diameter/thickness) simply by using membranes with different pore size. The figure on the right show SEM and AFM analysis of Janus discs produced with the same SBM triblock terpolymer but varying membrane pore sizes of 0.3µm, 0.8µm, and 2.0µm. The thickness is very similar (55nm-60nm), while the average diameter increases from 0.19, 0.41 und 1.13 µm. We are interested in their nanomechanical properties, difussion behaviour and interfacial properties.