Jinhye Bae

Programming Reversibly Self‐Folding Origami with Micropatterned Photo‐Crosslinkable Polymer Trilayers

Self-folding microscale origami patterns are demonstrated in polymer films with control over mountain/valley assignments and fold angles using trilayers of photo-crosslinkable copolymers with a temperature-sensitive hydrogel as the middle layer. The characteristic size scale of the folds W = 30 μm and figure of merit A/ W (2) ≈ 5000, demonstrated here represent substantial advances in the fabrication of self-folding origami.

Multifunctional nanoparticle-loaded spherical and wormlike micelles formed by interfacial instabilities.

Hybrid spherical and wormlike amphiphilic block copolymer micelles are formed through evaporation-induced interfacial instabilities of emulsion droplets, allowing the incorporation of pre-synthesized hydrophobic inorganic nanoparticles within the micelle cores, as well as co-encapsulation of different nanoparticles. This encapsulation behavior is largely insensitive to particle surface chemistry, shape, and size, thus providing a versatile route to fabricate multifunctional micelles.

Osmotically Driven Formation of Double Emulsions Stabilized by Amphiphilic Block Copolymers

Double emulsions are valuable for the formation of multi-compartmental structures. A variety of pathways to prepare double emulsions have been developed, but high-throughput routes to droplets of controlled size and architecture remain scarce. A new single-step process is introduced for preparation of water-in-oil-in-water double emulsions by a previously unexplained process of self-emulsification. We show that the origin of this process is the osmotic stress resulting from the presence of salt impurities within the amphiphilic block copolymers used for emulsion stabilization. Further, we utilize osmotically driven emulsification to tailor the structures of multiple emulsions, which upon solvent evaporation can yield multi-compartmental capsules or hierarchically structured porous films.

Fluorescence imaging of nanoscale domains in polymer blends using stochastic optical reconstruction microscopy (STORM)

High-resolution fluorescence techniques that provide spatial resolution below the diffraction limit are attractive new methods for structural characterization of nanostructured materials. For the first time, we apply the super-resolution technique of Stochastic Optical Reconstruction Microscopy (STORM), to characterize nanoscale structures within polymer blend films. The STORM technique involves temporally separating the fluorescence signals from individual labeled polymers, allowing their positions to be localized with high accuracy, yielding a high-resolution composite image of the material. Here, we describe the application of the technique to demixed blend films of polystyrene (PS) and poly(methyl methacrylate) (PMMA), and find that STORM provides comparable structural characteristics as those determined by Atomic Force Microscopy (AFM) and scanning electron microscopy (SEM), but with all of the advantages of a far-field optical technique.

Measuring the Elastic Modulus of Thin Polymer Sheets by Elastocapillary Bending.

We describe bending by liquid/liquid or liquid/air interfaces as a simple and broadly applicable technique for measuring the elastic modulus of thin elastic sheets. The balance between bending and surface energies allows for the characterization of a wide range of materials with moduli ranging from kilopascals to gigapascals in both vapor and liquid environments, as demonstrated here by measurements of both soft hydrogel layers and stiff glassy polymer films. Compared to existing approaches, this method is especially useful for characterizing soft materials (<megapascals in modulus), thin sheets with sub-millimeter in-plane dimensions, and samples immersed in a variety of liquid media. The measurement is independent of the three-phase (liquid/solid/medium) contact angle for appropriately chosen wetting conditions, therefore requiring only knowledge of the liquid/medium surface tension and the sheet thickness to characterize sheets with specified shapes. Using the method, we characterize photo-cross-linkable polyelectrolyte hydrogel sheets swelled to equilibrium in an aqueous medium and demonstrate good agreement with predicted scalings of the modulus and swelling ratio with cross-link density.

Programmable and reversible assembly of soft capillary multipoles

The capillary assembly of stimulus-responsive hydrogel particles with programmed multipolar interactions defined by their prescribed three-dimensional (3D) shapes is demonstrated. Low-energy bending deformations of the particles, driven by surface tension, modifies the interactions between particles, while their temperature-dependent swelling enables switchable assembly.