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Liquid Nanofabrication of Functional Multiphasic Soft Matter by Capillary Binding and Interfacial Templating

Orlin D Velev- North Carolina State University

We will present two new engineering strategies which use multiphasic liquid-liquid-polymer systems to make a rich variety of novel colloidal structures and materials. The capillary forces originating at the liquid/liquid interfaces can serve for reconfigurable binding in soft matter systems, including Pickering emulsions, novel responsive capillary gels, and compositions for 3D printing. Alternatively, the liquid/liquid interfaces can also template the formation of a variety of polymer nanomaterials. We will first present responsive structures made of filaments from lipid-coated magnetic nanoparticles suspended in water-oil systems. The nanocapillary binding results in ultra-high filament flexibility. As an example of the application of such structures, we will discuss the development of new 3D printing inks consisting of water, crosslinked PDMS microbeads and liquid PDMS phase. These Homocomposite Thixotropic Pastes (HTPs) can be directly extruded and shaped on a 3D printer. The curing of the PDMS bridges yields remarkably elastic, flexible and biocompatible structures. The HTP-3DP inks enable new opportunities for 3D printing of “active” and magnetically reconfigurable structures. In the second new materials synthesis approach the liquid/liquid droplet interfaces template the formation of a variety of polymer nanomaterials, including nanoparticles, nanofibers, nanoribbons, microrods and microsheets. The interfacial polymer precipitation in turbulently sheared liquid media results in a new class of soft dendritic polymer microparticles (“dendricolloids”) with hierarchical morphology similar to molecular-scale polymer dendrimers, but two orders of magnitude larger in scale. The dendricolloids combine the properties of fascinating soft matter systems – the freely-suspended dendritic particles have very large excluded volume, while in contact their nanofiber corona possesses the highly adhesive abilities of the nanofiber-padded gecko legs. Thus, the polymer dendricolloids possess highly unusual properties – gelation at very low volume fractions, strong adhesion to surfaces and to each other, and ability to bind strongly and form coatings, nonwoven sheets, and ultrasoft membranes.