A Translucent Nanocomposite with Liquid Inclusions of a Responsive Nanoparticle Dispersion

Microgravity Removes Reaction Limits from Nonpolar Nanoparticle Agglomeration

Gravity can affect the agglomeration of nanoparticles by changing convection and sedimentation. The temperature-induced agglomeration of hexadecanethiol-capped gold nanoparticles in microgravity (µ g) is studied at the ZARM (Center of Applied Space Technology and Microgravity) drop tower and compared to their agglomeration on the ground (1 g). Nonpolar nanoparticles with a hydrodynamic diameter of 13 nm are dispersed in tetradecane, rapidly cooled from 70 to 10 °C to induce agglomeration, and observed by dynamic light scattering at a time resolution of 1 s. The mean hydrodynamic diameters of the agglomerates formed after 8 s in microgravity are 3 times (for low initial concentrations) to 5 times (at high initial concentrations) larger than on the ground. The observations are consistent with an agglomeration process that is closer to the reaction limit on thground and closer to the diffusion limit in microgravity.

Gold Nanoprobes Exploring the Ice Structure in the Aqueous Dispersion of Poly(Ethylene Glycol)-Gold Hybrid Nanoparticles

Ice structures and their formation process are fundamentally important to cryobiology, geoscience, and physical chemistry. In this work, we synthesized gold nanoprobes by grafting water-soluble polyethylene glycol (PEG) onto spherical gold nanoparticles and analyzed the structure of ice formation in the vicinity of the resulting hybrid PEG-Au nanoparticles (AuPEGNPs). Temperature-dependent in situ small-angle X-ray scattering (SAXS) indicated that AuPEGNPs, like PEG, caused the formation of bulk spherulite ice. Unlike for PEG, we observed the formation of lamellar ice with a periodicty of 4.6 nm, which is thermodynamically less stable than the bulk form. The lamellar ice formed after AuPEGNP agglomeration during cooling at -19 °C, and it remained during subsequent heating from -20 to -11 °C and melted at around -10 °C, far below the melting temperature of bulk ice. We explain different effects of AuPEGNP and free PEG on ice formation by the topological differences. The highly concentrated PEG chains on the agglomerated Au cores lead to the formation of PEG-hydrates that assemble into lamellar ice with a periodicity of 4.6 nm.

Polymeric Microparticles Generated via Confinement-Free Fluid Instability

In-fiber fluid instability can be harnessed to realize scalable microparticles fabrication with tunable sizes and multifunctional characteristics making it competitive in comparison to conventional microparticles fabrication methods. However, since in-fiber fluid instability has to be induced via thermal annealing and the resulting microparticles can only be collected after dissolving the fiber cladding, obtaining contamination-free particles for high-temperature incompatible materials remains great challenge. Herein, confinement-free fluid instability is demonstrated to fabricate polymeric microparticles in a facile manner induced by the ultralow surface energy of the superamphiphobic surface. The polymer solution columns break up into uniform droplets then form spherical particles spontaneously in seconds at ambient temperature. This method can be applied to a variety of polymers spanning an exceptionally wide range of sizes: from 1 mm down to 1 µm. With the aid of microfluidic spinning instrument, a large quantity of microparticles can be obtained, making this method promising for scaling up production. Notably, through simple modification of the feed solution configuration, composite/structured micromaterials can also be produced, including quantum-dots-labeled fluorescent particles, magnetic particles, core-shell particles, microcapsules, and necklace-like microfibers. This method, with general applicability and facile control, is envisioned to have great prospects in the field of polymer microprocessing.

Reversible magnetism switching of iron oxide nanoparticle dispersions by controlled agglomeration

The controlled agglomeration of superparamagnetic iron oxide nanoparticles (SPIONs) was used to rapidly switch their magnetic properties. Small-angle X-ray scattering (SAXS) and dynamic light scattering showed that tailored iron oxide nanoparticles with phase-changing organic ligand shells agglomerate at temperatures between 5 °C and 20 °C. We observed the concurrent change in magnetic properties using magnetic particle spectroscopy (MPS) with a temporal resolution on the order of seconds and found reversible switching of magnetic properties of SPIONs by changing their agglomeration state. The non-linear correlation between magnetization amplitude from MPS and agglomeration degree from SAXS data indicated that the agglomerates' size distribution affected magnetic properties.

Droplets Self-Born in the Dynamic Polymer for Generating Functional Coatings

Droplet-embedded structures are useful in functionalizing polymer composites but difficult to prepare. Herein, we report a facile self-born method for creating droplets in supramolecular gels to mediate the material's functions. This method is based on the amplification of the defects of polymer matrices generated in curing by swelling-driving reconfiguration of supramolecular polymer networks. The system of poly(urea-co-polydimethylsiloxane) that can cross-link via hydrogen-bond interaction is used to demonstrate our concept. The elastomer matrices are prepared via a casting method and exhibit a heterogeneous structure with both strong- and weak-cross-linking domains. When these materials are swelled in solvents, solvent molecules concentrate in the weak-cross-linking domains to nucleate. With the reconfiguration of the matrices, the nuclei grow into pure droplets, leading to the formation of droplet-embedded structures. This method is applicable to different material systems. We also show that obtained coatings with such droplet-embedded structures exhibit various interesting properties including self-replenishment of the surface liquid, mechanoresponsiveness, and self-healing ability. Moreover, after the droplets are consumed, this method can be used to regenerate the droplet-embedded structure for refunctionalizing the materials. Therefore, we envision its applications in preparation of many useful polymer composites.

Magnetically Addressable Shape-Memory and Stiffening in a Composite Elastomer

With a specific stimulus, shape-memory materials can assume a temporary shape and subsequently recover their original shape, a functionality that renders them relevant for applications in fields such as biomedicine, aerospace, and wearable electronics. Shape-memory in polymers and composites is usually achieved by exploiting a thermal transition to program a temporary shape and subsequently recover the original shape. This may be problematic for heat-sensitive environments, and when rapid and uniform heating is required. In this work, a soft magnetic shape-memory composite is produced by encasing liquid droplets of magneto-rheological fluid into a poly(dimethylsiloxane) matrix. Under the influence of a magnetic field, this material undergoes an exceptional stiffening transition, with an almost 30-fold increase in shear modulus. Exploiting this transition, fast and fully reversible magnetic shape-memory is demonstrated in three ways, by embossing, by simple shear, and by unconstrained 3D deformation. Using advanced synchrotron X-ray tomography techniques, the internal structure of the material is revealed, which can be correlated with the composite stiffening and shape-memory mechanism. This material concept, based on a simple emulsion process, can be extended to different fluids and elastomers, and can be manufactured with a wide range of methods.