We describe an approach to prepare co-continuous microstructured blends of polymers and nanoparticles by formation of a percolating network of particles within one phase of a polymer mixture undergoing spinodal decomposition. Nanorods or nanospheres of CdSe were added to near-critical blends of polystyrene and poly(vinyl methyl ether) quenched to above their lower critical solution temperature. Beyond a critical loading of nanoparticles, phase separation is arrested due to the aggregation of particles into a network (or colloidal gel) within the poly(vinyl methyl ether) phase, yielding a co-continuous spinodal-like structure with a characteristic length scale of several micrometers. The critical concentration of nanorods to achieve kinetic arrest is found to be smaller than for nanospheres, which is in qualitative agreement with the expected dependence of the nanoparticle percolation threshold on aspect ratio. Compared to structural arrest by interfacial jamming, our approach avoids the necessity for neutral wetting of particles by the two phases, providing a general pathway to co-continuous micro- and nanoscopic structures.

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.

The directed or dynamic assembly of molecular components in solution is a simple and effective strategy to confine materials in desired geometries and length scales. We use a kinetic control strategy with block copolymer blending to construct complex nanoparticles through the demixing of unlike block copolymers within the same nanoscale particle. Successful nanoparticle construction relies on kinetic trapping of unlike block copolymers into the same nanoparticle with solution processing. Not only can we make nanoparticles with multiple internal compartments of a desired size, but we can also make nanoparticles of hybrid geometries (e.g. a blend of cylindrical and spherical geometries). These combination particles are kinetically trapped, non-equilibrium structures. However, the block copolymers are able to phase separate locally within the nanoscale particle, thus producing internal compartments and hybrid geometries.

The ability to tune the state of dispersion or aggregation of nanoparticles within polymer-based nanocomposites, through variations in the chemical and physical interactions with the polymer matrix, is desirable for the design of materials with switchable properties. In this study, we introduce a simple and effective means of reversibly controlling the association state of nanoparticles based on the thermal sensitivity of hydrogen bonds between the nanoparticle ligands and the matrix. Strong hydrogen bonding interactions provide excellent dispersion of gold nanoparticles functionalized with poly(styrene-r-2-vinylpyridine) [P(S-r-2VP)] ligands in a poly(styrene-r-4-vinyl phenol) [P(S-r-4VPh)] matrix. However, annealing at higher temperatures diminishes the strength of these hydrogen bonds, driving the nanoparticles to aggregate. This behavior is largely reversible upon annealing at reduced temperature with redispersion occurring on a time-scale of ~30 min for samples annealed 50 °C above the glass transition temperature of the matrix. Using ultraviolet-visible absorption spectroscopy (UV-vis) and transmission electron microscopy (TEM), we have established the reversibility of aggregation and redispersion through multiple cycles of heating and cooling.

Nanoparticles (NPs) segregated to the liquid/liquid interface form disordered or liquid-like assemblies that show diffusive motions in the plane of the interface. As the areal density of NPs at the interface increases, the available interfacial area decreases, and the interfacial dynamics of the NP assemblies change when the NPs jam. Dynamics associated with jamming was investigated by X-ray photon correlation spectroscopy. Water-in-toluene emulsions, formed by a self-emulsification at the liquid/liquid interface and stabilized by ligand-capped CdSe-ZnS NPs, provided a simple, yet powerful platform, to investigate NP dynamics. In contrast to a single planar interface, these emulsions increased the number of NPs in the incident beam and decreased the absorption of X-rays in comparison to the same path length in pure water. A transition from diffusive to confined dynamics was manifested by intermittent dynamics, indicating a transition from a liquid-like to a jammed state.

Emulsion droplets can be stabilized against coalescence by many types of interfacially active species, including proteins, small-molecule surfactants, polymers, nanoparticles and microparticles. When the fluid-fluid interface of an oil-inwater (o/w), or water-in-oil (w/o), emulsion is stabilized by adsorption of particles at the interface, a "Pickering emulsion" is obtained in which the particles occupy the fluid-fluid interface and prevent, or retard, droplet coalescence. Pioneering work of Ramsden [1] and Pickering [2] on paraffin/water emulsions containing solid particles, such as iron oxide, silicon dioxide, barium sulfate, and kaolin clays demonstrated the critically important role of particles in such interfacial stabilization. Theoretical treatment of nanoparticle-stabilized droplet structures, reported for example by Pieranski [3] and Binks, [4][5][6] describe the reduction of the overall surface energy of the system due to nanoparticle interfacial segregation as a function of particle size and the relative interfacial energies of the system (oil-water, oil-particle, and water-particle).The tendency of particles to localize to oil-water interfaces opens opportunities to fabricate new materials based on the individual and collective properties of the particles, including: 1) the optical properties derived from colloidal crystallization, [7,8] 2) self-assembled conducting structures, [9,10] and 3) encapsulation and release technologies. [11,12] For example, Weitz and co-workers reported the oil-water interfacial assembly of polystyrene microspheres into hexagonally packed capsule structures termed "colloidosomes." [13] For nanoparticles, the energy holding each particle at the fluid-fluid interface is smaller than that for microscale objects; nonetheless, there have been numerous reports of nanoparticle-stabilized emulsion droplets, in which the droplets are stable for hours, days, or longer. CdSe QDs, [14,15] Au NPs, [16][17][18] Fe 3 O 4 NPs, [19] "Janus" nanoparticles [20] and plantderived virus particles [21] all prove amenable to stabilizing fluid-fluid interfaces of different types. Moreover, embedding functional ligands on nanoparticle surfaces provides access to further droplet stabilization through chemical cross-linking of the ligands, thereby converting these dynamic self-assembled systems into robust structures. [22] Double-emulsion droplets, whether water-in-oil-in-water (w/o/w), or oil-in-water-in-oil (o/w/o), are attractive for providing a means to control release from the inner phase to the outer phase, while effectively shielding the interior phase from the continuous phase. Double emulsions can be prepared by a one-or two-step emulsification process, in the presence of a relatively hydrophilic surfactant that stabilizes o/w droplets, and a relatively hydrophobic surfactant that stabilizes the w/o interfaces.[23] Such emulsions have been generated during phase inversion processes, that is, when the continuous phase of the immiscible liquid-liquid dispersion becomes the dispersed phase. We n...

Emulsion droplets can be stabilized against coalescence by many types of interfacially active species, including proteins, small-molecule surfactants, polymers, nanoparticles and microparticles. When the fluid-fluid interface of an oil-inwater (o/w), or water-in-oil (w/o), emulsion is stabilized by adsorption of particles at the interface, a "Pickering emulsion" is obtained in which the particles occupy the fluid-fluid interface and prevent, or retard, droplet coalescence. Pioneering work of Ramsden [1] and Pickering [2] on paraffin/water emulsions containing solid particles, such as iron oxide, silicon dioxide, barium sulfate, and kaolin clays demonstrated the critically important role of particles in such interfacial stabilization. Theoretical treatment of nanoparticle-stabilized droplet structures, reported for example by Pieranski [3] and Binks, [4][5][6] describe the reduction of the overall surface energy of the system due to nanoparticle interfacial segregation as a function of particle size and the relative interfacial energies of the system (oil-water, oil-particle, and water-particle).The tendency of particles to localize to oil-water interfaces opens opportunities to fabricate new materials based on the individual and collective properties of the particles, including: 1) the optical properties derived from colloidal crystallization, [7,8] 2) self-assembled conducting structures, [9,10] and 3) encapsulation and release technologies. [11,12] For example, Weitz and co-workers reported the oil-water interfacial assembly of polystyrene microspheres into hexagonally packed capsule structures termed "colloidosomes." [13] For nanoparticles, the energy holding each particle at the fluid-fluid interface is smaller than that for microscale objects; nonetheless, there have been numerous reports of nanoparticle-stabilized emulsion droplets, in which the droplets are stable for hours, days, or longer. CdSe QDs, [14,15] Au NPs, [16][17][18] Fe 3 O 4 NPs, [19] "Janus" nanoparticles [20] and plantderived virus particles [21] all prove amenable to stabilizing fluid-fluid interfaces of different types. Moreover, embedding functional ligands on nanoparticle surfaces provides access to further droplet stabilization through chemical cross-linking of the ligands, thereby converting these dynamic self-assembled systems into robust structures. [22] Double-emulsion droplets, whether water-in-oil-in-water (w/o/w), or oil-in-water-in-oil (o/w/o), are attractive for providing a means to control release from the inner phase to the outer phase, while effectively shielding the interior phase from the continuous phase. Double emulsions can be prepared by a one-or two-step emulsification process, in the presence of a relatively hydrophilic surfactant that stabilizes o/w droplets, and a relatively hydrophobic surfactant that stabilizes the w/o interfaces.[23] Such emulsions have been generated during phase inversion processes, that is, when the continuous phase of the immiscible liquid-liquid dispersion becomes the dispersed phase. We n...

No abstract