Search

Monodisperse colloidal particlesof polystyrene-b-polybutadiene (PS-b-PB) block copolymers (BCPs)were successfully prepared, in which uniform emulsions containingBCPs were first generated by cross-flow membrane emulsification usingtubular Shirasu porous glass (SPG) membrane, and then unique internalnanostructures were developed by controlled evaporation of solventinside emulsion. The diameter of those BCP particles could be controlledfrom 200 nm to 5 μm by tuning the pore diameter of the membrane.With symmetric BCPs, onion-like nanostructures inside particles wereformed. Coiled cylinders in the BCP particles were also developedby adding homopolymers, in which the assembled BCP structure is stronglydependent on the particle size, demonstrating the importance of ourmembrane method in generating monodisperse BCP particles. Furtherinvestigation of process parameters showed that for a given pore diameter,the operation pressure (P) and surfactant concentrationwere critical parameters for narrow size distribution of the particles.Uniform emulsions were produced when the ratio of the operation pressureto the critical pressure (P/Pc) was less than 4.33. In addition, uniformlysized, hierarchically structured particles of BCPs and nanoparticles(NPs) were produced, in which oleylamine-coated, 3 nm sized Au NPswere incorporated selectively into the PB domains inside the particles. [ABSTRACT FROM AUTHOR]

Theconfined self-assembly of block copolymers (BCPs) can be usedto generate hierarchically structured composite microspheres. In thisstudy, microspheres of gold-cored BCP (Au-BCP) spheres were firstproduced from an evaporative toluene-in-water-emulsion in which polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) BCPsincorporated with Au precursors (AuCl4–) were dissolved in toluene. Interestingly, the addition of cetyltrimethylammoniumbromide (CTAB) into the microspheres resulted in the selective extractionof Au precursors within the Au-BCP spheres near the surface of themicrosphere because of the strong electrostatic attraction betweenthe CTAB and Au precursors. Therefore, regular-patterned porous nanostructureson the surface of Au-BCP microspheres were formed, of which the sizecould be varied by controlling the molecular weight of the PS-b-P4VP polymers. In addition, the depth of the pores couldbe modulated independently by tuning the amounts of Au precursorsthat were incorporated into the Au-BCP spheres (λ). This methodwas then generalized using other additives (i.e., thiol-terminatedmolecules) that had a favorable interaction with the Au precursors,producing both controlled inner and surface morphologies of the microspheres.Pores at surface could be used to successfully load various metalnanoparticles, potentially making them useful in optical, catalytic,and drug-delivery or therapeutic applications. [ABSTRACT FROM AUTHOR]

Although ferroelectric composites have been reported to enhance the performance of triboelectric (TE) devices, their performances are still limited owing to randomly dispersed particles. Herein, we introduce high-performance TE sensors (TESs) based on ferroelectric multilayer nanocomposites with alternating poly(vinylidenefluoride- co -trifluoroethylene) (PVDF-TrFE) and BaTiO 3 (BTO) nanoparticle (NP) layers. The multilayers comprising alternating soft/hard layers can induce stress concentration and increase the effective stress-induced polarization and interfacial polarization between organic and inorganic materials, leading to a dielectric constant (17.06) that is higher than those of pure PVDF-TrFE films (13.9) and single PVDF-TrFE/BTO nanocomposites (15.9) at 10 kHz. As a result, the multilayered TESs with alternating BTO NP layers exhibit TE currents increased by 2.3 and 1.5 times compared to pure PVDF-TrFE without BTO NPs and PVDF-TrFE/BTO nanocomposites without multilayer structures, respectively. The multilayered TESs exhibit a high pressure sensitivity of 0.94 V/kPa (48.7 nA/kPa) and output power density of 29.4 μWcm -2 , enabling their application in the fabrication of highly sensitive healthcare monitoring devices and high-performance acoustic sensors. The suggested architecture of ferroelectric multilayer nanocomposites provides a robust platform for TE devices and self-powered wearable electronics.

The tuning of interfacial properties at selective and desired locations on the particles is of great importance to create the novel structured particles by breaking the symmetry of their surface property. Herein, a dramatic transition of both the external shape and internal morphology of the particles of polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) was induced by precise positioning of size-controlled Au nanoparticle surfactants (Au NPs). The size-dependent assembly of the Au NPs was localized preferentially at the interface between the P4VP domain at the particle surface and the surrounding water, which generated a balanced interfacial interaction between two different PS/P4VP domains of the BCP particles and water, producing unique convex lens-shaped BCP particles. In addition, the neutralized interfacial interaction, in combination with the directionality of the solvent-induced ordering of the BCP domains from the interface of the particle/water, generated defect-free, vertically ordered porous channels within the particles. The mechanism for the formation of these novel nanostructures was investigated systemically by varying the size and the volume fraction of the Au NPs. Furthermore, these convex lens-shaped particles with highly ordered channels can be used as a microlens, in which the light can be concentrated toward the focal point with enhanced near-field signals. And, these particles can possess additional optical properties such as unique distribution of light scattering as a result of the well-ordered Au cylinders that filled into the channels, which hold great promise for use in optical, biological-sensing, and imaging applications.

Gold-decorated block copolymer microspheres (BCP-microspheres) displaying various surface morphologies were prepared by the infiltration of Au precursors into polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) microspheres. The microspheres were fabricated by emulsifying the PS-b-P4VP polymers in chloroform into a surfactant solution in water, followed by the evaporation of chloroform. The selective swelling of the P4VP domains in the microspheres by the Au precursor under acidic conditions resulted in the formation of Au-decorated BCP-microspheres with various surface nanostructures. As evidenced by transmission electron microscopy (TEM) and scanning electron microscopy (SEM) measurements, dotted surface patterns were formed when microspheres smaller than 800 nm were synthesized, whereas fingerprint-like surface patterns were observed with microspheres larger than 800 nm. Au nanoparticles (NPs) were located inside P4VP domains near the surfaces of the prepared microspheres, as confirmed by TEM. The optical properties of the BCP-microspheres were characterized using UV-vis absorption spectroscopy and fluorescence lifetime measurements. A maximum absorption peak was observed at approximately 580 nm, indicating that Au NPs are densely packed into P4VP domains on the microspheres. Our approach for creating Au-NP-hybrid BCP-microspheres can be extended to other NP systems such as iron-oxide or platinum NPs. These precursors can also be selectively incorporated into P4VP domains and induce the formation of hybrid BCP-microspheres with controlled surface nanostructures., (© 2012 American Chemical Society)

We propose a novel and robust strategy for creating continuous conducting polymer films with ultralow percolation thresholds using polymer-coated gold nanoparticles (Au NPs) as surfactant. Continuous poly(triphenylamine) (PTPA) films of high internal phase polymeric emulsions were fabricated using an assembly of cross-linked polystyrene (PS) colloidal particles as template. Polymer-coated Au NPs were designed to be thermally stable even above 200 °C and neutral to both the PS and PTPA phases. Therefore, the Au NPs localize at the PS/PTPA interface and function as surfactant to efficiently produce a continuous conducting PTPA polymer film with very low percolation thresholds. The volume fraction threshold for percolation of the PTPA phase with insulating PS colloids (as measured by electron microscopy and conductivity measurements) was found to be 0.20. In contrast, with the addition of an extremely low volume fraction (φ(p) = 0.35 vol %) of surfactant Au NPs, the volume fraction threshold for percolation of the PTPA phase was dramatically reduced to 0.05. The SEM and TEM measurements clearly demonstrated the formation of a continuous PTPA phase within the polyhedral phase of PS colloids. To elucidate the influence of the nanoparticle surfactant on the blend films, the morphology and conductivity of the blends at different PS colloid/PTPA volume ratios were carefully characterized as a function of the Au NP concentration. Our approach provides a methodology for a variety of applications that require a continuous phase for the transport of molecular species, ions, or electrons at low concentrations and a second phase for mechanical support or the conduction of a separate species., (© 2011 American Chemical Society)