The creation of three-dimensionally engineered nanoporous architectures via covalently interconnected nanoscale building blocks remains one of the fundamental challenges in nanotechnology. Here we report the synthesis of ordered, stacked macroscopic three-dimensional (3D) solid scaffolds of graphene oxide (GO) fabricated via chemical cross-linking of two-dimensional GO building blocks. The resulting 3D GO network solids form highly porous interconnected structures, and the controlled reduction of these structures leads to formation of 3D conductive graphene scaffolds. These 3D architectures show promise for potential applications such as gas storage; CO2 gas adsorption measurements carried out under ambient conditions show high sorption capacity, demonstrating the possibility of creating new functional carbon solids starting with two-dimensional carbon layers.

In this paper, we report the development of a versatile platform for a highly efficient and stable graphene oxide (GO)-based optical sensor that exhibits distinctive ratiometric color responses. To demonstrate the applicability of the platform, we fabricated a colorimetric, GO-based pH sensor that responds to a wide range of pH changes. Our sensing system is based on responsive polymer and quantum dot (QD) hybrids integrated on a single GO sheet (MQD-GO), with the GO providing an excellent signal-to-noise ratio and high dispersion stability in water. The photoluminescence emissions of the blue and orange color-emitting QDs (BQDs and OQDs) in MQD-GO can be controlled independently by different pH-responsive linkers of poly(acrylic acid) (PAA) (pKa=4.5) and poly(2-vinylpyridine) (P2VP) (pKa=3.0) that can tune the efficiencies of Förster resonance energy transfer from the BQDs to the GO and from the OQDs to the GO, respectively. As a result, the color of MQD-GO changes from orange to near-white to blue over a wide range of pH values. The detailed mechanism of the pH-dependent response of the MQD-GO sensor was elucidated by measurements of time-resolved fluorescence and dynamic light scattering. Furthermore, the MQD-GO sensor showed excellent reversibility and high dispersion stability in pure water, indicating that our system is an ideal platform for biological and environmental applications. Our colorimetric GO-based optical sensor can be expanded easily to various other multifunctional, GO-based sensors by using alternate stimuli-responsive polymers.

Monodispersed colloidal particles of polystyrene-b-polybutadiene (PS-b-PB) block copolymers (BCPs) were successfully prepared, in which uniform emulsion containing BCPs were firstly generated by cross-flow membrane emulsification using tubular Shirasu porous glass (SPG) membrane and then unique internal nanostructures were developed by controlled evaporation of emulsions. The diameter of those BCP particles could be controlled from 200 nm to 5 µm by tuning the pore diameter of the membrane. With symmetric BCPs, onion-like nanostructures inside particles were formed by slow evaporation of emulsion. Coiled-cylinders in the BCP particles were also developed by adding homopolymers, in which the assembled BCP structure is strongly dependent on the particle size, demonstrating the importance of our membrane method in generating monodispersed BCP particles. Further investigation of process parameters showed that for a given pore diameter, the operation pressure (P) and surfactant concentration were critical parameters for narrow size distribution of the particles. When the ratio of the operation pressure to the critical pressure (P/P c ) was less than 4.33, uniform emulsions were produced with a sufficient amount of sodium dodecyl sulfate surfactants in the continuous phase. In addition, uniformly-sized, hierarchically structured particles of BCPs and nanoparticles (NPs) were produced, in which oleylamine coated, 3-nm sized Au NPs were incorporated selectively into the PB domains inside the particles.

Surface-engineered, 10 nm-sized graphene quantum dots (GQDs) are shown to be efficient surfactants for producing 3-pentadecyl phenol (PDP)-combined poly­(styrene-b-4-vinylpyridine) (PS-b-P4VP­(PDP)) particles that feature tunable shapes and internal morphologies. The surface properties of GQDs were modified by grafting different alkyl ligands, such as hexylamine and oleylamine, to generate the surfactant behavior of the GQDs. In stark contrast to the behavior of the unmodified GQDs, hexylamine-grafted GQDs and oleylamine-grafted GQD surfactants were selectively positioned on the PS and P4VP­(PDP) domains, respectively, at the surface of the particles. This positioning effectively tuned the interfacial interaction between two different PS/P4VP­(PDP) domains of the particles and the surrounding water during emulsification and induced a dramatic morphological transition to convex lens-shaped particles. Precise and systematic control of interfacial activity of GQD surfactants was also demonstrated by varying the density of the alkyl ligands on the GQDs. The excellent surface tunability of 10 nm-sized GQDs combined with their significant optical and electrical properties highlight their importance as surfactants for producing colloidal particles with novel functions.

In this study, we developed a novel strategy to control the orientation of microdomains in block copolymer thin films by introducing either selective or neutral gold nanoparticles (Au NPs) that were thermally stable. The Au NPs were modified with thiol-terminated polymeric ligands, poly[(methyl methacrylate-r-styrene)-b-azidostyrene] (P[(MMA-r-S)-b-S-N3]-SH), having different compositions of methyl methacrylate (MMA) and styrene in P(MMA-r-S) block to precisely tune the interfacial interaction between the Au NPs and block copolymer template, poly(styrene-b-methyl methacrylate) (PS-b-PMMA). These Au NPs have a cross-linked polymeric shell, via UV cross-linking of P(S–N3) block, and thus were stable under thermal annealing at temperatures up to ∼200 °C. The selective Au NPs, which had 80 mol % PMMA in the P(MMA-r-S) block, were located within the PMMA domain of the PS-b-PMMA block copolymer. In contrast, the neutral Au NPs, which had 20 mol % PMMA in the P(MMA-r-S) block, were localized at the interface between the PS and PMMA blocks of the PS-b-PMMA. When these Au NPs were incorporated into PS-b-PMMA thin films, these different locations of Au NPs resulted in a remarkable difference in orientation of the block domains. When the selective Au NPs were added and were located in the PMMA domains, the microdomains were oriented parallel to the substrate. In contrast, when the neutral Au NPs that localize at the block copolymer interfaces were added, they induced a transition in the orientation of microdomains from parallel to perpendicular to the substrate. The lateral and vertical location of the Au NPs in the film was investigated by top-view and cross-sectional transmission electron microscopy (TEM). Also, we employed self-consistent mean field theory (SCFT) simulations to explain our experimental results.