Flexible, paper-based graphene and graphene oxides are
now emerging
as a new class of materials with a variety of applications in electrochemical
devices, novel composites, antibacterial agents, separation membranes,
and so on. But the tight layer and the poor permeability limit their
applications in the fields requiring permeable layers and tunable
layer spacing. We demonstrate that the temperature-dependent decomposition
reaction of ammonium nitrate can be utilized to modulate the layer
spacing of graphene oxide paper and modify its permeability. Unlike
the commonly used intercalation method, our strategy enables the layer
spacing of the paper to be expanded over large range (123%–20 000%)
and avoids the occupation of layer room by guest molecules. Dependent
on the expansion amplitude, the papers exhibit a variety of interesting
applications, including the highly efficient exclusion of small organic
molecules, the separation of ultrathin nanoparticles, and the loading
of polar and nonpolar guest molecules. Further, owing to the recovery
of the electrical conductivity, the modified papers with large permeability
should be also potential materials for flexible, paper-based electrochemical
devices.
Preparation of anisotropic particles based on phase separation of prefabricated seeds in polymerizations generally involves multiple process steps. In conventional one-pot dispersion polymerization, only spherical particles are produced. Herein, anisotropic particles with asymmetrical core-shell structure, multiple compartments, and continuously tunable surface roughness and sizes were synthesized by a modified one-pot dispersion polymerization. A mixture of polar solvents, ethylene glycol (EG), and water (6/4, vol.) was used as medium for polymerization of styrene (St). In the presence of ammonium persulfate (APS) and vinyl acetate (VA), divinylbenzene (DVB, 16.1-66.4 %) and (St, 50.3-0 %) were added at 60, 180, and 360 min, respectively. Dense crosslinking was confined to exterior of swollen growing particles, resulting in phase separation and formation of snowman-like particles with coarse, core-shell structured body, and smooth, no or partially cross-linked head. The newly formed compartments were also inhomogeneously cross-linked and their phases separated, producing three and four compartment anisotropic particles with an aspect ratio up to 2.3. Gel content of final particles was less than 75 %. Due to a sequential crosslinking from growing particle to newly formed compartments, reaction stability and particle monodispersity were maintained even when high amounts of DVB were added. Asymmetrical morphologies, structures, sizes, and surface roughness of particles were continuously tuned by varying DVB amount and its start addition time. This one-pot method provides a simple, efficient route for synthesis of anisotropic particles.
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