Synthesis and Characterization of Carbon Microbeads

Abstract

We report a microfluidic-based droplet generation platform for synthesizing micron-sized porous carbon microspheres. The setup employs carbon materials such as graphite, carbon nanotubes, graphene, fullerenes, and carbon black as starting materials. Custom composition, structure, and function are achieved through combinations of carbon materials, cross-linkers, and additives along with variations in process parameters. Carbon materials can be assembled into spheres with a mean diameter of units to hundreds of μm with relatively tight size distribution (<25% RSD). Pore structure and size (tens to hundreds of angstrom) can be modulated by incorporating porogen/coporogen dilutants during synthesis. The microbeads have excellent mechanical stability with an elastic modulus of hundreds of MPa. They can sustain high dynamic fluid flow pressures of up to 9000 psi. This work lays the foundation for synthesizing novel tailorable and customizable carbon microbeads. It opens avenues for applying these novel materials for composite and additive manufacturing, energy, life science, and biomedical applications.

Figure 1

(a) Depiction of the customizable carbon microbead platform. Carbon sources are combined through a microdroplet assembly to create mechanically stable spheres. (b) Various feedstock inputs serve as a combinatorial library or “toolbox” to custom tailor end products with desired physical and chemical attributes.

Figure 2

(a) Depiction of the synthesis setup. Inset: flow-focusing and coflow nozzle designs. A viscous suspension containing a mixture of natural carbon powder and a cross-linker (carbon slurry) is passed through a microfluidic nozzle device to generate uniform size droplets. A UV lamp facilitates the in situ binding of the mixture in microbeads. The microbeads are collected, washed, and dried. (b) Flowchart of carbon microbead synthesis steps.

Figure 3

(a) Bright view and SEM microscopic images illustrating the spherical conformation and surface texture of carbon microbeads produced with various carbon sources. (b) Size analysis of 3 representative samples of carbon microbeads synthesized in the 10 μm (left), 50 μm (mid), and 150 μm (right) size distributions. Sample: natural graphite using the BDDMA binder. (c) Mean pore diameter and specific surface area of cured microbeads are controlled by the choice of slurry components and porogen. Sample 1: graphite with the divinylbenzene (DVB) binder. Sample 2: graphite with the 1,4-butanediol dimethacrylate (BDDMA) binder. Porogen: 1-propanol.

Figure 4

(a) Stability analysis. Backpressure as a function of column volumes. No statistically significant difference in backpressure was observed for the carbon microbeads packed in a liquid chromatography column for a continuous 24 h test. (b) Mechanical stability analysis. Representative SEM image of microbeads unpacked from the column after being continuously flushed for 24 h with water/acetonitrile (80:20) mobile phase. No indication of mechanical failure of the bead structure or the presence of fines in a packed bed.