Formation Mechanism of Flower-like Polyacrylonitrile Particles

Abstract

Flower-like polyacrylonitrile (PAN) particles have shown promising performance for numerous applications, including sensors, catalysis, and energy storage. However, the detailed formation process of these unique structures during polymerization has not been investigated. Here, we elucidate the formation process of flower-like PAN particles through a series of in situ and ex situ experiments. We have the following key findings. First, lamellar petals within the flower-like particles were predominantly orthorhombic PAN crystals. Second, branching of the lamellae during the particle formation arose from PAN’s fast nucleation and growth on pre-existing PAN crystals, which was driven by the poor solubility of PAN in the reaction solvent. Third, the particles were formed to maintain a constant center-to-center distance during the reaction. The separation distance was attributed to strong electrostatic repulsion, which resulted in the final particles’ spherical shape and uniform size. Lastly, we employed the understanding of the formation mechanism to tune the PAN particles’ morphology using several experimental parameters including incorporating comonomers, changing temperature, adding nucleation seeds, and adjusting the monomer concentration. These findings provide important insights into the bottom-up design of advanced nanostructured PAN-based materials and controlled polymer nanostructure self-assemblies.

Tunable 1D and 2D Polyacrylonitrile Nanosheet Superstructures

“…Meanwhile, the intensity of the ring was stronger in the low azimuthal angle region near the q z axis, indicating that the polymer chains oriented parallel to the surface of the substrate, in the nanosheets that grew in the normal direction on the surface . The nanosheets observed here is similar to our previous report . The chemical composition of the nanosheet arrays was characterized by X-ray photoelectron spectroscopy (XPS), where the C and N signals were observed, attributed to the PAN structure (Figure h).…”

“…33 At Q ≈ 0.1 Å −1 of Figure 4k(i), a small shoulder appeared, corresponding to the thickness of the PAN nanosheets (∼8 nm) according to our previous assignment. 33 Further to the left (Figure 4j,k(iii)), another shoulder and a small valley were observed, corresponding to the Guinier region and the first oscillation valley of the Porord region. Fitting this part of the curve provided size distributions of the nanofibers, with results that were consistent with the SEM images.…”

“…In our previous reports, we studied the formation of flower-like PAN particles during free-radical polymerization of acrylonitrile in acetone. , Here, building upon this chemistry, we prepared 2D PAN nanosheet arrays instead of spherical particles, as shown Figure a. Detailed synthesis procedures can be found in the Methods section.…”

“…However, many of the PAN and carbon superstructures require complex synthesis procedures, which increase the cost and limit their large-scale production . In our recent work, we reported flower-like PAN and its carbon derivatives, which are particularly appealing due to their simple synthesis process. , Meanwhile, these flower-like PAN superstructures have shown great potential due to their advantages, such as improved mass transport and more exposed active sites. − The flower-like PAN superstructures are formed due to the self-assembly of PAN nanosheets . Nonetheless, the particles are typically spherical, although they offer advantages such as easy processing and dense packing in specific applications.…”

Bioinspired crowding directs supramolecular polymerisation

“…2d+e). The morphology of Agg1C observed by scanning electron microscopy (SEM) is best described as a complex hierarchical flower-like structure, which has been previously observed in the selfassembly of two-dimensional sheets [40][41][42] . This observation points to a new self-assembly pathway of 1 under crowded conditions, as the selfassembly in the absence of crowding agents solely leads to the formation of bundled one-dimensional fibres, irrespective of the concentration (see supporting information for details, Supplementary The individual height of these sheets (h = 4.8 nm) matches the molecular dimensions of 1 assuming a slightly tilted arrangement as a consequence of a small translational offset in the molecular stack.…”