Probing the Stability of Halogenated Carbon Atomic Wires in Electrospun Nanofibers via Raman Spectroscopy

Abstract

Carbon atomic wires (CAWs) are one-dimensional (1D) sp-carbon nanostructures with remarkable electronic, mechanical, and optical properties, but their instability limits their practical applications. Embedding them in solid matrices can enhance their stability. This work reports the first example of electrospun nanofibers embedding halogenated CAWs. A solution of poly-(methyl methacrylate) and CAWs in N,N-dimethylformamide was electrospun using various parameters to investigate the effects on fiber morphology and diameter. Halogenated CAWs were successfully incorporated with a minimal morphological impact. Raman spectroscopy confirmed effective embedding and CAWs stability during electrospinning. The halogenated CAWs showed resistance to degradation for at least six months and demonstrated enhanced thermal stability when embedded within nanofibers. Additionally, our work investigated the influence of different halogen terminations on the degradation kinetics of CAWs upon exposure to these conditions. Similarly, photodegradation studies revealed improved photostability within fibers and demonstrated how CAWs chemical structure affects degradation pathways, including possible homolytic C-X bond cleavage. This work introduces electrospun nanofibers as a novel platform for stabilizing CAWs, offering advantages over thin films, such as better homogeneity, larger surface area, and comparable stability. These findings open new perspectives for CAWs-based nanocomposites in electronics, electrochemistry, and energy-related applications.

1

Chemical structure of the C₄X halogenated CAWs (X = Cl, Br, I) with the relative SEM images and diameter distributions (calculated from approximately 100 diameters) of the electrospun PMMA nanofibers embedding the halogenated CAWs.

2

(a) In the top panel, Raman spectra of electrospun nanocomposites embedding C₄X halogenated CAWs (X = Cl, Br, I). In the central panel, Raman spectra of powders of the same CAWs. In the bottom panel, Raman spectrum of PMMA powder. (b) Enlargement of the ECC region of the top and central panels of (a).

3

Ratio between the areas of the CAWs ECC band and the PMMA CH-stretching band for electrospun membranes (solid symbols) and drop-cast films (hollow symbols), measured at different positions across the samples, from the center to the edges.

4

(a) Raman spectra of the electrospun membranes containing C₄X halogenated CAWs (X = Cl, Br, I) measured at 0, 7, and 158 days from deposition (from dark to light, respectively) after electrospinning. The ECC region is highlighted in yellow. (b) Time evolution of the ratio between the areas of the CAWs ECC band and the PMMA CH-stretching band for the electrospun membranes containing C₄X halogenated CAWs (X = Cl, Br, I). (c) Time evolution of the ratio between the areas of the CAWs phenyl band and the PMMA CH-stretching band for the same membranes.

5

(a) Raman spectra of the electrospun membranes containing C₄X halogenated CAWs (X = Cl, Br, I) measured after heating at 90 °C for different times. The symbols * and ° indicate the position of the CAWs ECC and the secondary peak, respectively. In the top panel of (b), the time evolution of the ratio between the areas of the CAWs ECC band and the PMMA CH-stretching band for the electrospun membranes containing C₄X halogenated CAWs. In the bottom panel of (b), the evolution over time of the ratio between the areas of the secondary band and the PMMA CH-stretching band for the electrospun membranes containing C₄X halogenated CAWs.

6

Evolution of the CAWs ECC Raman bands areas for the electrospun membranes (a) and the powders (b) of the C₄X halogenated CAWs (X = Cl, Br, I) after exposure to light irradiation (532 nm) for different times. In (a), the ratio between areas of the CAWs ECC band and the PMMA CH-stretching band is considered. In (b), the area of the CAWs ECC band is considered.