We have recently demonstrated a new methodology for producing an electrically conductive composite that exhibits thermoviscous properties consistent with that of an amorphous glass. The composite contains carbon nanofibers uniformly dispersed in an intermediate-Tg glass matrix with the aid of an organic surfactant. Hot-pressed bulk samples produced from such a mixture exhibit record-high enhancement of the electrical conductivity when compared to that of the matrix glass alone.
Motivated by previous work in the field of electronic devices formed from multimaterial fibers, we present here the results of incorporating such a composite into a thermally drawn fiber with a simple core/cladding architecture. Throughout the course of the investigation, we discovered that, due to the volatility of the glass phase and the reactivity of the carbon nanofibers, thermal drawing into fibers was most successful when the preform was constructed with the composite in a cold-pressed, powder form.
We also observed that the incorporation of carbon nanofibers altered the viscoelastic behavior of the glass matrix when transitioned to a melt state. In addition to its phenomenological effect on the thermal drawing process, the viscous flow of the composite plays a crucial role in the densification of the composite phase, and thereby its conductivity, in the final fiber. As such, we further present a strategy involving viscosity-matching between the composite and cladding glasses so as to maximize the continuity and electrical performance of the composite core in the thermally drawn fiber. We demonstrated this strategy by drawing a few combinations of different glasses in the cladding and composite.
Finally, we embedded a crystalline metal wire inside the conductive composite powder at the preform level and thermally drew the three-phase architecture into a continuous fiber. The resultant fiber exhibits boosted conductivity indicative of a continuous metallic phase fully surrounded by the composite glass, thereby demonstrating successful thermal-drawing of a multimaterial fiber with markedly varying thermoviscous properties across its material phases.