# Unraveling radial dependency effects in fiber thermal drawing

## TL;DR

This paper introduces a new model for fiber thermal drawing that accounts for radial velocity variations, enabling better prediction and control of fiber properties in complex multimaterial preforms for advanced applications.

## Contribution

It presents a versatile model that incorporates radial velocity effects in fiber drawing, improving upon the traditional cross-sectional average approach.

## Key findings

- Model predicts radial variations in electrical conductivity.
- Unraveled deformation of initial fiber lines during drawing.
- Dependence of properties on draw ratio and radial position.

## Abstract

Fiber-based devices with advanced functionalities are emerging as promising solutions for various applications in flexible electronics and bioengineering. Multimaterial thermal drawing, in particular, has attracted strong interest for its ability to generate fibers with complex architectures. Thus far, however, the understanding of its fluid dynamics has only been applied to single material preforms for which higher order effects, such as the radial dependency of the axial velocity, could be neglected. With complex multimaterial preforms, such effects must be taken into account, as they can affect the architecture and the functional properties of the resulting fiber device. Here, we propose a versatile model of the thermal drawing of fibers, which takes into account a radially varying axial velocity. Unlike the commonly used cross section averaged approach, our model is capable of predicting radial variations of functional properties caused by the deformation during drawing. This is demonstrated for two effects observed, namely, by unraveling the deformation of initially straight, transversal lines in the preform and the dependence on the draw ratio and radial position of the in-fiber electrical conductivity of polymer nanocomposites, an important class of materials for emerging fiber devices. This work sets a thus far missing theoretical and practical understanding of multimaterial fiber processing to better engineer advanced fibers and textiles for sensing, health care, robotics, or bioengineering applications.