  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.
