Roll‐to‐Roll (R2R) Processing of Large‐Area Flexible Piezoresistive Films with Magnetically Z‐Aligned Nickel Microcolumnar Morphology

Abstract Flexible pressure sensors are highly sought after for applications like rehabilitation healthcare, advanced wearable electronics, automotive safety, etc. This work demonstrates a scalable method for fabricating functional piezoresistive films using external magnetic fields to engineer the columnar microstructures. The continuous roll‐to‐roll processing involves directed self‐assembly of ferromagnetic Nickel particles within a flexible elastomer to achieve quasi 1–3 composites with low particle concentrations. In this process, polymer precursor‐microparticle system is subjected to a spatiotemporal evolution of temperature and magnetic fields simultaneously. Offline techniques like in‐plane alignment, through‐thickness light transmission, and viscosity evolution determine the influence of transient process conditions on final column morphology. Real‐time visualization in the X‐Y plane quantified by image analysis allowed tracking of morphological evolution where columns are formed separated by particle depletion zones leading to optical transparency. This characteristic is used to determine the kinetics of column formation via out‐of‐plane light transmission during Z‐alignment. Isothermal and non‐isothermal rheokinetics identified the gel point required to “freeze” the column structures. The scalability of the process is demonstrated by producing a 5.18 m long and 15.24 cm wide piezoresistive film with columns in thickness direction. The piezoresistive performance of produced anisotropic films is demonstrated under continuous uniaxial loading‐unloading cycles.