Abstract

The orientation of particles and fibers within polymer matrices plays a pivotal role that influences the multifunctional performance of composite materials. In particular, shear-stress alignment has emerged as a low-cost controllable strategy for tailoring filler orientation, especially in non-Newtonian polymer fluids, where complex rheological behavior governs microstructural properties. This review provides a comprehensive overview of the underlying physical mechanisms and theoretical models describing alignment under shear flow. Rather than emphasizing detailed parameterization, the discussion focuses on the general principles governing filler orientation in complex fluids. The review further highlights how shear-induced alignment enhances mechanical strength, electrical and thermal conductivity, piezoelectric response, and biological performance in advanced applications. Key challenges, such as achieving uniform alignment in complex geometries and scaling predictive frameworks, are critically examined. Unlike previous reviews that address either theoretical modeling or experimental processing in isolation, this work integrates both perspectives to present a unified understanding linking shear physics, filler orientation dynamics, and multifunctional performance. A systematic literature review was conducted following the PRISMA methodology, using multiple databases and the search equation: (“shear alignment” OR “particle orientation” OR “filler orientation”) AND “polymer composites.”. © 2025 Society of Plastics Engineers.