3-D thermodynamic analysis of helical fiber-matrix interfacial wettability

In recent years, the advancement of material design has highlighted the importance of integrating bionic principles into the design process. Helical bionic fibers have garnered considerable attention in advanced materials. Unlike conventional fibers, 3-D helical fibers exhibit curvature-driven spatial topologies that enhance surface tension interactions with polymer matrices, thereby resulting in distinct fiber-matrix interfacial wetting. However, the absence of quantitative thermodynamic models has limited the ability to predict such interfacial phenomena. In this study, a novel 3-D thermodynamic model based on Gibbs free energy is proposed for the first time to assess the fiber-matrix wettability in pre-cured composites. This model explicitly captures the free-energy landscape associated with spatial topology, and uniquely elucidates previously unexplored mechanisms of wetting transitions between Cassie-Baxter and Wenzel states. By adjusting the spatial topology of individual fibers, the effects of the morphological evolution on the helical fiber-matrix interfacial wettability were systematically investigated, enabling the prediction of optimal helical configurations. The number of individual fibers has a dual effect on interfacial wetting, revealing the interplay between the helical fiber design and matrix wetting behaviour. These findings reveal a new mechanism by which fiber curvature and arrangement govern capillary-driven wetting and interfacial stability. This study integrates spatial topology with thermodynamic principles, offering insights into helical fiber design for improved matrix wettability. The proposed model not only enhances the understanding of fiber-matrix interactions, but also establishes a new theoretical framework to fabricate fiber-reinforced polymer composites (FRPs) with tailored interfacial properties.