Aggregation‐Controlled Vat Dyeing of Meta‐Aramid Fibers: Mechanistic Insights and Suppression of Surface Dye Deposition

ABSTRACT Meta‐aramid fibers (MAFs) exhibit poor dyeability because their highly crystalline structure restricts dye diffusion and fixation. Herein, we investigate how the supramolecular aggregation of an anthraquinone‐based vat dye governs interfacial adsorption and dyeing behavior in carrier‐assisted MAF systems. Using spectroscopy, particle‐size analysis, quantum chemical calculations, and fiber structural characterization, a supramolecular structure‐activity relationship linking dye aggregation, interfacial adsorption, and dyeing performance is established. Controlled reduction generates stable leuco species that promote moderate aggregation and favorable dye‐fiber interactions, whereas excessive reduction, strong alkalinity, and carrier‐enhanced aggregation produce oversized assemblies that hinder diffusion and increase surface deposition. Structural analysis reveals a pronounced size mismatch between dye aggregates and the compact MAF microstructure, indicating that dye uptake is governed primarily by aggregate‐mediated interfacial adsorption rather than bulk diffusion. Aggregate size increased from 243 nm in the unreduced state to 291–564 nm after reduction, while the optimally reduced system achieved the highest color strength (K/S = 4.51) and fiber strength (7.1 cN). Temperature regulated the adsorption‐diffusion equilibrium, with 110°C–120°C providing optimal dyeing performance. These findings establish a mechanistic framework that links supramolecular aggregation, interfacial adsorption, and dye transport and provide a strategy for suppressing surface dye deposition in high‐performance fibers.