Hollow fiber membrane governed microjet flow regime for confined crystallization of large‐sized crystal aggregates

Abstract Confined crystallization can realize controllable nucleation and growth of crystals with targeted morphologies in a restricted region. Here, we achieved confined reactive crystallization within a novel micro columnar jet flow regime constructed by the hollow fiber membrane. The interface of the jet flow corresponds as the restricted region for reactive crystallization, and the large‐sized calcium carbonate (CaCO 3 ) crystals aggregates with millimeter length can ordered and self‐assembly grow along the boundary of this region. Formation mechanism of the jet flow was systematically investigated by real‐time observation and force analysis. The detected detachment‐regrowth cycle during the experiments furtherly uncovered the potential for continuous operation. Linear (diameter: 0.12–0.3 mm; length: 1.5–3.1 mm) and lamellar crystals (thickness of 200–300 nm and average area of 0.21 mm 2 ) were obtained by effectively manipulating the diameter and effective length of jet flow.