The overestimated capability of fluid shear to induce secondary nucleation: an urgent call for diligently executed control experiments

Abstract

Many examples from the literature emphasize the important role of fluid shear in secondary nucleation. Moreover, they confidently state that fluid shear alone is surely capable of inducing secondary crystal formation. In this article, inspired by the most representative works in the field, four sets of experiments were designed to specifically isolate this fluid shear-induced secondary nucleation phenomenon. Great care was taken to meticulously conduct control experiments (avoiding attrition, but also initial breeding and primary nucleation), thus ensuring the envisioned isolation of secondary nucleation from fluid shear. Contrary to current conception in the community, no fluid shear-induced secondary nucleation could be observed in the conducted experiments, suggesting that its occurrence is much rarer than currently perceived. Based on these results, we also strongly encourage crystallization scientists to review their experimental procedures (control experiments) as to guarantee that secondary nucleation from fluid shear is indeed the acting nucleation phenomenon in their studies.