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Contact‐mediated nucleation in melt emulsions investigated by rheo‐nuclear magnetic resonance
Author(s) -
Kaysan Gina,
Schork Nicolas,
Herberger Sabrina,
Guthausen Gisela,
Kind Matthias
Publication year - 2022
Publication title -
magnetic resonance in chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.483
H-Index - 72
eISSN - 1097-458X
pISSN - 0749-1581
DOI - 10.1002/mrc.5228
Subject(s) - nucleation , chemistry , shear rate , crystallization , subcooling , contact angle , shear (geology) , thermodynamics , shear flow , chemical physics , chemical engineering , rheology , materials science , composite material , organic chemistry , physics , engineering , boiling
Increasing the efficiency of disperse phase crystallization is of great interest for melt emulsion production as the fraction of solidified droplets determines product quality and stability. Nucleation events must appear within every single one of the μm‐sized droplets for solidification. Therefore, primary crystallization requires high subcooling and is, thus, time and energy consuming. Contact‐mediated nucleation is a mechanism for intensifying the crystallization process. It is defined as the successful nucleation of a subcooled liquid droplet induced by contact with an already crystallized droplet. We investigated contact‐mediated nucleation under shear flow conditions up to shear rates of 457 s −1 for a quantitative assessment of this mechanism. Rheo‐nuclear magnetic resonance was successfully used for the time‐resolved determination of the solids fraction of the dispersed phase of melt emulsions upon contact‐mediated nucleation events. The measurements were carried out in a dedicated Taylor–Couette cell. The efficiency of contact‐mediated nucleation λ sec decreased with increasing shear rate, whereas the effective second order kinetic constant k coll , effincreased approximately linearly at small shear rates and showed a linear decrease for shear rates higher than about 200 s −1 . These findings are in accordance with coalescence theory. Thus, the nucleation rate is optimal at specific flow conditions. There are limitations for successful inoculation at a low shear rate because of rare contact events and at a high shear rate due to too short contact time.