  Interfacial undercooling is of significant importance on microscopic pattern
formation in the solidification of colloidal suspensions. Two kinds of
interfacial undercooling are supposed to be involved in freezing colloidal
suspensions, i.e. solute constitutional supercooling (SCS) caused by additives
in the solvent and particulate constitutional supercooling (PCS) caused by
particles. However, quantitatively identification of the interfacial
undercooling of freezing colloidal suspensions is still absent and it is still
unknown which undercooling is dominant. The revealing of interfacial
undercooling is closely related to the design of ice-templating porous
materials. Based on quantitative experimental measurements, we show that the
interfacial undercooling mainly comes from SCS caused by the additives in the
solvent, while the PCS can be ignored. This finding implies that the PCS theory
is not the fundamental physical mechanism for patterning in the solidification
of colloidal suspensions. Instead, the patterns in ice-templating method can be
controlled effectively by adjusting the additives.
