Not yet reviewed by Pith; the record is open.

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.