Abstract
Interfacial undercooling in the complex solidification of colloidal suspensions is of significance and remains a puzzling problem. Two types of interfacial undercooling are supposed to be involved in the freezing of colloidal suspensions, i.e., solute constitutional supercooling (SCS) caused by additives in the solvent and particulate constitutional supercooling (PCS) caused by particles. However, quantitative identification of the interfacial undercooling in the solidification of colloidal suspensions, is still absent; thus, the question of which type of undercooling is dominant in this complex system remains unanswered. Here, we quantitatively measured the static and dynamic interface undercoolings of SCS and PCS in ideal and practical colloidal systems. We show that the interfacial undercooling primarily comes from SCS caused by the additives in the solvent, while PCS is minor. This finding implies that the thermodynamic effect of particles from the PCS is not the fundamental physical mechanism for pattern formation of cellular growth and lamellar structure in the solidification of colloidal suspensions, a general case of ice-templating method. Instead, the patterns in the ice-templating method can be controlled effectively by adjusting the additives.
Highlights
The question of which type of undercooling is dominant in the solidification of colloidal suspensions remains an unsolved but important issue
The thermodynamic effect of particles from the particulate constitutional supercooling (PCS) is not the fundamental physical mechanism for cellular growth and lamellar structure that are associated with the solidification of colloidal suspensions[48] which inevitably contains a large number of solutes, especially in the ice-templating method
We considered the puzzling phenomenon of interfacial undercoolings in the solidification of colloidal suspensions via quantitative measurements of solute constitutional supercooling (SCS) and particulate constitutional supercooling (PCS)
Summary
A1, a2, a3 and a4 are fitting parameters of П In this theory, the PCS comes from the depressed equilibrium melting point caused by the osmotic pressure of concentrated particles ahead of the freezing interface, which includes consolidated physical foundations[38]. By using the original fitting parameter for Z(φ), the theoretical PCS in the PS systems investigated here is approximately 10−9 K, shown as prediction A, which is too small to be detected Both these theoretical results and the present measurements demonstrated that the PCS is minor compared with the SCS. The interface position comparisons of the static SCS and PCS for alumina suspensions are shown in Fig. S3 (Supplementary Information). The concentrated layer of particles in front of the freezing interface scarcely causes dynamic PCS under different pulling speeds. The present experimental results clearly demonstrate that the effects of additives are dominant in the ice-templating process[12,13,17,48]
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