Particles redistribution and structural defects development during ice templating

TL;DR

This paper investigates how suspension composition and electrostatic interactions influence defect formation during ice templating, revealing mechanisms behind structural defects and property variability in porous materials.

Contribution

It provides systematic in situ analysis of defect formation mechanisms, highlighting the impact of particle interactions and flocculation during ice templating.

Findings

Flocculation in intercrystal space destabilizes the solid/liquid interface.

Defect formation is linked to particle electrostatic interactions.

Structural defects cause variability in mechanical properties.

Abstract

The freezing of colloidal suspensions is encountered in many natural and engineering processes. It can be harnessed through a process known as ice templating, to produce porous materials and composites exhibiting unique functional properties. The phenomenon by itself appears simple: a solidification interface propagates through a colloidal suspension. We are nevertheless still far from a complete understanding and control of the phenomenon. Such lack of control is reflected in the very large scattering of mechanical properties reported for ice-templated ceramics, largely due to the formation of structural defects. Through systematic in situ investigations, we demonstrate here the role of the suspension composition and the role of particle-particle electrostatic interactions on defect formation during ice templating. Flocculation can occur in the intercrystal space, leading to a destabilisation of the solid/liquid interface triggering the growth of crystals perpendicular to the main ice growth direction. This mechanism largely contributes to the formation of structural defects and explains, to a large extent, the scattering of compressive strength values reported in the literature.