Tailoring the microstructure of lamellar Ti3C2Tx MXene aerogel by compressive straining

Aerogels are attracting increasing interest due to their functional properties, such as light-weight and high porosity, which make them promising materials for energy storage and advanced composites. Compressive deformation allows the nano- and micro- structure of lamellar freeze-cast aerogels to be tailored towards the aforementioned applications, where a 3D nanostructure of closely spaced, aligned sheets is desired. Quantitatively characterising their microstructural evolution during compression is needed to allow optimisation of manufacturing, understand in-service structural changes, and determine how aerogel structure relates to functional properties. Herein we have developed methods to quantitatively analyse lamellar aerogel domains, sheet spacing and sheet orientation in 3D and to track their evolution as a function of increasing compression through synchrotron phase contrast X-ray micro computed tomography (μCT). The as-cast domains are predominantly aligned with the freezing direction with random orientation in the orthogonal plane. Generally the sheets rotate towards flat and their spacing narrows progressively with increasing compression with negligible lateral strain (zero Poisson’s ratio). This is with the exception of sheets close to parallel with the loading direction (Z), which maintain their orientation and sheet spacing until ~60% compression, beyond which they exhibit buckling. These data suggest that a single-domain, fully aligned as-cast aerogel is not necessary to produce a post-compression aligned lamellar structure and indicate how the spacing can be tailored as a function of compressive strain. The analysis methods presented herein are applicable to optimising freeze-casting process and quantifying lamellar micro-domain structures generally.