Mapping MXene Alignment under Shear: An In Situ SAXS Study of Size-Dependent Orientation Dynamics.

Area of Science:

• Materials Science
• Nanotechnology
• Fluid Dynamics

Background:

• Controlling the macroscopic properties of 2D nanomaterials requires precise alignment in solution.
• Fundamental factors governing this alignment, especially for titanium carbide MXene (Ti3C2Tx) sheets, are not well understood.
• Understanding these factors is crucial for advancing solution-based processing of nanomaterials.

Purpose of the Study:

• To investigate the disorder-to-order transition states of Ti3C2Tx MXene sheets.
• To examine the influence of sheet size, concentration, and shear rate on MXene sheet orientation.
• To provide insights for fabricating ordered structures from MXene dispersions.

Main Methods:

• Investigated Ti3C2Tx MXene sheets in solution.
• Varied sheet sizes (large ~5 μm, small ~250 nm) and concentrations (up to 30 mg mL-1).
• Applied controlled shear rates and conducted fiber wet-spinning experiments.

Main Results:

• Sheet size significantly impacts alignment: large sheets align spontaneously at high concentrations, forming liquid crystalline phases.
• Small sheets require a minimum shear rate (~0.11 s-1) for alignment but lose order quickly, especially at low concentrations.
• Shear rate directly correlates with sheet alignment and the electrical conductivity of resultant fibers.

Conclusions:

• Sheet size, concentration, and shear rate are critical parameters for controlling Ti3C2Tx MXene alignment in solution.
• Tailoring these parameters enables the fabrication of ordered nanomaterial structures.
• Findings are vital for optimizing solution processing of MXenes and other anisotropic nanomaterials.