Dissolved Cellulose Couples with Flow and Capillarity to Affect Ionic Liquid Crystallization: An X-ray Diffraction...

Area of Science:

• Materials Science
• Polymer Chemistry
• Physical Chemistry

Background:

• Cellulose, a semicrystalline polymer, exhibits limited solubility due to its hydrogen-bond network and solvophobic forces.
• Ionic liquids offer a non-derivatizing dissolution method for cellulose and can function as green solvents.
• Understanding ionic liquid behavior, particularly crystallization, is crucial for material processing.

Purpose of the Study:

• To investigate the crystallization behavior of 1-butyl-3-methylimidazolium chloride (bmimCl) in the presence of cellulose and varying water content.
• To determine how low-temperature treatments influence the structural transitions and conformations of bmimCl.
• To explore the role of cellulose and fluid flow dynamics in these phase transitions.

Main Methods:

• Mixtures of bmimCl, cellulose (1-3 wt%), and water (0-2.7 wt%) were subjected to repeated low-temperature cycles (-25 °C or -17 °C).
• Fourier-transform/dispersive Raman spectroscopy and wide-angle X-ray scattering were employed for structural analysis.
• Varying glass vessel diameters (2 mm and 9 mm) were used to study capillarity effects on fluid flow.

Main Results:

• Two distinct low-temperature treatments induced fluid flow with either laminar or turbulent character.
• Laminar flow promoted extended AA butyl chain conformation and orthorhombic (O) crystal structure.
• Turbulent flow favored GA conformation and monoclinic (M or M0) crystal structures, with cellulose potentially shifting towards extended conformations.

Conclusions:

• The flow dynamics (laminar vs. turbulent) significantly influence bmimCl crystallization and butyl chain conformation.
• Cellulose can indirectly affect bmimCl conformation, potentially through interactions or by influencing flow patterns.
• Findings are vital for controlling ionic liquid phase transitions, cellulose-ionic liquid interactions, and flow-induced material structuring across multiple length scales.