Percolation and phase behavior in cellulose nanocrystal suspensions from nonlinear rheological analysis

Area of Science:

• Materials Science
• Rheology
• Colloid Science

Background:

• Surface charge significantly influences the behavior of cellulose nanocrystal (CNC) suspensions.
• Desulfation reduces CNC surface charge, increasing inter-particle attractive forces.
• Comparing sulfated and desulfated CNCs allows investigation of varying percolation and gel-point concentrations relative to phase transitions.

Purpose of the Study:

• To investigate the influence of surface charge on CNC suspension percolation, gel-point, and phase behavior.
• To correlate these properties with the nonlinear rheological response of CNC suspensions.
• To understand how nonlinear deformations affect the observed microstructure and material response.

Main Methods:

• Utilized rheological measurements, including linear viscoelasticity (LVE) and nonlinear rheology.
• Employed polarized optical microscopy to observe phase transitions.
• Compared sulfated and desulfated cellulose nanocrystal suspensions.

Main Results:

• Nonlinear rheology indicates a weakly percolated network at lower concentrations, irrespective of the gel-point's relation to phase transitions.
• Nonlinear material parameters are sensitive to phase and gelation behavior above the percolation threshold.
• Nonlinear response changes can occur at higher concentrations than static methods suggest, potentially due to microstructural distortion.

Conclusions:

• Surface charge critically impacts CNC suspension phase and gelation behavior.
• Nonlinear rheology provides insights into network formation and microstructural dynamics.
• Nonlinear deformations can alter the apparent microstructure, influencing the interpretation of suspension behavior.