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Using Rheology and Image Processing to Study the Effects of Cellulose Nanocrystal Sedimentation
Sadat Kamal Amit1, Virginia A Davis1
1Department of Chemical Engineering, Auburn University, 212 Ross Hall, Auburn, Alabama 36849, United States.
Langmuir : the ACS Journal of Surfaces and Colloids
|October 18, 2024
Summary
Sedimentation alters cellulose nanocrystal (CNC) dispersions, fractionating longer CNCs. This impacts rheology and self-assembly, showing how polydispersity changes affect nanomaterial mesogen behavior.
Area of Science:
- Colloidal science
- Materials science
- Nanotechnology
Background:
- Lyotropic liquid crystalline dispersions are sensitive to storage conditions.
- Understanding sedimentation effects is crucial for dispersion stability and application.
- Cellulose nanocrystals (CNCs) form complex mesophases.
Purpose of the Study:
- To investigate the impact of sedimentation-induced fractionation on CNC dispersion properties.
- To analyze changes in rheology and self-assembly after a single sedimentation step.
- To correlate CNC length fractionation with altered phase behavior and film morphology.
Main Methods:
- Sedimentation of aqueous CNC dispersions for one month.
- Separation of isotropic top and biphasic bottom phases.
- Atomic force microscopy (AFM) and intrinsic viscosity measurements (Fedor's equation).
- Rheological testing (storage modulus) and quantitative image processing of self-assembled films.
Main Results:
- Sedimentation led to preferential fractionation of longer CNCs into the bottom phase.
- The bottom phase exhibited a lower isotropic-biphasic transition concentration.
- Significant differences in storage modulus and self-assembled film structures (tactoids, chiral helices) were observed.
- Fractionation impacted the proportion of different self-assembly structures.
Conclusions:
- Even a single sedimentation step significantly alters CNC dispersion polydispersity.
- Changes in CNC length distribution profoundly affect rheological properties and self-assembly.
- Sedimentation-induced fractionation is a key factor influencing the behavior of nanomaterial mesogens.
