Gel Development Using Cellulose Nanocrystals
Date
2020-06-18 0:00
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Abstract
Cellulose Nano Crystal (CNC) are naturally derived nanoparticles with a slender shape that own a remarkably high aspect ratio. Due to its mechanical properties with Young modulus in the range of 120-160 GPa and proven biocompatibility, CNC is an attractive nanoparticle for many applications. In the acid-based method of CNC production, the particles develop naturally negative charges, inducing an electrostatic repulsion between CNC particles and, consequently, when suspended in the water, a stable suspension. Upon introducing a coagulant, such as NaCl above a threshold value in the CNC suspension, phase separation happens where the system evolves toward gelation. The individual CNC particles, through aggregation, contribute to building a 3D gel fractal structure. Where a porous self-similar 3D structure spans in space, the design and synthesis of CNC-based gels are tunable and flexible. Mechanical properties of the hydrogels can also be tuned when CNC is coupled with polymers such as Polyvinyl alcohol (PVA).
Herein, the CNC-based gelation process is monitored, and the formed gels are characterized. The zeta potential and Dynamic Light Scattering are employed to measure the hydrodynamic radii and the surface charges of particles in different CNC-coagulant loadings. The gel morphology and CNC cluster fractal dimensions are recorded using Scanning Election Microscopy (SEM) and Transmission Electron Microscopy (TEM). The CNC-based gel behavior under large amplitude strains is also characterized by non-linear rheology. The gel collapse behavior and the self-healing dynamics of CNC-based gels are also quantified using fluorescence recovery after photobleaching (FRAP) analysis.
It is shown that CNCs can coagulate upon increasing the ionic strength of the medium, where the mechanical stability of the CNC-based gels (i.e., storage modulus), is an increasing function of NaCl and CNC concentration. Non-linearity of the gel was shown to be more influenced by NaCl concentration. The addition of PVA makes the CNC hydrogels mechanically robust, where two jumps in values of storage modulus as a function of frequency is observed. The jumps are attributed to the network formation between CNCs and CNC-polymer. Finally, the FRAP analysis using Confocal Laser Scanning Microscopy reveals that the CNC mobility in gel media is influenced by both CNC and NaCl concentration. The result of this study can be used in controlling CNC hydrogels properties, such as the gel self-healing and mechanical properties, and in assembling a 3-D hydrogel structure with CNC. In practice, the developed CNC-based hydrogels can be used in tissue engineering.
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Colloidal Science, Cellulose Nano Crystals (CNC), Polymer, Confocal laser microscopy (CLSM), Large-Amplitude Oscillatory Shear (LAOS), Microstructure Characterization, Hydrogels, Complex Fluids, Soft matter, Interfaces