Characterization Science of Manufactured Nanomaterials

Overview: 

Synthesis and Electrophoretic Seperation of Nanocrystalline Celluose

Cellulose is ubiquitous, and is utilized by a number of industries. However, to what extent nanocrystalline cellulose exists naturally is not known. The objective of this research project is to investigate the use of electrophoretic deposition as a means of separating cellulose nanoparticles from water.  In the scope of this work, the development and optimization of the synthesis of nanocrystalline cellulose were of particular importance. Two methods of synthesizing nanocrystalline cellulose (NCC) were investigated, mechanical fracturing and acid hydrolysis .The mechanical fracturing of micron sized material yielded a mixed sized sample.

Upon comparison of NCC particles from both methods, acid hydrolysis proved to be the optimum process due to the narrower distribution of NCC particles, higher yields, and stability.

More homogeneous nanocrystalline cellulose product resulted from hydrolysis with sulfuric acid. Further successful narrowing of particle size distribution was conducted via differential centrifugation.

Maximum yields of 65% were obtained upon analysis of the freeze dried NCC particles. Size readings of the resultant particles were measured using a transmission electron microscope (TEM) and the dynamic light scattering method (DLS). The lengths of the NCC whiskers ranged from 70 nm – 300 nm, and widths from 15 nm - 30nm. Zeta potential and electrophoretic mobility of the final suspension were also measured using a Malvern Zetasizer resulting in average values of -45.3 mV and -3.55 µmcm/Vs respectively. Investigation of the zeta potential at different pHs indicated the increased stability of NCC particles at higher pHs in water.

Conditions were determined for the long term suspension of  NCC particles in water, with stability increasing from low to neutral pHs. From these suspensions, Stable suspensions were then used in electrophoretic deposition experiments using pulsed Direct Current (DC).  Substrate surfaces were examined using Atomic Force Microscope to observe the surface coverage, Infrared Spectroscopy to detect the molecular structure of the deposited film, and Energy Dispersive Spectroscopy for the elemental analysis of the deposited film. The resulting spectra were synonymous with cellulose.

Both AFM and Kelvin Force microscopy were used for characterizations of films deposited on silicon and on silver-silicon nanocomposite substrates. The experiments confirm the stabilization and separations of NCC from aqueous fluids by EPD.