Evaluating the Stability of Cellulose Nanofiber Pickering Emulsions Using MRI and Relaxometry

Abstract

Magnetic resonance imaging (MRI) relaxometry and diffusion methods were used to highlight the instability mechanisms of oil-in-water Pickering emulsions stabilized by cellulose nanofibers (CNFs). Four different Pickering emulsions using different oils (n-dodecane and olive oil) and concentrations of CNFs (0.5 and 1.0 wt %) were systematically investigated over a period of one month after emulsification. The separation into a free oil, emulsion layer, and serum layer and the distribution of flocculated/coalesced oil droplets in several hundred micrometers were captured in MR images using fast low-angle shot (FLASH) and rapid acquisition with relaxation enhancement (RARE) sequences. The components of the Pickering emulsions (e.g., free oil, emulsion layer, oil droplets, and serum layer) were observable by different voxelwise relaxation times and apparent diffusion coefficients (ADCs) and reconstructing in the apparent T 1, T 2, and ADC maps. The mean T 1, T 2, and ADC of the free oil and serum layer corresponded well with MRI results for pure oils and water, respectively. Comparing the relaxation properties and translational diffusion coefficients of pure dodecane and olive oil obtained from NMR and MRI resulted in similar T 1 and ADC but significantly different T 2 depending on the sequence used. The diffusion coefficients of olive oil measured by NMR were much slower than dodecane. The ADC of the emulsion layer for dodecane emulsions did not correlate with the viscosity of the emulsions as the CNF concentration increased, suggesting the effects of restricted diffusion of oil/water molecules due to droplet packing.

Encapsulation of the Biocontrol Agent Beauveria bassiana in Cellulose Nanomaterial-Stabilized Pickering Emulsion for Foliar Application

“…79 It was reported that Ostwald ripening could occur due to the local packing structure of oil droplets and slow olive oil diffusion rate. 80 It was also reported that the entanglement of CNF between CNF-stabilized Pickering emulsion droplets caused flocculation as CNF concentration increased. 75 Surprisingly, the CNF-stabilized Pickering emulsion developed in this study did not show flocculation, coalescence, or Ostwald ripening, even at high CNF concentration.…”

“…Emulsified olive oil using fine-sized TEMPO-oxidized CNF could form a stable Pickering emulsion; however, droplet ripening was observed due to limited emulsification by CNF when CNF increased to 1 wt % or more in 7 days . It was reported that Ostwald ripening could occur due to the local packing structure of oil droplets and slow olive oil diffusion rate . It was also reported that the entanglement of CNF between CNF-stabilized Pickering emulsion droplets caused flocculation as CNF concentration increased .…”