(634d) Fabrication , Rheology and Microstructure of Cellulose Acetate Stabilized Pickering Emulsions with Internal Hydrophobic Moieties

Pickering emulsions offer a powerful platform to entrap functional hydrophobic moieties that can act as active ingredients (AI) for various applications as in drug delivery and agriculture. For instance, modern agriculture relies on the use of various agricultural AI many of which are hydrophobic. These AI are generally used in the form of emulsifiable concentrates which may contain large quantities of organic solvents and surfactants (J. Feng, et al., Nanoemulsions Formulation, Applications, and Characterization, Academic Press 2018). Herein we propose (T. Pirzada and M. Sohail, Adv. Funct. Mater. 32, 2270107 2022).a suitable environmental friendly alternative to emulsifiable concentrates entailing use of cellulose acetate (CA) nanoparticles (NP) as Pickering emulsifiers to produce surfactant free stable emulsions. CA is a widely used cellulose ester due to its ease of processing, biodegradability, and biocompatibility. The nanoparticles are produced from an easily scalable nanoprecipitation process (M. Sohail, T. Pirzada et al., ACS Sustain. Chem. Eng., 11,15178–15191, Oct. 2023) and are used to stabilize a model oil/water system. We probe the effect of CA concentration and the oil/water ratio on the emulsion rheology and stability. The emulsions display gel-like characteristics with both G’ and G’’ being independent of frequency (Fig 1a). Yield stress is measured by the elastic stress method wherein we observe that while increase in CA concentrations increases the yield stress, at lower concentrations the elastic stress curve flattens showing evidence of double yielding (Fig 1b). We attempt to explain these trends based on the emulsion droplet size and distribution along with the morphology of the CA NP, correlating the rheology data with microscopic evidence. We postulate that the presence of NP network strands between the droplets at higher CA concentration (Fig 1c) leads to the sharp distinct microstructure breakdown. While at lower CA concentrations, larger and broader emulsion droplets with insufficient NP linkages show a more discontinuous microstructure breakdown. On the application front we investigate the viability of the synthesized emulsions with two distinct model agricultural cargo including a hydrophobic nematicide, abamectin and a plant growth promoting microbe, Pseudomonas simiae, verifying their performance with a diverse spectrum of tests. While loading of abamectin can allow us control over its release profile thereby maintaining sustained release, loading of microbes can help enhance their viability and enable their incorporation into a shelf stable product. Thus, this project goes the complete wheel, quantifying the fundamental emulsion microstructure through rheology and demonstrating their utility as a suitable loading platform for various cargos.