Pickering/Non‐Pickering Emulsions of Nanostructured Sulfonated Lignin Derivatives
Nasim Ghavidel, Pedram Fatehi
Abstract
Abstract Sulfoethylated lignin (SEKL) polymeric surfactant and sulfoethylated lignin nanoparticles (N‐SEKL) with a size of 750±50 nm are produced by using a facile green process involving a solvent‐free reaction and acidification‐based fractionation. SEKL forms a liquid‐like conventional emulsion with low viscosity that has temporary stability (5 h) at pH 7. However, N‐SEKL forms a gel‐like, motionless, and ultra‐stable Pickering emulsion through a network of interactions between N‐SEKL particles, which creates steric hindrance among the oil droplets at pH 3. The deposition of SEKL and N‐SEKL on the oil surface is monitored by a using a quartz crystal microbalance. Experimentally, the formation of emulsions at pH 7 is found to be reversible owing to the low adsorption energy Δ E of SEKL on the oil droplet (Δ E ≈15 k B T ), which is determined with the help of three‐phase contact‐angle measurements. However, the high desorption energy (Δ E ≈6.0×10 5 k B T ) of N‐SEKL makes it irreversibly adsorb on the oil droplets. SEKL is too hydrophilic to attach to the oil interface (Δ E ≈0) and thus does not facilitate emulsion formation at pH 11. Therefore, it is feasible to apply SEKL for the formulation of Pickering or non‐Pickering emulsions in the form of nanoparticles or polymeric surfactants, depending on the targeted application.