Oil-In-Water or Water-In-Oil Pickering Emulsion: Role of Lignocellulose-Based Nanoparticle Wettability and Geometry.

Abstract

Pickering emulsion behavior is governed by particle wettability, surface chemistry, and geometry, yet stabilization mechanisms for renewable lignocellulosic nanoparticles remain unclear, limiting surfactant‑free design. This study tests hypothesis that tuning the surface energy of lignin nanoparticles shifts emulsion type from oil-in-water to water in oil, while combining spherical and fibrillar particles achieves high emulsification capacity and stability through synergy. Influence of spherical lignin nanoparticles (LNPs) and lignin‑containing cellulose nanofibrils (LCNFs) on emulsion type, droplet size, emulsification capacity, and stability is investigated by optical microscopy, dynamic light scattering, conductivity, and field-emission scanning electron microscopy (FESEM). Unmodified kraft LNPs (K-LNPs; water contact angle in oil θ o/w = 81.6°) form oil-in-water emulsions, whereas lauric-acid-esterified LNPs (LA-LNPs; θ o/w = 106.4°) favor water-in-oil emulsions, confirming wettability-controlled emulsion type. LNPs generated smaller droplets, but LCNFs stabilized larger oil fractions at lower dosages, demonstrating fibrillar-geometry efficiency. LCNFs outperform CNFs, emphasizing residual lignin benefits. Synergistic effects of LNPs and LCNFs enhance stability at substantially lower individual concentrations (0.01 wt% LCNFs and 0.02 wt% LNPs) when added together. FESEM reveals that LNPs assembly at oil-water interface, while LCNFs entrap and bridge droplets forming stabilizing network. Tunable geometry and wettability of lignocellulosic nanoparticles enable rational, sustainable Pickering emulsions for diverse applications.

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