Effect of geometry, wettability, and Janus amphiphilicity on the interfacial attachment strength of peanut-shaped solid particles in Pickering emulsions

Pickering emulsion are stabilized by solid particles adsorbed at the oil–water interface. The strength of particle interfacial attachment is governed by particle morphology and wettability. This study examines peanut-shaped particles and determine how their geometry and wettability affect particle attachment energy, first as homogeneous particles (uniform wettability) in comparison to the spherical case, and then as Janus particles with one hydrophobic and one hydrophilic face. Homogeneous peanut-shaped particles exhibit more negative attachment energies than a sphere with the same volume, indicating stronger interfacial attachment. To distinguish whether this enhanced attachment arises from the peanut’s larger interfacial contact area or from genuine geometric effects, we compare the peanut against four spherical controls: volume-matched, interfacial-area-matched (cross-section-matched), total-surface-area-matched, and two independent lobe spheres. The results reveal that the peanut’s advantage arises primarily from its larger interfacial contact area, with a smaller but consistent additional contribution from its continuous neck geometry. We then study Janus peanut-shaped particles, where the hydrophobic–hydrophilic boundary is defined by an angle \(\alpha \) , and the wettability contrast \(\beta \) quantifies the amount by which both face contact angles deviate equally from 90°. The angular position of the oil–water interface \({\alpha}_{v}\) is then obtained from the minimum free energy. Pinning occurs if, at the minimum energy state, the oil–water interface aligns with this Janus boundary ( \({\alpha}_{v}=\alpha \) ). For symmetric Janus particles ( \(\alpha \) = 90°), pinning occurs regardless of the wettability contrast between the two faces. However, for asymmetric particles ( \(\alpha \) ≠ 90°), pinning happens only when the wettability contrast exceeds a critical value \({\beta}_{c}\) . The more asymmetric the particle (the farther \(\alpha \) is from 90°), the larger \({\beta}_{c}\) must be. Importantly, peanut-shaped Janus particles require a higher \({\beta}_{c}\) than spherical Janus particles with the same \(\alpha \) . This shows that elongation not only strengthens attachment, but also requires a larger wettability contrast to achieve the pinned configuration. Together these two effects highlight peanut-shaped Janus particles as promising candidates for stronger interfacial attachment in Pickering emulsion applications.