Development of water-in-oil pickering emulsions from sodium oleate surface-modified nano-hydroxyapatite

The stabilisation of water-in-oil (W/O) Pickering emulsions is still a challenge for the scientific community. In this work, sodium oleate (SO) surface modified nano-hydroxyapatite (n-HAp) particles were produced and tested as W/O stabilisers. The modified n-HAp particles presented a wettability dependent on the used SO content, switching from hydrophilic (initial state) to hydrophobic (one SO layer) and back to hydrophilic (two SO layers). The Pickering emulsions produced with the particles holding one SO layer (contact angle ~90 ◦) showed their tight adsorption at the water-oil interface (confocal analysis), and maintained the stability up to 15 days. Overall this work provides new developments in the field of W/O Pickering emulsions, a topic less studied than O/W, opening new avenues for several applications.This work was financially supported by: Base- UIDB/50020/2020 and Programmatic- UIDP/50020/2020 Funding of LSRE-LCM, funded by national funds through FCT/MCTES (PIDDAC), and Base Funding - UIDB/00690/2020 of CIMO - Centro de Investigação de Montanha - funded by national funds through FCT/MCTES (PIDDAC). Andreia Ribeiro acknowledges her PhD fellowship funded by Project NORTE-08-5369-FSE-000028, supported by N2020, under PT2020, through ESF. Authors thank Fluidinova S.A. for providing samples of nanoXIM-102Paste.