Effect of stearic acid modified HAp nanoparticles in different solvents on the properties of Pickering emulsions and HAp/PLLA composites

- HAp-E has higher activation ratio and grafting ratio compared with HAp-W and HAp-C.
- Pickering emulsion with higher stability was prepared using HAp-E as the stabilizer.
- Microstructures and pore size are different when HAp-W, HAp-C and HAp-E were used, respectively.

Stearic acid (Sa) was used to modify the surface properties of hydroxyapatite (HAp) in different solvents (water, ethanol or dichloromethane(CH2Cl2)). Effect of different solvents on the properties of HAp particles (activation ratio, grafting ratio, chemical properties), emulsion properties (emulsion stability, emulsion type, droplet morphology) as well as the cured materials (morphology, average pore size) were studied. FT-IR and XPS results confirmed the interaction occurred between stearic acid and HAp particles. Stable O/W and W/O type Pickering emulsions were prepared using unmodified and Sa modified HAp nanoparticles respectively, which indicated a catastrophic inversion of the Pickering emulsion happened possibly because of the enhanced hydrophobicity of HAp particles after surface modification. Porous materials with different structures and pore sizes were obtained using Pickering emulsion as the template via in situ evaporation solvent method. The results indicated the microstructures of cured samples are different form each other when HAp was surface modified in different solvents. HAp particles fabricated using ethanol as solvent has higher activation ratio and grafting ratio. Pickering emulsion with higher stability and cured porous materials with uniform morphology were obtained compared with samples prepared using water and CH2Cl2 as solvents. In conclusion, surface modification of HAp in different solvents played a very important role for its stabilized Pickering emulsion as well as the microstructure of cured samples. It is better to use ethanol as the solvent for Sa modified HAp particles, which could increase the stability of Pickering emulsion and obtain cured samples with uniform pore size.

Hydroxyapatite (HAp) nanoparticle stabilized Pickering emulsion was fabricated with poly(L-lactic acid) dissolved in dichloromethane (CH2Cl2) solution as oil phase and stearic acid (Sa) modified HAp in different solvents as particles emulsifier. Stable O/W and O/W type emulsions were prepared using unmodified and Sa modified HAp particles which confirmed the enhancement hydrophobicity of HAp particles after surface modification. SEM results indicated the microstructures of cured samples using emulsion as the template are different form each other when HAp was surface modified in different solvents. Pickering emulsion with higher stability and cured porous materials with uniform morphology were obtained using ethanol as the solvent. In conclusion, it is better to use ethanol as the solvent for Sa modified HAp particles, which could increase the stability of Pickering emulsion and obtain cured samples with uniform pore size.198