Factors Influencing The Properties Of Hap Stabilized Pickering Emulsion

Pickering emulsion is stabilized by solid particles which has advantages such as excellent stability, low toxicity and thus could be used as a template to prepare multi-structure materials.Accordingly, it could be used in many fields, especially in the fields of biomaterials. Owing to its excellent biocompatibility, hydroxyapatite (Ca10(PO4)6(OH)2, HAp) has also been used as the stabilizer of Pickering emulsion, and materials with microsphere or porous structures could be obtained.In this paper,Hydroxyapatite (HAp) nanoparticles stabilized Pickering emulsions were fabricated with poly(L-lactic acid) dissolved in dichloromethane (CH2Cl2) solution as oil phase and HAp dispersed in distilled water as aqueous phase. Subsequently, Pickering emulsions were cured via in situ evaporation solvent method. Effect of PLLA concentrations, pH values, HAp concentrations, oil-water ratios, emulsification rates and times were studied on emulsion stability, emulsion type and cured materials, etc. Additionally, in order to obtain stable W/O type emulsion, stearic acid (Sa), KH-570 and PLLA were used to modify the surface chemical properties of HAp particles, further emulsions were prepared and cured using them as stabilizer.Surface chemical properties of HAp particles (grafting ratio, chemical properties), emulsion properties (emulsion stability, emulsion type, droplet morphology) as well as the cured materials (morphology, average pore size) were studied.The results indicated that emulsion stability increased with the increase of HAp concentration, emulsification rate and time; it is very stable when pH value of aqueous phase was adjusted to 10 with no droplet coalescence even stand for 120h. It is worth noting that stable W/O type emulsion was fabricated successfully using unmodified HAp particles as stabilizer. SEM results indicated that both microsphere and porous material were fabricated using emulsion stabilized by unmodified HAp nanoparticles,implying that both W/O and O/W emulsion type were obtained using unmodified HAp as the stabilizer.Stable W/O type emulsions were prepared using modified HAp which is attributed to the change of HAp surface chemical properties after being modified. FT-IR results indicated hydrophobicity groups (CH2 or CH3) were introduced on the surface of HAp particles, and thus stable W/O type emulsions were obtained with cured materials being porous structure.Additionally, the solvents of HAp surface modification played a very important role for its stabilized Pickering emulsion as well as the microstructure of cured materials. 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.