Surface modification of hydroxyapatite. Part I. Dodecyl alcohol.

The influence of esterification reactions on the surface chemistry and colloid stability of hydroxyapatite (HAP) was studied by aging nanophase HAP in dodecyl alcohol at elevated temperatures (115 degrees C and 190 degrees C). The esterified HAP particles were characterized by X-ray diffraction, transmission electron microscopy, diffuse reflectance infra-red Fourier transform spectroscopy (DRIFTS), thermal gravimetric analysis, sedimentation time studies, and electrophoretic mobility (mu) measurements in water and ethyl alcohol. DRIFTS analysis revealed that the HAP surface was modified by dodecyl groups based on the appearance of C-H stretch vibrational modes at 2962, 2930, and 2860cm(-1). Dodecyl alcohol modified HAP exhibited a larger TGA mass loss upon heating (up to 4.8%) compared to untreated HAP (2.5-3.2wt%). Sedimentation studies revealed the following stability trends: HAP dispersed in water was approximately the same as esterified HAP in water (a few hours) <HAP in ethyl alcohol (1-7 days) << esterified HAP in ethyl alcohol (115 degrees C, 70h; 190 degrees C, over 65 days). The differences in colloid stability are attributed to Lewis acid/base interactions for the untreated HAP and steric stabilization effects for the nanophase HAP with surface dodecyl groups.