Surface free energies of hydroxyapatite, fluorapatite and calcium fluoride

Abstract Surface free energies of hydroxyapatite, fluorapatite and calcium fluoride have been determined from contact angle measurements and compared with available literature data. Surface free energies Y s of the above materials against vacuum are all rather high in the range between 72 and 95 mJ.m −2 , whereas surface free energies Y sy of the materials in the presence of saturated vapor are fairly low between 28 and 48 mJ.m −2 . It is discussed that this difference is due to the presence of an adsorbed film originating from the liquid droplets employed in the measuring procedure. Literature data on the surface free energies of the above materials obtained by independent techniques and theories show an extremely large variation but nevertheless confirm the results on hydroxyapatite and fluorapatite.