Influence of Dodecylamine Hydrochloride Adsorption on the Dissolution Kinetics of Hydroxyapatite
The adsorption of dodecylamine (DAC) onto hydroxyapatite (HAP) crystal surfaces and its influence on the dissolution rate behavior of HAP crystal suspensions have been studied. The sigmoidal nature of adsorption isotherms indicates that there was considerable cooperativity among the DAC molecules in the adsorbed state leading to patchwise adsorption of “islands” which could completely stop the dissolution from the HAP surface beneath them. This mechanism is consistent with the observation that there was an almost quantitative, simple inverse type relationship between the adsorption and the dissolution rate of HAP in an acidic media. At the highest DAC concentration and maximum DAC adsorption, there is a residual dissolution rate component which is about 15% of the zero DAC rate. It is suggested that this residual rate may be due to either incomplete adsorption because maximum adsorption occurs near the critical micelle concentration or due to the presence of another dissolution site(s) on the HAP crystal that is insensitive to rate inhibition by DAC.
KeywordsCritical Micelle Concentration Dissolution Rate Dissolution Kinetic Kink Site Dicalcium Phosphate Dihydrate
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