Evidence for a fragmentation mechanism during the formation of calcium carbonate organo-nano-particles

13C NMR and Langmuir trough measurements have been used to monitor physico-chemical changes taking place during the carbonation of a calcium hydroxide in hexadecane suspension in the presence of calixarene and stearic acid as stabilizers. The initial reaction, before carbonation, is characterized by neutralization of the outer surface of the suspended calcium hydroxide particles by the surfactant species present. However, it is observed that after approximately 30% carbonation, particles close to the final size (ca. 6 nm diameter) are formed; these are then converted into calcium carbonate nano-particles without significant further change in size. It is therefore proposed that a fragmentation process is responsible for the rapid reduction in particle size. Inferences are made regarding the composition of the carbonate ‘core’ and the surfactant surface on the basis of the 13C NMR results.