Effect of anionic surfactants on crystal growth of calcium hydrogen phosphate dihydrate

The effect of anionic surfactants (single-chained sodium n-dodecyl sulfate (SDS), asymmetric double-chained sodium bis(2-ethylhexyl) sulfosuccinate (AOT), and two-headed disodium oleoamido PEG-2 sulfosuccinate) on the crystallization process of calcium hydrogen phosphate dihydrate (DCPD) was investigated. All surfactants, depending on the type and actual concentration, showed inhibitory effects on the overall crystallization process. Below the critical micelle concentration (cmc), electrostatic adsorption, of surfactant anions on lateral crystal faces inhibited crystal growth and changed crystal morphology. Above the cmc, SDS and AOT caused phase changes; that is, a mixture of DCPD and octacalcium phosphate was formed.