Preparation and characterization of coverage-controlled CaCO3 nanoparticles.

CaCO(3) nanoparticles were coated with stearate through a salt-exchange procedure. Their coverage had been successfully controlled by extraction in a Soxhlet apparatus, based on which a series of CaCO(3) nanoparticles were obtained with different surface coverages. They were characterized with thermogravimetric analysis, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. It was found that free stearate, intercalated stearate and chemically-bonded alkyl chains could be extracted sequentially with the Soxhlet apparatus. Thus, the coverages of CaCO(3) nanoparticles could be adjusted through carefully extracting the stearates from the CaCO(3) nanoparticles with multi-layer coverage. Spectroscopic results revealed that the alkyl chains tended to adopt an extended-chain conformation in the monolayer coverage as well as the bi-layer coverage, but less ordered conformation in partially-coated coverage and random orientation at the outmost surface of the coated nanoparticles.