Surface modification of nanosized CaCO₃ with zircoaluminate coupling agent and palmitic acid was carried out. The surface structure of prepared samples was characterized by XRD, FTIR, contact angle and rheological behavior determination. It was confirmed by XRD that the modified nanosized CaCO₃ samples kept the same bulk structure as unmodified CaCO₃. According to the spectra of FTIR, it was inferred that chemical binding and physical adsorption between surface modifiers and the nanosized CaCO₃ had happened during the modification reaction. The surface free energies and polar components of the nanosized CaCO₃ modified with zircoaluminate coupling agent and palmitic acid were calculated by measuring contact angles for water and benzene on the palletized surfaces. It was found that the surface energies and polar components of the nanosized CaCO₃ modified with palmitic acid were lower than those of the nanosized CaCO₃ modified with zircoaluminate coupling agent, and the contact angle for water on the surfaces of unmodified nanosized CaCO₃, nanosized CaCO₃ modified with zircoaluminate coupling agent and the nanosized CaCO₃ modified with palmitic acid were 0°, 40° and 104°, respectively. It was confirmed that the nanosized CaCO₃ modified with palmitic acid was of intense lipophilicity, while the nanosized CaCO₃ modified with zircoaluminate coupling agent was of both hydrophilicity and lipophilicity. The rheological behavior of the suspensions composed of the unmodified and modified nanosized CaCO₃ with paraffin was compared. The results showed that the apparent viscosity, dynamic elastic storage modulus and viscid loss modulus of the modified nanosized CaCO₃ suspension were lower than those of the unmodified nanosized CaCO₃ suspension, while the loss factor was higher.

Key words: nanosized CaCO₃, modification, wettability, surface free energy, rheological behavior