A Study On The Interaction Of Calcium Carbonate Nanoparticles With Surfactants

The in situ surface activation of unmodified CaCO₃ nanoparticles by interaction with a series of sodium carboxlayes with carbon number between C6 and C12 as well as dioctyl sodium sulphosuccinate (AOT) were studied and the impact of this on the stabilization and phase inversion of toluene-water emulsions were assessed. By using complementary experiments including measurement of particle Zeta potentials, adsorption isotherms of amphiphile, and relevant contact angles, the mechanism of this activation was revealed. The results show that the non-surface active CaCO₃ nanoparticles can be surface activated by interaction with sodium carboxylates and AOT, no matter they are surface active or not. Both the electrostatic interaction between the positive charges on particle surfaces and the negative charges of anionic amphiphile headgroups and the hydrophobic effect of the amphiphile results in monolayer adsorption of the amphiphile at the particle-water interface and transforms the particles from hydrophilic to partially hydrophobic such that particles become surface active and can stabilize O/W(1) emulsions and induce O/W(1)?W/O phase inversion, depending on the alkyl length of the carboxylate molecules. At high amphiphile concentration bilayer or hemi-micelle adsorption may occur at the particle/water surface due to chain-chain interaction of the amphiphile molecules, which turns particle back to strongly hydrophilic and to desorb from interface, and a second phase inversion, W/O?O/W(2) which is mainly stabilized by amphiphile, may occur, depending on the surface activity of the amphiphile. CaCO₃ nanoparticles can therefore be made good stabilizers of both O/W and W/O emulsions once surface activated by mixing with trace of suitable anionic amphiphile.In addition the ultrastable pesticide emulsions stabilized by in situ surface activated CaCO₃ and SiO₂ nanoparticles were tested using both a liquid pesticide, thiobencarb, and a solid pesticide, Beta cypermethrin which was dissolved in toluene, respectively. The results show that the CaCO₃ nanoparticles in situ surface activated by SDS can give ultra stabile O/W emilsions, but the droplet size is relatively big, ca, 100μm, whereas using SiO₂ nanoparticles in situ surface activated by CTAB and by adding less amount of nonionic surfactant TX-10, ultrastable O/W pesticide emilsions can be obtained with droplet size being as small as 10μm, which are also stable during hot and cool storage as well as diluting with standard hard water.