Surface modification of CaCO3 nanoparticles by alkylbenzene sulfonic acid surfactant

Surface modification of CaCO3 nanoparticles by two kinds of anionic surfactants, such as linear alkylbenzene sulfonic acid (LABSA) and branched alkylbenzene sulfonic acid (BABSA), was investigated by a quartz crystal microbalance with dissipation monitoring (QCM-D) measurement and contact angle analysis. Basically, both surfactant systems showed the same trend in the measurements of QCM-D and contact angle. Contact angle measurement has shown that CaCO3 surface becomes more hydrophobic as surfactant concentration increases. However, the use of excess surfactant has led to the reverse change in surface property of CaCO3 particles from hydrophobic to hydrophilic. QCM-D measurement using a quartz crystal coated with CaCO3 revealed that monolayer adsorption of surfactant molecules at the particle water interface occurs in a low surfactant concentration region and the thickness of forming molecular layers was found to be in the order of the length of a single surfactant molecule. On the other hand, both mass of adsorbed surfactant molecules and the thickness of molecular layers indicated bilayer adsorption of surfactant molecules in a high surfactant concentration region, which evidently resulted in an increase in hydrophilicity of CaCO3 surface. Visual floating test has shown a good agreement with measurements of contact angle and QCM-D. (C) 2014 Elsevier B.V. All rights reserved.