Interrelations of structure, electric surface charge, and hydrophobicity of organo-mica and –montmorillonite, tailored with quaternary or primary amine cations. Preliminary study of pyrimethanil adsorption

Abstract

In this work, organo-montmorillonite (organo-Mt) and organo-synthetic mica (organo-mica), obtained by quaternary or primary amine cations (octadecyltrimethylammonium (ODTMA) or octadecyl-amine (ODA), respectively) exchanged at 50% and 100% of their respective CEC, were thoroughly characterized and tested for pyrimethanil uptake. The interlayer entrance of both surfactants for Mt loaded at 50% and 100% CEC indicated a close basal space (of around 1.5 and 1.8 nm, respectively). However, for synthetic mica (Na-Mica-4) the basal space shifted to higher values (3.5 and 3.9 nm and 4.7 and 5.0 nm, for ODTMA and ODA at 50% and 100% CEC, respectively) than those of organo-Mts, keeping the interlayer surface partially free for ODTMA-Mica-4 samples. Tg analysis revealed that the actual ODA loadings were around 40% and 80% for both clays and for ODTMA exchanged Mts, while the actual ODTMA loading for organo-mica samples did not exceed 10.6%. The decrease of negative zeta potential evidenced the presence of ODA or ODTMA at the external surfaces of organo-Mt, while the zeta potential curves for organo-mica samples described the system as a mixture of individual surfactants and Na-Mica-4 sample. Total specific surface area (TSSA) and contact angle (CA) measurements revealed a general hydrophobicity increment with the presence of both surfactants. Interrelations of these parameters point out the different affinity and steric hindrance of the polar head of both surfactants with the solid surfaces, which also conditioned pyrimethanil adsorption.