Estudo de camadas mistas de ácidos fosfônicos

Abstract

Mixed self-assembled monolayers, bilayers and other structures of mixed phosphonic acids were investigated using scanning probe microscopy. Octadecylphosphonic acid (OPA - 18 carbons on the alkyl chain) was mixed in solution with octylphosphonic acid (OcPA - 8 carbons on the alkyl chain) and deposited onto mica substrates. Starting with pure OPA and up to 5 OPA to 10 OcPA ratio, monolayers were formed with no evidence of phase separation. It was seen that water has a crucial role on the morphology of the self-assembled structures and time evolution of both solutions and samples. OcPA dominant behavior is observed for high water content (both on solution and atmosphere). Mechanical and thermal resistance tests were performed on mixed and pure OPA or OcPA samples and revealed different properties that can be correlated to sample composition. The mixed monolayers are more deformable and less thick than the pure OPA monolayer. They also seem to lose material during annealing processes.