The Role of Annealing Treatment on the Morphological Evolution and Swelling of ZnPc Layer on A QCM Sensor

Morphological evolution and swelling were observed in the zinc phthalocyanine (ZnPc) layer on a quartz crystal microbalance (QCM) sensor treated with annealing. The morphology affects the swelling during analyte injection. The swelling effect can shorten the QCM sensor recovery time. The ZnPc layer was deposited on the surface of the polystyrene/QCM by evaporation technique. The annealing process was conducted for 1 h at 3 temperature variations: 100, 150, and 220 °C. The swelling experiments were carried out by injecting PBS and Tris-HCl solution into the layer. The surface morphology characterization of ZnPc was observed using an SEM/EDX before and after swelling. The morphological evolution from the network into fibers change to disentangled of the ZnPc molecular chain and broke into a shorter fiber. The diffractogram revealed a monoclinic phase for the samples annealed at 100 and 150 °C. On the other hand, the sample annealed at 220 °C showed a triclinic phase. The formation of ZnPc crystal confirms the disordering structure leading to the morphology change. Further, the ZnPc fibers swell after the injection of PBS and Tris-HCl. Tris-HCl injection at high temperature annealing (220 °C) resulted in fiber tattering. Investigations on diffusion mechanisms were conducted by measuring the change in frequency. The ionic strength of the solutions controlled the diffusion. The PBS diffuses faster than the Tris-HCl into the ZnPc layer.