Key role of milling in the optimization of TiO₂ nanoinks

Abstract

Nanostructured films of TiO 2 are becoming more and more attractive as a consequence of their improved sensing properties. Screen printing represents an important low-cost alternative for the production of high-performance devices for the automotive industry. However, to obtain films with superior properties, the composition and each step of the ink production must be carefully controlled. Milling strongly influences the rheological properties of the ink and, as a consequence, the quality of the deposited film. The as-prepared ink was homogenized in a four steps-process with a three-roll mill, and the rheological properties at each intermediate stage were measured. The results showed the dramatic effect of the milling on the flow properties of the nanoink and suggested the importance of a careful control of this step. The rheological behavior of the inks was explained using the basic idea of the transient network theory (TNT) for physically cross-linked networks of polymer solutions. Only an optimized cycle of milling can assure the necessary reproducibility of the ink properties as well as their time stability.

Alternative route for the preparation of Zr-doped TiO2 layers for energy and environmental applications

“…Both systems denote high starting values of viscosity and an almost linear dependence on the shear rate, in addition a small variation is registered between the values of viscosity of the upward and downward curves. This behavior is a consequence of an highly structured and reticulated powderbinder network, resulting in a reduced effect of the shear applied by the rheometer on the microstructural changes of the ink [27]. On the other hand TZ1 presents a different trend characterized by a reduction in viscosity of about one order of magnitude in the first region of the curve and an increased gap between the two sweeps, signals of an augmented thixotropy of the system.…”

“…6). Shear rate values were chosen, accordingly to a standard procedure reported in literature, in order to simulate the actual conditions of the screen printing process [27].…”

Preparation and influence of highly concentrated screen-printing inks on the development and characteristics of thick-film varistors

“…The last parameter is the slope in the final stage of recovery (k) fitted from the last 200 points of the SST viscosity curve and is an indication of how far the system is from reaching equilibrium conditions after the stress is released; the larger the value of k, the farther away the system is from equilibrium conditions, while for k = 0 the line is perfectly horizontal and the system is in equilibrium. The parameters k was determined based on the report of Sanson et al [14]. Levelling has direct effects on the roughness of the thick film [19].…”

“…After the shear is released, the free and dangling chains from the macro-agglomerates produces more junctions between the macro-agglomerates and consequently form a structured network that causes an increase in the viscosity, which in turn results in a stiff structure of the film being formed. After deposition the levelling should be slow enough to eliminate mesh imprints and quick enough to eliminate the creeping defect [13][14][15]. The explanations are based on the transient network theory (TNT) developed by Tanaka and Edwards [15], the application of which to the screen-printing inks was demonstrated by Sanson et al [14].…”

“…After deposition the levelling should be slow enough to eliminate mesh imprints and quick enough to eliminate the creeping defect [13][14][15]. The explanations are based on the transient network theory (TNT) developed by Tanaka and Edwards [15], the application of which to the screen-printing inks was demonstrated by Sanson et al [14].…”