Viscosity changes during film formation

Some water-thinned industrial paints exhibit anomalous viscosity changes during drying and therefore need careful control of air flow and humidity to ensure satisfactory film formation. 

Another method to measure flow properties after application involves the application of microdielectric measurements that have shown promise for characterizing fihn formation and cure (5,10-13). In this technique, the paint is applied to a thin, flat sensor connected to a frequency generator, an impedance analyzer and a computer. The sensor monitors the dielectric properties of the paint film at and near the interface between the sensor and the coating. The dielectric parameter used to estimate flow is called ion viscosity, but really is electrical resistivity rather than a trae viscosity. Ion viscosity is a measure of both the number and mobility of ions in a specimen. It is affected by changes in temperature, loss of solvent, crosslinking and other chemical reactions, formation of physical structure (such as by a thixotrope), ionic impurities, and ionic additives. The advantage of this technique is that measurements can be made in situ during application, flash, and the bake. 

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