*Article* **In-Depth Rheological Characterization of Tungsten Sol-Gel Inks for Inkjet Printing**

**Urša Opara Krašovec 1, Tjaša Vidmar 1, Marta Klanjšek Gunde 2, Romana Cerc Korošec <sup>3</sup> and Lidija Slemenik Perše 4,\***


**Abstract:** The inkjet printing of the functional materials prepared by the sol-gel route is gaining the attention for the production of the variety of the applications not limited to the printed boards, displays, smart labels, smart packaging, sensors and solar cells. However, due to the gelation process associated with the changes from Newtonian to non-Newtonian fluid the inkjet printing of the sol-gel inks is extremely complex. In this study we reveal in-depth rheological characterization of the WO3 sols in which we simulate the conditions of the inkjet printing process at different temperature of the cartridge (20–60 ◦C) by analyzing the structural and rheological changes taking place during the gelation of the tungsten oxide (WO3) ink. The results provide the information on the stability of the sol and a better insight on the effects of the temperature on the gelation time. Moreover, the information on the temperature and the time window at which the inkjet printing of the sol-gel inks could be performed without clogging were obtained. The WO3 ink was stable in a beaker and exhibited Newtonian flow behavior at room temperature over 3 weeks, while the gelation time decreased exponentially with increasing temperature down to 0.55 h at 60 ◦C.

**Keywords:** rheology; inkjet printing; tungsten oxide; sol-gel
