Morphology Modulation of Direct Inkjet Printing by Incorporating Polymers and Surfactants into a Sol-Gel Ink System

Many methods have been reported to prevent the nonuniformity of inkjet printing structures. Most of them depend on the balance of the capillary flow in the printing pattern during the evaporation of the solvent. However, as the relation of evaporation and capillary flow can obviously vary among different ink systems, it is difficult for a method to fit most of the situations. Therefore, it would be a promising way to eliminate any capillary flow before solvent evaporation so that morphology of the printing structure will not be affected by the evaporation behavior of the ink system. In this paper, a novel method of direct inkjet printing of a uniform metal oxide structure is reported. We introduce a polymer polyacrylamide and a surfactant FSO into a sol-gel ink system, and the new ink system can gel from the printing pattern edge to center as temperature increases because of the cross-linking of the polymer chains. By that means, transport of solute molecules and solvent molecules is limited. Meanwhile, the surfactant can ensure that the solute in the central liquid phase deposits uniformly by enhancing the Marangoni flow during the gelation process. The ZrO₂ film with uniform morphology was fabricated by drying and annealing the gelating film and afforded a leakage current density of 7.48 × 10^-7 A cm^-2 at 1 MV and a breakdown field of 1.9 MV cm^-1 at an annealing temperature of 250 °C.