Experimental studies on formation, spreading and drying of inkjet drop of colloidal suspensions

In this study the dynamic characteristics of inkjet drops from generation to drying are investigated experimentally. The inkjet drops were made from suspensions of 2. μm polystyrene spheres dispersed in octanol or heptanol. The particle loading was 5-25. vol%. Bare glass surfaces and aldehyde coated surfaces were used as solid substrates. The result shows that the presence of particles in the liquid is insensitive to the drop generation characteristics and the particles are uniformly distributed within the drop. At the impact stage, the spreading characteristics are practically the same regardless of Weber number considered here and presence particles. At the capillary spreading stage, the drop of suspension in octanol shows the same behavior as the drop of pure octanol. The drying characteristics are quite different depending on the presence of particles and/or the wetting characteristics of the solid substrate. Especially, the drying stage is closely related with the spreading stage in the case of suspensions. On the small contact angle surface, particles are arranged parallel to the contact line during the capillary spreading stage. They become fully arranged in the crystalline form over the whole surface at the last stage of drying by the attractive surface tension force between partially immersed particles. On the large contact angle surface, particles move toward the rim by the outward flow. It is demonstrated that a crystalline monolayer of particles can be obtained by the inkjet technique.