Morphologies of conductive looped liquid lines inkjet-printed on substrate surfaces

We have investigated the morphologies of conductive liquid lines inkjet-printed onto homogeneous substrate. Various liquid lines, featured with closed to open loops at micrometer scale, can be formed by picoliter droplets composed of Ag nanoparticles solution. These lines with two-dimensional geometry in x and y directions are not simultaneously generated from the current printing algorithm and system. In theory, those microdroplets may undergo complex but fundamental phenomena such as slipping (de-pinning), replenishing and shrinking due to interfacial free energy during evaporation. In experiments, with the (printing) time and (interfacial) pressure difference, the printed uniform widths of the liquid lines from 10 picoliter droplets were spontaneously broken to be uneven after drying. Experimental results indicated that capillary flows within the lines were self-induced and oriented from the slipping segments to the pinning segments. As a result, morphological measurements showed relatively uniform thickness of the self-formations along the looped lines: no remarkable coffee-ring effect was found in both the line segments formed.