| Ink jet printing is a cheap, effective method for printing photo-quality images. Because current technology only allows printer throughputs of about one page per minute when printing the best quality images, one focus of improvement involves reducing the time it takes to print high-quality photo images. The speed of printing such images is not limited by the printing mechanism but by print defects that arise from interactions between drops resting on the porous medium. One such problem commonly encountered in high-speed printing is ink-drop coalescence, a loss of control over dye distribution that results in image mottling. Addition of surfactants to the dye vehicle (ink) helps retard coalescence but not in a manner consistent with the surface tension reduction provided by each. Instead, the performance appears to correlate with the rate of diffusive surfactant transport to the air-liquid interface. However, surfactant adsorption dynamics are not well understood at the concentrations employed in inks due the presence of surfactant self-aggregates (e.g., micelles). One goal of this study is to examine how surfactant chemistry, surfactant concentration, and micelle transport affect interfacial adsorption dynamics in systems relevant to ink jet printing. Because coalescence is a consequence of interactions between adjacent drops, it is useful to understand how surfactant addition affects drop spreading and absorption on commercial glossy photographic papers. To this end, the simultaneous spreading and penetration of surfactant solutions is investigated. The existence of phenomena such as transitions from non-wet to wetting drop regimes and spreading driven by surface tension reduction and surface tension gradients is observed. An energy-based model that allows prediction of the transient behavior of surfactant laden drops on porous media is derived and applied to real systems with the goal of better understanding the transport mechanics driving spreading and absorption. |
