When a buoyant viscous drop is injected into a viscous fluid, it evolves to form a distended shape that detaches via the rapid formation and pinching of a neck. The effects of surfactants in altering this process are studied numerically. In the absence of surfactants, surface contraction is fastest in the vicinity of the neck. Thus, when surfactants are present, they accumulate there and alter the ensuing dynamics by reducing the surface tension that drives the contraction. The surface tension is described by a nonlinear surface equation of state that accounts for the maximum packing of surfactant in a monolayer. When surfactant adsorption-desorption is very slow, interfaces dilute significantly during drop expansion, and drops form necks which are only slightly perturbed in their dynamics from the surfactant-free case. When adsorption-desorption dynamics are comparable to the rate of expansion, drops thin to form a primary neck at low surfactant coverage, to form both primary and secondary necks at moderate coverages, form only a secondary neck at higher coverages, or fail to neck at elevated coverages. When surfactant adsorption-desorption kinetics are rapid, the surface remains in equilibrium with the surrounding solution, and drops behave like surfactant-free drops with a uniform surface tension. These arguments are used to construct a phase diagram of drop neck shapes as a function of surfactant coverage. A map of neck/no-neck thresholds is also constructed as a function of surfactant coverage and sorption dynamics, suggesting that drop detachment can be used as a means of characterizing surfactant dynamics.

The purposes of this work are scaled-up synthesis of silver nanowires (AgNWs), assessment of their growth mechanism and measurement of the rheological properties of nanowire suspensions suitable for screen printing conductive circuits. A polyol synthesis process was used. The morphology and microstructure at various stages of the process were characterized by scanning electron microscopy (SEM). Aqueous silver nanowire inks with dispersant and binder were formulated. The rheological behavior of the inks was characterized by Stress Sweep Step (SSS), Steady State Flow Step (SSFS), Frequency Sweep Step (FSS) and Peak Hold Step (PHS) with a parallel plate rheometer. Rheological measurements under conditions that mimic the screen printing process have been done on the conductive inks through the PHS test to assess viscoelastic properties induced by flow alignment of the wires. Finally, the effect of silver nanowires on the rheological behavior of the ink has been compared with the effect of silver three-dimensional (3D) nanoparticles (AgNPs). Since most of the available commercial silver inks suitable for screen printing process are non-aqueous solvent based, a contribution of this study is formulation of an environmentally benign water based nanowire ink.