  Phospholipid bilayers are a major component of the cell membrane that is in
contact with physiological electrolyte solutions including salt ions. The
effect of salt on the phospholipid bilayer mechanics is an active research area
due to its implications for cellular function and viability. In this manuscript
we utilize droplet interface bilayers(DIBs), a bilayer formed artificially
between two aqueous droplets, to unravel the bilayer formation and separation
mechanics with a combination of experiments and numerical modelling under the
effects of K$^+$, Na$^+$, Li$^+$, Ca$^{2+}$ and Mg$^{2+}$. Initially, we
measured the interfacial tension and the interfacial complex viscosity of lipid
monolayers at a flat oil-aqueous interface and show that both properties are
sensitive to salt concentration, ion size and valency. Subsequently, we
measured DIB formation rates and show that the characteristic bilayer formation
velocity scales with the ratio of the interfacial tension to the interfacial
viscosity. Next, we subjected the system to a step strain by separating the
drops in a stepwise manner. By tracking the evolution of the bilayer contact
angle and radius, we show that salt influences the bilayer separation mechanics
including the decay of the contact angle, the decay of the bilayer radius and
the corresponding relaxation time. Finally, we explain the salt effect on the
observed bilayer separation by means of a mathematical model comprising of the
Young-Laplace equation and an evolution equation.
