Figure . Schematic drawing of the formation of the compressed amphiphilic monolayer when a microbubble shrinks. The shrinking of a large bubble leads to a decrease in surface tension. Once a minimum in the average area occupied by each surfactant molecule is reached, the compressed amphiphile monolayer is formed. For the compressed amphiphile monolayer, the interfacial free energy for the nanobubble is dominated by the curvature free energy.