Ruptures in Mixed Monolayers Under Tension and Supercooling: Implications for Plant Nanobubbles

Mixed phospholipid and glycolipid monolayers likely coat the surfaces of pressurised gas nanobubbles within the hydraulic systems of plants. The lipid coatings bond to water under negative pressure and are thus stretched out of equilibrium. In this work, we have used molecular dynamics simulations to produce trajectories of a biologically relevant mixed monolayer, pulled at mild negative pressures (−1.5 to −4.5 MPa). Pore formation within the monolayer is observed at both 270 and 310 K, and proceeds as an activated process once the lipid tails fully transition from liquid condensed/liquid expanded coexistence to the liquid expanded phase. Pressure : area isotherms showed reduced surface pressure in the undercooled trajectory at all observed areas per lipid. Rayleigh-Plesset simulations were used to predict evolving nanobubble size using the calculated pressure : area isotherms as dynamic surface tensions. We confirm the existence of a critical radius with respect to runaway growth, above the homogeneous cavitation radius, coinciding with the area per lipid at which pore formation occurs.