Surface geometry regulates heat-flux-dependent transition from nucleate to film boiling in nanoscale R1234yf liquid films

Nanoscale liquid film boiling plays a crucial role in thermal management of high heat flux devices; however, the regulation mechanism of surface geometry remains unclear. In this study, non-equilibrium molecular dynamics simulations are performed to investigate the boiling behavior of R1234yf nanofilms on smooth, pitted, and protruded copper surfaces under different heating conditions. Results reveal a strong heat-flux-dependent mechanism transition. At 400 K (nucleate boiling), the smooth surface exhibits the highest area-normalized heat flux (1.171 GW·m⁻²), because unconstrained lateral bubble coalescence enhances per-area energy conversion. At 500 K (film boiling), the pitted surface shows the highest (0.301 GW·m⁻²), as cavities retain liquid pockets that better utilize the enlarged area, whereas the protruded surface exhibits the lowest (0.240 GW·m⁻²) due to poor sidewall utilization under vapor-layer coverage. These findings reveal that surface geometry regulates boiling via area enlargement and topological perturbation, with the dominant pathway switching from the latter to the former as heating intensity increases. Further analysis shows that vibrational density of states (VDOS) matching primarily affects the initial energy transfer stage. A normalized frequency-domain overlap parameter S is introduced to quantify interfacial coupling, with values of 0.356 (protruded), 0.349 (smooth), and 0.347 (pitted), indicating slightly stronger coupling for protruded structures in the key frequency band (5–10 THz). Meanwhile, surface geometry regulates molecular desorption by modifying potential energy constraints, thereby controlling bubble nucleation and phase transition dynamics. Overall, the dominant role of surface geometry shifts from nucleation enhancement to vapor layer regulation with increasing thermal driving.