Next, we analyze the LE/LC domains based on the hydrophobic thickness parameter 𝑡 𝐶𝐸 . Figure demonstrates temperature dependence of the monolayer domains, similar to the images obtained from AFM experiments (SI, Figure ). At 293 K, the LE domains are substantially large and embedded in the LC phase, with more or less regular boundaries, indicating the existence of a line tension at the LE-LC interface. Increasing the temperature results in increasingly irregular boundaries and smaller domains, indicating a reduction in line tension. At 313 K and 324 K, the LE and LC domains appear to be mixed, consistent with the behavior near and above the critical point. The distributions 𝑃(𝑡 𝐶𝐸 ) of hydrophobic thickness parameter at different areas per lipid and temperatures in S400 (solid lines) and L3200 (dashed lines) systems are provided in Figure . At low 𝑎 𝐿 (53 𝐴 𝑜 2 ), 𝑡 𝐶𝐸 of the dominant LC phase peaks at 1.3 nm ≈ 𝑡 𝐶𝐸 𝑚𝑎𝑥 , which indicates complete extension of the lipid tails along the z-direction. Note that in the distributions, 𝑡 𝐶𝐸 takes larger values because the instantaneous values can be larger due to the stretching of beads about the harmonic bonds. With increase in 𝑎 𝐿 , the peaks heights decreases, developing a second peak corresponding to LE phase in the range 𝑡 𝐶𝐸 = 0.4 -0.5 𝑛𝑚. For the intermediate values of 𝑎 𝐿 = 64 -82𝐴 𝑜 2 , the distributions appear to be double-peaked, indicating the LE-LC coexistence. The complete LE phase at 𝑎 𝑙 ≥ 99 𝐴 𝑜 2 peaks at 𝑡 𝐶𝐸 ≈ 0.45 𝑛𝑚. As the temperature increases, double peak distributions of LE-LC coexistence become single peaked increasing the 𝑡 𝐶𝐸 values between 0.5 nm and 1 nm. The LC peak heights also decrease with temperature. Figure presents the fraction of the LE phase defined as 𝑞 𝐿𝐸 = 𝐴 𝐿𝐸 /𝐴 𝑀 , where 𝐴 𝐿𝐸 is the total area of the LE phase and 𝐴 𝑀 is the total area of the monolayer. While 𝑞 𝐿𝐸 seems to depend non-linearly on 𝑎 𝐿 , it increases with temperature more substantially in the LE-LC coexistence region.