Hemimicelle formation of semi-fluorocarbon chains at air-water interface: coarse-grained molecular dynamics study with an extension of the SPICA force field

HOS Yadav and S Harada and AT Kuo and S Urata and W Shinoda, MOLECULAR PHYSICS, 119, e1910355 (2021).

DOI: 10.1080/00268976.2021.1910355

The hemimicelle formation of long-chain semi-fluorocarbon diblocks at the air - water interface is studied using coarse-grained molecular dynamics simulations with a SPICA force field. From a series of simulations with varying the number of chains, the critical saturated size of a single micelle was predicted; its structural metrics such as the hexagonal chain packing order, density distribution, shape, mean diameter, and the orientation of the fluorinated (F-blocks) and hydrogenated segments (H-blocks) at the interface were found to be consistent with the previous experimental and atomistic simulation results. The diblock assemblies larger than the saturated size spontaneously split into multiple micelles separated by a metastable parallel phase (P-phase). This P-phase could be the reason for the non- coalescence and elastic behaviour of the hemimicelle assemblies. From the simulation with a low molecular arrangement area, the mechanism of the micelle formation of saturated sizes is illustrated. The results reveal that the mutual-phobicity and interfacial tension difference of F- and H-blocks with the water are sufficient to drive the self-assembly and can provide a significant thermodynamic stability to the micelles, where the increasing packing strain between the layer curvature and the planarizing water surface tension can determine the size of the saturated hemimicelles.

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