Self-assembled nanodomains of semi-fluorinated alkanes on phospholipid monolayers

The incorporation of semi-fluorinated alkanes into phospholipid monolayers modulates their interfacial behavior and structural organization through fluorocarbon-hydrocarbon interactions. While prior studies demonstrated hierarchical self-assembly of a semi-fluorinated tetrablock in dipalmitoylphosphatidylcholine (DPPC) monolayers, it remains unclear how variations in the hydrocarbon chain length and molecular architecture of the semi-fluorinated alkane influence phase behavior and multilayer formation. We hypothesize that comparing diblocks and tetrablocks will reveal key structural determinants governing nanodomain formation and vertical stacking.

We studied Langmuir monolayers composed of DPPC mixed with semi-fluorinated diblocks C₁₀F₂₁C_mH_2m+1 (F10Hm, m = 16 and 20) and tetrablocks ((C₁₀F₂₁CH₂)(C_mH_2m+1)CH-CH(C₁₀F₂₁CH₂)(C_mH_2m+1) (di(F10Hm), m = 16 and 20). Surface pressure-area and surface potential-area isotherms were recorded, and fluorescence and atomic force microscopies were employed to examine domain morphology. Additionally, compression-expansion cycles were performed to assess the stability of the observed assemblies.

All (F-alkyl)alkanes formed nanodomains at low surface pressures, which reorganized into vertically stacked multilayers upon compression. However, while di(F10H16) forms flower-like hierarchical structures at the phase boundary of DPPC, driven by chain-length compatibility and dipolar interactions, di(F10H20) shows more diffuse assemblies. We analyze the difference in assembling behavior between the two derivatives and highlight the critical role of hydrocarbon segments' length and symmetry in governing vertical segregation and domain morphology, thus offering new insight into the design of responsive interfacial materials.