Structural and thermodynamical characterisation of mixed binary Langmuir films of Perfluoroalkylalkanes

July 24, 2024

Perfluoroalkylalkanes (CnF2n+1CmH2m+1; FnHm) are diblock molecules formed by a hydrogenated (CH) and a perfluorinated (CF) blocks. Both are hydrophobic and mutually phobic. Despite lacking a polar group, these primitive surfactants form Langmuir films on water or hydrophilic substrates. The films comprise well-defined, hexagonally ordered, monodispersed hemimicelles, whose internal structure and size were recently elucidated by atomistic Molecular Dynamics simulations. The hemimicelles’ size depends on the CH and CF blocks lengths, due to geometrical packing constraints and the balance of in-plane interactions. Herein, we report thermodynamics and structural measurements (GIXD and GISAXS) results on monolayers composed by two FnHm with different CH block lengths (F8H14/F8H20). Results indicate that mixed films are not completely segregated (Figure 1). Indeed, the collapse of the mixed films occurs at an intermediate surface pressure between that of the pure cases and the parameter of the hexagonal lattice of hemimicelles is lower than that expected by Vergard's law. This suggests that cross-interactions are favoured over interactions between identical micelles or molecules. However, it is unclear if the film is formed by pure hemimicelles of two different sizes or mixed hemimicelles of intermediate sizes. This should be determined by AFM measurements on transferred mixed monolayers. These results are promising and shed light on the fundamental principles driving the self-assembling phenomenon and, ultimately, the prediction and control of the film morphology, envisaging their use as templates for surface nanopatterning and nanotechnology applications. The ongoing work focuses on AFM experiments to discern between the two proposed scenarios, as well as studying other binary films of FnHm with different CF and CH blocks lengths.

Authors in the community:

• 

  P

  Pedro Manuel Ribeiro Silva

  ist180790

AO - Author's Original

https://ecof.events.chemistry.pt

Conference Proceedings

Évora, Portugal

July 22, 2024

July 25, 2024

physical-sciences - Physical sciences

eng - English

Financing entity

Fundação para a Ciência e a Tecnologia

Title of the project, award or grant: PhD Grant

Visit project

Identifier for the funding entity: https://doi.org/10.13039/501100001871

Type of identifier of the funding entity: Crossref Funder

Number for the project, award or grant: SFRH/BD/149192/2019