Aurély Araminthea, Alae El Haitamia, Bence Kővágób, Fabrice Cousinc, Pablo Sanchez-Pugad, John Robert Peter Webstere, Philipp Gutfreundd, Ellen H. G. Backusb and Sophie Cantina
a CY Cergy Paris Université, LPPI F95000 Cergy, France,
b Institute of Physical Chemistry, Faculty of Chemistry, University of Vienna, Währinger Strasse 42, 1090 Vienna, Austria and University of Vienna, Vienna Doctoral School in Chemistry (DoSChem), Währinger Strasse 42, 1090 Vienna, Austria
c Laboratoire Léon Brillouin, Université Paris-Saclay, CEA-CNRS UMR 12, F-91191 Gif-sur-Yvette, France,
d Institut Laue-Langevin, 71 Avenue des Martyrs, 38000 Grenoble, France
: Langmuir 2026, 42, 12, 8548–8566
https://doi.org/10.1021/acs.langmuir.5c06510
Two-dimensional polymer blends confined at interfaces provide a powerful platform for tuning interfacial structure and properties. This work investigates blends composed of the amphiphilic triblock copolymer polyethylene oxide-polypropylene oxide-polyethylene oxide (PEO-PPO-PEO) and hydrophobic polydimethylsiloxane (PDMS) spread at the air-water interface to form Langmuir films, with the aim of understanding their miscibility and phase behavior under nanoconfinement.
A multiscale experimental approach combining surface pressure–area isotherms, Brewster angle microscopy, neutron reflectometry, and sum-frequency generation spectroscopy was used to construct a surface pressure–composition phase diagram revealing two distinct first-order phase transitions. This approach enabled the determination of both the lateral and vertical structure of the films and helped unravel polymer–polymer and polymer–water interactions.
While Brewster angle microscopy detected no lateral phase separation at any surface pressure or composition, neutron reflectometry played a key role by providing nanometer-resolved depth profiles of the films through contrast variation. These measurements revealed vertical segregation and structural transitions from homogeneous monolayers to bilayer configurations. In particular, due to its high hydrophobicity, PDMS segregates above the PEO-PPO-PEO layer in copolymer-rich blends upon compression, whereas PDMS-rich blends form bilayers whose thickness evolves with surface pressure. This analysis led to the identification of three distinct regions in the phase diagram.
Importantly, the blends can be stabilized as homogeneous monolayers over a wide range of compositions and surface pressures, due to strong interactions between PEO-PPO-PEO and water.
These findings provide new insights into polymer self-assembly at interfaces and highlight the unique capability of neutron reflectometry to resolve nanoscale vertical organization in complex interfacial systems, opening perspectives for the design of functional coatings.
Figure : Surface pressure – composition phase diagram of PEO-PPO-PEO/PDMS blends at the air-water interface (Langmuir films), showing two phase transitions that delimit three distinct regions, in which the film structure is schematically represented.
