Mechanism of High Surface Pressure Generation in Water-Spread Block Copolymer Micelle Films

The development of a first-of-its-kind polymer lung surfactant (PLS) therapy requires a biocompatible material capable of effectively reducing high air-water surface tension. A promising class of materials for this application consists of block copolymer (BCP) micelles with a highly hydrophobic, rigid core block and an amphiphilic, hydrophilic poly(ethylene glycol) (PEG) corona. These PLS materials demonstrate a remarkable ability to reduce air-water surface tension to nearly 0 mN/m. This behavior is particularly surprising, as BCP micelles are stable in aqueous suspension but strongly anchor to the air-water interface, even under high compression, when spread onto it. The results presented in this talk indicate that the micelle film is almost entirely submerged in the water subphase. The substantial increase in surface pressure is attributed to the buildup of osmotic pressure within the PEG corona layer in the subphase. At low surface pressure, the micelle films exhibit hexagonal symmetry, but this ordering is disturbed by film undulations as the monolayer is compressed beyond its packing limit. At very high surface pressure, the monolayer collapses, coinciding with increased surface roughness and the appearance of wrinkling features. These fundamental characterizations provide valuable insights into the air-water interfacial behavior of water-spread BCP micelles, which are essential for advancing this potentially life-saving technology.