Deformation of block copolymer nanoparticles at air/water interfaces

Surface-active polymeric nanoparticles (NPs) are essential in novel emulsions, foams, and bioengineered membranes. We investigated the in situ state of deformation of soft NPs made of amphiphilic block copolymer at a dynamic surface of water using contrast-matched neutron reflectometry (NR). The core-forming polystyrene block was selectively deuterated to distinguish it from the polyethylene glycol brush, and NR was taken using subphases of mixed light and heavy water whose scattering length densities were matched to those of either the deuterated core or the bare brush ("contrast matching"). The data clearly show that both the areal densities of the core and brush components increase with the surface pressure and further reveal the change in core thickness due to deformation at high pressure. Furthermore, temperature-varied measurements verified that the glass transition of the core significantly affects the mode of NP deformation in response to surface tension (which exerts biaxial stretching on the spherical core). The results demonstrate unambiguous and insightful identification of the multi-component NP monolayer structure, thereby leading to future optimized design of surface-active NPs to meet tremendous needs regarding engineered interfaces.