(522c) Interfacial Mechanical Properties of Similarly Charged Hydrophilic-Hydrophobic Colloidal Particles at the Air-Water Interface

Colloidal particles can be used to stabilize interfaces in applications such as emulsions and foams. The stabilization mechanism relies on the formation of a particle network, which is dependent on the interparticle interactions taking place. There are several ways of controlling how particle monolayers self-assemble by either tuning particle properties such as shape and chemistry, or bulk phase properties such as pH and ionic strength. Recent studies have shown that by using different types of particles simultaneously, i.e., particles with opposite charges and/or different surface chemistry (hydrophobic and hydrophilic) one can control the self-assembly process. Thus, mixed monolayer compositions can be in turn used to generate microstructures that range from crystalline to fractal-like to bi-continuous. Furthermore, synergism was shown to take place as mixed monolayers exhibited higher surface shear moduli when compared to the monolayers formed by either particle type. Nevertheless, not much is known about how these monolayers respond to dilational stresses, especially monolayers formed by particles of similar charges with different chemical nature. In this work we investigate the mechanical dilational response of the monolayers formed by not previously studied similarly charged particles with different surface chemistry at a number of mixed surface compositions via both dynamic extensional stresses via oscillatory drop rheology and extreme compression and expansions via a Langmuir Trough coupled with an inverted microscope. We analyze the interparticle interactions present in such systems, and the collapse mechanism for the resulting interfacial films under applied compressions. Our results show that one can modify the interfacial mechanical properties by tuning the surface composition of the mixed particle system, which affects the resulting balance between the capillary interactions and the dipolar repulsion through air.