New Collapse Mechanism of Colloidal Particle Monolayers via Depletion Pressure: Formation of Large-Area Particle Multilayers at the Air−Water Interface

Various collapse mechanisms of colloidal particle layers (e.g., wrinkling, flipping, folding, etc.) at a fluid−fluid interface have been reported, but formation of particle multilayers with large areas has not been observed yet. With the help of depletion pressure that provides a resistance to out-of-plane deformations of a colloidal particle monolayer, we report a new collapse mechanism of the particle monolayer at an air−water interface, which forms large-area particle multilayers with more than two layers. Furthermore, by adjusting the strength of the depletion pressure or the compression distance at the state of collapse, we also observe that the number of layers of particle multilayers varies significantly, and these results agree well with classical theories for thin elastic films floating atop water.