Cheerios effect

Abstract: Solid particles floating at a liquid interface exhibit a long-ranged attraction mediated by surface tension. In the absence of bulk elasticity, this is the dominant lateral interaction of mechanical origin. Here, we show that an analogous long-range interaction occurs between adjacent droplets on solid substrates, which crucially relies on a combination of capillarity and bulk elasticity. We experimentally observe the interaction between droplets on soft gels and provide a theoretical framework that quantitatively predicts the interaction force between the droplets. Remarkably, we find that, although on thick substrates the interaction is purely attractive and leads to drop–drop coalescence, for relatively thin substrates a short-range repulsion occurs, which prevents the two drops from coming into direct contact. This versatile interaction is the liquid-on-solid analog of the “Cheerios effect.” The effect will strongly influence the condensation and coarsening of drops on soft polymer films, and has potential implications for colloidal assembly and mechanobiology.

Abstract: We demonstrate the transport and positioning of water droplets on macro-patterned lubricant-impregnated surfaces. The macro-patterning produces menisci features in the impregnating liquid layer which interact with a droplet via a capillary mechanism similar to the Cheerios effect. These interactions control the droplet motion and positioning on an otherwise completely slippery surface. We present experimental results using a V-shape channel geometry as a model system. The interaction between deformations on the lubricant layer induced by the droplet and the underlying V-shape geometry leads to both local and global equilibrium positions for the droplet within the channel. We present a mathematical model to quantify the transition from local equilibrium states to the global equilibrium state and show that the latter can be described on the basis of a force balance along the apparent contact line of the droplet. We highlight possible applications where lubricated macro-patterned surfaces can be used to control the motion and localisation of droplets.

Abstract: Objects that float at the interface between a liquid and a gas interact because of interfacial deformation and the effect of gravity. We highlight the crucial role of buoyancy in this interaction, which, for small particles, prevails over the capillary suction that is often assumed to be the dominant effect. We emphasize this point using a simple classroom demonstration, and then derive the physical conditions leading to mutual attraction or repulsion. We also quantify the force of interaction in some particular instances and present a simple dynamical model of this interaction. The results obtained from this model are then validated by comparison to experimental results for the mutual attraction of two identical spherical particles. We conclude by looking at some of the applications of the effect that can be found in the natural and manmade worlds.

Abstract: Oral drug administration has an important role in medical treatment. Attempts to develop drug microcarriers with desired features for extended duration and improved absorption is highly sought. Herein, inspired by the physical phenomenon of the Cheerios effect, a novel microfluidic electrospray microbubble carrier is presented that can suspend and actively adhere to the stomach for durable oral delivery. Compared with conventional fabrication methods, the present strategy shows stability and controllability of the product. Benefiting from their uniform hollow structure, the resultant microbubbles present the same behavior of the Cheerios and can float in the gastric juice, adhere and remain to the stomach wall, which thus enhance the duration and absorption of the loaded drugs. Based on these, it is demonstrated as a proof of concept that the dexamethasone-loaded hollow microbubbles can be applied to oral administration and remain suspended and adhered to the stomach of murine for more than 1 d, showing good therapeutic effect in treating lupus erythematosus. Thus, it is believed that the microbubbles floating system will find important values in long-term oral administration.