Low gas permeability of particulate films slows down the aging of gas marbles

Including solid particles in liquid films drastically change their properties: "gas marbles" can resist overpressure and underpressure without deforming contrary to their pure liquid counterparts, also known as soap bubbles. Such gas marbles can therefore prove useful as gas containers able to support stresses. Yet, as their liquid counterparts, they can undergo gas transfer, which can reduce the scope of their applications. However, their permeability have never been characterized. In this paper, we measure the gas permeability of gas marbles through dedicated experiments. Our results show that particulate films are less permeable to gas than their pure liquid counterparts. We attribute this limited overall gas flux to the particles that reduce the surface area through which gas diffuses. Liquid droplets or bubbles are promising tools to encapsulate small volumes of gas or liquid which can prove useful in various fields. For example, spray drying, where fine powders are produced by the rapid drying of aerosol droplet, has become the method of choice for manufacturing large quantities of pharmaceuticals 1. In biology, aphids have developed an efficient way of handling their excreted honeydew droplet. By encapsulating them with a secreted powdery wax, they are able to convert the droplets into liquid marbles, that can be rapidly and efficiently moved 2. Such liquid marbles, which can be self-propelled by electric, magnetic or gradients of surface tension open a diversity of microfluidics applications 3,4. In this spirit and inspired by the way nature encapsulates liquids, a start-up came up with an innovative way of packaging drinkable water by encircling water in an edible elastic membrane made of algae. These large drops have the convenience of plastic bottles while limiting the environmental impact (see http://oohowater.com/). In all these applications, bubbles/droplets must be stabilized under coalescence and meet specific features such as high mobility or sensitivity to an external field to induce controlled delivery 5. As a common feature of sub-millimetric bubbles and drops is that they are governed by capil-larity, hence an efficient way to modify their global properties is to tune their surface properties. To do so, additives of different sizes have been successfully incorporated to bubbles and drops interfaces. This has been proven useful to modify the mechanical properties of additive laden interfaces. At the molecular scale, macromolecules (such as proteins) or surfactants adsorbed at the interface delimiting a bubble/drop lower its intern overpressure (Laplace pressure) by lowering the surface tension, while droplets