Colloid-stabilised bubbles: particle expulsion triggered by external fields

Colloidal particles at fluid interfaces are used as precursors in many applications and for the manufacture of novel material, principally because they give outstanding stability to foams and emulsions. The stability is attributed to the large decrease in energy associated with the adsorption of a particle at a fluid-fluid interface, of the order of a million times the thermal energy kT for micrometric particles. In some applications, particle removal from fluid-fluid interfaces is needed, for example, when reactions use expensive colloidal particles, or to achieve phase separation. However, because of the strong attachment, particle removal from fluid-fluid interfaces is challenging. There is a need for new techniques for particle removal that can be controlled and precisely triggered. We study the destabilisation of particle-coated bubbles using two external fields: temperature and pressure. We choose particle-coated bubbles because they are the paradigm of stabilisation by particles. The destabilisation via temperature is triggered by cooling the external liquid. Cooling the external phase results in an enhanced gas diffusion. In this way, we obtained a steady delivery of all the adsorbed particles. The destabilisation via pressure is achieved by applying ultrasound waves to bubbles to drive them into ultrafast volumetric oscillations. These oscillations cause strong interfacial deformations capable of delivering particles in under a millisecond. The techniques developed to manipulate coated bubbles and trigger desorption are remotely triggered and scaleable, with relevance to various applications such as controlled particle delivery and recovery.Open Acces