Growing a particle-stabilized aqueous foam

Hypothesis: Certain gas-filled colloidal particles expand upon heating. If such particles are surface-active and stabilize aqueous foams, do the foams grow with temperature as particles expand?

Experiments: Aqueous foams were stabilized with hollow micro-spherical particles that are partially wetted by water and grow upon heating. Foams were prepared using two different approaches, both of which led to their growth. In the first, water was heated to various temperatures (40–80 °C) and aerated in the presence of the particles. In the second, water at room temperature was aerated in the presence of the particles and then heated to various temperatures (40–85 °C).

Findings: Regardless of the method, foam volume began to increase on raising the temperature to the onset of particle growth (60 °C) as expected and increased with increasing temperature. However, placing the particles on hot water (80 °C) and waiting for several minutes (≤2.5) before aeration resulted in more growth. The volume of foam after growth remained unchanged after cooling for over six months, giving rise to ultra-stable foams.