**4.3 Effect of temperature**

 Foam is a metastable state system which goes through coarsening and rupturing when the liquid drains from the lamella and plateau borders [58]. An improved stability foam could be achieved when the viscosity of foaming solution is increased [59]. The increase in temperature causes thermal thinning of foam film which quickly drains liquid leaving behind thin lamella [60]. **Figure 6** shows the foams generated using a mixing approach at two different temperatures (20 and 50°C). It is clear that the foam texture at high temperature is relatively coarser and it has a wide range of bubble size distribution whereas at low temperature, uniform and fine textured foam is noticed. Hence, when the temperature is increased, the rate of foam lamella drainage and coalescence of bubbles are quick, resulting in a significant decrease in foam apparent viscosity [8, 60–62]. High fluctuations in temperature may form holes in the lamella which would increase both bubble coalescence and lamella rupturing [62]. Hence, the rising temperature causes significant reduction in the apparent viscosity of supercritical CO2 foam [8, 63].
