(660i) Lattice Boltzmann Simulations of Foam Drainage and Oscillation and Comparison with Experiments on Microfluidically Generated Foams

The bubble coalescence and free drainage of a two dimensional (wet) foam is modelled using a 2D mesoscopic Lattice Boltzmann method. The disjoining pressure between the bubbles, which controls the coalescence, is implemented in the LBM by using repulsive long-range and frustrated short range pseudo-potentials. The disjoining pressure as a function of the film thickness separating the bubbles is determined for different pseudo-potentials. Simulations of the drainage rate are undertaken for different area fractions of the foam (textures), and different disjoining pressure isotherms (pseudopotentials) and capture step-wise profiles of the drainage rate. LBM simulations of the oscillatory response of the foam are also included to detail the foam rheology and fitted to a Herschel-Bulkley model.

Furthermore, the LBM simulations are compared to free drainage experiments of foams. A microfluidic cell which uses flow focusing to create a monodisperse train of bubbles is directed into a chamber to form a two dimensional wet foam. The gravity driven drainage of this foam is imaged, and the coalescence (interfacial area) and foam height are measured as a function of time. These results are compared to the LBM simulations by directly comparing simulation and experimental images, and fitted by varying the pseudopotential or disjoining pressure isotherm. We demonstrate that the isotherm (the pseudopotential) controls the bubble coalescence and wet/dry foam transition.