Time-dependent and flow properties of foams

Foams have been prepared from water added with a surfactant and a polymer. A controlled stress rheometer was used to study the changes of their rheological properties during aging by the mean of different rheological tests: shear viscosity measurements, creep compliance tests at a constant low shear stress and dynamic experiments have been performed. It has been observed that apparent viscosity decreases with aging. A thixotropic behaviour was also found, loading and unloading curves present an hysteresis. Then, the choice of the stress ascent time is of primary importance to study the time-dependent properties of the foam. The viscosity was found to decrease with the stress ascent time while the thixotropic area decreases. Creep flow and harmonic tests have shown important viscoelastic properties of the foams. The second part of this work is concerned with the study of the flow properties of the foams. Pressure drops were measured during flow in capillary tubes in laminar regime. Pronounced wall slip effects were found. While the Mooney method for slip correction is not applicable, the Oldroyd-Jastrzebski method leads to satisfactory results. The Metzner and Reed correlation method was found to be applicable in the case of the corrected data.