TY - JOUR
T1 - Strain and Liquid Content of Sheared Stretching Foams
T2 - A Model for Dynamic Dilatancy
AU - Embley, B.
AU - Grassia, P.
N1 - Special Issue: Current Research on Foams (A compilation of papers presented at the 7th EUFOAM conference, edited by M. Adler, J. J. Cilliers, O. Minster and S. Vincent-Bonnieu)
PY - 2009/7/20
Y1 - 2009/7/20
N2 - In drainage experiments for liquid–gas foams, a sufficiently large liquid flow rate results in a downwards convection of bubbles. This ‘wet’, downwards-convecting region of foam can coexist with stationary ‘dry’ regions or with ‘dry’ regions that convect upwards. A possible explanation of this phenomenon is dilatancy. We introduce and develop a model that considers the dynamic dilatancy of a foam via force balances on a continuously sheared sample with a finite liquid fraction. Using microstructural information for the strain of typical foam structures (e.g. Kelvin and Weaire–Phelan foams) and the notion of stretching Plateau borders (i.e. foam channels) within a non-uniform bubble velocity field, the model can estimate the liquid content within a convective roll. Alternatively liquid content can be obtained via previously established relations between applied shear rate and foam osmotic pressure. The continuously sheared, downwards-convecting portion of foam is predicted to subsist at higher liquid content than an adjacent, unyielded, upwards-convecting portion of foam. Sustainable liquid content variations in the dynamic dilatancy model are comparable to or greater than those associated with static foam dilatancy.
AB - In drainage experiments for liquid–gas foams, a sufficiently large liquid flow rate results in a downwards convection of bubbles. This ‘wet’, downwards-convecting region of foam can coexist with stationary ‘dry’ regions or with ‘dry’ regions that convect upwards. A possible explanation of this phenomenon is dilatancy. We introduce and develop a model that considers the dynamic dilatancy of a foam via force balances on a continuously sheared sample with a finite liquid fraction. Using microstructural information for the strain of typical foam structures (e.g. Kelvin and Weaire–Phelan foams) and the notion of stretching Plateau borders (i.e. foam channels) within a non-uniform bubble velocity field, the model can estimate the liquid content within a convective roll. Alternatively liquid content can be obtained via previously established relations between applied shear rate and foam osmotic pressure. The continuously sheared, downwards-convecting portion of foam is predicted to subsist at higher liquid content than an adjacent, unyielded, upwards-convecting portion of foam. Sustainable liquid content variations in the dynamic dilatancy model are comparable to or greater than those associated with static foam dilatancy.
U2 - 10.1016/j.colsurfa.2009.02.028
DO - 10.1016/j.colsurfa.2009.02.028
M3 - Article
SN - 0927-7757
VL - 344
SP - 24
EP - 32
JO - Colloids and Surfaces A: Physicochemical and Engineering Aspects
JF - Colloids and Surfaces A: Physicochemical and Engineering Aspects
ER -