Mechanical Properties of Foams

Abstract

The density [ρ] of a foam is the mass of the foam divided by its volume [V]. As the total mass is the sum of the gas and liquid masses (m ₁ and m ₂), the equation for [ρ] is

$$[\rho ] = \frac{{{m_1} + {m_2}}}{{[V]}}$$

((7.1))

The reproducibility and the stability of foams are so poor that a precise determination of [ρ] is unnecessary; hence it is permissible in practically all instances to neglect the mass m ₁ of the gas phase and to use the equation

$$[\rho ] = \frac{{{m_2}}}{{[V]}}$$

((7.2))

For aqueous foams the approximation ρ ₂ = 1.0 usually is sufficient; ρ ₂ is the density of the liquid phase. Thus the mass (grams) of the liquid in the foam is numerically equal to its volume (V ₀ cm³). In general,

$$\frac{{[\rho ]}}{{{p_2}}} = \frac{{{V_0}}}{{[V]}}$$

((7.3))

especially for nonaqueous foams the correct value for ρ ₂ must be used.