A study on the kinetics of liquid drainage from colloidal gas aphrons (CGAs)

A kinetic model was proposed to describe the liquid drainage profiles of colloidal gas aphrons (CGAs). The liquid drainage profiles themselves were determined by reading the volume of the liquid drained as a function of time in the presence of various concentrations of sodium dodecyl sulphate (SDS), hexadecyltrimethyl ammonium bromide (HTAB), and Tween 80 under the conditions of different temperatures. Effect of the surfactant concentration and system temperature on the kinetic stability of CGAs was discussed. Drainage behavior was fitted by the empirical equation Vt = Vmaxtn/(Kn + tn), where Vt refers to the volume of drained liquid at time t, Vmax refers to the maximum volume of drained liquid, n describes the sigmoidal character of the curve and K is equal to the half-life (t1/2) of drainage. Rate constants (kd) and the half-life (t1/2) of liquid drainage could be calculated from parameters Vmax, K, and n. This kinetic model was tested successfully with the use of the Arrhenius equation, which relates in its logarithmic form the logarithm of the kinetic constant (ln kd) linearly to the reciprocal of the absolute temperature (1/T). Two distinct stages of CGAs drainage determined by two independent mechanisms were identified from analysis of the rate of liquid drainage as a function of time.