Frumkin interaction coefficient

Fig. 4.8 The Frumkin adsorption isotherm. The value of the interaction coefficient a is indicated at each curve. The transition in the metastable region is indicated by a dashed...

Table 5.1 Saturation coverages (rs), adsorption coefficients (fi) and Frumkin interaction parameters (g) for single- and two-component mono-layers of 2,7-AQDS and 1,4-AQClOH.

The intrinsic parameter that characterizes this type of interaction is the Frumkin interaction parameter a (in the nomenclature followed by Mirceski et al., 2007), which is positive for attractive forces and negative for repulsive ones. In the presence of lateral interactions, the response is controlled by the kinetic parameter, the charge transfer coefficient, and the interaction product aO. Thus, the kinetic parameter and the interaction product can be unified into a complex kinetic parameter, defined as ... 

Since the use of gaseous constitution equation underestimates the surface pressure, Sadhal and Johnson s result underestimates the cap angle and consequently the drag coefficient. He et al. [1991] obtained a more realistic value for the cap angle by allowing for nonlinear interactions. In their study, Frumkin s equation of state (Frumkin Levich, 1947, Chapter 2)... 

The parameter g typically has units of J/mol per mol/cm, and it expresses the way in which increased coverage changes the adsorption energy of species i. If g is positive, the interactions between neighboring adsorbed molecules on the surface are attractive and if g is negative, the interactions are repulsive. As g 0, the Frumkin isotherm approaches the Langmuir isotherm. This isotherm can also be written in the form (including activity coefficients in the j8 term)... 

It was shown in Chapter 2 that the theoretical models defined by Eqs. (3.1)-(3.10) can be used also to describe the behaviour of the solutions of ionic surfactant RX in absence and presence of inorganic electrolyte XY. In this case, the Frumkin constant, in addition to the Van der Waals interaction, involves also the inter-ion interaction in the surface layer. Now instead of the concentration c the corresponding adsorption isotherms should be a function of the mean ionic products c = f (Crx xy rx > where f is the average activity coefficient of ions in the solution bulk. An equation accurately representing measured values of f. is the Debye-Hiickel euqation corrected for short-range interactions... 

---