Surfactant adsorption surface free energy

Using this approach, a model can be developed by considering the chemical potentials of the individual surfactant components. Here, we consider only the region where the adsorbed monolayer is "saturated" with surfactant (for example, at or above the cmc) and where no "bulk-like" water is present at the interface. Under these conditions the sum of the surface mole fractions of surfactant is assumed to equal unity. This approach diverges from standard treatments of adsorption at interfaces (see ref 28) in that the solvent is not explicitly Included in the treatment. While the "residual" solvent at the interface can clearly effect the surface free energy of the system, we now consider these effects to be accounted for in the standard chemical potentials at the surface and in the nonideal net interaction parameter in the mixed pseudo-phase. 

From thermodynamics, the lowering of surface free energy due to surfactant adsorption is given by the Gibbs adsorption equation for a binary, isothermal system containing excess electrolyte ... 

Each surfactant adsorption isotherm (that of Langmuir, Volmer, Frumkin, etc.), and the related expressions for the surface tension and surface chemical potential, can be derived from an expression for the surface free energy, F, which corresponds to a given physical model. This derivation helps us obtain (or identify) the self-consistent system of equations, referring to a given model, which is to be applied to interpret a set of experimental data. Combination of equations corresponding to different models (say, Langmuir adsorption isotherm with Frumkin surface tension isotherm) is incorrect and must be avoided. 

A consequence of surfactant adsorption at an interface is that it provides an expanding force acting against the normal interfadal tension. If % is this expanding pressure (surface pressure), then y = /solvent Thus, surfactants tend to lower interfadal tension. If a low enough value of y is reached, emulsification can take place because only a small increase in surface free energy is required, for example, when Jt /solvent- solute-solvent forces are greater than solvent-solvent forces. 

Adsorption of surfactants on CaCOs and its effect on surface free energy... 

In the following, we consider the equilibrium and kinetics of adsorption of surfactants at the air-water interface on the basis of Langmuir s theory of adsorption of gases on solids. According to Langmuir s theory, it is assumed that the adsorption surface consists of sites, which can be occupied by adsorbed molecules. These sites correspond to the minimum of surface free energy. At achieving the balance between the adsorbed molecules and molecules of gas, only some parts of the potentially available adsorption sites are occupied by gas molecules. This part is equal to 0, and the total number of molecules Na adsorbed on the surface obeys the ratio... 

Our understanding of a tendency to minimize surface free energy as the general cause of adsorption can be enhanced by emphasizing the role of the chemical potential in the transition of surfactant molecules to the interface. It is the gradient of chemical potential that always determines the direction of mass transfer resulting in the equalization of the chemical potential in aU of the phases in contact. 

Surfactant-Enhanced Fiber Branching The interfacial adsorption of surfactant molecules has long been well known. A surfactant molecule is amphiphihc, with a hydrophilic head and one or two hydrophobic tails. This contributes to its strong adsorption at the interface of two phases (i.e., water-air, two solvents) with different polarity in order to reduce the interfacial tension (or surface free energy). 

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