Air-water interface adsorption

S.2.5.2. Correlation of chain structure with its solubility and surface activity At the air/water interface adsorption is essentially an airophilic process of the hydrocarbon chains. Hence the change in free energy can be represented by the relationship for the vaporization process ... 

Proteins, like other macromolecules, can be made into monolayers at the air-water interface either by spreading, adsorption, or specific binding. Proteins, while complex polymers, are interesting because of their inherent surface activity and amphiphilicity. There is an increasing body of literature on proteins at liquid interfaces, and here we only briefly discuss a few highlights. 

Domenek S., Petit E., Ducept F., Mezdoura S., Brambati N., Ridoux C., Guedj S., Michon C. 2008. Influence of concentration and ionic strength on the adsorption kinetics of gelatin at the air/water interface. Colloids and Surfaces A Physicochem. Eng. Aspects 331, 48-55. 

The process of adsorption of polyelectrolytes on solid surfaces has been intensively studied because of its importance in technology, including steric stabilization of colloid particles [3,4]. This process has attracted increasing attention because of the recently developed, sophisticated use of polyelectrolyte adsorption alternate layer-by-layer adsorption [7] and stabilization of surfactant monolayers at the air-water interface [26], Surface forces measurement has been performed to study the adsorption process of a negatively charged polymer, poly(styrene sulfonate) (PSS), on a cationic monolayer of fluorocarbon ammonium amphiphilic 1 (Fig. 7) [27],... 

One important advantage of the polarized interface is that one can determine the relative surface excess of an ionic species whose counterions are reversible to a reference electrode. The adsorption properties of an ionic component, e.g., ionic surfactant, can thus be studied independently, i.e., without being disturbed by the presence of counterionic species, unlike the case of ionic surfactant adsorption at nonpolar oil-water and air-water interfaces [25]. The merits of the polarized interface are not available at nonpolarized liquid-liquid interfaces, because of the dependency of the phase-boundary potential on the solution composition. 

The interaction between the adsorbed molecules and a chemical species present in the opposite side of the interface is clearly seen in the effect of the counterion species on the HTMA adsorption. Electrocapillary curves in Fig. 6 show that the interfacial tension at a given potential in the presence of the HTMA ion adsorption depends on the anionic species in the aqueous side of the interface and decreases in the order, F, CP, and Br [40]. By changing the counterions from F to CP or Br, the adsorption free energy of HTMA increase by 1.2 or 4.6 kJmoP. This greater effect of Br ions is in harmony with the results obtained at the air-water interface [43]. We note that this effect of the counterion species from the opposite side of the interface does not necessarily mean the interfacial ion-pair formation, which seems to suppose the presence of salt formation at the boundary layer [44-46]. A thermodynamic criterion of the interfacial ion-pair formation has been discussed in detail [40]. 

Defeijter, J. A. Benjamins, J. Veer, F. A., Ellipsometry as a tool to study adsorption behavior of synthetic and biopolymers at air water interface, Biopolymers 1978, 17, 1759 1772... 

Figure 19. Schematic representation of the cooperative adsorption and desorption of DOPC molecules between an air/water interface and a sublayer.

In addition to the studies in the volume, the adsorption properties of the polyelectrolyte-surfactant complexes at the air-water interface have also been... 

C. Monteux, C.E. WiUiams, J. Meunier, O. Anthony, and V. Bergeron Adsorption of Oppositely Charged Polyelectrolyte/Surfactant Complexes at the Air/Water Interface Formation of Interfacial Gels. Langmuir 20, 57 (2004). 

It may be noted that similar lyotropic series for the anions have been observed at other interfaces in addition to the air-water interface. Beutner s series (see p. 249) for the oil-water interface adsorption is... 

Interfacial transfer is the transport of a chemical across an interface. The most studied form of interfacial transfer is absorption and volatilization, or condensation and evaporation, which is the transport of a chemical across the air-water interface. Another form of interfacial transfer would be adsorption and desorption, generally from water or air to the surface of a particle of soil, sediment, or dust. Illustration of both of these forms of interfacial transfer will be given in Section l.D. 

Fig. 8 Results of the regression analysis of Eq. 56 for surface potential of the air-water interface with the adsorption of alkali dodecyl sulfate molecules as a function of the surfactant concentration in the bulk solution...

The dispersion interaction between the surface active ions and the water-air interface was recently considered in the modeling of the equilibrium adsorption [62]. The molecular dynamic simulations are used in the recent years to describe the surfactant adsorption at the air-water interface [63-65],... 

Calculate the surface energies of each of these liquids and plot a graph of y for the CTAB solutions as a function of logio(conc.). Use your results and the Gibbs adsorption equation (see later) to estimate the minimum surface area per CTAB molecule adsorbed at the air-water interface. 

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