Interfaces charged monolayers

Films spread at liquid-liquid interfaces or on liquids other than water are discussed followed by the important effects of charged monolayers on water. Finally, the most technologically important application of Langmuir films, the Langmuir-Blodgett film deposited on a solid substrate, is reviewed. 

Zhao X L, Ong S W and Eisenthal K B 1993 Polarization of water-molecules at a charged interface. Second harmonic studies of charged monolayers at the air/water interface Chem. Phys. Lett. 202 513-20... 

The physical depth of the microscopic interfacial region can be estimated to correspond to the distance over which interfacial molecular and ionic forces exert their influence. Although molecules or ions experience no net forces in the interior of the bulk phases, these forces become unbalanced as the ions or molecules move toward the interface. On the aqueous side of the interfaces, where monolayers of charged molecules or polar groups can be present, these forces can be felt over several nanometers. On the organic side of the interface, where van der Waals forces are mainly operative, the interfacial region generally extends for tens of nanometers. The van der Waals forces decrease with the seventh power of the intermolecular distances, so molecules experience essentially symmetric forces, once they are a few molecular diameters away from the interface. 

Electric double layers at phase boundaries pervade the entire realm of Interface and colloid science. Especially in aqueous systems, double layers tend to form spontaneously. Hence, special precautions have to be taken to ensure the absence of charges on the surfaces of particles. Insight into the properties of double layers is mandatory, in describing for Instance electrosorption, ion exchange, electrokinetics (chapter 4), charged monolayers (Volume III), colloid stability, polyelectrolytes and proteins, and micelle formation of ionic surfactants, topics that are intended to be treated in later Volumes. The present chapter is meant to Introduce the basic features. 

The presence of both oriented vaterite and calcite crystals on charged monolayers indicates that the electrostatic interactions between nuclei and the organic surface are influenced by structural relationships at the interface. The nucleation of vaterite on films of positive and negative charge indicates that Ca binding is not a prerequisite for stabilization of this metastable phase. Oriented calcite, on the other hand, requires Ca binding at the carboxylate head-groups. ... 

Charged monolayers have been successfully employed as active interfaces for controlling electron transfer at electrode supports [87, 88]. Negatively charged monolayers associated with electrodes have been shown to discriminate between the electrochemical reactions of a mixture of positively and... 

Entropies of Compression of Charged Monolayers at Aqueous Interfaces... 

Monolayers are more expanded at the O/W interface than at the A/W interface this has been generally confirmed since the early work of Davies (19). The condensing effect on fully ionized monolayers from increasing the electrolyte concentration (19) is shown in Figures 3-5. The equimolar Ci8 suIfate-Ci8 TAB monolayers are more condensed than the single-component charged monolayers shown by Phillips and Rideal (17, 18) and Brooks and Pethica (14) although in the present... 

We describe in a companion paper (33) the salient features of our procedures for measuring low surface pressures, and we provide n-A isotherms for octadecyl trimethylammonium bromide (Ci8 TAB) and sodium octadecyl sulfate (Ci8 sulfate) monolayers spread at A/W and O/W interfaces. Here we extend some of these data to higher A using, in some instances, some of our earlier reported measurements. We have also taken from literature the few reported isotherms for dilute charged monolayers and discuss them in the light of our results and the predictions of Equations 7 and 8. 

Kretzschmar Voigt (1989) have recently examined the contribution of interacting forces in surfactant adsorption layers to the film pressure. A detailed knowledge of the geometry of the electrical double layer with respect to the plane of the interface is an essential item in the theoretical description of charged monolayers, thin liquid films and membranes. Fig. 2.12. shows an illustration of structural and energetic aspects of the surfactant monolayer formation. 

S. J. Miklavic, J. Colloid Interface Set., 171, 446 (1995). Mean-Field Potential for Heterogeneous Electrical Double Layers, with Application to the Surface Pressure of Charged Monolayers. 

Petrov, J. G. Moebius, D. Determination of the electrostatic potential of positively charged monolayers at the air/water interface by means of fluorometric titration of 4-heptadecyl-7-hydroxycoumarin. Langmuir 1990, 6,746-751. 

In some cases, e.g., the Hg/NaF q interface, Q is charge dependent but concentration independent. Then it is said that there is no specific ionic adsorption. In order to interpret the charge dependence of Q a standard explanation consists in assuming that Q is related to the existence of a solvent monolayer in contact with the wall [16]. From a theoretical point of view this monolayer is postulated as a subsystem coupled with the metal and the solution via electrostatic and non-electrostatic interactions. The specific shape of Q versus a results from the competition between these interactions and the interactions between solvent molecules in the mono-layer. This description of the electrical double layer has been revisited by... 

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],... 

---