Formation of Monolayers

On the other hand, with macroscopic interfaces, the adsorbed amount is often difhcnlt to assess accurately, but the interfacial tension is readily measurable. Then r can be obtained from y(c), again by applying Gibbs adsorption equation. 

When comparing the characteristics of an adsorbed monolayer on dispersed particles with those of a monolayer at a flat macroscopic surface, one should be aware of ambiguities and pitfalls as a consequence of the intricate rupture and recoalescence processes involved in the formation of emulsion droplets and foam bubbles, the composition and orientation of the surfactant molecules at the interface may not be in complete equilibrium and deviate from the situation for a monolayer at a quiescent macroscopic interface. We return to this in Chapter 18. 

By way of example, the data given in Table 5.4 predict that, at 20 C, benzene spreads over an air/water interface S = 72.8 - 28.9 - 35.0 = 8.9 mJ m- ). However, benzene and water are not completely immiscible and after some time mutual 

FIGURE 7.2 Cross section of a sessile drop of liquid y at an interface between a and p. The 

When a surfactant is added to a spreading solvent, and are reduced leading to a more positive value for and, hence, to a stronger spreading tendency. 

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Bain C D, Troughton, E B Tao Y T, Evall J and Whitesides G M 1989 Formation of monolayer films by the spontaneous assembly of organic thiols from solution onto gold J. Am. Chem. Soc. Ill 321-35... 

Recently, the newly developed time-resolved quasielastic laser scattering (QELS) has been applied to follow the changes in the surface tension of the nonpolarized water nitrobenzene interface upon the injection of cetyltrimethylammonium bromide [34] and sodium dodecyl sulfate [35] around or beyond their critical micelle concentrations. As a matter of fact, the method is based on the determination of the frequency of the thermally excited capillary waves at liquid-liquid interfaces. Since the capillary wave frequency is a function of the surface tension, and the change in the surface tension reflects the ion surface concentration, the QELS method allows us to observe the dynamic changes of the ITIES, such as the formation of monolayers of various surfactants [34]. 

Bain CD, Evall J, Whitesides GM (1989) Formation of monolayers by the coadsorption of thiols on gold variation in the head group, tail group, and solvent. J Am Chem Soc 111 7155-7164... 

Fig. 22. Structures proposed to account for the A (y/7 x y/l) and B (3x3) structures observed in the formation of monolayer of CdTe. Adapted from ref. [279],...

Deposition of PAHs on surfaces and the formation of monolayers by UHV-techniques is experimentally demanding. Therefore it is important that monolayers of soluble alkyl substituted HBCs can also be obtained by physisorption from solution. 

Nucleation and growth processes of the metal lattice. Understanding of the nucleation and growth of surface nuclei, formation of monolayers and multilayers, and growth of coherent bulk deposit is based on knowledge of condensed-matter physics and physical chemistry of surfaces. 

In general, the formation of monolayers with silanization reagents requires a precise reaction scheme regarding humidity, the selection of solvents, temperature, and reaction time. Often, not enough consideration is given to these factors. As a result a number of authors concluded that the reproducibility of homogeneous silane-monolayers is insufficient, that their stability in aqueous solution is limited, or that they are prone to the formation of multilayers. 

In the Chapter 7, formation of monolayers in air-liquid interfaces and the resulting film pressure and phase transitions are discussed. This chapter also includes a brief discussion of adsorption on solid surfaces from solutions. 

List a few applications of monolayers. List a few applications in which the formation of monolayer at a fluid-fluid interface is used in industry. 

All four types of polymerizable lipids shown in Fig. 4 have been realized synthetically. In this context, one need not attempt to reproduce mother nature slavishly (Fendler 8)). Kunitake 9) was able to show that simple molecules like dialkyldimethyl-ammonium salts also form bilayer assemblies. Fuhrhop 10) and Kunitake U) could accomplish the formation of monolayer liposomes with molecules containing only one alkyl chain and two hydrophilic head groups. Acryloylic and methacryloylic groups (type a and d, Table 1), as well as diacetylenic, butadienic, vinylic and maleic acid groups (type b and c), have been used as polymerizable moieties. A compilation of amphiphilic, photopolymerizable molecules is given in Table 1. 

The formation of monolayers and their thermodynamic investigation was described in the last chapter. A good introduction to the classic experimental techniques and results is given by Refs. [587] [588], We start by discussing optical techniques. 

Because like dissolves like, when placed into water the surfactant molecule will strive to get the greasy, nonpolar hydrocarbon tail away from the polar water molecules. There are three potential strategies for achieving this outcome formation of monolayers, formation of bilayers, and formation of micelles. 

Here preferential adsorption of proflavine occurs in the interlamellar space of the aggregates with formation of monolayers of monomers and quenching of the fluorescence with increasing loading does not occur to an appreciable extent. 

Although reactions resulting in the formation of monolayers attached to the surface via Si-C bonds have received the bulk of the attention, some work aimed at varying the nature of the silicon-molecule link has been reported. For example, alcohols have been observed to react thermally with H/Si(lll) and are thought to result in the formation of Si-OR monolayers... 

Even though metallosiufactants are scarce compared to their nonmetallic organic counterparts, there is an increasing interest due of their multiple applications in fields such as probes in emulsion (53), formation of monolayers (52,54-56), thin film... 

Recent reports on monomeric and polymerized bolaamphiphiles1 provide evidence for their potential application in the broader field of molecular organizates (1,2). Thus monomeric bolaamphiphiles have been employed in the formation of monolayer lipid membranes or vesicles (1-3). formation of micelles (4-5) and also for spanning bilayer membranes (1-6) The latter process has resulted in the stabilization of membranes. 

Figure 27 (A) Diagrammatic representation of the potential lubricant effect of adsorbed dendrimers between two flat surfaces, and (B) the formation of monolayers and multilayers of dendrimers. Source-. From Ref. 93.

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