Aggregation monolayer

Buijnsters, P. J. J. A., Garcia Rodriguez, C. L., WiUighagen, E. L. et al. (2002) Cationic gemini surfactants based on tartaric acid synthesis, aggregation, monolayer behaviour and interaction with DNA. Eur. J. Org. Chem, 8, 1397-1406. 

The polystyrene latex particles carry a charge in aqueous solution resulting from the surface sulfate groups, and as mentioned the particle dispersions are stable. Particle monolayers can be formed at air/solution surfaces as well as at oil/solution interfaces. There is obviously an electrical double layer formed around the parts of the particle surface in contact with the aqueous phase. Lateral repulsions in the monolayer due to double-layer interactions can be screened by addition of inert electrolyte to the aqueous phase. Images of relatively dilute monolayers on 10 mM aqueous NaCl are depicted in Fig. 18. Monolayers at the air/0.01 M NaCl solution surface are much less ordered than those at the octane/solution interface, although there is very little particle aggregation. Monolayers at the octane/solution interface retain... 

In general, it appears that the surfactant present in the aqueous phase leads to a reduction in monolayer structure at the oil/aqueous solution interface [23]. At concentrations close to the critical micelle concentration (cmc) the particles are almost completely aggregated. We show images of such aggregated monolayers in Fig. 22. Because the particles carry a negative charge... 

Surface Area. The most important features influencing the performance of carbon blacks are aggregate size and surface area. Surface area is measured by gas- and Hquid-phase adsorption techniques, and depends on the amount of adsorbate required to form a surface monolayer. If the area occupied by a single-adsorbate molecule is known, a simple calculation will yield the surface area. A low temperature nitrogen absorption method, based on the original method of Bmnauer, Emmett, and Teller (BET) (30), has been adopted by ASTM as standard method D3037-86 (2). 

Figure 6-25. Fluorescence spectra at 4.2 K of T,. thin lilms with morphology characterized by a) grains b) layers c) islands d) sub-monolayer. The lower density ol aggregate states in the sub-monolayer architecture decreases the energy transfer efficiency to low energy stales and the fluorescence acquires dominant excitonie character (sec Section 6.6.2.2J.

Tarek et al. [388] studied a system with some similarities to the work of Bocker et al. described earlier—a monolayer of n-tetradecyltrimethylammonium bromide. They also used explicit representations of the water molecules in a slab orientation, with the mono-layer on either side, in a molecular dynamics simulation. Their goal was to model more disordered, liquid states, so they chose two larger molecular areas, 0.45 and 0.67 nm molecule Density profiles normal to the interface were calculated and compared to neutron reflectivity data, with good agreement reported. The hydrocarbon chains were seen as highly disordered, and the diffusion was seen at both areas, with a factor of about 2.5 increase from the smaller molecular area to the larger area. They report no evidence of a tendency for the chains to aggregate into ordered islands, so perhaps this work can be seen as a realistic computer simulation depiction of a monolayer in an LE state. 

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