Colloidal solution structure

In this article we shall focus on recent work involving dilute aqueous surfactant solutions. As a background the thermodynamics and statistics of these solutions will be discussed first (Section II). The distribution of substrate molecules in microheterogeneous solution is considered in Section m. It is decisive for the kinetics of elementary photochemical reactions (Section IV), which depend on the peculiar colloidal solution structure. Effects of the microscopic environments on photochemical reactions are treated in Section V. Finally, the use of known photochemical systems as probes for studying details of the structure of surfactant solutions will be considered in Section VI. 

Colloidal crystals . At the end of Section 2.1.4, there is a brief account of regular, crystal-like structures formed spontaneously by two differently sized populations of hard (polymeric) spheres, typically near 0.5 nm in diameter, depositing out of a colloidal solution. Binary superlattices of composition AB2 and ABn are found. Experiment has allowed phase diagrams to be constructed, showing the crystal structures formed for a fixed radius ratio of the two populations but for variable volume fractions in solution of the two populations, and a computer simulation (Eldridge et al. 1995) has been used to examine how nearly theory and experiment match up. The agreement is not bad, but there are some unexpected differences from which lessons were learned. 

In 1997, a Chinese research group [78] used the colloidal solution of 70-nm-sized carboxylated latex particles as a subphase and spread mixtures of cationic and other surfactants at the air-solution interface. If the pH was sufficiently low (1.5-3.0), the electrostatic interaction between the polar headgroups of the monolayer and the surface groups of the latex particles was strong enough to attract the latex to the surface. A fairly densely packed array of particles could be obtained if a 2 1 mixture of octadecylamine and stearic acid was spread at the interface. The particle films could be transferred onto solid substrates using the LB technique. The structure was studied using transmission electron microscopy. 

Fulda and Tieke [77] studied the effect of a bidisperse-size distribution of latex particles on the structure of the resulting LB monolayer. For this purpose, a mixed colloidal solution of particles la and lb was spread at the air-water interface. Particles la had a diameter of 434 nm, particles lb of 214 nm. The monolayer was compressed, transferred onto a solid substrate, and viewed in a scanning electron microscope (SEM). In Figure 10, SEM pictures of LB layers obtained from various bidisperse mixtures are shown. 

Figure 2. On the left hand side is the HRTEM image of Ti-Beta nanoparticles obtained from the colloidal solution that was thermally treated for 28 hours. In the inset a selected area electron diffraction ofTi-Beta nanpoarticles shows their crystalline structure. On the right hand side are the 29Si MAS and H - 29Si CPMAS spectra of the sample g).

Avdeev MV, Khokhryakov AA, Tropin TV, Andrievsky GV, Klochkov VK, Derevyanchenko LI, Rosta L, Garamus VM, Priezzhev VB, Korobov MV, Aksenov VL (2004) Structural features of molecular-colloidal solutions of C-60 fullerenes in water by small-angle neutron scattering. Langmuir 20 4363 4368. 

Lack of steady flow of a liquid-bearing colloidal solution requires the existence of a space-filling, three-dimensional structure. As we might select a perfect crystal as a csuionical solid, or liquid argon as a prototypical liquid, we csui choose the covalently crosslinked network, without any entanglements, to represent the ideal gel state. Then an appropriate time scale for reversible gels would be the lifetime of a typical crosslink bond if subjected to conditions that would cause flow in a pure... 

Magini, M. (1977) Structural relationships between colloidal solutions and hydroxide gels ofiron(lll) nitrate. J. inorg. nucl. Chem. 39 409-412... 

The color of the colloidal solutions of gold depends on the size of colloidal particles (clusters). Several methods have been used for the preparation of such clusters (for a review see [578]). Since the size of clusters may change from one to several hundred angstroms, their electronic structure may vary between that of single atoms and the solid metal. 

PETN differs from other nitric esters in failing to produce a colloid solution with nitrocellulose. This is the result of the symmetrical structure of PETN, which has a zero dipole moment. PETN is completely non-hygroscopic. Its specific gravity in crystalline form is 1.77. On compression the following density values are obtained ... 

Saponins consist of a terpenoid core (the aglycone), having oxygenated positions bound to sugar moieties (up to ten monosaccharidic units). In water they form colloidal solutions which foam on shaking and precipitate cholesterol. When saponins are near cell membranes, their interaction with cholesterol may create pore-like structures that eventually cause the membrane to burst. Hemolysis is an example of this phenomenon (i.e. the distraction of erythocyte membranes, but not hemoglobin). Occasionally, they cause hypersecretion, which could explain their expectorant activities and also their toxicity to fish. 

M/SC nanoparticles in size from 1 to 10 nm are of greatest interest because their electronic structure depends markedly on the particle size [4-6]. There are now a lot of methods for a deposition of M/SC and dielectric on solid substrates from liquid or gaseous phase to produce composite films containing M/SC nanoparticles inside or on a surface of a dielectric matrix. Liquid-phase technique uses colloidal solutions of M/SC nanoparticles. Such solutions are formed by chemical reactions of various precursors in the presence of stabilizers, which are adsorbed on the surface of nanoparticles and preclude their aggregation. But it is necessary to take into account, that... 

Some of these products, when beaten in a Waring Blender, for example, change in character from fibrous structures containing a large amount of water, to gel-like viscous colloidal solutions (52). These show promise for applications as thickeners and dispersing agents. 

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