Solutions, colloidal

Kneipp K, Kneipp H, Deinum G, Itzkan I, Dasari R R and Feld M S 1998 Single-molecule detection of a cyanine dye in silver colloidal solution using near-infrared surface-enhanced Raman scattering App/. Spectrosc. 52 175-8... 

If a dilute acid is added to this solution, a white gelatinous precipitate of the hydrated tin(IV) oxide is obtained. It was once thought that this was an acid and several formulae were suggested. However, it now seems likely that all these are different forms of the hydrated oxide, the differences arising from differences in particle size and degree of hydration. When some varieties of the hydrated tin(IV) oxide dissolve in hydrochloric acid, this is really a breaking up of the particles to form a colloidal solution—a phenomenon known as peptisation. 

In special cases (as in colloidal solutions) some particles can be considered as essential and other particles as irrelevant , but in most cases the essential space will itself consist of collective degrees of freedom. A reaction coordinate for a chemical reaction is an example where not a particle, but some function of the distance between atoms is considered. In a simulation of the permeability of a lipid bilayer membrane for water [132] the reaction coordinate was taken as the distance, in the direction perpendicular to the bilayer, between the center of mass of a water molecule and the center of mass of the rest of the system. In proteins (see below) a few collective degrees of freedom involving all atoms of the molecule, describe almost all the... 

The salts of monoalkyl sulphates are frequently encountered as commercial detergents (for example, dreft, gardinol and pentrone ) they are usually sodium salts, the alkyl components contain 12 or more carbon atoms, and give colloidal solutions. They are hydrol3 sed by boiling with dilute sodium hydroxide solution ... 

In the process ia the center of Figure 17, complete hydrolysis is allowed to occur. Bases or acids are added to break up the precipitate iato small particles. Various reactions based on electrostatic iateractions at the surface of the particles take place the result is a colloidal solution. Organic binders are added to the solution and a physical gel is formed. The gel is then heat treated as before to form the ceramic membrane. 

Hydrated Stannic Oxide. Hydrated stannic oxide of variable water content is obtained by the hydrolysis of stannates. Acidification of a sodium stannate solution precipitates the hydrate as a flocculent white mass. The colloidal solution, which is obtained by washing the mass free of water-soluble ions and peptization with potassium hydroxide, is stable below 50°C and forms the basis for the patented Tin Sol process for replenishing tin in staimate tin-plating baths. A similar type of solution (Staimasol A and B) is prepared by the direct electrolysis of concentrated potassium staimate solutions (26). 

Tungsten trisulfide [12125-19-8] chocolate-brown powder, slightly soluble in cold water, but readily forming a colloidal solution in hot... 

Naphthol AS Coupling Components. Naphthol AS components are the aryhdes of either o-hydroxyarylcarboxycHc acids or acylacetic acids. They are free of sulfo and carboxyl groups, but form salts with bases these salts dissolve in water to give colloidal solutions, which couple with diazo components to form colored pigments. The whole class derives from the anilide of 3-hydroxy-2-naphthoic acid [92-70-6] Naphthol AS (85) (Cl Azoic Coupling Component 2). 

Tyj)e of dryer Applicable with dry-product recirculation True and colloidal solutions emulsions. Examples inorganic salt solutions, extracts, milk, blood, waste liquors, rubber latex, etc. Pumpable suspensions. Examples pigment slurries, soap and detergents, calcium carbonate, bentonite, clay sbp, lead concentrates, etc. does not dust. Recirculation of product may prevent sticking Examples filter-press cakes, sedimentation sludges, centrifuged sobds, starch, etc. 

Paper with enhanced wet-strength may be obtained by incorporating melamine resin acid colloid into the pulp. Melamine resin acid colloid is obtained by dissolving a lightly condensed melamine resin or trihydroxymethylmelamine, which are both normally basic in nature, in dilute hydrochloric acid. Further condensation occurs in solution and eventually a colloidal solution is formed in which the particles have a positive charge. Careful control over the constitution of the colloidal solution must be exercised in order to obtain products of maximum stability. 

What was recognised from the beginning was that colloidal solutions are two-phase materials. 

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. 

R. Zsigmondy (Gottingen) demonstration of the heterogeneous nature of colloid solutions by methods which have since become fundamental in modem colloid chemistry. 

Discussion. J. Nessler in 1856 first proposed an alkaline solution of mercury(II) iodide in potassium iodide as a reagent for the colorimetric determination of ammonia. Various modifications of the reagent have since been made. When Nessler s reagent is added to a dilute ammonium salt solution, the liberated ammonia reacts with the reagent fairly rapidly but not instantaneously to form an orange-brown product, which remains in colloidal solution, but flocculates on long standing. The colorimetric comparison must be made before flocculation occurs. 

In preparing the membrane, a clear sol was obtained by the addition of acid into the aluminum sec-butoxide sol to peptise the sol and obtain a stable colloid solution. Aluminum monohydroxides formed by the hydrolysis of aluminum alkoxides, which are peptisable to a clear sol. Peptisation was performed by the addition of acid and heat treatment for a sufficient time. It was found that stable sols cannot be obtained when the concentration of the peptisation acid is too low. The critical range for inorganic acids such as nitric, hydrochloric and perchloric acids is 0.03-0.1 mole/mole of hydroxide. In this study, nitric acid was used as the peptising agent. The resulting sols are poured into Petri dishes and dried in an oven at a controlled drying rate to obtain a gel layer. The molar ratio of zirconia salt... 

Modern experiment has proved beyond doubt that the so-called colloidal solutions are systems composed of two or more phases, i.c., heterogeneous, characterised by an enormously great extent of division, in which the surface of contact has, so to speak, been spread out throughout the whole mass. Capillary phenomena are therefore predominant here (cf. Ostwald, Kolloidchemic, Leipzig, 1909 Freundlich, Kapillarchemie, Leipzig, 1909). 

Extremely small particle, typically 10-5 to 10 7 cm in diameter. Colloidal solutions or hydrosols contain colloidal particles that are electrically negatively charged, which contributes to their fine dispersion and the difficulty of sedimentation and clarification. Coagulation is usually carried out by causing the particles to adsorb positively charged ions, such as aluminum from alum. 

Some colloidal solutions, such as that in Fig. 8.45, appear at first glance to be solutions. What quick, simple procedure can you use to distinguish colloids from solutions ... 

Sedimentation from colloidal solution using ultracentrifuges [126-129]... 

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. 

In addition to the preparation of Langmuir and Langmuir-Blodgett films, the use of self-assembly techniques also plays an important role in the formation of particle films. Both physisorption, as, for example, electrostatic adsorption of charged particles from colloidal solution, and chemisorption onto a substrate have been investigated. In Section V.A, electrostatic adsorption will be reviewed chemisorption is the subject of Section V.B. 

However, in subsequent studies [23-25,88-90] it was demonstrated that in reality the particle deposition is not a purely geometric effect, and the maximum surface coverage depends on several parameters, such as transport of particles to the surface, external forces, particle-surface and particle-particle interactions such as repulsive electrostatic forces [25], polydispersity of the particles [89], and ionic strength of the colloidal solution [23,88,90]. Using different kinds of particles and substrates, values of the maximum surface coverage varied by as much as a factor of 10 between the different studies. 

In Figure 16, SEM pictures of substrates dipped into a colloidal solution of particles Ic for different time periods are shown [93,98]. After 10 seconds, a number of particles are adsorbed. Most of the particles are present in a nonaggregated state, indicating that singleparticle adsorption is the dominating process. With dipping time, the coverage of the sur-... 

The UV-visible spectrum (Fig. 6) of the aggregates described earlier shows a 0.25-eV shift toward lower energy of the plasmon peak with a slight decrease in the bandwidth (0.8 eV) compared to that observed in solution (0.9 eV). As observed earlier with monolayers, by washing the support, the particles are redispersed in hexane and the absorption spectrum remains similar to that of the colloidal solution used to make the self-assemblies. 

Iron Dextran 5000- 7500 (complex with ferric chloride) Colloidal solution In 0.9% w/v sodium chloride injection Autoclave Deep IM non-deficiency anaemia (oral therapy ineffective or impractical) IV (slow infusion) non-deficiency anaemia (oral therapy ineffective or impractical)... 

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