Colloidal Solutions and Dispersions

Some colloids consist of well-defined molecules, with constant molecular weight and definite molecular shape, permitting them to be ordered in a crystalline array. Proteins have molecular masses ranging from about 10,000 to several hundred thousand. 

Graham introduced the words sol for a colloidal solution (a dispersion of a solid substance in a fluid medium) and gel for a dispersion that has developed a structure that prevents it from being mobile. A solution of gelatin in water at high temperatures is a sol and at low temperatures a gel. A hydrosol is a dispersion in water, and an aerosol is a dispersion of a solid substance in air. 

Inorganic sols may be made by dispersing a solid substance that is normally insoluble, such as gold, ferric oxide, and arsenious sulfide, in water. Gold sols, made by adding a reducing agent to a dilute solution of 

Ordinary soap is made by heating fat in an iron kettle with a strong aqueous solution of sodium hydroxide until the fat is completely hydrolyzed. Fats are the glyceryl esters of long-chain fatty acids, such as palmitic acid (Section 13-5). For example, glyceryl tripalmitate has the structural formula 

A soap made by the reaction of this fat with sodium hydroxide consists of sodium palmitate, CisHgiCOONa. The sodium soaps are solid at room temperature, and the potassium soaps are liquid. Potassium soaps (soft soap) used to be made by heating wood ashes, fat, and water (wood ashes contain potassium hydroxide or potassium carbonate). 

---

Viscosities of dilute colloidal solutions and dispersions Functions of viscosity... 

Figure 1 shows Arrenius plots of the spin probe effective rotational frequency (log x 1 vs. 1/T) in liquid and frozen colloid solutions and dispersions of carbon nanoparticles. The plots are presented for different concentrations of nanoparticles and for water. Linearization of individual segments of the plots (T< 250 K) allowed calculating the thermodynamic parameters of the spin probe motional activation. No significant difference in the spin probe motional activation parameters has been... 

The structures of four of the synthetic carotenoids (beta-carotene, canthaxanthin, beta-apo-8 -carotenol, beta-apo-8 -carotenoic acid) are shown in Fig. 8.2. By virtue of their conjugated double bond structure, they are susceptible to oxidation but formulations with antioxidants were developed to minimize oxidation. Carotenoids are classified as oil soluble but most foods require water soluble colorants thus three approaches were used to provide water dispersible preparations. These included formulation of colloidal suspensions, emulsification of oily solutions, and dispersion in suitable colloids. The Hoffman-LaRoche firm pioneered the development of synthetic carotenoid colorants and they obviously chose candidates with better technological properties. For example, the red canthaxanthin is similar in color to lycopene but much more stable. Carotenoid colorants are appropriate for a wide variety of foods.10 Regulations differ in other countries but the only synthetic carotenoids allowed in foods in the US are beta-carotene, canthaxanthin, and beta-8-carotenol. 

The difference between macroscopic and microscopic objects is clear from everyday experience. For example, a glass marble will sink rapidly in water however, if we grind it into snb-micron-sized particles, these will float or disperse freely in water, prodncing a visibly clondy soln-tion , which can remain stable for honrs or days. In this process we have, in fact, prodnced a colloidal dispersion or solution. This dispersion of one (finely divided or microscopic) phase in another is quite different from the molecular mixtures or true solutions formed when we dissolve ethanol or common salt in water. Microscopic particles of one phase dispersed in another are generally called colloidal solutions or dispersions. Both nature and industry have found many uses for this type of solution. We will see later that the properties of colloidal solu-... 

The easiest way to calibrate a light scattering photometer is to use a suitable standard as a reference. Although polymer solutions and dispersions of colloidal silica have been used for this purpose, commercial photometers are equipped with opal glass reference standards. 

Dialysis is particularly useful for removing small dissolved molecules from colloidal solutions or dispersions - e.g. extraneous electrolyte such as KNO3 from Agl sol. The process is hastened by stirring so as to maintain a high concentration gradient of diffusible molecules across the membrane and by renewing the outer liquid from time to time (Figure 1.5). 

From the analysis of their experimental results of the investigation of the charge carrier recombination kinetics in titanium dioxide colloidal solutions and in dispersions Serpone et al. and Bowman and co-workers have also assumed the existence of two different traps [5,6]. 

Figure 1. Arrenius plots of the spin probe effective rotation frequency (log r"1 vs. 1/T) for water and frozen colloid solutions and carbon nanoparticles dispersions of different concentrations (1) - liquid water including supercooled water at -13°C and frozen water (experimental points within the temperature range of supercooling were taken on rising temperature) (2)- 0.1 mg/ml C6o/C7o (3) - 0.1 mg/ml C6o/C7o + 0.015 M NaCl (4) -1 mg/ml ShC (5) - 10 mg/ml ShC (unstable dispersion) (6) - 0.1 mg/ml ShC.

Properties Light-tan to dark-brown powder no pronounced odor. Stable in dry form and relatively stable in aqueous solution. Nonhygroscopic, no definite mp, decomposes above 200C, d about 1.5. Forms colloidal solutions or dispersions in water practically insoluble in all organic solvents. 

These may look completely clear, if the colloidal particles are smaller than 0.1 micron and they look hazy, if the dispersed phase is bigger than 0.1-1 p. However, clarity or haziness are by no means criteria by which solutions and dispersion can be differentiated. 

Colloidal solutions (or dispersions) 2-1000 10 -10 Pass through filters but not ultrafilters, visible under an ultramicroscope but not a microscope, disperse in the solution with some difficulty and dialyze very slowly, settle very slowly... 

The main peculiarities of phase separation of polyampholytes - random copolymers of 2M5VP-AA that are insoluble at the lEP - were considered by authors [63-65] from the colloid chemical point of view. Tables 7 and 8 summarize some physico-chemical characteristics of polyampholytes used. The surface tension O, viscosity [rj] and electro conductivity x of PA-3 solution and dispersion are minimal at the lEP (Fig. 13). In the semilogarithmic coordinates the dependence of surface tension o on IgC has breaking points. They correspond to the critical concentration of polyampholytes that reflects the saturation of the adsorp-... 

Solute particles (in solutions) and dispersed phase particles (in colloids) cannot be seen and do not settle under the influence of gravity. However, solute particles do not scatter or reflect light, whereas dispersed phase particles do. This and other variations in properties result from the principal difference between solutions and colloids, the size of the particles making up the solute or dispersed phase. The dissolved solute in a solution is present in the form of tiny particles (small molecules or ions) that are less than about 10 cm (0.1 pm) in diameter. The dispersed phase of colloids is made up of much larger particles (very large molecules or small pieces of matter) with diameters of 10 to 10 cm (0.1-10 pm). As a result of light scattering, colloids often appear to be cloudy. When a... 

The layered silicate can improve thermal stability of collagen and depending on the collagen morphology (gel or colloidal solutions) and on the method used for silicate dispersion, a variety of lamellar structures and morphologies - intercalated or exfoliated- can be obtained (Vuluga et al., 2007). 

Acoustosizer IIs (Colloidal Dynamics, Warwick, USA) with a built-in conductivity meter and thermometer was used to measure the potential and conductance of solutions of phosphoric and oxalic acid solutions in mixed (water-ethanol and water-methanol) solvents and of Ti02 dispersions (1-10 % by mass). The apparatus was kept in a fume-hood. A flow-through system and stirrer prevented sedimentation of dispersions. An external thermostat was used to keep the solutions and dispersions at 25 1 °C. 4 mL of 1 M acid was added in 0.1 mL portions to 170 mL of initial solution or... 

Two methods are used to prepare the colloid solution the dispersion method and the condensation method. In the dispersion method, the dispersoid and dispersant are ground repeatedly by a colloid grinder until they meet the required degree of dispersion. The condensation method includes two options. One is the chemical reaction option through hydrolysis or metathesis, and the other is the change solvent option. 

A very frej uently used dis persion method is electrical disintegration introduced by Bredig h An electric arc is maintained under water between two metal electrodes. Clouds of finely dispersed metal pass then into colloidal solution and with patience... 

The observation of the displacement in an electric field of the boundary between a colloidal solution and the colloid-free dispersion medium offers another way of determining the electrophoretic velocity. A simple apparatus for this method is represented in Fig. 7. 

Determine the net DLVO interaction (electrostatic plus dispersion forces) for two large colloidal spheres having a surface potential 0 = 51.4 mV and a Hamaker constant of 3 x 10 erg in a 0.002Af solution of 1 1 electrolyte at 25°C. Plot U(x) as a function of x for the individual electrostatic and dispersion interactions as well as the net interaction. 

---