Particle flocculation of colloidal

The chapter summary below is presented in a programmed format to review the main points covered in this chapter. It is used most effectively by filling in the blanks, referring back to the chapter as necessary. The correct answers are given at the end of the summary. 

A solid that seems to disappear when stirred with water is said to,  

The relationship among the volume of a solution taken for dilution (Vj), its molar concentration (Mi), the volume of the diluted solution (Vj), and the concentration 

HCl that must be diluted with water to make 5 L of 1.5 m HCl is  

The equation that defines pH is. A pH less than 7 indicates a solution that is. The maximum amount of solute that can dissolve in a particular volume of solution is called the solute s.  

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For the period from around 1840 to the early 1970s paper was usually made in an acidic environment at pHs of around 4-5. This was because many grades required the use of rosin and aluminium sulfate for the control of water penetration (sizing), and solutions of aluminium sulfate exhibit a pH of around 4.5. Aluminium sulfate has also been popular with paper makers because it assists the flocculation of colloidal particles and therefore behaves as a mildly... 

The flocculation of colloidal particles can be divided into two main types (i) diffusion-controlled flocculation (ii) agitation-induced flocculation. The diffusion-controlled flocculation has been analyzed theoretically by von Smoluchowski (5). 

It is well known that the presence of an excess of nonadsorbed polymer can result in flocculation of colloidal particles by the so-called depletion flocculation mechanism [13], In the clay-PEO system, the excess PEO molecules in the supernatant fluid would exert an osmotic pressure on the gel, and the effect should be similar to that of applying an external pressure to the gel indeed, because the... 

Most turbidity occurring in wine is due to the flocculation of colloidal particles caused by chemical reactions that leave the solution clear. It is certain that the presence of natural polysaccharides, with their protective colloid properties, prevent the formation of turbidity and deposits. It is also clear that, in some cases, it may be useful to enhance this protective effect by adding a colloid such as gum arabic. 

Many soft systems are formed slightly differently, as a growing cluster in which particles aggregate to form a larger-scale structure. One example of this process is the flocculation of colloidal particles. Particles in a solution tend to stick to each other (we will learn more about why this can happen in Chapter 5), so dispersed particles in a liquid are attracted to each other, forming tenuous clusters. As these clusters grow, it becomes impossible for newly added particles to penetrate to the center of the cluster, and they can only stick on the exterior therefore, a loose internal structure is developed and an interesting soft material is created. 

Gregory, I., 1984b. Flocculation and filtration of colloidal particles. In Emergent process methods for high temperature ceramics, Eds. R.F. Dvais etai. Plenum Press, London p. 59. 

Comprehension of the interactions among microstructures composed of tethered chains is central to the understanding of many of their important properties. Their ability to impart stability against flocculation to suspensions of colloidal particles [52, 124, 125] or to induce repulsions that lead to colloidal crystallization [126] are examples of practical properties arising from interactions among tethered chains many more are conceivable but not yet realized, such as effects on adhesion, entanglement or on the assembly of new block copolymer microstructures. We will be rather brief in our treatment of interactions between tethered chains since a comprehensive review has been published recently of direct force measurements on interacting layers of tethered chains [127]. 

Honeyman and Santschi 1989). Therefore, flocculation of colloids to form settling particles in estuaries is an important mechanism for trace element removal (Sholkovitz 1977). This is particularly true of Fe, which is a ubiquitous colloidal species and is removed at low salinities. Additional removal may occur by adsorption onto floes, as demonstrated by mixing of organic-rich waters with seawater in the laboratory (Sholkovitz 1977). 

Adsorption of polyelectrolyte on interfaces is concerned with various applications such as flocculation and steric-stabilization of colloidal particles in an aqueous phase, oil recovery, and soil conditioning. In these cases, both the adsorbance of polyelectrolytes and the conformation of the adsorbed polymer, which is connected with the thickness of the adsorbed layer, are very important. 

Ion bridging is a specific type of Coulombic interaction involving the simultaneous binding of polyvalent cations (e.g., Ca, Fe, Cu ) to two different anionic functional groups on biopolymer molecules. This type of ionic interaction is commonly involved in associative self-assembly of biopolymers. As a consequence it is also an important contributory factor in the flocculation (via bridging or depletion) of colloidal particles or emulsion droplets in aqueous media containing adsorbed or non-adsorbed biopolymers (Dickinson and McClements, 1995). 

MullerJ studied by dark-field microscopy the flocculation of colloidal gold upon the addition of NaCl to the aqueous sol. For a sample in which the gold particles have a 36.9-A radius, the following particle counts were observed at different times after the colloid was made about 0.2 M with NaCl ... 

Stability in mixtures of colloidal particles and polymer molecules, dispersed in a solvent, has been the subject of experimental and theoretical investigations for a long time and it has applications in diverse fields such as paint technology, wastewater treatment, emulsion polymerization, biology etc. It has now been well recognized that polymer molecules can be used to induce either stabilization or flocculation (phase separation) in colloidal dispersions. It is important to distinguish between polymers which are adsorbed on the particle surface and those that are free in solution because the two situations usually lead to qualitatively different effects. Stability imparted by adsorbed polymers is known as steric stabilization and the flocculation or phase separation caused by the free polymer is due... 

The U.S. Soil Salinity Laboratory Staff (1954) reported that SAR values of 10-15 (mmol L )1/2 usually correspond to ESP values in the range of 10-15 at which values clays will undergo dispersion. This relationship may vary among colloids with different mineralogy (Oster et al., 1980) and/or mixtures of colloids with different mineralogy (Arora and Coleman, 1979). Consequently, the force by which given types of colloidal particles attract or repulse each other in a Na-Ca or Na-Mg solution is a function of the total concentration of the salt, the type of divalent cation (Ca or Mg), and SAR. Therefore, pH, salt concentration, type of divalent cation, and SAR are expected to play important roles on soil colloid flocculation. 

Increased depletion attraction. The presence of nonadsorbing colloidal particles, such as biopolymers or surfactant micelles, in the continuous phase of an emulsion causes an increase in the attractive force between the droplets due to an osmotic effect associated with the exclusion of colloidal particles from a narrow region surrounding each droplet. This attractive force increases as the concentration of colloidal particles increases, until eventually, it may become large enough to overcome the repulsive interactions between the droplets and cause them to flocculate (68-72). This type of droplet aggregation is usually referred to as depletion flocculation (17, 18). 

This process is enhanced by the addition of polymers, alum, or other flocculants. This chemical addition provides for coagulation and flocculation of colloidal oils and solids into larger particles that can be easily removed. 

Imagine a suspension of colloidal particles in water. What causes stability, and what, imder changing solution conditions like addition of salt causes flocculation (precipitation of the suspension) Two opposing forces were considered to operate between two such particles. The one, attractive, is the quantum mechanical van der Waals force and treats an intervening liquid as if it has bulk liquid properties up to the interfaces of the particles (theme (i)). The other, repulsive, due to charges formed by dissociation of ionisable surface groups, is electrostatic in origin, and depends on salt concentration. 

In conventional latices, the colloidal stability of the particles arises from the predominance of the electrostatic forces of repulsion over the London-van der Waal s forces of attraction. These electrostatic forces of repulsion result from the electric double layer formed by the emulsifier ions adsorbed on the hydrophobic polymer particle surface and the counterions from the aqueous phase. The London-van der Waal s forces of attraction are strongest when the particle-particle distance is very small. Therefore, in most particle-particle collisions, the particles repel one another until the particle-particle distance is decreased to the point where the London-van der Waal s forces of attraction are predominant over the electrostatic forces of repulsion. Thus, many conventional latices remain stable indefinitely without significant stratification or flocculation of the particles. 

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