Electrostatic attraction, clay particles

Most particulate matter in the ocean, such as clay minerals, metal oxyhydroxides, and POM, possess a small net negative charge at the pH of seawater. Hence, metal cations are electrostatically attracted to the particle surfaces. As shown in Figure 11.6, these... 

Individual particles of clay minerals consist of stacks of layers, which in some systems are separated by interlayer materials. The individual layers are held together by secondary forces (i.e. van der Waals attractive forces, hydrogen bonding or weak electrostatic attraction). 

Class C—emulsions of various organic substances, increasing the electrostatic attraction and introducing ultra-fine particles to cement paste. The following compounds, among many others, are in this group acryl emulsions and water dispersions of clay. 

Students may believe that sediments become hard rocks simply by being compacted together. This is only the case with fine-grained sediments, such as clays, where electrostatic attraction helps to hold the particles together. Sands and coarser-grained sediments require some form of natural cement to bind the particles together. Ask a student to take a handful of sand and see if it is possible to make a rock by squeezing it as hard as possible. They will find that they cannot do it. 

While the electrokinetic surface, or -potentials, originate from the surface or interfacial properties of solid materials, they are actually situated about 0.3 to 0.5 nm outside a material s surface and have to be extrapolated inward to the (i/>o) potential at the actual surface, using Eq. 5.54. The electrostatic free energy of interaction, AG, between two surfaces, 1, reaches a value of about -M.O mJ/m at V o 75 mV, in an aqueous medium with a 100 mM salt content of a mono-mono-salt see Table 5.1. Now various clay and other mineral particles can have V o-potentials that are between 50 and 90 mV, in which case AG, while not dominant, is no longer negligible. For instance for a contact between two platey clay particle surfaces over about 100 nm (= 10 ° cm ) an attraction of 1 mJ/m still corresponds to w 2,500 kT. Thus, it is always wise to measure -potentials, from which the actual surface, or V o-potential can be derived. 

Polyelectrolytes provide excellent stabilisation of colloidal dispersions when attached to particle surfaces as there is both a steric and electrostatic contribution, i.e. the particles are electrosterically stabilised. In addition the origin of the electrostatic interactions is displaced away from the particle surface and the origin of the van der Waals attraction, reinforcing the stability. Kaolinite stabilised by poly(acrylic acid) is a combination that would be typical of a paper-coating clay system. Acrylic acid or methacrylic acid is often copolymerised into the latex particles used in cement sytems giving particles which swell considerably in water. Figure 3.23 illustrates a viscosity curve for a copoly(styrene-... 

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