Silicon-oxygen chains

More important than the simple metasilicate chain, in the structure of crystals, is the double chain found in the amphiboles. This structure is shown in Fig. XXVI-3, looking down on the top. A unit of the chain contains four silicons, eleven oxygens, as we see by counting, and it has 

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Washing removes the natural coating of protective oil that gives hair its body and shine. To counter this, shampoos and conditioners contain hydrophobic oils that cling to the surface of hair and remain in place upon rinsing. Dimethicone, shown in our inset, is an artificial oil that contains hydrophobic silicon-oxygen chains and methyl groups. 

Such a network can be described as a series of spiral silicon-oxygen chains crosslinked with each other by oxygen bonds. If some of the oxygen aLoms are replaced wiLh organic snbsLiuients. a linear polymer will result ... 

Fig. 9, from Warren s 1929 paper on the crystal structure and chemical composition of amphiboles 48>, is a physical picture of the silicon-oxygen chain in diopside. Large circles represent van der Waals-like domains of oxide ions (r = 1.40 A 2>) smaller, dashed circles represent van der Waals-like domains of silicon cations [r = 0.41 A 2>). 

Fig. 9. The silicon-oxygen chain in diopside 48>. Or, a localized molecular orbital representation of a hydrocarbon (see text)...

The simplest silicones are the methyl silicones. These substances exist as oils, resins, and elastomers (rubberdike substances). Methyl silicone oil consists of long molecules, each of which is a silicon-oxygen chain with methyl groups attached to the silicon atoms. A short siii cone molecule would have the following structure ... 

Silicon oxygen chains have long bonds and relatively flat valence angles. The C-E bond is quite polar and, in fact, some fluoropolymers do not have low surface energies. However dipoles are vectors, and in the case of PI PE, their mutual opposition means that the molecules as a whole are non-polar. 

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