Silica gel is interesting stuff. Apparently you make it by taking Sodium Silicate and reacting it with Hydrochloric acid
Na2SiO3 + 2 HCl → H2SiO3 + 2 NaCl
the silicic acid (H2SiO3) then looses water
H2SiO3 → SiO2 + H2O
the SiO2 then comes out of solution with each silicon bonding to other silicons via an oxygen
| |
O O
| |
- O - Si - O -Si - O -
| |
O
| |
- O - Si - O -Si - O -
| |
O O
| |
although it is 3D and probably roughly a tetrahederal structure and not very regular
These form loads of microscopic spheres between 0.5nm to 3μm which end up fusing together to form a structure wih loads of surface area - about 400m2 per gram
[diagram=49_0]
It is then washed and dried out, and then baked to drive off the water. If you then put it in a moist condition the water will stick to the surface again, and because it has so much surface it can absorb a lot of water about 25% of it's weight.
Silicone is a different structure, CH3 groups are added to stop it bonding away from the chain.
CH3 CH3
| |
O - Si - O -Si - O
| |
CH3 CH3
So you get long molecules (polymers) which can slide past one another, hence it is flexible