Journal of Nanomaterials and Devices

Sol Gel Process

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The sol-gel process is a way to make solid materials from small molecules mixed in a liquid. A "sol" is a liquid that has very tiny solid particles spread evenly in it. These tiny particles can have no clear shape (amorphous) or have an organized crystal shape. An aerosol is when tiny particles are floating in a gas, like air. A sol is when tiny particles are spread in a liquid. A gel is a soft, solid-like material that holds liquid inside it. In a colloidal gel, the solid part is made by small particles sticking together. In a polymer gel, the solid part is made from groups of even smaller particles that are joined into long chains. In most sols, the particles stick to each other using weak forces, like van der Waals forces or hydrogen bonds. A gel can also form when long chains of molecules (polymers) join together. In most gels made for materials, these chains are held together by strong chemical bonds (covalent bonds), and once the gel forms, it can’t go back to liquid. But if the chains stick together in weaker ways, the gel can sometimes turn back into liquid.

The sol-gel process is a chemical procedure used to make glass-like or ceramic materials at fairly low temperatures. It uses a wet process, starting with making a liquid mixture called a sol, turning that sol into a gel, and then removing the liquid hold inside the small connected spaces in the gel. The sol-gel method has many advantages. It is very resourceful as it gives better control over the structure, like how porous the material is and how big the particles are. It also allows adding tiny particles (nanoparticles) and even organic materials into the final product. The sol-gel method can make many different types of oxides and even some materials that are not oxides. It can also create new materials that unite organic and inorganic parts, which is missing in nature. Another advantage is that the materials made this way are very consistent and pure because the mixing happens at the smallest level, with the molecules themselves. Sol-gel also uses less energy since the materials can form at much lower temperatures compared to methods that need melting. This method can be used to make coatings, thin films, solid pieces (monoliths), mixed materials (composites), membranes with tiny holes (porous membranes), powders, and fibers. On top of that, sol-gel does not need any special or very expensive equipment, which makes it easier and cheaper to use.