In the toothpaste we use daily, silicon dioxide is an indispensable component. Is it hydrophilic or hydrophobic in it? The answer is that the silica used in toothpaste is usually hydrophilic.
Hydrophilic silica, also known as precipitated silica, exhibits excellent hydrophilicity due to its surface being rich in a large number of hydroxyl groups, which can form hydrogen bonds with water molecules. This characteristic makes it play multiple roles in toothpaste. On the one hand, as an abrasive, hydrophilic silica has a fine texture and can gently remove dental plaque, food debris and exogenous pigments on the surface of teeth, while not excessively wearing down the enamel and ensuring dental health. On the other hand, it can also be evenly mixed with water to form a stable paste structure, maintaining the good texture and shape of the toothpaste and making it convenient to use.
Hydrophobic silica, on the other hand, has undergone special surface treatment, with hydroxyl groups replaced by other groups, which leads to a decrease in its affinity for water and makes it more prone to combine with oil substances. Among the main functional requirements of toothpaste, hydrophobic silica cannot effectively achieve the functions of cleaning and stabilizing the paste as hydrophilic silica does. Therefore, except for a small amount of hydrophobic silica which may be used in some special functional toothpastes (such as those with waterproof film effects), the vast majority of ordinary toothpastes use hydrophilic silica as a key ingredient.