Cation exchange is one of the most important properties of montmorillonite. The cations adsorbed between montmorillonite layers have exchangeability, and the total amount of these cations is called cation exchange capacity (CEC). In aqueous media, other exchangeable cations and water molecules can enter the interlayer, and this process is reversible. By utilizing the cation exchange properties of montmorillonite, various products such as sodium based bentonite, lithium based montmorillonite, activated clay, pillared montmorillonite, and organic montmorillonite can be prepared.

Montmorillonite contains a large number of hydroxyl groups in its structure, with strong hydrophilicity and significant water absorption and swelling characteristics. Expansion is mainly based on the hydration of interlayer cations, which adsorb water molecules to form a hydration film, increasing the interlayer spacing and causing expansion. After absorbing water, the volume can expand several times to dozens of times to form gel-like substances. The hydration expansion of montmorillonite mainly includes three stages:

• Surface hydration
• Ionic hydration
• Permeation hydration

In aqueous media, due to the negative charge of montmorillonite particles, they repel each other and are difficult to form large particle aggregates at low concentrations. Therefore, they have good suspension properties and can be used as suspension agents. Generally, suspension properties increase with pH value, and are better under alkaline conditions than under neutral and acidic conditions.

When mixed with water, montmorillonite hydrates and expands, forming a massive three-dimensional network structure. The water molecules and lotion particles are wrapped and isolated to increase their motion resistance, so as to achieve a thickening effect. As time goes on, this colloidal structure tends to stabilize.

During stirring, the colloidal structure is disrupted, the viscosity of the system decreases, and it becomes a sol. When standing still, the colloidal structure recovers, and the viscosity of the system increases in the form of gel. The process of restoring the colloidal structure is reversible and is known as the thixotropy of montmorillonite.

Montmorillonite is a natural inorganic mineral material with good stability and weather resistance.

• Good Chemical Stability: Montmorillonite is insoluble in water and various solvents, and is not reduced or oxidized at room temperature. It has a wide range of pH resistance and its structure is not easily affected by acids, bases, or salts. It has good compatibility with organic anions and alcohol solvents.
• Good Thermal Stability: The dehydroxylation temperature of montmorillonite is generally 550°C–750°C, at which the structural hydroxyl groups are removed but the layer structure is not destroyed, exhibiting good thermal stability.
• Good Biological Stability: Montmorillonite is not affected by bacteria or microorganisms. Its suspension is not easily moldy or spoiled under humid and hot conditions. It does not undergo enzymatic hydrolysis, odor, or viscosity reduction like organic thickeners such as cellulose and xanthan gum, and has superior anti-corrosion and anti-degradation properties.