Colloidal Silica

Description

In general terms, colloidal silica is a dispersion of amorphous silicon dioxide (silica) particles in water. These amorphous silica particles are produced by polymerizing silica nuclei from silicate solutions under alkaline conditions to form nanometer-sized silica sols with high surface area. A charge is then induced on the silica nanoparticle surface, allowing the silica particles to repel one another and form a stable dispersion, or colloid.

Chemical Properties

Colloidal silicas are produced in a variety of grades that range in several factors. Particle size typically varies from 5nm to 40nm, and particle size distribution can vary from narrow to wide depending on the manufacturing process. Standard colloidal silica is stable at a pH of 8 - 10.5 and carries an anionic surface charge that is stabilized with sodium or ammonium. In certain grades, some silicon atoms in the silica particle are replaced with aluminate ions to enhance stability in a wider pH range, usually 3.5 - 10.5.

Application

Colloidal silica is extensively used as a rheological additive in personal care products to control flowability. Recently, mesoporous silica nanoparticles have been explored as nanocarriers for delivering drugs and genes. Silica nanoparticles possess a wide range of particle sizes, controllable pore volumes, a high drug-loading capacity, and abundant silanol groups for surface modification and functionalization, and they have been widely used in drug delivery. Increasing efforts have been made to investigate their skin penetration ability and toxicity.