TONY O’LENICK
SurfaTech Corporation, Lawrenceville, Ga, USA

Abstract

When formulating personal care products, aesthetics is an absolute requirement. Consumers simply will not accept even a well formulated product if it does not have the anticipated aesthetics. Silica is an additive that can provide important benefit to formulations and can be overlooked. Products formulated using silica can alter skin feel, mattify formulations, alter rheology and improve tactile qualities providing the highly prized dry powdery feel. The chemistry, nomenclature used and formulation of high performance products using this important class of raw materials is presented.

SILICON COMPOUNDS
There is a great deal of confusion related to molecules that contain silicon. Silicon is the 14th element. Silicon (Si) is on the periodic table directly below carbon. It is the second most abundant element on earth after oxygen (1). Elemental silicon is rare in nature but makes up 25% of the earth’s crust as the oxide of silicon. Elemental silicon is a shiny solid shown in figure 1 (2).

Figure 1. Elemental Silicon (2).

Silicic Acid

The term silicic acid has traditionally been used as a synonym for silica, SiO2. Strictly speaking, silica is the anhydride of orthosilicic acid, Si(OH)4 (3).

Si(OH)₄ ⇌ SiO₂↓ + 2H₂O

The simplest soluble form of silica, orthosilicic acid ‘Si(OH)4’, is a weakly acidic molecule (Pak 9.8) with silicon tetrahedrally coordinated to four hydroxyl groups (4, 5). It is fou ...