PROPERTIES AND STRUCTURE OF SILICAS 513 300 250 . 200 ,, 150 Z cl IO0 MINERAL OIL DRYING-UP CAPACITY OF PRECIPITATED SILICAS 50 3øø F 250 A B C D E F SILICA Figure 15. Mineral oil drying-up capacity of precipitated silicas SORBITOL DRYING-UP CAPACITY OF PRECIPITATED SILICAS ' 200 D 150 z lOO 5o A B C D E F SILICA Figure 16. Sorbitol drying-up capacity of precipitated silicas

514 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS H. GLYCERINE, SORBITOL AND MINERAL OIL DEMAND INDEX VERSUS SILICA STRUCTURE Precipitated silicas are used for converting the liquids into dry, free-flowing powders. This technique is used for ease of handling and dry blending "liquids" into many formulations. The drying-up capacity of precipitated silicas increases with the increase in the silica structure level. This is shown in Figures 15-17 and data are listed in Ta- ble V. V. DENTIFRICE PROPERTIES OF CONTROLLED-STRUCTURE PRECIPITATED SILICAS A. THICKENING AND VISCOSITY BUILDING PROPERTIES The thickening and viscosity building properties of the six controlled-structure silica samples (for physical properties of silica, see Table IV) were studied in a nonhydrogen- bonding liquid (mineral oil), as well as a hydrogen-bonding liquid, such as glycerine (poly functional alcohol). The effect of silica concentration on the viscosity of mineral oil and glycerine is shown in Figures 18 and 19, respectively. The thickening and viscosity building properties of the precipitated silicas are influenced by the following factors: 1) nature of the liquid medium, 2) structure of the precipitated silica, 3) concentration of the silica, 4) particle size and surface area of the silica, 5) silanol group density, 6) degree of dispersion, 7) nature of additives, if any, and 8) pH of the system. ,00[ 250 GLYCERINE DRYING-UP CAPACITY OF PRECIPITATED SILICAS - 200 ,', 150 z c) lOO 50 B C D E SILICA Figure 17. Glycerine drying-up capacity of precipitated silicas