Rheological and drug release properties of oil gels containing colloidal silicon dioxide.

The rheological properties of oil gels prepared by dispersing colloidal silica in n-dodecane and 1-dodecanol were examined. The differences in gel strength using these two media were accounted for by the difference in the extent of hydrogen bond formation between the silanol groups on the silica surface. The incorporation of methyl salicylate further modified the rheological properties of the gels. The drug was capable of hydrogen bonding with silanol groups in the n-dodecane gels, which increase gel strength at low concentrations; at high concentrations, the drug acted as a plasticizer. In 1-dodecanol systems, the drug acted solely as a plasticizer. Adsorption studies showed that methyl salicylate was adsorbed only on the silica particles in the n-dodecane medium. Interaction of the drug with the silanol groups in the n-dodecane systems did not appear to effect methyl salicylate release from the gels.