Technical Note 1 - Hydrophobicity Characterization of Silane-Treated Titania

Samples of six different lots of high purity rutile titania produced by Primet’s Nano-Scission™ process were treated with an alkoxysilane and characterized with respect to hydrophobicity. Prior to silane treatment, the BET specific surface area of these materials ranged from 62 to 116 m2/g and the equivalent spherical diameter (ESD) from 22.7 to 12.1 nm.

Two different methods were used to evaluate the hydrophobicity of the treated titanias: wettability by a series of methanol/water solutions and contact angle with a methanol/water solution.

The wettability test is a simple indicator test. A small quantity of dried silane-treated titania is sprinkled onto the surface of a series of methanol/water mixtures with increasing concentration of methanol, and the concentration of methanol at which the powder disperses into the solution is recorded (Figure 1).

Contact angles were measured by Augustine Scientific of Newbury, Ohio using the Washburn technique. This special method for studying the wetting properties of porous solids, including powders and fibrous materials, is described in their Application Note 402. A 60/40 (v/v) methanol/water mixture was used as the test liquid, based on the results from Primet’s indicator tests.

Table 1 summarizes test results from both methods. In each case, higher values indicate greater hydrophobicity.

Table 1 – Results of hydrophobicity evaluation of silane-treated titanias.

*ESD: equivalent spherical diameter