Optical viscometry of spinning sol coatings

Optical interferometric monitoring of spin coating (optospinography) has al lowed close observation of the temporal evolution of a thin silicate sol fi lm (typically at 2000 rpm, 100 Hz data acquisition). The kinematic viscosit y data obtained, using a simple analytical model, are validated with those from a mineral oil standard, with agreement well within the experimental un certainties. For spin coating in open air, the influence of variations in r efractive index, rheological properties and air flow are discussed. Inflect ions in the temporal evolution of the optical thickness of silicate sol fil ms are analyzed, which indicate the usefulness of optospinography, particul arly when applied in the proximity of the rotation axis and evaporation is minimized, to monitor time variations in the kinematic viscosity of these s ols during spin coating.