Measurements of real and imaginary capacitance (C′ andC″) have been made during the drying of a film-forming latex. In one experiment dielectric measurements at frequencies between 1 Hz and 100 kHz were made simultaneously with gravimetric measurements on a microbalance. It was found that both the rate of water evaporation and the a.c. conductance decrease sharply at high polymer volume fraction. These results are discussed qualitatively in terms of a model for the film-forming process. In another experimentC′ andC″ were recorded at 10 Hz along with automatic measurements of the build-up of the scratch resistance of the film. It was found that the mechanical response to film-formation appears significantly earlier than the dielectric response. This is also discussed qualitatively in terms of the model.
Authors:M. Bahra, D. Elliott, M. Reading, and R. Ryan
A novel instrument is described called the Thin film Analyser (TFA) which quantitatively measures changes in mechanical and rheological properties of drying films in-situ on a test panel. It is based around a simple force-sensing device, capable of carrying various probes, which can be positioned in anX-Y plane over the panel. Temperature control is achieved by means of a heating block under the sample. By imposing a thermal gradient along the block, measurements can be obtained at a series of temperatures in a single experiment. Several applications of the TFA to the drying of curable and latex-based coatings are discussed, as well as some more specialized uses. The TFA concept represents a novel approach to the thermal analysis of thin films.