DETERMINING THE COMPACTING OF LATEX FILMS UPON DRYING BY INTERFERENCEMEASUREMENTS - AN APPROACH FOR THE INVESTIGATION OF FILM FORMATION

The decrease of optical thickness of drying latex coatings is measured interferometrically. Through data processing film thickness and polym er volume fraction are obtained, which are a measure of particle spaci ng and deformation. The applied criterion for film formation is the at tainment of a dense polymeric material. In this sense the method can b e used to check film formation under a variety of conditions. The kine tics of film formation is monitored as well. Since the method is sensi tive to changes in optical properties, different modes of drying can b e distinguished. The solids content determined by this method is not a veraged over the whole film but represents the exact state of drying a t the measured spot. Another advantage is that due to the simple setup of the experiment, it works under a broad variety of conditions and w ithout restrictions regarding the nature of the latex. Also, simultane ous measurements at two angles of incidence allow refractive index ind ependent data interpretation. Drying of different dispersions, both fi lm forming and non-film forming under the given conditions, has been i nvestigated, demonstrating the potential of the technique.