LARS-EINAR FRYKLOF Apotekarsocietetens laboratorieavdelning, Stockli olni THE USE OF THE BROOKFIELD SYNCHRO-LECTRIC VISCOMETER IN RHEOLOGICAL INVESTIGATIONS OF COATING AND OTHER VISCOELASTIC MATERIALS*

ABSTRACT: The Brookfield Viscometer is described and its use in rheo-logical measurements is analyzed and discussed. The significance of spindle shape and rotational speed for different types of viscoelastic fluids is de-termined. Methods for using this viscometer to obtain the greatest amount of significant information are def ied. HE BROOKFIELD Synchro-Lectric Viscometer is probably one of the most T commonly used rotational viscometers. A relatively large number of publica-tions, of which several are pharmaceutical, provide evidence of its use both for industrial plant control and for scientific investigations. It therefore seemed important to the author to make an attempt to find a mathematical background for a correct interpretation of the experimental results obtained with the Viscometer. In addition, a method of measurement for plastic materials was developed for this apparatus which exploits, in a better manner than the methods recommended by the manufacturer and used in the investigations so far published, the possibilities for obtaining information concerning the rheological properties of the material investigated. Because of the shape of those spindles which were specially designed for measurements on plastic materials, it is clear that the Brookfield Viscometer should often be more suitable for such purposes than, for example, concentric cylinder/viscometers or cone and plate viscometers. DESCRIPTION OF THE INSTRUMENT The principle of the Brookfield Viscometer is quite simple. A synchronous motor drives at a constant speed a spindle which is immersed in the material under investigation. The force which is necessary to overcome the resistance of the material to the rotation of the spindle is provided by a calibrated spring, the tension of which is read as a deflection of a pointer over a graduated scale rotating with th