First experiences with the new XL-I AUC: Applications in polymer and colloid science

Abstract

In our lab we have transformed all the application of the analytical ultracentrifuge (AUC) in colloid and polymer science from the Schlieren optical system of the Beckman model-E to the interference optics of the Beckman XL-I. Two basic experiments, the sedimentation velocity run and the density gradient run are described in this paper. The advantages of the interference optics together with the sedimentation velocity run are a much higher data density that gives together with the “dc/dt”-analysis method of W. Stafford very accurate results. In the field of colloid science this means that very precise particle size distributions are available, with an especially high resolution for small particles. Density gradient experiments were carried out and gave very good interference pictures. These pictures were analyzed after the formation of the density gradient was complete and also during its formation (“dynamic density gradient”). The method of analysis described in the paper is the same for both cases resulting in very good values for the particle density of the sample. The method is based on the determination of the absolute refractive index of the gradient forming medium and the transformation of the refractive index into a radial density distribution within the measuring cell.