METHYL-HYDROXYPROPYL CELLULOSE - SHEAR-INDUCED BIREFRINGENCE MEASUREMENTS IN THE SEMIDILUTE REGIME

The present study was induced by unexpected findings with this and oth er not fully substituted cellulose derivatives. Although fully transpa rent aqueous solutions were prepared, static light scattering (LS) rev ealed a strong aggregation. A detailed analysis of the LS-data as well as transmission electron-microscope pictures gave evidence for fringe d micelles as aggregate structure. These particles consist of several side-by-side aligned chains that form a compact core from which many d angling chains emerge. The core in this model has a geometrical anisot ropic shape and flow birefringence became detectable when orienting th e particles by the action of shear forces. Induced now birefringence i s a common feature of many other materials and therefore a set-up was constructed that could be attached to a common constant stress rheomet er of Bohlin. The reported experiments present first examples measured with this set-up and demonstrate the efficiency of this technique. In the following the equipment is briefly described and the results obta ined so far are tentatively interpreted.