Abstract
The storage and loss shear moduli, G′ and G″, have been measured for dilute solutions of bovine fibrinogen in 68% aqueous glycerol and of intermediate fibrin polymer in 6__M__ hexamethylene glycol, by the Birnboim‐Schrag multiple‐lumped resonator apparatus with titanium alloy resonators. The frequency range was 100–5800 Hz, the concentration range 1–6 g/l., and the temperatures 10.0 and 25.0°C. The shear moduli G′ and G″ at finite concentration, and the extrapolated instrinsic shear moduli [G′] and [G″], as functions of frequency, were compared with the predictions of various molecular theories. For fibrinogen, the frequency dependence agreed quite well with the calculations of Hassager for a trinodular rod as modified for the presence of small amounts of dimeric and trimeric aggregates which were deduced from parallel measurements of oscillatory flow birefringence. It was not possible, however, to distinguish between a linearly rigid configuration and one which is freely jointed at the central nodule. A model of a soft elastic sphere (simulating the cage model of Köppel) appeared to be very unlikely. The relaxation time for a rigid trinodular rod and the longest relaxation time for a jointed trinodular rod, calculated from molecular dimensions on the basis of electron microscope measurements, are somewhat smaller than the corresponding observed values; the discrepancy suggests that the molecule is swollen in solution. For the intermediate polymer (which was formed under conditions where ligation is expected), the frequency dependence agreed quite well with that predicted either for a prolate ellipsoid (Cerf‐Scheraga‐Saitō) or for a cylindrical rod (Yamakawa). The relaxation time obtained by fitting to theory agrees quite well with that calculated for a cylindrical rod with molecular dimensions based on a degree of polymerization of 20 and lateral binary association with staggered overlapping.