The gelation kinetics of gelatin has been exhaustively studied using oscillatory rheometry for six molecular weight distributions, three concentrations, and four temperatures. Measurements lasted up to 3 1 /2 months, much longer than previous studies. Remarkably, all of the data can be superimposed on a single master curve using suitable shift factors. The existence of a master curve shows that, over the broad range of variables studied, the gelation processes are identical; altering the variables just changes the scaling factors for elasticity and time. Empirically, it is found that neither high nor low molecular weight chains contribute to the elasticity. A statistical network model has been developed, based on Flory's phantom network formalism. It gives reasonable fits to the experimental gel times and is compatible with the observed dependence of elasticity on molecular weight distribution. A second order reaction kinetics model has also been developed which satisfactorily models the early stages of gelation.
The osmotic fragility of the erythrocyte membrane to hypotonic solutions is investigated theoretically. The fragility curves exhibit a strong transmittance rise. This variation is assumed to result from changes in the scattering properties of erythrocytes under dialysis resulting from swelling and hemolysis. The refractive indices of erythrocytes are obtained through the Lorentz-Lorenz relation based on hemoglobin and water contents. The scattering cross sections (needed to calculate the collimated transmittance) and the forward scattered intensity (needed to calculate the incoherent transmittance) are expressed according to the simple algebraic relations of the anomalous diffraction approximation. It is shown that swelling (or shrinking) has no influence on the collimated transmittance. Hemolysis alone causes the abrupt sigmoidal increase of the collimated transmittance with time. The possible transmittance increase (decrease) observed during swelling (shrinking) is due to incoherent transmittance and depends on the detecting solid angle value of the experimental setup.
A physical optics approximation based on Presnel's laws is developed to calculate the intensity of light scattered by a three-axis ellipsoid of any orientation and any refractive index. Some results concerning totally reflecting spheres and dielectric spheroids are presented. An approach suitable for large scatterers is particularly good for small scattering angles. The angular intensities, i(1) and i(2), are then plotted versus θ for large axially oriented ellipsoids of various thicknesses. Theoretical small-angle light-scattering patterns are also presented and discussed. The data from one of them correspond to red cells in a shear flow.
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